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Basic Radiological Sciences Division, Department of Radiology, University of Michigan, Ann Arbor, Michigan, USA When exposed to sufficiently high ultrasound pressures, microbubbles can be generated spontaneously in tissue and undergo inertial cavitation where collapses result in physical effects. These effects range from petechial haemorrhage to complete cellular disruption, termed Histotripsy, depending on ultrasound parameters.
This presentation will explore the mechanisms associated with histotripsy along with the tissue effects and the wide range of potential applications for this mechanical disruption method. Stanford School of Medicine, Stanford, California, USA In this lecture, we will compare the design of clinical trials that led to approval of MR guided focused ultrasound for the treatment of uterine fibroids and osseous metastases.
The impact of these trials on the evidence base, and thus on adoption by users and coverage by insurers will be compared. We will also review the process of expanding approved FUS applications, either via investigator- or industry-initiated studies or through off-label clinical use. SonaCare Medical, Indianapolis, Indiana, USA In this lecture, present status of focused ultrasound for the treatment of localized prostate cancer ablation will be discussed. High intensity focused ultrasound (HIFU) has been used for the ablation of prostate over two decades and has treated thousands of prostate cancer patients. Meanwhile, prostate cancer management is undergoing significant improvements as molecular markers, targeted biopsy and advanced multi-parametric MRI are routinely used to accurately localize the prostate cancer.
These advances offer a unique opportunity for focal ablation of localized prostate cancer with HIFU as it plays a significant role in reducing morbidity and treatment cost. This presentation will focus on hardware design, software architecture and HIFU features of the devices. Presentation will demonstrate localization of prostate with ultrasound imaging, treatment planning with 3D volumetric rendering of the prostate with ultrasound and MRI fusion techniques for focal treatment and finally HIFU dose setting with guidance using real time Tissue Change Monitoring (TCM) with the Sonablate device.
The presenter will encourage exchange of ideas and discussion for research topics. Institut Langevin, Paris, France In this lecture, the use of transcranial low intensity focused ultrasound for neuromodulation will be discussed. A historical review will be presented, with an emphasis on the experimental setups and the acoustical parameters. Models ranging from slice cultures to intact rodents and primates will be presented, together with recent trials on humans. Potential mechanisms will be described. Based on our own experience, exciting successful neuromodulation as well as disappointing failures will be presented.
Stanford School of Medicine, Stanford, California, USA This talk will cover image-based thermometry methods for guiding focused ultrasound. MR Thermometry based on the proton resonance frequency shift with temperature is linear and reversible in aqueous tissues and is utilized in clinical practice with common temperature resolutions of 1°C. Ultrasound based thermometry based on the speed of sound change with temperature can be used to 45°C in aqueous tissue. Both methods are sensitive to the presence of fat within the aqueous tissue, as well as motion.
This talk will cover these basic concepts as well as their use in clinical practice. InSighTec, Haifa, Israel MRgFUS treatment is a disruptive, non-invasive, outpatient treatment alternative that is capable to treat tumours and functional disorders under real-time monitoring and control via MR thermometry. Transforming this breakthrough technology from the lab to a mainstream treatment alternative requires gaining the support and the agreement to change by a whole array of stakeholders in different areas some interrelated and some conflicting. The stakeholders’ current position, changes they will need to go through and possible changes engines are mentioned below: ▪ Physicians (surgeons) need to transform into image guided surgeons where knowledge and understanding of the disease play a dominant role in the procedure outcome. The benefit is the confidence in the safety and efficacy coupled with income that wouldn’t decline.
The change engine could be the patients and the payers. ▪ Payers should benefit from covering MRgFUS by saving cost and addressing patients’ demands.
The change engine in this case should be the patients, governments and physicians. ▪ Governments should see the benefit of very fast recovery, very low level of adverse events and productivity enhancement. In this case patients and physicians should drive the change. ▪ Patients should benefit from safer treatment, fast recovery next day back to your life, minimal trauma and morbidity. The significant benefit to them should transform them to the dominant driver of this change.
They will need to influence physicians, payers and providers to adopt this new treatment. ▪ Providers should adopt the technology and provide this treatment since the data exist proving safety and efficacy, proven cost savings and physicians and patients demand.
The current Medical ecosystem is biased against new technologies since the incumbent system/treatments are reimbursed while the new technologies are not. Could governments perform economic analysis and if found beneficial (example: saving money and improving productivity) decide on limited 2 years reimbursement during which RCT data will be collected based on which private insurance will decide to cover. This model should incentivize the physician, payers and providers to try the new technology. Stanford School of Medicine, Stanford, California, USA In this lecture, the use of MR guided focused ultrasound for the treatment of soft tissue and osseous tumours will be discussed. Results of treatment of these different types of tumours will be reviewed, including lessons learned from challenging patient treatments.
Technical aspects of all parts of a treatment, including patient preparation, positioning, imaging, planning, thermometry, and methods of evaluation, will be described. The talk will also focus on methods developed to address these current challenges and opportunities for future development. 1Sheba Medical Center, Ramat-Gan, Israel; 2Tel-Aviv University, Tel-Aviv, Israel, 3InSighTec, Haifa, Israel Objectives MR guided focused ultrasound (MRgFUS) has been extensively studied in recent years as a non-invasive treatment modality.
Initial clinical trials have indicated promising treatment response to ablative FUS treatments of patients with brain tumours, neuropathic pain, essential tremor, obsessive compulsive disorder, and Parkinson’s disease. Apart from the ablative applications of FUS, this technology has been extensively evaluated for less destructive applications such as thrombolysis, blood–brain barrier disruption for increased drug delivery, and recently also neuro-modulation. The objective of the presented study was to demonstrate non-invasive, non-destructive, reversible FUS-induced neuro-modulation in small (rats) and large (pigs) animals by inducing temporary suppression of auditory evoked potentials. Methods All animal experiments were performed under full anaesthesia. Rats were anesthetized by Xylazine/Ktalar and pigs were anesthetized by Propofol.
Rat’s heads were shaved prior to treatment but they did not undergo craniotomy. Pigs underwent craniotomy to avoid FUS reflection/aberration by the skull. EEG was recorded using 3 small cup-shaped electrodes attached to the skin/dura with metal particles-containing gel for optimal sound conductivity (Fig. ). See text for description The audio stimulation system consisted of a pulse generator connected to the EEG trigger input and to speakers placed near the animal ears, producing a square-wave form at 10 KHz, resulting in 150 “click” sounds per min (Fig. ). Each measurement consisted of 200 repetitions enabling acquisition of a full measurement in 1’20” min. The ExAblate Neuro system (InSightec, Tel Aviv, Israel) is a combination of a standard MRI scanner and a FUS delivery system. The FUS device is in the shape of a helmet consisting of 1024 transducers which deliver US energy in the form of “sonications”.
The system is designed to provide real-time therapy, planning, thermal dosimetry, and closed loop therapy control. Treatment starts with conventional MRI scans, displayed on the ExAblate computer, used to determine regions of interest of the target volume. During the procedure, the beam path is periodically reviewed to confirm the planned direction through the tissue. The set of sonication volumes is sequentially applied to cover the entire planned volume.
The current experiments were performed with a modified ExAblate version developed for neuro-modulation as part of the MAGNET programs supported by the Israeli Ministry of Commerce. Baseline auditory evoked potentials were recorded by EEG prior to FUS treatment, with the animals in the prone position. The animals were then placed in the supine position, with the skull dipped in degassed water at the centre of the FUS system, for localization MRI scanning followed by FUS treatment. The animals were then returned to the prone position for continuous post-treatment EEG recordings. Rats which did not show recovery of the auditory evoked potentials 30–60 min post treatment were monitored again 48 hours or 1 week post treatment. The animals were treated by FUS for 52 sec using the Exablate Neuro system at 220 KHz, 12 W, and 100 ms on/ 2900 ms off pulses.
Two rats were treated in the thalamus region (targeted at deep auditory tracks) and another two in the frontal cortex region (targeted at peripheral auditory tracks). Two sham rats underwent a similar procedure without activation of the FUS system. One pig was treated in the thalamus region and another in the right motor cortex region. Results Auditory evoked potential EEG signals shapes varied from one animal to the other but all were detected 2–10 ms after the trigger. The maximal peak-to-peak height was calculated for each measurement. The sham rats showed no significant change in the auditory evoked potentials EEG signal. The rats treated in the thalamus regions showed 50% and 65% suppression of the baseline auditory evoked potentials EEG signal.
The first showed no recovery 2 hours post treatment with full recovery measured 1 week post treatment. The second showed no recovery for 1 hour post treatment and full recovery 48 hours post treatment. The rats treated in the cortex regions showed 50% and 67% suppression of the baseline EEG signal. The first showed no recovery 30 min post treatment with full recovery measured 1 week post treatment. The second showed initial recovery 14 min post treatment reaching full recovery within 28 min post treatment. The pig treated in the thalamus region showed 90% suppression of the baseline signal with no recovery 30 min post treatment.
The second pig, treated in the cortex region, showed complete suppression of the baseline signal immediately post treatment with initial recovery noted 18 min post treatment, reaching full recovery 63 min post treatment (Fig. ). Faculty of Biomedical Engineering & Russell Berrie Nanotechnology Institute, Technion – Israel Institute of Technology, Haifa, Israel Objectives Low intensity US can noninvasively suppress or excite central nervous system (CNS) activity using different combinations of stimulation parameters. While applications are already emerging, the underlying biophysics remains unclear regarding the relative contribution of possible mechanisms: extracellular bubble cavitation, thermal effects, acoustic radiation pressure and US-induced intramembrane cavitation within the bilayer membrane (the bilayer sonophore or BLS model). Interestingly, both radiation pressure and intramembrane cavitation can induce plasma membrane capacitance changes. Here, we use detailed predictive modelling and find that only intramembrane cavitation can explain all the observed aspects of ultrasonic neuromodulation.
Methods We analyzed the relevant experimental literature using modified Rayleigh–Plesset intramembrane cavitation BLS biomechanics and acoustic radiation pressure gradients (RPG) - induced membrane dynamics. By coupling these biomechanical models to biophysical membrane models we predict dynamical biophysical responses of artificial bilayer membranes, and of three common neocortical single cell Hodgkin-Huxley type models: i) Regular Spiking (RS) cortical pyramidal neuron, ii) Fast Spiking (FS) cortical inhibitory neuron and iii) Low Threshold Spiking (LTS) cortical inhibitory neuron, RS-FS-LTS Hodgkin-Huxley based network model and CNS axon model. In addition, live brain tissue RPG subjected areal strains were evaluated in a viscoelastic brain model. Results Only the Neuronal Intramembrane Cavitation Excitation (NICE) models were able to explain US-induced action potential generation through BLS-type pulsating nano-bubbles inside the bilayer plasma membrane: the leaflets' periodic vibrations induce US-frequency membrane capacitance and potential oscillations, leading to slow charge accumulation across the membrane (on a time scale of tens of milliseconds), until action potentials are generated.
In contrast, the analysis of RPG-induced membrane capacitance variations associated with membrane area changes explain artificial membrane results, but were found to be highly unlikely sources for neural excitation, when considering the areal strains expected to form in brain tissue during normal sonication. Further, the NICE-LTS inhibitory neurons show a much higher relative sensitivity to sparse ultrasonic stimulation compared to the other neurons, resulting from their T-type voltage gated calcium channels.
This model-based prediction was found to explain the results of a significant body of suppression and excitation experimental studies, including in humans. Conclusions These results provide a unified theoretical framework for a large body of experiments in multiple preparations across the field of US neuromodulation, lending further support to the hypothesis that intramembrane cavitation is responsible for ultrasonic neuromodulation. They could thus pave the way towards new CNS therapeutic protocols, using the only method that currently allows targeted non-invasive neuromodulation with millimetre spatial resolution essentially anywhere in the brain. 1ELSC Center for Brain Sciences, Hebrew University, Jerusalem, Israel; 2Biomedical Engineering, Technion- Israel Institute of Technology, Haifa, Israel; 3Faculty of Life Sciences, Bar Ilan University, Ramat Gan, Israel Objectives Following previous in vivo stimulation of the retina, we aimed to achieve a first direct measurement of the response of mammalian retinal neurons to ultrasonic (US) stimuli, and to study and characterize this response. Methods We coupled a high-density phased array (986 elements on a 25x35 mm 2 area) to a system for multi-electrode-array (MEA) recording with 256 contacts. Mouse retinas were dissected and placed on the MEA, and sonicated at 2.3 MHz, applying varying durations and intensities, as well as stimulated by light. The acquired data were processed to detect action potentials (spikes) elicited by retinal ganglion cells, and analysed to reveal the relations between the stimuli and the responses.
Results We found prominent spike responses for stimuli in the range of 4.3-7.3 W/cm 2 and 0.5-1 s, which disappeared when the focus was steered 1.5 mm away. Furthermore, we found that the relation between the response strength and the stimulation intensity, or duration, followed a logistic sigmoid curve, while the response latency was described by a decreasing exponent. Lastly, we found indications that the observed responses to US stimuli are related to the '2 nd OFF' component in the responses to light stimuli. Conclusions These findings are the first direct demonstration of the response of the mammalian retina to US stimulation. The properties of the US transducer and the stimulation frequency indicate that non-invasive US stimulation of human retina is feasible, and may potentially evolve as an important tool for diagnosis and treatment of retinal diseases.
1Focused Ultrasound Foundation, Charlottesville, Virginia, USA; 2Neurosurgery, University of Virginia, Charlottesville, Virginia, USA; 3Ocean System Engineering, Jeju National University, Jeju, Korea (the Republic of); 4Biology, University of Virginia, Charlottesville, Virginia, USA; 5Pathology, University of Virginia, Charlottesville, Virginia, USA Objectives The objective of this research is to investigate the effects of thermal dose (TD) delivered by magnetic resonance-guided focused ultrasound (MRgFUS) on in vivo pig brain tissue. In current clinical applications of transcranial MRgFUS systems, continuous acoustic wave emission is used to heat brain tissue to peak temperatures over 58°C. However, there are some situations where it has proven difficult to reach the desired peak temperature due to high absorption of acoustic energy by skull bone. There are reports that thermal effects on tissue are well correlated with thermal dose, which suggest that treatment delivery could be prescribed in terms of thermal dose rather than peak temperature or electric/acoustic power.
It is also been demonstrated that the thermal dose threshold for permanent tissue damage is about 240 cumulative equivalent minutes (CEM) at 43°C for most of tissue. Currently available transcranial MRgFUS systems only allow the prescription of acoustic power and duration. In order to investigate the effects of thermal dose on in vivo brain tissue, we have developed a closed-loop control system to allow prescription thermal dose. This system monitors tissue heating via MR thermometry and provides pulse width modulation of output acoustic power in order to hold target tissue at a fixed temperature, and hence receives a nearly constant dose rate. Methods A FUS system (ExAblate 4000 Neuro 650 kHz system, InSightec) was used for sonication and an MRI system (Discovery MR75-3.0T, GE Medical systems) was used for thermometry and pre- and post-imaging.
A closed-loop control system was implemented on a personal computer to control pulse width modulation of the FUS system acoustic power in order to maintain a specified temperature based on the MR thermometry. Accumulated thermal dose was calculated in real time and used to stop the sonication so that a prescribed thermal dose was delivered to the targeted tissue. Phantom studies were performed to test the control system to prepare for animal experiments. One acute and six chronic experiments (with three day survival) were conducted to observe the effects of TD on pig brain by behaviour observation and post MR imaging of the brain (1 hour and 70 hours post procedure). Craniotomy was performed to create an acoustic access window, and sonication was applied on 4 spots in the thalamus of each pig.
Histology was also performed to compare it with MR imagery. Temperature in the pig brain tissue was estimated by rectal temperature for the MR thermometry baseline. TD was varied from 7 to 200 CEM while the target temperature was changed from 46 to 52 °C with appropriate acoustic power depending on target position and individual pig. This study was approved by the University of Virginia Institutional Animal Care and Use Committee. Results From the acute experiment, we could observe the lesions on MR images after 1 hour of sonication and histology subsequently confirmed the lesions.
For the chronic experiments, no obvious problem was observed in the behavior of any of the six animals. Eighteen sonication spots in 5 pigs were analyzed through MR images. One pig experiment failed to control temperature due to introduction of air bubbles between the brain and scalp during surgery procedure, and 2 sonication spots were excluded due to technical problems.
Large tissue changes were observed in MR images in all 6 spots over 100 CEM. The diameter of those tissue changes in MR T2-weighted axial images were measured and averaged to 2.9 ± 0. There is inconsistency in generating lesions for TD below 100 CEM. No lesion was shown in some lower TD from 7 CEM and 61 CEM, while some smaller lesions (.
Pig chronic study results showing the relations of lesion diameter (mm) based on enhancing region appearing in T2-weighted axial MR images with applied thermal dose in CEM. Conclusions These preliminary results from pig brain tissue generally confirmed the previous results from rabbit brain tissue in generating tissue changes over a certain TD, even though there are some differences in the FUS systems and the experimental procedures and analysis. For lower thermal dose below 61 CEM, there is significant variability in generating of tissue changes, while large tissue changes whose average diameter is 2.9 mm were observed in MR T2-weighted axial images for higher TD over 100 CEM, which were reported with similar tendency but a little difference in TD from the rabbit brain study.
These results may contribute to open the way to prescribe the thermal dose rather than peak temperature or acoustic power for brain treatments, and expand the treatment envelope beyond the current limitations in selecting targets and patients. This project is ongoing and will be further pursued with additional experiments for consolidation of the results and analysis. 1Hospital for Sick Children, Toronto, Ontario, Canada; 2University of Washington, Seattle, Washington, USA; 3Sunnybrook Research Institute, Toronto, Ontario, Canada; 4University of Toronto, Toronto, Ontario, Canada; 5Philips Healthcare, Markham, Ontario, Canada Objectives To determine if a clinical focused ultrasound system (Philips Sonalleve) can be used to perform mechanical liquefaction of brain tissue for neurological lesioning through a simulated fontanelle in a porcine model (simulating neo-natal patients). This work will determine the power of the system required to induce lesions using a boiling histotripsy (BH) pulsing protocol. Post-treatment, the lesion volume and border will be measured with MRI imaging and histological examination. Methods A porcine model was used as the in vivo model with a maximum weight. 1Guided Therapy Systems, LLC, Mesa, Arizona, USA; 2School of Medicine, University of Arizona, Tucson, Arizona, USA Objectives Chronic Plantar fasciitis (CPF) is a common cause of plantar heel pain that is a result of a degenerative process of the plantar fascia and its surrounding perifascial structures .
It is the most common cause of heel pain, affecting 10% of the U.S. Population, and one of the most common foot and ankle problems. More than twenty different treatments have been used for plantar fasciitis. Conservative treatments (rest, ice, stretching and NSAIDs) have been shown to effectively treat symptoms but 10% of patients fail conservative management and continue to have symptoms within 12 months and beyond.
Surgery consisting of partial PF release is often considered with 50% of patients having residual symptoms, in addition to surgical risk exposure. High frequency ITU, a novel potential approach to treating Plantar Fasciosis, was studied for the creation of small thermal injuries noninvasively inside symptomatic Plantar Fascia (PF). It has been shown to initiate a tissue repair cascade and promote collagen generation in musculoskeletal tissue [2, 3]. A double blinded, randomized, sham controlled clinical study for ITU treatment of chronic Plantar Fasciitis has been conducted by IRB approved clinical protocol to access clinical efficacy of the procedure. Methods Custom 3.2 MHz high intensity (10 kW/cm 2) ultrasound therapy system was designed and fabricated (GTS, Mesa, AZ, USA). Field simulations, testing and Schlieren images verified intensity, high focal pressure (17.3 MPa) and focal distance of 13–15 mm.
Each treatment consisted of 250–320 100 ms pulses creating matrices of small ablative thermal lesions of 4–5 joules at pre-programmed pitch of 1.6 mm. Each patient underwent two treatment sessions in 2 weeks, each treatment time did not exceed 12 minutes.
ITU placebo group consisted of the same treatment with energy set to 0. Treatment effects were assessed with diagnostic imaging ultrasound at 12 MHz (Spark, Ardent Sound, Mesa, AZ, USA) by a certified sonographer. Ultrasound images were analysed to determine symptomatic hypoechoic lesion size with PF. Patient reported outcomes consisted of PROMIS physical function computer adaptive test (PF-CAT), PROMIS global health, Foot Function Index pain subscale (FFIPS) [4, 5] and a non-validated heel pain specific questionnaire. Clinical protocol included (35) patients diagnosed with chronic heel pain due to Plantar Fasciitis (more than 3 months) and failed conventional therapy treatments.
Patients were randomized to standard therapy (anti-inflammatory pills, stretching and gel heel cups) plus ITU (“Treatment” group, n=26) of standard therapy plus sham ITU (“Control” group, n=9). Primary investigator, sonographer and study coordinator administering the study were blinded to group assignments. P-values were calculated via 2-tailed paired T-tests for both treatment and control groups. Results Patient-Reported Outcome Measures: Compared to the baseline assessment of Pain, the Treatment Group showed significantly improved pain scores compared to the Control (sham treatment) Group in follow-up visits including 12 weeks after the initial treatment. Foot Function Index Pain Score: Compared to the baseline assessment, the treatment group pain scores also showed significant improvement compared to the sham group. Diagnostic Ultrasound Imaging: During the 12 week follow-up period changes to the overall thickness of the PF were not statistically significant, while calculated volume size of hypoechoic lesions within the PF, just distal to the Calcaneus, showed significant change.
For the experimental group (n=28) the average hypoechoic lesion volume reduction was followed and compared to the baseline measurements just before the first Treatment; 2 week follow-up and 2nd treatment date (−28%), 4 weeks (−50%), 6 weeks (−66%) and 12 weeks (−80%). For the control group (n=10), the average hypoechoic lesion volume was followed and compared to the baseline just before the first Treatment; 2 weeks and 2nd sham treatment (+9%), at 4 weeks (+16%), 6 week (+29%) and 12 weeks (+31%). Unlike the experimental group, these lesions grew in size during the follow-up period. P-values calculated for all outcome results discussed above for both treatment and control groups were below.01, showing the statistical significance of the results.
Conclusions •. Intense Therapeutic Ultrasound has shown potential for effective treatment of Chronic Plantar Fasciitis.
Better designed studies with increased # of subjects will be considered to support ITU as an effective tool for the proposed clinical treatment. References  Neufeld S.K. And Cerrato R.; Plantar fasciitis: evaluation and treatment. J Am Acad Orthop Surg, June 2008, 16(6): p.
 Slayton M. And Barton J.; Healing tissue response with ITU (Intense Therapy Ultrasound) in musculoskeletal tissue, feasibility study. Ultrasonics Symposium (IUS), 2014 IEEE International, Chicago, USA, p.1654–1657.
 Slayton M. H., Amodei R. C., McNelly A. L.; Intense Therapy Ultrasound (ITU) for the treatment of Chronic Plantar Fasciitis: Preliminary Results of Clinical Study. 37th International Conference of the IEEE Engineering in Medicine and Biology; Milan, Italy, August 2015.  Rose, M., Bjorner, J.B., Becker J., Fries J.F.
And Ware J.E.; Evaluation of a preliminary physical function item bank supported the expected advantages of the Patient-Reported Outcomes Measurement Information System (PROMIS). Epidemiology, January2008, 61(1): p.  Budiman-Mak E., Conrad K. E.; The Foot Function Index; a measure of foot pain and disability. Epidemiology, 1991, 44(6): p.
1Guided Therapy Systems, Mesa, Arizona, USA; 2The CORE Institute, Phoenix, Arizona, USA Objectives Acute and Chronic pain of the Common Extensor Tendon (CET) region, lateral epicondylitis or tennis elbow is a common pathology of both athletes and non-athletes affecting up to 3% of the population at large , while the prevalence of chronic problems caused by overuse in tennis players can be as high as 40%. Elbow tendinopathy represents an important set of pathologies that account for lost recreation time, decreased quality of life, and work-related disability claims. Conservative treatment of the Epicondylitis or -osis is recommended as the initial strategy by most authors. This strategy includes identification and correction of possible etiological factors, and a symptom related approach. Generally, the initial treatment consists of a multifactorial approach that may include a combination of rest (complete or modified activity), medication (NSAIDs for Epicondylitis), stretching and strength training.
More aggressive treatments for CET include: Cortisone injection, Plasma Rich Platelets (PRP), Tenotomy, ESWT. High frequency ITU, a novel potential treatment for CET, was studied for the creation of small thermal injuries noninvasively inside symptomatic Common Extensor Tendon (CET). It has been shown to initiate a tissue repair cascade and promote collagen generation in musculoskeletal tissue [2–5]. A blinded, randomized, clinical study for ITU treatment of chronic Lateral Epicondylitis has been conducted by IRB approved clinical protocol to assess clinical efficacy of the procedure.
Methods Custom 4.5 MHz high intensity (47.9 KW/cm 2) ultrasound therapy system was designed and fabricated (GTS, Mesa, AZ, USA). Field simulations, testing and Schlieren images verified intensity, high focal pressure (37.9 MPa) and focal distance of 6 mm. Each treatment consisted of 80 14 ms pulses creating matrices of small ablative thermal lesions of 1 joule at manually targeted area set by diagnostic ultrasound imaging.
Each subject underwent two treatment sessions 4 weeks apart. Each treatment time did not exceed 10 minutes.
Treatment effects were assessed with diagnostic imaging ultrasound at 20 MHz (Spark, Ardent Sound, Mesa, AZ, USA) by a certified sonographer. Ultrasound images were analysed to determine changes in the peri-tendon region, including hypoechoic areas, calcifications and dependent free fluid.
Subject reported outcomes consisted of PRTEE survey , physical examination, Universal Analog Visual Pain Score17 and a Patient Reported Satisfaction Survey . Clinical protocol includes 25 subjects diagnosed with chronic Tennis Elbow, or Lateral Epicondylosis (more than 3 months) and failed conventional therapy treatments.
Subjects were subjected to standard therapy (stretching and strength exercises, hot and cold compresses and compression support) plus ITU. Primary investigator, sonographer and study coordinator administering the study were blinded to group assignments.
P-values were calculated via 2-tailed paired T-tests at each visit of the clinical study. Results The results presented below are initial findings for the first 12 subjects currently being followed through the study. PRTEE: Patient Reported Tennis Elbow Evaluation Final Score is a weighted Pain Score based on 15 questions grouped into 3 categories: Overall Pain, Functional Disability and Usual Activities. Subjects respond to each question with a Pain Score of 0–10. Each category is then summed and weighted with a maximum score of 100 (Overall Pain 100%, Functional Disability 50% and Usual Activities (50%), n=12, Fig.. See text for description Diagnostic Ultrasound Images: Diagnostic Ultrasound Images show a consistent increase of free fluid 2 weeks after the first treatment, with a progressive reduction in free fluid at 8 weeks in subjects with no to mild peri-tendon calcifications.
These subjects correlated well with improving PRTEE survey scores. Subjects with little or no improvement in PRTEE scores consistently presented with moderate to severe peri-tendon calcifications. P-values calculated for the above reported outcomes were not statistically significant for Visits 2 and 3 (P>0.05) while results for Visits 4 and 5 demonstrated P. Significant reduction of pain scores per activities (PRTEE) and Self-Reported Outcome Measures (83% improvement) with average Universal Pain Scores reduction from 5.0 to 2.0 were statistically significant (p. 1LabTAU - U1032, INSERM, Lyon, France; 2Centre Leon Berard, Lyon, France Objectives Managing colorectal liver metastases (CLM) is a major clinical challenge, and surgery remains the only potentially curative treatment.
Five-year survival rates of up to 51% have recently been reported. However, only 10–20% of patients are eligible for surgery, which is often precluded by the number, size and/or location of metastases, or because the necessary resection will leave insufficient volume of functional liver. Radiofrequency ablation (RFA) is the main technology that has been used in association with surgery as a tool to expand the number of patients who may be candidates for liver directed therapy. However, RFA has several limitations. There is a risk of inadequate treatment due to the heat sink effect of blood flow, RFA does not allow reliable real-time monitoring, and it require intra-parenchymal introduction of a probe.
Moreover, only small hepatic volumes can be targeted. These limitations could explain the high rates of local recurrence seen after RFA. High intensity focused ultrasound (HIFU) has been proven effective in a wide range of clinical applications, especially prostate cancer. The ablation achieved by conventional HIFU is small and ellipsoidal. The dimensions vary according to transducer characteristics but are typically 1–3 mm (transverse) and 8–15 mm (along beam axis). In clinical practice, hundreds of superimposed ablations are required; and the procedure may take up to two hours. Even so, HIFU has several potential advantages in the treatment of liver tumours: there is no need to puncture the parenchyma, the extent of the thermal lesions achieved is not reduced by hepatic perfusion, and it is possible to monitor the effects of therapy in real time.
However, extra-corporeal treatment of the liver is difficult because presence of the ribcage may stop propagation of ultrasound waves and respiratory motion may cause targeting problems. HIFU treatment of CLM needs to be improved, and reducing the duration of surgical intervention by increasing the size of ablated fields is particularly important. A HIFU device enabling destruction of larger liver volumes has been developed based on toroidal transducers. Preliminary in vitro and preclinical work demonstrated the potential, feasibility and safety of such HIFU ablations.
During laparotomy in a porcine model we demonstrated that this HIFU device achieves reproducible ablations with an average volume of 7 cm3 (with 20 mm diameter and 25 mm long axis) in 40 seconds. Such preclinical work has to be translated into clinical practice through controlled trials, and the aim of this study was to assess the feasibility and safety of HIFU ablation in patients undergoing hepatectomy for CLM, as well to collect efficacy and accuracy data. This study is registered with Clinical-Trials.gov (). Methods This study was a prospective, single-centre phase I/II study evaluating the feasibility, safety and accuracy of HIFU during surgery in patients with CLM. The protocol was reviewed and validated by a national ethics committee (CPP Sud-Est IV) according to French and European directives. Since this study was the first use in man of intra-operative hepatic HIFU, ablations were made only in areas of liver scheduled for resection. This allowed real-time evaluation of HIFU ablation while protecting participating patients from any adverse effects related to this new technique.
The transducer has a toroidal shape 70 mm in diameter and is divided into 32 ultrasound emitters of 0.13 cm 2 operating at 3 MHz. The radius of curvature is 70 mm. A 7.5 MHz ultrasound imaging probe was placed in the centre of the device and was used to guide the treatment.
The imaging plane was aligned with the HIFU focal zone. Six patients were included in the Phase I. Two single thermal ablations were created in each patient. Thirteen patients were included in Phase IIa and two HIFU ablations were to be placed precisely in a target previously identified in ultrasound images (step 1) and then at distance (step 2) from a target. Five patients were included in Phase IIb until now.
HIFU ablations were created to ablate metastases (20 mm maximal diameter) with safety margins in all directions. The exposure time varied from 40 s to 370 s according to the diameter of the metastases to be treated.
Results In agreement with preclinical studies, the demarcation between ablated and non-ablated tissue was clearly apparent in ultrasound images and histology. The dimensions measured on ultrasound imaging were correlated (r=0.88, p3 mm in all directions) in 370 seconds. The dimensions of HIFU ablations created in 370 s were a diameter of 48 mm and a long axis of 51 mm. Conclusions This new HIFU device safely achieved large volume liver ablations in 40 s, with a precision of one to two millimetres under real-time monitoring. HIFU ablations of small metastases (.
Department of Oral Maxillofacial and Head Neck Oncology, Shanghai 9th People's Hospital, Shanghai, China Objectives To evaluate the efficacy and the main side-effects during the clinical trial of this new ultrasound hyperthermia system combined with chemotherapy in oral cancer, meanwhile, to observe the preliminary clinical response of this combined therapeutic modality. Methods Thirty four cases of oral squamous cell carcinoma entered this clinical trial, from which 23 had advanced oral carcinoma and were treated with new ultrasound hyperthermia system combined plus docetaxel–cisplatin–fluorouracil regimen (test group). Eleven patients only received chemotherapy with docetaxel–cisplatin–fluorouracil regimen (control group).
The thermo-index were detected during the course of hyperthermia, the chief-complain of the patients were also recorded. The systemic physiological, biochemical and immunological index were tested before and after the treatment respectively. The therapeutic response was estimated 1 month after 2 cycles of the treatment. Results Twenty three cases of oral squamous cell carcinoma enrolled the clinical trial of local ultrasound hyperthermia combined with chemotherapy. 230 times of ultrasound hyperthermia in total were performed. The ultrasound hyperthermia system operated smoothly, no malfunction was found. The main thermo-index were: the maximum heating temperature was108 F, the average heating temperature was 106 F, the minimum heating temperature was 104 F, the fraction of heating time more than 108 F was 0.46, the average treatment time was 37.74±8.88min.
PR+CR was 71% (test group). The main local side-effects were low-grade pain (6/23). The incidence of adverse effects was similar between both study groups, no bone marrow suppression (over III). Conclusions The system combined with docetaxel–cisplatin–fluorouracil regimen is effective and safe in the treatment of advanced oral cancer.
The main side-effects of local ultrasound hyperthermia combined with chemotherapy are low-grade pain or tolerable pain. There is no immune function and obtains satisfying short-term response. 1The School of Biomedical Engineering, Science and Health Systems, Drexel University, Philadelphia, Pennsylvania, USA; 2Department of Surgery, College of Medicine, Drexel University, Philadelphia, Pennsylvania, USA; 3Biostatistics and Epidemiology, University of Pennsylvania, Philadelphia, Pennsylvania, USA Objectives This talk examines the challenges associated with the design of clinically viable ultrasound applicators operating at the relatively low frequency (20 kHz) and intensity (. 1Radiology, Brigham and Women's Hospital, Boston, Massachusetts, USA; 2Neurobiology, Harvard Medical School, Boston, Massachusetts, USA Objectives Thermal ablation with transcranial MRI-guided focused ultrasound (TcMRgFUS) is being tested clinically for as an alternative to surgery for functional neurosurgery and brain tumour resection. The current TcMRgFUS system, which operates at 650–670 kHz, is limited by skull heating to a small central region in the brain.
Use of a lower acoustic frequency will reduce skull heating, but at the same time the focal heating will decrease and the risks of uncontrolled cavitation (the formation of microbubbles) increase. The purpose of this study was to evaluate the feasibility of thermal ablation in nonhuman primates using a system that operates at a lower acoustic frequency and to determine whether it can increase the “treatment envelope” for TcMRgFUS. Methods The experiments were approved by our institutional animal committee.
Thermal ablation with the 230 kHz ExAblate Neuro system (InSighTec) was tested over five sessions in three rhesus macaques. In each session a target in the thalamus was sonicated transcranially at 40–50 s at acoustic power levels ranging from 90–560 W. The TcMRgFUS system software modulated the acoustic power in real time with a closed-loop controller that maintained a low-level of acoustic emissions, which are correlated with cavitation activity.
MR temperature imaging (MRTI) was acquired at 3T (LX, GE) in a single plane using a 14 cm surface coil (TR/TE: 29/13 ms; flip angle: 30°). Measurements of the peak temperature rise at the focus and on the outer brain surface were compared for the different animals as a function of the applied acoustic energy. For the brain surface we measured the average temperature at the hottest 5% of the voxels and over a two voxel wide strip and we also normalized the measurement by the outer skull area.
Temperature measurements were used to calculate the accumulated thermal dose, which was then compared to post-sonication T2-weighted, T2*-weighted, and contrast-enhanced T1-weighted MRI. The focal and skull-induced heating on the brain surface were compared to an earlier study performed in macaques with a 650 kHz version of this system. Results Focal heating sufficient to create an MRI-evident thermal lesion was achieved in 4/6 targets; the peak thermal dose exceeded 240 CEM43°C at these targets (Fig. ). Heating at the focus was slightly higher than that measured on the brain surface. The focal heating increased linearly as a function of the applied energy at a rate of 3.2 ± 0.4°C per kJ (R2: 0.81).
The surface area of the outer skull ranged from 47–55 cm2. For the hottest 5% of the voxels on the brain surface included in the MRTI imaging plane, the temperature rise increased linearly as a function of temperature at a rate of 126.6 ± 7.3°C per kJ/cm 2. For a two voxel wide strip over the entire brain surface, this increase was 62.7 ± 7.5°C per kJ/cm 2. The extent of MRI-evident changes (apparent oedema in T2-weighted MRI, BBB disruption post-contrast, no petechiae in T2*-weighted MRI) were consistent with 240 CEM43°C contours.
One lesion imaged one week after FUS increased in size. MRTI ( top) and post-FUS imaging ( bottom) obtained in two sessions in Monkey 1. Thermal dose contours at 30 (orange) and 240 (red) CEM43C were calculated from the MRTI. Immediately after each session, a small lesion was observed in contrast-enhanced T1-weighted.
Conclusions Analyses of the MRTI and post-sonication MRI suggest that the lesions were consistent with thermal mechanisms. The temperature rise increased linearly with the applied energy, and no evidence of cavitation-related petechiae were evident after sonication. The MRI-evident lesions were consistent with isodose contours drawn at 240 CEM43°C, a conservative threshold often used to guide thermal ablation. However, since it is known that thermal damage can take several hours to manifest in MRI and the lesion we imaged at one week increased in size, it is likely that the size of the lesion was underestimated by this dose value. Similar tests in macaques with a version of this system operating at 670 kHz (Hynynen et al., Eur J Radiol 2006; 59: 149–56) measured skull-induced heating of 130°C per kJ/cm 2 of outer skull surface, more than twice of that measured here (63°C per kJ/cm 2).
While no or minimal focal heating was observed at 670 kHz, with this 230 kHz system we were able to reach ablation-level thermal dose values. Thus, these preliminary results thus suggest that this low frequency system can expand the area of the brain that can be targeted for thermal ablation without overheating the skull. The closed-loop feedback system successfully maintained a low level of acoustic emission (and presumably microbubble activity) and immediately stopped the sonication when excessive levels were detected.
However, additional work is needed to understand whether low-level cavitation activity played a role in the focal heating, to characterize the lesions in histology, and to examine whether safe cavitation levels can be maintained in tumours where the cavitation threshold may vary. 1Radiology and Nuclear Medicine, Radboud University Medical Center, Nijmegen, Netherlands; 2Radiology, Brigham and Women's Hospital, Boston, Massachusetts, USA Objectives HER2-targeting antibodies prolong survival in patients with HER2-positive breast cancer metastases outside the brain. However, the response of brain metastases to these drugs is poor and it is hypothesized that the blood–brain barrier (BBB) limits drug delivery to the brain. We aim to improve delivery by temporary disruption of the BBB using focused ultrasound (FUS). Here we evaluate the treatment benefit of combining two antibody therapies that target the HER2-receptor with FUS-mediated BBB disruption in a breast cancer brain metastasis model. Methods MDA-MB-361 HER2-positive human cancer cells were injected in the right brain hemisphere of nude rats.
The animals were divided in three treatment groups of 10 animals each: the control-group received no treatment; the antibody-only group received trastuzumab and pertuzumab (antibodies that target the HER2-receptor); and FUS+antibody-group received trastuzumab and pertuzumab in combination with FUS-mediated BBB disruption. The six weekly treatments started five weeks after tumour implantation, when the tumour diameter was around 2 mm. The FUS treatments took place in a 7T MR-scanner using a single-element, spherically-focused 690 kHz-transducer. Trastuzumab and pertuzumab were injected before the first sonication.
At the start of each sonication (duration 60s, 10-ms bursts, burst repetition frequency 1 Hz), the ultrasound contrast agent Optison (100 μl/kg) was injected. The complete tumour was treated in 4 to 14 sonications that were separated 1 to 1.5 mm. Peak negative pressure amplitudes in water between 0.46 and 0.62 MPa were used. Before and after the sonications, MR imaging was performed consisting of T2-weighted (T2w), T1w and T2*w imaging to locate the tumour, confirm BBB disruption and study the presence of hemorrhages.
In two animals tumour leakiness was studied by comparing T1w imaging before and after gadolinium injection before the tumours were sonicated. The difference in signal intensity change in pre- and post-contrast T1w images was determined between the tumour and contralateral brain region (= SI%). In all FUS-treated animals BBB disruption was confirmed with contrast-enhanced T1w imaging and quantified using the same method as for the tumour leakiness. Pre- and post-sonication T2*w images were inspected for hypo-intense regions, which can indicate extravasated erythrocytes. Every other week, high-resolution T2w imaging was performed to determine tumour volume.
The growth rate (r) was determined by fitting the tumour volumes to the following formula: volume(t)=a*exp(r*t), in which t is the time in days. The growth rate of each tumour was determined for the treatment period (week 5 to 11) and the follow-up period (week 11 till sacrifice). An animal was classified as ‘responder’ if the growth rate was lower than the mean growth rate of the control animals minus two standard deviations. The animals were euthanized if the tumour size exceeded 13 mm in diameter or if the condition of the animal was poor.
From nine animals, histology was obtained (hematoxylin and eosin (H&E)) and the brains of five animals were stained for HER2. Results BBB disruption was successful in all sessions with an average SI% of 21.2% (range 4.5 – 77.6%). The mean SI% of two tumours before BBB disruption during the six treatment weeks were 0.4% and 0.6%, indicating that the tumours were not leaky before disruption (Fig. ). In 33% (20/60) of the FUS-sessions, regions were present that were clearly more hypo-intense on post- than on pre-sonication T2*w images, suggesting hemorrhages.
In the remaining 67% of the sessions, no or a small difference in hypo-intensity was observed. A T1weighted image before contrast administration. The red arrow indicates the tumour.
B No difference in enhancement of the tumour is observed after contrast administration (SI=0.4%). C After focused ultrasound-mediated blood–brain barrier disruption. In the FUS+antibody-group, 4/10 animals were classified as responders during the treatment period (week 5 to week 11) with an average growth rate of 0.010±0.007, compared to 0.043±0.013 for the non-responders.
There was no difference in the average SI% of the responding rats (21.8%±16.7) and the non-responding rats (20.7%±9.7). None of the control or antibody-only animals were classified as responder. When the FUS+antibody-animals are grouped, no significant differences in mean growth rates were observed between the control, antibody-only and FUS+antibody animals for the treatment period, nor for the follow-up period. High-resolution T2w imaging showed that the tumour was homogenous in almost all animals till week 13–15, when cystic and necrotic areas started to develop. The tumours showed also a heterogeneous appearance on H&E stained sections and the complete tumour was expressing the HER2-receptor in the examined animals.
Conclusions In this study, we demonstrate that FUS-mediated BBB disruption in combination with antibody therapy can slow down the growth of brain metastasis from breast cancer. As the tumours were not leaky before BBB disruption and no difference in growth rates was observed in the antibody-only group, the disruption of the BBB is necessary for drug delivery to these brain metastasis. Interestingly, only part of the rats responded to the treatment, the other animals had the same growth rate as the control-group. This is in line with a previous study (Park et al. Release), where antibody therapy was combined with FUS in a different brain metastasis model and in part of the animals a strong response was observed, while the other animals did not respond.
We did not observe a difference in tumour volume at the start of the treatment, in HER2 expression on histopathology, or in contrast-enhancement on MR images between the responders and non-responders to explain this. Better understanding of why certain animals respond is needed and will help in translating this technique to the clinic. 1Surgery (Neurosurgery), University of Toronto, Toronto, Ontario, Canada; 2Sunnybrook Health Sciences Centre, Toronto, Ontario, Canada; 3Surgery (Neurosurgery), University of Alberta, Edmonton, Alberta, Canada Objectives To determine the factors influencing outcome after MR-guided focused ultrasound (MRgFUS) thalamotomy for essential tremor. Methods Between May 2012 and February 2013, 6 patients were treated with MRgFUS thalamotomy. The first 4 patients have been reported (Lipsman et al., Lancet Neurol.
2013 May; 12(5): 462–8). Prospective recording of data from preoperative screening to 3 month follow up according to an experimental protocol using the clinical rating scale for tremor (CRST), and then a 2 year follow up examination and assessment were done.
Maximum temperature at the focus of sonication was determined and post-treatment day 1 MRI scans were reviewed for lesion size and location. A point derived by our current method of determining the probable location of the ventral intermediate nucleus (VIM) of the thalamus was taken as the starting point for each treated case and a deviation vector from that point to the centre of each lesion produced was plotted. Results For the 6 patients, the mean CRST A scale (rest, posture and action) for the treated hand and arm prior to treatment was 7.2. At 1 week post-treatment, the mean CRST A was 0.67. At 3 months, the mean CRST A was 0.83 and at 2 years approximately 3.33.
(At 2 years, the CRST A for 2 patients was estimated from a narrative account). Mean lesion size, excluding one very large lesion with a volume 2.7 times the mean volume of the other 5 patients, was 90.2 mm 3. Only 2 patients had no decline in thalamotomy effect. Of these, one had a relatively large lesion of 107.5 mm 3, which was located at the predicted location of the VIM nucleus. The other patient’s lesion was located 2.4 mm lateral to the predicted VIM location.
He had prominent ataxia following his treatment. This subsided by 3 months. The patient with the large lesion, treated for left hand tremor, had persistent tingling of the left side of his mouth, and his left thumb and 3 fingers but excellent early relief of tremor. Although there was some persisting reduction of tremor at 2 years, he could no longer write, nor drink without spilling.
The centre of his lesion was 1.3 mm lateral and 0.3 mm posterior to the expected VIM location. In its superior-inferior dimension his lesion measured 9.4 mm. The maximum temperature achieved at treatment was 63°C, higher than the mean of 58°C. This decline may, in part, be due to the progress of his condition, with increasing tremor on his untreated side and the onset of tremor in both legs.
Two of the patients with a decline in function had relatively small lesions. Conclusions Not all patients have lasting benefit from MRgFUS thalamotomy. The effect of relatively large lesions may be more durable, but lesioning temperatures of greater than 60°C should likely be avoided.
1Sunnybrook Health Sciences Centre, Toronto, Ontario, Canada; 2Surgery (Neurosurgery), University of Toronto, Toronto, Ontario, Canada Objectives To determine the factors that lead to bone marrow injury in the skulls of patients undergoing MRgFUS cerebral ablations for the treatment of movement disorders such as ventral intermediate (VIM) nucleus thalamotomy for tremor and pallidotomy for L-dopa induced dyskinesia (LID), and to follow the course of healing. Methods All patients undergoing functional cerebral ablations produced for the mitigation of movement disorders are followed with serial MRI scans according to study protocol to assess the evolution of the cerebral lesions.
In one patient subjected to very high power sonication in the attempt to produce a pallidotomy for LID, skull lesions were noticed on a follow up MRI scan, produced 4 months after his MRgFUS procedure. A review of other treated patients is currently underway. Results Multiple ovoid lesions throughout the calvarium, new since the immediate post-treatment MRI scan done January 30, 2015, were seen on the MRI scan done May 12, 2015 (Fig. ).
Their appearance resembles that of bone infarcts. The MRI scan was repeated on October 2, 2015. Many of the ovoid lesions were still visible.
This patient underwent sonication increasing to a maximum power of 1100 W for 31 seconds. During the procedure, the scalp and skull were constantly cooled with flowing degassed water at 13 °C. Despite this sonication, the target locus in the globus pallidus reached only 48 °C.
1Cyprus University of Technology, Limassol, Cyprus; 2City University, London, United Kingdom Objectives In this paper an extensive study of using MR-guided focused pulsed ultrasound system is presented for the treatment of stroke using thrombolytic drugs in a model in vitro. Methods A single element spherically focused transducer of 4 cm diameter; focusing at 10 cm and operating at 1 MHz was used. The transducer was mounted in an MR compatible robotic system of 3 axes. The artery was modelled using a silicone tube.
Tissue was modelled using agar-evaporation-silica gel. Coagulated blood was used to model thrombus. A thermocouple was placed in the thrombus in order to measure the thrombus temperature.
Results The effect of power, presence of bubbles, temperature, presence of agar-evaporation milk-siligal gel, time of sonication, pulse repetition frequency, presence of standing waves, flow velocity were investigated. The goal was to maintain a temperature increase of less than 1°C during the application of pulsed ultrasound (called safe temperature). With the application of ultrasound alone or thrombolytic drug alone there was no notable destruction of the thrombus.
Conclusions With the combination of ultrasound and thrombolytic drugs sufficient destruction occurred after 30 min, but the rate of destruction of thrombus (mL/min) is considered low. Thus, the clinical use of focused ultrasound for sonothrombolysis despite the full parametric study that we performed is considered pessimistic. 1INSIGHTEC, Tirat Carmel, Israel, 2Weizmann Institute, Rehovot, Israel, 3Sheba Medical Center, Ramat Gan, Israel Objectives Current trans-cranial Magnetic Resonance guided Focused Ultrasound Surgery (tcMRgFUS) treatments are limited to the targets that are located at the centre of the skull. Superficial and peripheral targets are prone to lower acoustic intensity reaching the focal point due to the geometry of the skull and the ultrasound transversal through it.
A possible solution for this problem is reduction of the transmitting frequency. Reducing the frequency is a trade-off between higher skull penetration and lower tissue absorbing.
In addition, lower frequency has a lower threshold to induce cavitation. Previously it was reported () that the transient cavitation threshold for the muscle tissue acts linearly with frequency as where P th is the cavitation pressure threshold and f is the transmitting frequency. However this threshold was not reported to cause any unintentional pathological damage.
In the presented work, different levels of acoustic intensities resulting in various occurrences of cavitation were applied to an in-vivo pig brain model, reaching various temperature levels and causing various pathological effects. Methods 36 subjects underwent craniotomy and were sonicated using various ultrasonic parameters (ExAblate Neuro low frequency system, 220 Khz, by INSIGHTEC, Ltd). The temperature rise was measured using MR thermometry (1.5T GE HDx MRI by GE Healthcare, with an integrated Head Coil, by InSighTec) and cavitation signal was measured and recorded using integrated hydrophones.
20 subjects underwent 2 weeks follow up with post procedural MR imaging one, five, seven and fourteen days after the procedure. The brains were harvested, fixed in formalin and sliced to 3 mm slices.
Macro-pathological slices for randomly selected subjects were also performed. Results Figure represents the graph of temperature rise as a function of applied energy. Figure represents the graph of cavitation activity as a function of maximal acoustic power. Figure shows a follow up imaging for 2 lesions performed on a single subject, Fig.
Is a macro pathology slide for the subject presented in Fig.. In general the temperature rise grew linearly with the applied acoustic energy; the cavitation activity was linearly dependent to the maximum applied acoustic power. For sonications that were in the central cavitation activity area as presented on Fig. The lesions were well defined and increased in size till the 5 th day follow up and then reduced in size becoming scarf tissue as presented on Figs. Macro pathology revealed that tissue rapture is seen on the micro level; however it is well defined and limited within the lesion area.
Macro pathology of the slides presented on Fig.. Only one lesion was detected Conclusions Cavitation threshold levels that were observed in brain agree with the levels reported in literature. Additional levels of cavitation were observed and associated with effects on tissue as seen in MRI and histology. The data collected suggests cavitation levels that can be applied while keeping lesioning effect to the confined area and avoiding haemorrhages in tissue. Integrating a real time control over the level of cavitation and keeping the level below the safety threshold results in safe and effective tissue ablation in brain.
1Biomedical Engineering, Columbia University, New York, New York, USA; 2Radiology, Columbia University, New York, New York, USA; 3Neuroscience, Columbia University, New York, New York, USA Objectives Real-time cavitation monitoring during the focused ultrasound (FUS) induced blood–brain barrier (BBB) opening is crucial in assessing and controlling the BBB opening outcomes and safety. Currently, passive cavitation detection using a single-element detector for quantification of the stable and inertial cavitation doses has shown good correlation with the opening volume and the molecular delivery efficiency in nonhuman primates (NHPs). However, an off-line magnetic resonance imaging (MRI) is required for confirming the targeting or opening area in the brain after the FUS procedure. It is therefore essential to develop transcranial cavitation mapping in providing the spatial distribution of cavitation intensity in real time in order to precisely assess and control the BBB opening outcomes with accurate targeting during the procedure. The aim of this study is to develop real-time cavitation mapping using time-exposure acoustics and passive sparse matrix beamforming with the performance evaluated in both the in vitro primate skull (NHP and human) experiments and the in vivo NHP experiments during BBB opening.
Methods Similar to array-based passive cavitation detectors, a linear probe (L7-4, Philips) with a programmable data acquisition system (Vantage, Verasonics) was used to acquire cavitation signal passively during the sonication (frequency: 0.5 MHz, pulse length: 10 ms, PRF: 5 Hz, pressure: 150–600 kPa) with in-house made microbubbles (lipid-shelled and monodisperse with a diameter of 4–5 μm) and a single-element FUS transducer with a coaxially aligned flat-band hydrophone as a single-element passive cavitation detector. Time-exposure acoustics for an integration of a series of passive cavitation images over the exposure time reconstructed by dynamic receive beamforming using sparse matrix calculation in graphic processing unit (GPU; Tesla K40, NVIDIA) were developed for the reconstruction of passive cavitation maps in real time. For the in vitro experimental setup, a phantom with a channel of 4 mm in diameter and an infusion pump was used to mimic the vessel with microbubble circulation (a concentration of 2×10 5 bubbles/mL with a flow rate of 1 mL/min), and the FUS transducer and the linear array were both focused at the channel orthogonally. B-mode imaging with the linear array was performed before acquiring the passive cavitation signal in order to confirm the alignment of both the linear array and the FUS transducer to the channel.
Three sets of passive cavitation maps were acquired using this in vitro setup: 1) without the skull, 2) with the NHP skull and 3) with the human skull placed between the phantom and the linear probe. The effects of acoustic pressure, exposure time and aperture size to the intensity and focal size of the cavitation maps were all evaluated, as well as the computational cost in GPU and the sensitivity through the skull. Furthermore, the in vivo cavitation maps were acquired during the sonication for BBB opening in NHPs (duration: 2 min) and compared with the BBB opening outcomes in the MRI. Results The results of the in vitro experiments showed that the cavitation location corresponded to the microbubble disruption in B-mode images, and both the intensity and the focal area of the cavitation maps increased with pressure. Increasing the exposure time eliminated the interference outside of the focus and enhanced the focalization by minimizing the focal area, while both the intensity and the focal area reached a plateau at the exposure time of 62.5 μs. The focal size especially in the axial direction increased with decreasing aperture size, suggesting an improved focalization by using a larger aperture size of the array-based PCD.
The computational time for the exposure time of 62.5 μs was 9.5 s, which can be decreased to 0.27 s in achieving real-time monitoring by decreasing the exposure time to 1.44 μs. By placing the skull, it was found that the cavitation signals were still detectable through the NHP and human skulls at 300 kPa and 600 kPa with the mapping system, respectively.
For the in vivo experiments, the BBB opening in NHP were successfully monitored with passive cavitation mapping targeting at the caudate and the hippocampus, the deep subcortical structure in the brain. Conclusions A real-time cavitation mapping technique using time-exposure acoustics and passive sparse matrix beamforming has been developed with the performance and the sensitivity through the primate skull evaluated, and was used for monitoring of the BBB opening in NHPs. This novel transcranial monitoring technique providing both the spatial and intensity information of cavitation in real time during the FUS procedure is promising in assessing and controlling the targeting, treatment efficacy, and safety precisely. Cyprus University of Technology, Limassol, Cyprus Objectives An animal model that creates Amyloid beta (Ab) plaques in the brain was implemented by delivering high cholesterol diet in rabbits for 3 months. The goal was to reduce the plaques using focused ultrasound (FUS) in combination with external antibodies.
Methods A single spherically focused transducer was used which operates at 1 MHz, has focal length of 10 cm and diameter of 3 cm. The rabbit was placed in a custom made MRI compatible positioning device. Theoflavin staining was used in order to measure the plaque load at the end of each experiment. Results Using pulse FUS the blood brain barrier (BBB) was opened repeatedly up to 5 times at three day intervals. The opening of the BBB disruption was imaged using contrast-enhanced T1-weighted fast spin echo. By increasing the number of sessions, the number of plaques decreases (both for internal and external antibodies). With the use of FUS only (internal antibodies) the drop of average number of plaques/mm 2 was reduced by 20% (in 5 sessions).
The effect of external antibodies was more drastic. With 5 BBB sessions the average number of plaques/mm 2 was reduced by 60%. Conclusions This study demonstrated that by opening the BBB, it will be possible to deliver internal and external antibodies to the brain, which eliminates Alzheimer disease (AD) plaques. More important by opening the BBB frequently (up to 5 times in this study) the reduction in the number of plaques is enhanced. Therefore FUS has the potentials to be used non-invasively for the treatment of AD.
1Daegu-Gyeongbuk Medical Innovation Foundation, Daegu, Republic of Korea; 2Kyungpook National University, Daegu, Korea (the Republic of ) Objectives Blood–brain barrier (BBB) is composed of both physical barrier with tight junctions and functional barrier with active efflux transporters. Mechanism of the functional barrier is mediated by P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP) in brain endothelial cells. Past studies have shown that focused ultrasound (FUS) combined with microbubbles can disrupt the physical barrier of the BBB by exerting mechanical stress on the tight junctions; however, no study was performed to investigate the impact of FUS and microbubbles on the functional barrier of the BBB. Therefore, this study investigated the impact of BBB disruption induced by FUS and microbubbles on the expression of P-gp. We also investigated correlation between magnitude of the BBB opening and the down-regulation of P-gp. Methods A single target region was sonicated (0.5~0.7 MPa) transracially in one hemisphere in 3 rats using a 1 MHz FUS transducer; the other hemisphere served as a control. For the BBB disruption, 10 ms bursts were applied at 1Hz pulse repetition frequency (PRF) for 120 s and combined with IV injection of a microbubble ultrasound contrast agent (Definity 0.1 ml/kg).
An MR contrast agent (Magnevist 0.4 mM/kg) and Evans Blue (0.15 ml/kg) were injected immediately after the sonication to indicate area of the BBB disruption in MR image and fluorescence spectroscopy, respectively. In order to measure the P-gp expression using a confocal fluorescence microscopy, the brains were fixed after perfusion and then stained immunohistochemically with a monoclonal antibody (C219) which reacts with a P-gp epitope. Results A T1 contrast enhanced MR image and Evans Blue fluorescent intensity at the sonicated regions indicated localized BBB disruption (Fig. ).
Both the MR contrast intensity and the Evans Blue fluorescent intensity were significantly increased in the targeted regions compared to the control regions (p. A A T1 contrast MR Image of a rat brain at sonification region (the opposite hemisphere of the brain served as control). B The fluorescence intensity of the P-gp expression at the soicated locations were reduced by an average of 63.2±18.4% compared. Conclusions This study demonstrates that the BBB disruption induced by FUS and microbubbles reduces the expression of P-gp, and the level of the down-regulation of P-gp is significantly correlated with the magnitude of the BBB opening. These results suggest FUS + microbubble as a promising mean for the brain drug delivery through the BBB by overcoming both the physical and the functional barrier of the BBB. 1Radiology, Johns Hopkins University, Baltimore, Maryland, USA; 2Philips, Andover, Massachusetts, USA; 3National Cancer Institute, Bethesda, Maryland, USA Objectives MR-guided focused ultrasound (MRgFUS) can be used for a large range of non-invasive therapies using mechanical and thermal mechanisms.
For instance, it has been demonstrated that a combination of low intensity focused ultrasound and synthetic microbubble scan be used to safely, locally, and transiently disrupt the blood–brain barrier (BBB). Typically, transcranial MRgFUS thermal ablation requires large aperture phased arrays with many elements operating at lower frequencies and higher powers than body systems due to high transmission losses through the skull.
However, in low pressure applications at low duty cycles, such as BBB disruption or neuromodulation, it may be feasible to use 'body' systems that have smaller aperture transducers with fewer elements . The objectives of this study were to use a clinical body MRgFUS system to: •. A and b: Coronal and sagittal representations of the locations examined. C: Picture of the hydrophone and skull arrangement for one of the 'Left 45°' orientations. The transducer is below the table Results Hydrophone measurements demonstrated a great deal of variation in ultrasound transmission with changing transducer/skull incidence angle and skull thickness.
The pressure attenuation ranged from −5.8 dB to −9.3 dB (mean +/−standard deviation, −8 dB +/− 1 dB), and the FWHM varied between 1.83 mm and 3.79 mm (2.2 mm +/− 0.3 mm in the anterior/posterior direction, 2.7 +/− 0.7 mm in the left/right direction). The insertion losses as a function of depth at different orientations are shown in Fig.. The dorsal midline skull (with the ultrasound beam passing through the sagittal and coronal sutures) was thicker than either of the angled approaches (passing through the parietal and temporal bones) and experienced a greater insertion loss for most sonication target depths. For both angled approaches, the insertion loss decreased as the focus was moved away from the skull surface.
For the centered approach, the insertion loss increased slightly as the focus moved closer to the skull surface. It appears that the intervening skull thickness dominates the attenuation, though the angle of incidence seen by transducer elements also affects transmission. Insertion losses for different sonication orientations and depths Gadolinium enhancement in the brain on post-sonication T1-weighted MRI indicated successful BBB disruption.
Disruption accuracy is shown in Figs. For sonications of sufficient pressure to produce BBB disruption, the region of gadolinium enhancement did not appear to be shifted at all from the desired target. For higher estimated in situ pressures (>0.55 MPa), the disruption region was larger and less uniform, as evident in the 0.58 MPa point in Fig.. Even without element-by-element refocusing, the focusing quality and targeting precision appeared to be adequate. Post-experiment, there were no signs of gross damage to the animals to suggest significant off-target sonication. Sagittal images showing columns of BBB disruption produced by the labelled estimated in situ pressures. Ultrasound propagation is from the right to the left of these images.
Conclusions Transcranial FUS focal point distortion was minimal despite the lack of element-by-element transducer refocusing. The clinical MRgFUS body transducer and driving electronics had sufficient power and aperture to generate the in situ pressures for BBB disruption through a human skull, using a variety of clinically practical approaches and patient orientations. Though transcranial thermal ablation typically requires high acoustic powers, a lower operating frequency, and large aperture arrays with high number of elements, this study demonstrates that a clinical body MRgFUS system with a smaller transducer may be a safe and feasible alternative for non-invasive BBB disruption and other low-pressure therapeutic ultrasound transcranial applications, potentially offering a wide treatment envelope. References  Hynynen, K., et al. Radiology, 220(3), pp.  Airan, R.
1CarThera, Lyon, France; 2INSERM, U1032, LabTau, Lyon, France; 3Assistance Publique Hopitaux de Paris, Hopital de la Pitie Salpetriere, Department of Neurosurgery, Paris, Paris, France; 4Universite Paris, UPMC, Paris, France; 5Assistance Publique Hopitaux de Paris, Hopital de la Pitie Salpetriere, Department of Neuro-Oncology, Paris, France Objectives Pulsed ultrasound, coupled with peripheral injection of microbubbles, has been shown in pre-clinical studies to be an effective method for enhancing the delivery of chemotherapy to the brain. In this work, an intra-skull implantable ultrasound device, SonoCloud®, was developed for temporarily disrupting the BBB. The device was implanted in patients with recurrent glioblastoma (GBM) undergoing systemic carboplatin chemotherapy in a Phase 1 clinical trial and the safety of repeated BBB disruption was assessed. Methods A Phase 1 clinical trial began in July 2014 at a single centre at the Hospital Pitie Salpetriere in Paris, France. Patients with recurrent GBM with an enhancing volume of less than 35 mm in diameter were included in the trial. Participants were implanted with a 11.5-mm diameter biocompatible 1 MHz ultrasound transducer, which was fixed into the skull bone thickness. The device was either implanted during a regular surgical resection of the enhancing region or during a unique ambulatory procedure under local anaesthesia.
Once a month, the device was connected to an external radiofrequency generator using a transdermal needle, and patients received a two minute pulsed ultrasound exposure in combination with systemic administration of an ultrasound contrast agent (7 min mean total duration procedure). BBB disruption was assessed immediately after sonications using dynamic T1-weighted imaging with a gadolinium based MR contrast agent. Systemic intravenous injection of carboplatin chemotherapy was delivered immediately following MR imaging. Patients followed a progression of ultrasound dose in which the pressure was increased from 0.5 to 0.8 MPa throughout the course of the study. Results As of July 2015, eleven patients had been included in the study with a total of 25 BBB disruption procedures performed. No adverse effects were observed in patients treated. BBB opening was clearly observed in 12/25 treatments on contrast-enhanced T1w imaging.
The procedure was safely tolerated in all patients. No evidence of acute haemorrhage, petechia, ischemia or oedema was observed in post-sonication SWAN T2*, Diffusion or FLAIR MRI sequences. Conclusions The BBB was safely opened by pulsed ultrasound using an implantable ultrasound device in patients with recurrent glioblastoma. Additional follow up and recruitment will be used to further evaluate the safety and potential efficacy of such an approach.
Acknowledgments Work supported by CarThera and the Hospital Pitie Salpetriere. 1Siemens Healthcare, Salt Lake City, Utah, USA; 2Radiology, University of Utah, Salt Lake City, Utah, USA Objectives For MR guided focused ultrasound treatments in or close to bone, such as for transcranial applications focusing through the intact skull bone and treatments of bone metastases, significant heating can occur in the bone due to its high ultrasound absorption. MR imaging of bone is in general challenging due to the short T2 relaxation time of bone. For MR temperature imaging the short T2 also severely decreases the accuracy that can be achieved with the standard proton resonance frequency shift method.
Instead researchers have investigated the temperature dependence of the MR signal intensity (SI) and T1 relaxation time for temperature monitoring (1–4). Miller (1) and Fielden (3) et al.
Showed that the SI from cortical bone decreases with increasing temperature using ultrashort echo time (UTE) pulse sequences, and Ramsay et al. (2) found that, contrary to what Miller and Fielden observed, the SI increases with increasing temperature using a short TE gradient recalled echo (GRE) pulse sequence. (4) further showed that T1 increases with temperature, also using UTE. In this work we investigate the temperature dependence of the SI (dSI/dT) and the T1 and T2* relaxation times (dT1/dT and dT2*/dT, respectively) using a 3D UTE pulse sequence to investigate which parameter has the highest sensitivity to temperature change.
Methods All imaging was performed on a 3T MRI scanner (MAGNETOM PrismaFit, Siemens Healthcare, Erlangen, Germany) using a 3D UTE pulse sequence. The sequence utilizes radial, ramped sampling of k-space in 3D starting at the k-space centre after a 80 μs non-selective hard RF pulse, allowing TEs down to 50 μs. T2* was measured by performing an exponential fit to data acquired at TE = 50, 90, 130, 170, and 250 μs (other scan parameters are listed in Table ). The 50 μs TE was also used for dSI/dT calculations. T1 was measured using the variable flip angle (VFA) method (5) with TR = 11 ms and FA = 8 and 36° (other scan parameters are listed in Table ). Scan parameters An approximately 4-cm long bovine femur (marrow and connective tissue removed) was placed in a phantom holder that allowed heated water to circulate around the bone, Fig.. One fiber optic probe measured the water temperature, and three probes were inserted in 1-mm diameter, 2-cm deep, holes drilled in the bone to measure the temperature of the bone.
The water was warmed to ~22, 35, 50, and 65°C and data was collected when all 4 probes measured within 1°C. The whole setup was places in a 20-channel RF head coil for signal detection. A ~4 cm long bone sample was placed in a phantom holder that allowed water circulation to homogenously heat the bone. 4 fiber optic probes were used; 1 in the water and 3 in the bone sample.
Results Figure shows 2D maps of SI and T1 and T2* relaxation times for the 4 different temperatures. Mean and standard error values from a 9x9 ROI close to each probe is shown in Fig., together with calculated changes in%/°C.
A decrease in SI of 0.3-0.5%/°C, and increases in T1 and T2* of 0.5-0.9%/°C and 0.6-0.9%/°C, respectively, was observed. Using the temperature dependent spoiled GRE signal equation (6) and the observed values for dT1/dT and dT2*/dT, dSI/dT can be closely predicted.
Changes versus temperature for a SI, b T1, and c T2*. Mean and standard error value from a 9x9 voxel ROI close to each probe is shown Conclusions The decrease in SI is in accordance with previously published results by Miller and Fielden. The measured change in T1 using UTE agrees well with the 0.6%/°C reported by Han, although we measured higher absolute T1 values (~160-175 ms at 25°C, compared to ~115-125 ms as reported by Han).
The effect of T1 and T2* on SI are counter-acting each other (both increasing), which reduces the sensitivity of dSI/dT. This may suggest that dT1/dT and dT2*/dT are more suitable candidates for bone MR thermometry, and Fig. Also shows higher sensitivity for relaxation times that for SI.
However, it should be noted that SI can be detected from a single image, whereas T1 and T2* measurements utilize two or more images, therefor resulting in longer scan times. Future studies will acquire data with longer TEs (out to ~10 ms) to investigate the difference in temperature sensitivity for shorter and longer T2 components in the bone.
These results will be compared to the increase in SI with temperature observed by Ramsay using a TE ≈ 1 ms. The temperature dependence of the long and short T2* components can be found by a multi-exponential fit.
Flip angle mapping will also be implemented to improve the accuracy of the T1 measurements (7). 1Vanderbilt University, Nashville, Tennessee, USA; 2University of Virginia, Charlottesville, Virginia, USA; 3University Children's Hospital, Zurich, Switzerland Objectives MR-guided focused ultrasound (MRgFUS) brain systems deliver targeted thermal energy into the brain using a hemispheric array of transducers that surround the head with an intervening water bath (Fig. ). During treatment the localized heating (hot spot) is measured from a change in image phase between baseline (pre-treatment) and dynamic (during treatment) images.
Accelerating temperature mapping by undersampling k-space is desirable to increase spatiotemporal resolution and coverage, but is difficult to do with parallel imaging since coils must be placed outside the transducer, far away from the head. Multiple groups have instead developed accelerated temperature mapping methods that exploit temporal correlations between baseline and dynamic images [1, 2].
However, circulation of the water bath to cool the skull causes dynamic signal changes that are not captured by baseline images (Fig. ), which breaks those correlations and results in artefacts throughout the temperature maps. We propose a spatially-segmented approach for reconstructing temperature maps in brain MRgFUS, in which we separately estimate a water bath image without a baseline, and a temperature map in the brain with a baseline. The method can estimate artefact-free temperature maps from undersampled data during brain MRgFUS treatments using a single receive coil. A During MRgFUS treatment, the patient’s head is immobilized in the transducer and circulating water bath. B The water bath signal varies significantly during a single focused ultrasound (FUS) sonication ( arrow indicates sonication target). Methods Our iterative approach alternates between updating the parameters of a k-space hybrid signal model which is fit in the brain region of the image , and a baseline-free estimate of the water bath image. The fitting of k-space hybrid brain model results in a phase drift-corrected brain image without the temperature phase shift and a sparse temperature phase shift map.
An algorithm to fit the model is described in . The water bath is reconstructed using a POCS algorithm that alternately enforces data consistency, consistency with a water bath support mask (brain and water bath masks are obtained from a baseline image), and sparsity in the Coiflet domain using soft thresholding . Figure illustrates the overall undersampled dynamic image model. To test the method, a gel-filled human skull phantom was sonicated by an InSighTec ExAblate Neuro 4000 transcranial MRgFUS system (InSighTec Ltd, Haifa, Israel) while imaging with a GE 3T MR750 scanner (GE Healthcare, Waukeshaw, WI). 27 single-slice 2DFT gradient echo images were collected with the body coil and 28 x 28 x 0.3 cm3 field of view, 256 x 128 acquisition matrix, 30° flip angle, 13 ms TE, and 28 ms TR. Images and maps were reconstructed to a 128 x 128 matrix and retrospectively randomly undersampled by 2x, with full sampling over 22 central k-space lines. Temperature maps were reconstructed by fitting the k-space hybrid model to the entire image, or to the brain only with keyhole or POCS methods used to reconstruct the water bath image.
Results Figure shows the temperature reconstruction results. When the k-space hybrid model is fit to the entire image without distinguishing between the brain and water bath, phase artefacts obscure the hot spot in the reconstructed temperature map and (in this case) lead to an overestimation of the temperature rise in the sonicated region across image dynamics (RMSE across dynamics: 0.0121°C). Restricting the temperature reconstruction to within the brain, in combination with keyhole reconstruction of the water bath image (using the baseline image’s k-space to fill in missing k-space lines), produces temperature maps with lower errors in the hot spot but still large errors outside (RMSE across dynamics: 0.0039°C). The proposed k-space brain/POCS bath approach yields a more accurate estimate of the water bath image (not shown), resulting in much lower in-brain temperature artefacts (RMSE across dynamics: 0.0029°C). Conclusions Unpredictable water bath motion confounds model-based approaches to accelerated MR temperature mapping, resulting in large temperature artefacts due to aliased water bath signal.
We demonstrated that a spatially-segmented reconstruction that applies a model-based reconstruction in the brain and a POCS reconstruction in the water bath can reconstruct temperature maps without undersampling artefacts at a moderate acceleration factor using a single receive coil. Future work will focus on integrating the approach with other accelerated temperature mapping methods  and extending it to non-Cartesian trajectories . The method is compatible with multiple receive coils.
Acknowledgements This work was supported by the Focused Ultrasound Foundation and NIBIB T32EB014841. References  Gaur P et al. Magn Reson Med 2015;73: pp.  Todd et al. Magn Reson Med.  Lustig M et al.
Magn Reson Med 2007;58: pp.  Fielden et al. Proc Intl Soc Mag Reson Med 23.
Radiology, Stanford University, Stanford, California, USA Objectives MR-guided focused ultrasound (MRgFUS) brain treatments are currently guided by one thermometry sequence: single-slice 2DFT MR thermometry. In this work, we divided treatment monitoring into two tasks, with different thermometry design goals for each, and developed sequences optimized for these goals: “Focal Spot Localization” and “Monitoring”. These sequences achieve greater imaging performance by utilizing multi-echo spiral thermometry, region-specific update rates, and MASTER slice interleaving. Currently, focal spot targeting confirmation requires several low-power sonications to obtain high-resolution measurements in three dimensions. We developed a Focal Spot Localization sequence that obtains high-resolution measurements in-plane, at improved temperature precision compared to 2DFT, while also providing multiple-slices for through-plane characterization. This would reduce the number of sonications required, improving treatment time.
Additionally, even lower-power sonications could be detected, improving patient safety. During ablative treatment sonications, single-slice monitoring cannot detect through-plane shifts of the ultrasound focus, or unexpected out-of-plane heating. We developed a multi-rate thermometry Monitoring sequence that interleaves different sequences at different update rates to simultaneously achieve fast and precise focal monitoring, 3-dimensional focal spot measurement, and full brain monitoring. Fast and precise multi-slice monitoring of the focus ensures accurate thermal dose estimates for treatment feedback, while (slower) full-brain monitoring ensures patient safety.
Methods All sequences were implemented using RTHawk (HeartVista, Menlo Park, CA) on a GE 3T 750 Signa scanner (GE Healthcare, Milwaukee, WI) equipped with the InSighTec Exablate Neuro (InSighTec, Haifa, Israel). All imaging was performed with the body coil, as is normally used with the Exablate system. Conventional 2DFT was implemented as a gold standard for comparison. The new sequences all use a 36 cm FOV to ensure that the transducer and water bath do not alias.
Volunteer imaging was done with informed consent under IRB approval. Multi-frequency reconstruction was performed on all spiral data. Temperature uncertainty was measured as the per-voxel temporal standard deviation of temperature measurements, and averaged within manually segmented ROIs. Performance was also tested inside the transducer, using a gel phantom.
Sequence parameters are compiled in Table. Implemented Sequence Performance Parameters. TSNR efficiency is proportional to (δ xyz*√(T seq)*σ T) −1. For Monitoring - Background, median slice uncertainty reported The Focal Spot Localization sequence is a 5-slice 3-echo thermometry sequence, with doubled in-plane resolution as compared to conventional 2DFT (1.1x1.1 mm vs 1.09x2.18 mm), and acquisition time of 7 s. The Monitoring sequence interleaves 3 distinct sequences at different rates to monitor 29 total slices. The “Focus” is monitored using 3-slice 3-echo spiral imaging, for high-speed high-precision measurement of focal heating. Two adjacent slices, the “Boundary”, are monitored at half the temporal rate (also using 3-echo spiral) to fully characterize the focal spot.
The remaining 24 slices, “Background”, were acquired using 8 blocks of 3-slice MASTER, with spiral readouts. Use of MASTER improves temperature uncertainty, compared to traditional slice interleaving, by increasing echo time. Limiting each MASTER block to 3 slices reduces inherent diffusion and motion-encoding artefacts. The three component sequences were interleaved such that Focus utilized 45% (15% per-slice) of the timeline, Boundary used 15% (7.5% per-slice), and Background the remaining 40% (1.7% per-slice). Results Figure compares temperature uncertainty in vivo between 2DFT and Focal Spot Localization while Fig.
Compares 2DFT with Monitoring for the same volunteer. Large images compare the centre slice, while stacks of images at the right show additional slices monitored by the new sequences. Figure compares 2DFT and Monitoring uncertainty within the transducer.
The new sequences obtained better uncertainty than 2DFT, with average values compiled in Table. Relative “Efficiency” is also listed in Table, which accounts for differences in speed and voxel volume. Each multi-echo spiral sequence is more than 150% as efficient as 2DFT. Background is 69% as efficient (but collects 3 slices per TR, for an effective 120% efficiency). Temperature uncertainty comparisons between 2DFT and a Focal Spot Localization, in vivo; b Monitoring, in vivo; c Monitoring, phantom within transducer.
Large images compare centre slices, while stack of images at right show additional slices. Conclusions In this work, we have shown that multi-slice multi-echo spiral thermometry is an effective imaging approach for volumetric treatment monitoring. Improved imaging performance was successfully used to achieve imaging objectives for different aspects of ablative treatments. Focal spots may be localized faster and with reduced heating using the higher-resolution higher-precision Focal Spot Localization sequence. The mixed update rate Monitoring sequence successfully delivers high-speed high-precision monitoring of the targeted focus, while improving safety by simultaneously monitoring the full brain at a lower update rate. These sequences have also been validated within the transducer, to help ensure they will work in the clinical setting. Radiology, Stanford University, Stanford, California, United States Objectives To demonstrate how MRI can be used in FUS treatments near metallic hardware for treatment planning, sonication monitoring and treatment assessment.
Methods Using standard MRgFUS product sequences, we treated a 73-year-old patient with a metastasis in the right femur that was painful despite prior radiation and surgical stabilization with a metallic rod, demonstrating the inability of both echo-planar imaging (EPI) and gradient-recalled echo (GRE) imaging to be used for conventional proton resonance frequency (PRF) shift thermometry. Based on the experience from this patient treatment, we have proposed an imaging strategy for MRgFUS near metallic hardware using multi-spectral imaging (MSI) techniques (Fig. ).
Both MAVRIC-SL [Koch et al.; MRM 2011; pp. 65:71] and 2DMSI [Hargreaves et al.; ISMRM 2014, #615] are spin-echo-train-based imaging approaches that enable artefact-reduced imaging near metal.
MAVRIC-SL compensates for distortions induced by field inhomogeneities by additional encoding along the slice dimension. Its ability to adjust the image contrast makes it a promising candidate both for treatment planning and assessment. 2DMSI limits the excitation to finite spectral and spatial regions (“frequency bins”) that can be imaged with minimal artefact quickly enough to be used for sonication monitoring. A Components of the proposed imaging strategy for MRgFUS near metallic hardware. B GRE and EPI images underlying conventional PRF thermometry and a MAVRIC-SL image, all acquired in a patient with a femur stabilized with a metallic rod.
The dashed line. We preliminarily tested the feasibility of MAVRIC-SL for treatment planning and assessment in a 65-year-old patient without metal hardware and with a metastasis in the right pelvis undergoing MRgFUS treatment for pain palliation. We used a GE 3T MRI system equipped with an InSightec ExAblate2000 FUS system.
Proton density (PD) weighted MAVRIC-SL images were acquired prior to the treatment in addition to standard 2D fast-spin-echo (FSE) images. After treatment, T1-weighted MAVRIC-SL images were acquired before and after gadolinium injection in addition to standard 3D fast RF-spoiled GRE images with 2-point-Dixon fat suppression (LAVA-Flex, see Fig.
For details). We tested the feasibility of 2DMSI to monitor a 25 s sonication in an acrylamide egg-white phantom containing the CoCr stem of a knee replacement and a pork loin sample containing a CoCr augment plate from the same hardware, each placed in a container filled with water.
We acquired a time series of 10 single-slice 2DMSI images with a temporal resolution of 8 s/frame and the sonication starting after the third image. Each 2DMSI image was composed of 12 frequency bins ranging from −4.5 kHz to +5.4 kHz, and was acquired with TE = 30 ms, (bin) TR = 500 ms, 280 x 280 mm FOV, 5 mm slice thickness and 128 x 128 matrix size (effective number of phase encodings after half Fourier).
To monitor the temperature-induced signal change, we subtracted the mean signal of the 3 baseline images from all 10 images voxel-by-voxel. Results Figure shows the GRE and EPI image acquired in the patient with metallic hardware. With both techniques, the stabilized femur and its surrounding area are not visible due to distortions and signal dephasing. For comparison, the MAVRIC-SL image depicts the anatomy including the bone marrow surrounding the metallic rod. Figure presents the acquired images for treatment planning and assessment in the patient without metal.
PD-weighted MAVRIC-SL achieves a contrast comparable that of the conventional FSE image and allows for localization of the metastasis in the lower part of the right pelvis. Comme Un Aimant Rapidshare Free. The T1-weighted MAVRIC-SL pre/post contrast difference image reveals the treatment area similar to the LAVA-Flex water difference image. Figure shows the thermometry results in the phantom and the tissue sample.
In both cases, metal-induced field inhomogeneities of up to ± 4 kHz cause strong distortions and signal loss in the GRE image, whereas 2DMSI clearly depicts the area around the metal. In the phantom, the 2DMSI difference images yield a clear signal change at the focal spot next to the metallic stem and a noticeable change in signal at the focal spot next to the metallic plate in the tissue sample, despite a 70% reduction in SNR due to the lower water content. Averaging over the frames during sonication improves the localization of the focal spot. GRE and 2DMSI image and 2DMSI signal change during sonication in the phantom ( a) and the ex vivo tissue sample ( b). The 2DMSI difference images are cropped and masked to the dashed area.
For the tissue sample, the 2DMSI difference image in the lower right. Conclusions We have presented initial results for our proposed imaging strategy for MRgFUS in the presence of metallic hardware. MAVRIC-SL is an established technique for artefact-reduced imaging near metal. Here, we have shown that the image contrast can be adjusted to yield the relevant information for both planning and assessment of MRgFUS treatments.
The reduced image resolution compared to the standard FSE protocol (to keep the scan duration at an acceptable length) did not noticeably reduce diagnostic image quality for the treating radiologist. We have also demonstrated that 2DMSI enables the measurement of temperature-induced signal changes in close proximity to metallic hardware and thus in regions where conventional PRF shift thermometry fails.
The bin-selective approach allows for a temporal resolution of 8 s/frame, which is sufficiently high to resolve the temperature evolution in sonications as short as 20 s, which is the typical duration in MRgFUS treatments. In case of less severe metal-induced artefacts, the number of frequency bins could be reduced to increase the temporal resolution. Averaging over time frames could facilitate the detection of the focal spot in lower SNR cases. For the given temporal resolution and the low temperature sensitivity of the T2 relaxation time of aqueous tissues, the measured signal change is expected to be highly dominated by the temperature sensitivity of the PD, whereas a higher temporal resolution is expected to increase the T1 weighting. While the latter provides higher temperature sensitivity and thus lowers the SNR requirements, PD weighting offers the benefit of a tissue-independent temperature mechanism that could facilitate quantitative thermometry.
In conclusion, the proposed imaging strategy has the potential to enable MRgFUS treatments near metallic hardware. The patient population at greater risk for cancers, and hence osseous metastases, overlaps with the elderly demographic more likely to have metallic hardware such as joint replacements. Further, orthopaedic bone stabilization is often used as a treatment for osseous metastases at risk for fracture. Overcoming these technical limitations is therefore important to allow the use of MRgFUS in a larger patient population. The University of Tokyo, Tokyo, Japan Objectives Phase change nano droplets (PCND), whose diameters are 200–400 nm, are droplets of perfluorocarbon (PFC) covered with phospholipid layers. Since they can be vaporized by ultrasound and transformed to microbubbles, they will be utilized as ultrasound contrast agents and ultrasound therapy sensitizers.
There are several types of PCND which are often used in research, whose internal compositions are different, such as perfluoropentane (PFP) and perfluorohexane (PFH).Its boiling point can be adjusted by changing the mixture ratio of PFP and PFH. The lifetimes of generated microbubbles changed from PCND are different from type to type. In this study, the lifetime dependence to ambient temperature at the moment of its vaporization was investigated.
If remaining efficiency depends on the ambient temperature, this drug has a potential to be used as indicator of thermal memory effects and temperature monitoring agents. Methods Experimental setup for ultrasound exposure and high-speed imaging are shown in Fig..In this study, we used the two types of PCND, whose internal compositions were PFP and the mixture (MIX; PFP: PFH = 1:1), respectively. Their main differences are boiling points (PFP: 29°C, MIX: 40°C), and the boiling point of MIX is estimated by thermodynamic calculation. Experimental setup For the observation of the vaporization of PCND, we used two-layer structure of polyacrylamide gel phantom (layer with PCND and layer without PCND), and set the layer with PCND at the focal point of the transducer. PCND were vaporized by ultrasound (5 MHz centre frequency, 5 cycle bursts, Peak Negative Pressure = 3.5 MPa), which were irradiated with an arbitrary ultrasound beam controller (Verasonics) and a linear array transducer (EUP-L73S, Hitachi Aloka Medical). Time-lapse behaviours of PCND through phase changes were recorded with the high-speed camera (HPV-1A, SHIMADZU), coupled with inverted microscope (NIKON Eclipse Ti-U).
The ambient temperature (gel phantom temperature) conditions were controlled with a hot water bath and thermo plate (TOKAI HIT) on the stage of the microscope. Results First, we observed the vaporization of the two types of PCND at 37 °C. The high-speed images of vaporization at 37 °C are shown in Fig..
High Speed Images of Vaporization at 37 °C As to MIX (B.P. = 40 °C), generated microbubbles disappeared soon (within 10 μs) after the ultrasound exposure. On the other hand, as to PFP (B.P.=29 °C ), generated microbubbles remained for a while (more than thirty seconds). Because the main difference of these two types of PCND is the boiling point, we assumed that temperature is the key factor, and tried to control the difference between the boiling point and the ambient temperature. Then, we did some vaporization experiment at various temperatures.
Some of the high-speed images of vaporization at 26 °C, 48 °C are shown in Fig.. High speed images of vaporization at 26, 48 °C As to PFP (B.P.
= 29 °C), generated microbubbles disappeared soon after the sonication at 26 °C, although they remained for some time at 37 °C. As to MIX (B.P.=40 °C), generated microbubbles had long lifetimes at 48 °C, although they had very short lifetimes at 37 °C. It can be considered that the lifetimes of generated microbubbles are greatly affected by not only the internal composition, but also the ambient temperature. Besides, behaviours after vaporization at 26~48 °C are shown in Fig.. Whether generated microbubbles will remain or disappear was switched around the boiling point. Planning software and target ROI definition.
T1 map before BBB opening. T1 map after BBB opening. T1 difference between both images, arrow indicates the BBB opening on the targeted ROI Figure shows the typical spectra obtained before and during infusion of gas microbubbles. Level of harmonics increased significantly for third (+13.6 dB) and fourth harmonics (+21.6 dB), but no significant increase in broadband noise was detected, suggesting that no transient inertial cavitation occurred during the insonification.
After the experiment, the animal recovered and no side effects were observed during the 3 weeks following each BBB opening procedure. At the end of all the BBB opening procedures, T1-, T2- and T2*-weighted scans and DTI did not show any evidence of tissue damage (oedema, haemorrhages or bleeding) induced by the ultrasound procedures (Fig. ). Colour Coded fractional anisotropy. T1-weighted image. T2-weighted image d. T2*-weighted image.
No signs of oedema, haemorrhages or bleeding could be seen 3 weeks after BBB opening Conclusions The procedure allowed successful repeated transient opening of the BBB in a small ROI in a living primate with no side effects. No signatures of transient inertial cavitation were detected during experiments. This suggests that this method is safe for the animal. This study will be replicated in other animals with the long-term objective of developing a system suitable for human applications. Acknowledgements This work was supported by the Bettencourt Schueller Foundation and the 'Agence Nationale de la Recherche' under the program “Future Investments” with the reference ANR-10-EQPX-15. 1Biomedical Engineering, Columbia University, New York, New York, USA; 2Biological Sciences, Columbia University, New York, New York, USA; 3Radiology, Columbia University, New York, New York, USA Objectives Currently, the existing Central Nervous System (CNS) drug delivery techniques are confined to either targeted but invasive or to non-targeted and non-invasive methods.
Focused Ultrasound (FUS) coupled with the systemic administration of microbubbles has been proven to open the Blood Brain Barrier (BBB) locally, transiently and non-invasively, thus facilitating the diffusion of neurotrophic factors. Neurturin, a member of the glial derived neurotrophic factors (GDNF) family has been demonstrated to have restorative effects on the depleted by Parkinson’s disease dopaminergic neurons (DA). Moreover, our group has shown the bioavailability and downstream signalling of Neurturin in wild type mice and the restorative effect in Parkinsonian mice. Despite the promising results, the potential of multiple treatments with Neurturin in reversing the disease phenotype is still to be determined. The aim of the current study was to investigate the neurorestorative effect of triple delivery sessions of the neurotrophic factor Neurturin in a Parkinsonian mouse model. Methods For this study, twelve wild type mice (12 months old) were infused with sub-acute dosages of MPTP causing apoptotic degeneration in the nigrostriatal pathway. After the stabilization of the lesions and the decontamination period, the entire cohort was sonicated on the left hemisphere (ipsilateral side) targeting twice the Caudate Putamen region (CPu), to cover the entire area, and once the Sabstantia Nigra region (SN).
Half of the mice received an IV injection of 0.5mg Neurturin accounting for the treated group, FUS+/NTN+, while the rest constituted the control group, FUS+/NTN. Magnetic resonance imaging (MRI) was performed after each sonication to verify the accuracy of the BBB opening in terms of targeting. The procedure was repeated once biweekly to a total of three treatments. Following the third treatment, the survival period lasted for 28 days letting the neurotrophic factor to develop its restorative effects. On the 29th day, the mice were sacrificed and coronally sectioned for tissue processing.
The brain slices of both the SN and the CPu were stained for tyrosine hydroxylase positive cells (TH+) with a custom protocol. The stained slices were imaged to count the TH+ nerve cell nuclei on the SN while the axons and dendrites were quantified by a custom MATLAB algorithm.
For each mouse the contralateral side was compared to the ipsilateral side to eliminate inter-animal variation in the number of nuclei and projections. A quantification algorithm was used to compute the percentage of the relative difference (RD) between the two hemispheres, i.e., RD = (Ipsilateral – Contralateral)*100%.
The process was repeated for all slices that cover the entire SN region and averaged across the mice. The error of the technique was measured as the standard deviation from the mean. Results There was no significant difference in the number of neurons between the ipsi- and contralateral sides. This result was in accordance with our knowledge of Neurturin restoring impaired neurons and not regenerating them. The RD was found to be significantly higher for the FUS+/NTN+ compared to the FUS+/NTN- group. This significance strengthens with the negative percentage of the FUS+/NTN- group implying a possible sensitivity of the Parkinsonian brain in multiple sonications. Conclusions These findings indicate a potential of multiple treatments on the reversal of the Parkinsonian phenotype as is the first time significance is reported.
To strengthen this argument a second cohort of 20 mice is currently undergoing the same treatment aiming to apply various other imaging and quantification techniques to investigate the restoration of the functionality of the previously depleted neurons. Nonetheless, the current findings are essential considering the therapeutic effect of multiple treatments with FUS enhanced drug delivery in patients. 1Frank Laboratory, Radiology and Imaging Sciences, National Institute of Health, Bethesda, Maryland, United States; 2Center for Infectious Disease Imaging (CIDI), Radiology and Imaging Sciences, National Institute of Health, Bethesda, Maryland, United States; 3National Institute of Biomedical Imaging and Bioengineering, National Institute of Health, Bethesda, Maryland, United States Objectives One potential issue for using MR-guided pulsed Focused Ultrasound (pFUS) to open the blood brain barrier (BBB) is the lack of data on the long term effects. Safety determination in the brain have been limited to the MR characterization after repeated BBB opening that can be achieved without haemorrhage, oedema and behavioural changes in non-human primates [1,2]. We use multimodal imaging technics to characterize long term effects of pFUS + MB in the rat brain to evaluate the effects of repeated BBB opening by pFUS and microbubbles (MB) on morphology to the rat striatum and hippocampus as monitored by magnetic resonance imaging (MRI), positron emission tomography (PET) and histology over 12 weeks.
Methods Female rats were divided into two groups and received either pFUS + MB (OptisonTM, GE Healthcare, Little Chalfont, UK) once or six times targeting the striatum and the contralateral hippocampus. 200 μl of MB were administered intravenously over 1 minute starting 30 sec before pFUS. Rats received 3 daily doses of 300 mg/kg 5-Bromo-2′-deoxy-uridine (BrdU, Sigma Aldrich, St. Louis, MO) intraperitoneally before sonication to label proliferating cells in vivo.
0.3 MPa acoustic pressure was applied in 10 ms burst length and 1% duty cycle (9 focal points, 120 sec/9 focal points - striatum, 120 sec/4 focal points - hippocampus) using a single-element spherical FUS transducer (centre frequency 589.636 kHz; focal number 0.8; aperture 7.5 cm; FUS Instruments, Toronto, Ontario, Canada). T2, T2* and Gd-enhanced T1-weighted images were obtained by 3.0 T MRI (Philips, Amsterdam, Netherlands), T2, T2*, diffusion tensor imaging (DTI) and chemical exchange saturation transfer (CEST) imaging was performed by 9.4 T MRI (Bruker, Billerica, MA). Parameters for DTI: 3D spin echo EPI; TR/TE 700 ms/37 ms; b-value 800 s/mm2 with 17 encoding directions; voxel size 200 μm, isotropic. Diffusion weighted images were corrected for B0 susceptibility induced EPI distortion, eddy current distortions, and motion distortion with b-matrix reorientation using Tortoise.
Parameter for glucoCEST: 2D fast spin echo with (MT) and without (M0) magnetization transfer (MT) pulses (TR/TE 3.5 s/11.5 ms; in plane resolution: 200 μm, thickness: 0.8 mm; MT pulse: 3 μT, 1 s). The MT offset frequencies (Δω) were set from −2 kHz to +2 kHz with 100 Hz stepping to detect the proton metabolites of glucose (1.2 ppm, 2.1 ppm, 2.9 ppm). Fractional anisotropy (DTI-FA) and the asymmetry of magnetization transfer ratio (MTRasym) were derived for mapping structural injury and glucose metabolism.
Quantitative of glucose uptake was performed with FDG-PET (Siemens, Munich, Germany). Each rat received under anaesthesia (O2 3–4 L/min & Isoflurane at 3–3.5 4%) 0.7 – 1.1 mCi of 18F-FDG via tail vein injection and was allowed to regain consciousness for an uptake period of 30 minutes in total. They were anesthetized again and a PET/CT study was acquired using Siemens Inveon Multimodality scanner (Siemens Medical Solutions USA, Inc.). CT scan was performed for localization and attenuation correction purposes. PET images were reconstructed using OSEM3D/MAP algorithm, with Ramp projection filter, scattered corrected, 2 OSEM3D iterations, 18 MAP iterations, 128 × 128 image size, and approximately 0.5mm resolution at the centre of the field of view (FOV).
Animals were euthanized 6 or 12 weeks after the first pFUS treatment. Histological evaluation of brain and tracking of BrdU tagged cells was performed at different time points.
Values were compared to baseline. Results Preliminary results showed contrast enhancement on T1-weighted MRI in rats receiving a single sonication, indicating BBB disruption in the striatum and the hippocampus.
Gd-extravasation or T2 and T2* abnormalities were not seen in the brain 1 day post pFUS + MB at 9.4 T MRI. Hypointense regions appeared on T2* MRI 2 weeks after pFUS + MB (Figs. And ) consistently with microhemorrhage within the parenchyma that decreased in volumes by week 3.
White matter fiber structure- and gray matter-abnormalities on DTI MRI were detected in regions with T2* abnormalities (Fig. ) suggestive of increased astrogliosis (Fig. ) and transient axonal damage (Fig. ). GlucoCEST showed loss of contrast as early as 1 day post pFUS and these changes persisted up to week 3 (Fig. ). DTI and glucoCEST (9.4T MRI) of the rat brain (baseline, 1 day, 2 weeks and 3 weeks post pFUS) show changes in the grey and white matter tract at both sonicated locations. 2 weeks after pFUS + MB increased fractional anisotropy on DTI suggests astrogliosis.
Qualitative analysis of MRI and GlucoCEST as well as 18F-FDG uptake with PET showed no difference between the sonicated region and the contralateral hemisphere 6 weeks post sonication. Conclusions We have observed a complex graded molecular and cellular sterile inflammatory response in the brain up to 24 hrs after pFUS + MB. However, little is known about the long term effects in rats using advanced imaging techniques. The DTI data showed that pFUS caused a low degree of structural injury at the location of sonication. However, the decrease in glucose concentration revealed by glucoCEST indicated that the pFUS could cause hypo-metabolism in the brain even after 3 weeks post sonication. These preliminary results suggest the importance of long term monitor of the brain following low intensity pFUS + MB.
Further research investigations are in process to evaluate changes following multiple targeted treatments in the brain. References  Arvanitis, C.
D., et al., Cavitation-enhanced nonthermal ablation in deep brain targets: feasibility in a large animal model. J Neurosurg:1–10, 2015.  Downs, M. E., et al., Long-Term Safety of Repeated Blood–brain Barrier Opening via Focused Ultrasound with Microbubbles in Non-Human Primates Performing a Cognitive Task. PLoS One 10(5):e0125911, 2015. Frank Laboratory, Radiology and Imaging Sciences, National Institute of Health, Bethesda, Maryland, USA; 2National Institute of Biomedical Imaging and Bioengineering, National Institute of Health, Bethesda, Maryland, USA Objectives Very little is known about the graded cellular and molecular responses in the brain following pulsed Focused Ultrasound (pFUS) coupled with microbubbles (MB) exposures being advocated to increase drug or gene delivery through the disruption of the blood brain barrier (BBBD). We investigated the proteomic changes in the brain in response to Pulsed Focused Ultrasound (pFUS) + intravenous (IV) ultrasound contrast agent MB associated with BBBD.
Methods MRI-guided pFUS was performed at 0.3 MPa acoustic pressure, 10 ms burst length and 1% duty cycle (9 focal points, 120 sec/9 focal points) using a single-element spherical FUS transducer (centre frequency: 589.636 kHz; focal number: 0.8; active diameter: 7.5 cm; FUS Instruments, Toronto, Ontario, Canada). 200 μl of OptisonTM MB (GE Healthcare, Little Chalfont, UK) were administered IV over 1 minute starting 30 sec before pFUS. Gd-enhanced T1-weighted images were obtained with a 3.0 T MRI (Philips, Amsterdam, Netherlands). Quantitative protein and mRNA expression in the brain following pFUS + MB were analysed with Bio-Plex ProTM Assay (Bio-Rad Laboratories, Inc., CA), enzyme-linked immunosorbent assay (ELISA), Western blot, Real-Time PCR (RT-PCR) or immunofluorescent staining. Proteomics were normalized to sham and statistical analysis was performed by one-way ANOVA corrected for multiple comparisons. 2 fold increase in mRNA expression was determined as significant.
Rats were injected with 8 mg/kg Rhodamine encapsulated magnetic polymers (Biopal Inc., Worcester, MA) 3 days prior to pFUS to tag splenic macrophages. No evidence of damage or microhaemorrhage was observed on histology. Results The results of harvested brains at various times post sonication were as follows: •.
Evidence of influx of fluorescent bead labelled splenic macrophages in the brain by day 6 post pFUS along with activated astrocytes and microglia consistent with mild injury to the parenchyma. Conclusions The temporal molecular response to pFUS + MB is indicative of sterile inflammatory response (Gadani, et al. 2015) in the parenchyma originating from neurovascular unit. The pattern of pro-inflammatory cytokines immediately after pFUS + MB exposure is consistent with sterile inflammation initiated by DAMP that are released in response to ischemia or trauma associated with sterile inflammation observed with mild trauma or ischemia [1,2].
Increases in monocyte chemoattractant protein (MCP-1), vascular endothelial growth factors (VEGF), stromal derived factor 1 (SDF-1), erythropoietin (EPO) and brain derived neurotropic factor (BDNF) are associated with BBBD as well as stimulating angiogenesis, neurogenesis and stem cells migration consistent with mild injury following pFUS + MB exposure to the brain. These results indicate that pFUS + MB rapidly effects to the cerebral vasculature as evident by BBBD in addition to the shockwave from MB collapse induces mild stress within various cellular elements in the neurovascular unit. References  Chen, G. Nunez, Sterile inflammation: sensing and reacting to damage. Nat Rev Immunol 10(12): pp.
826–37, 2010.  Gadani, S. P., et al., Dealing with Danger in the CNS: The Response of the Immune System to Injury. Neuron 87(1): pp.
1Department of Medical Imaging and Radiological Sciences, Chang Gung University, Taoyuan, Taiwan; 2Department of Electrical Engineering, Chang Gung University, Taoyuan, Taiwan Objectives Burst-mode low-pressure focused ultrasound (FUS) has been shown to induce transient blood–brain barrier (BBB) opening, and has high potential for use in non-invasive and targeted delivery of therapeutic molecules into the brain. FUS-BBB opening requires imaging guidance mean during the intervention, yet current imaging technology only enables postoperative outcome confirmation. In this study, we propose an approach to visualize short-burst low-pressure focal beam distribution that allows to be applied in FUS-BBB opening intervention guidance.
Methods An backscattered acoustic-wave reconstruction method based on synchronization between emission from focused ultrasound and receiving diagnostic ultrasound elements and passively beam formed processing were developed. FUS transducers with the frequency ranging from 0.5-2 MHz were employed, and a commercialized diagnostic ultrasound was synchronously integrated with short-burst FUS excitation (burst length ranging from 0.01 to 10 ms). In-vitro phantom experiments were conducted to evaluate the constructed mapping, to quantitatively analyse its performance, and to evaluate the focal beam reconstruction limit.
In vivo experiments with prior MRI anatomical scans were conducted to verify the feasibility of guiding the transcranial FUS-BBB opening procedure as well as its BBB-opened accuracy and reliability on small animals. Results A focal beam can be successfully visualized at all FUS frequency exposures (0.5 – 2 MHz) without involvement of microbubbles or acoustic cavitation triggering. The detectable level of FUS exposure with 0.467 MPa 0.05 ms single-burst exposure was identified. The signal intensity (SI) of the reconstructions was linearly correlated with the FUS exposure both in-vitro and in-vivo (r 2 both higher than 0.9). Conclusions We confirmed that focal beam pattern can be visualized and allow successful guidance of FUS-BBB opening in small animals, with the SI level of the reconstructed focal beam correlated with the success and level of BBB-opening. The proposed approach provides a feasible way to perform real-time and closed-loop control of FUS-based brain drug delivery.
1Radiology, Stanford University, Stanford, California, USA; 2Bioengineering, University of Virginia, Charlottesville, Virginia, USA Objectives Diffusion-weighted imaging has been used to evaluate tissues ablated tissues using MR-guided focused ultrasound (MRgFUS), including uterine fibroids, prostate, and brain tissue [1–4]. Quantitative studies in canine prostate found a 36% reduction in the apparent diffusion coefficient (ADC) after either high intensity ultrasound ablation or cryoablation of the prostate, despite differences in histology .
More recently we studied the evolution of the ADC decrease and found that the time-course for the onset of ADC decrease after ablation of the canine prostate was inversely correlated to the thermal dose achieved . As a result, areas that saw high levels of thermal dose saw a more rapid irreversible decrease in ADC, making ADC an early marker for loss of tissue viability in the prostate. Diffusion-weighted EPI inside of the InSighTec ExAblate 4000 Neuro System following thalamotomy demonstrates poor image quality. As a result, T2-weighted imaging is the method of choice for lesion detection inside the transducer although it may not be the earliest marker for ablation. More recently, a double echo in steady state (DESS) pulse sequence has been proposed to monitor lesion development.
DESS generates two images, the first echo is mostly a gradient echo (GRE), the second echo is mostly a spin echo with some diffusion weighting . The purpose of this work was to investigate the time course of lesion contrast in a pig model of thalamotomy on a diffusion-weighted steady state sequence in comparison to T2-weighted FSE. In addition, we probe the thermal dose dependence of the contrast by evaluating thermal lesions of two different peak temperatures. Methods MRgFUS thalamotomy was performed in a porcine model (n=2) under MR thermometry guidance. In one lesion in one animal, image collection began approximately 40 minutes after a low peak temperature sonication T peak = 52°C in the thalamus.
In a second animal, two high peak temperature lesions T peak = 60°C were created in the thalamus, and image collection began immediately. In all cases, double-echo in steady-state (DESS) and fast spin echo (FSE) T2-weighted imaging acquisitions were interleaved. The parameters for both sequences are summarized in Table. Contrast to surrounding tissue was computed for all time points using regions of interest determined after lesion detection. Lesion Detection Using Fast spin echo (FSE) and Double Echo Steady State (DESS) images. Lesion is not visible with FSE until 60 min while the lesion is detected using DESS at 46min In the quantitative analysis, in all three lesions, DESS provided superior contrast to T2-weighted FSE images at the early time points (Fig. ), which equilibrated at the later time points. This is presumably due to the mixed diffusion and T2 contrast for the steady state sequence.
As edema increases, the steady state sequence loses its advantage over T2-weighted FSE. Contrast between lesion and surrounding healthy tissue as a function of time for fast spin echo (FSE) and Double Echo Steady State (DESS) images.
Contrast for DESS is initially higher for both treatments indicating DESS can serve as an early indicator. Higher peak temperature lesions demonstrate a faster time-course than the lower peak temperature lesion, seen in Fig.. In fact, both high temperature sonication lesions were conspicuous within minutes on the DESS sequence. Conclusions DESS provides a higher contrast between the lesion and the surrounding healthy tissue early after treatment is completed. This will allow for an earlier treatment evaluation while the patient is still in the brain transducer. Future work will include an in-depth simulation analysis on how both the diffusion weighting and T2-weighting contribute to the lesion detection time-course in FSE and DESS. Acknowledgements PO1 CA159992, RO1 CA111981, FUS Foundation, UVA-Coulter Translational Research Partnership.
References  Jacobs MA, et al. JMRI 2009; 29:649–656.  MacDannold N, et al. Radiology 2006;240:263–272.
 Wintermark M, et al. AJNR 2014;35:891–896.  Chen J, et al.  Plata J, et al.
 Chen L, et al.  Plata J, et al. 1Radiology, Stanford University, Stanford, California, USA; 2Radiation Oncology, University of California San Francisco, San Francisco, California, USA Objectives The apparent diffusion coefficient computed from diffusion weighted imaging has been shown to have a 36% signal drop following tissue destruction with high intensity ultrasound and cryoablation .
Since this MR contrast mechanism is endogenous, previous studies have looked at monitoring the apparent diffusion coefficient (ADC) , or temperature and ADC , during treatment in order to study the progression of the ADC signal to assess when tissue viability is lost. More recently, a double echo steady state (DESS) sequence (Fig. ) has been proposed to achieve a similar goal faster and with improved registration between the temperature images and the lesion monitoring images . Due to its sensitivity to ADC changes and its short TR, DESS could serve as a monitoring platform for both temperature and lesion formation. Since DESS is a steady-state sequence, there are multiple echo pathways that also contribute to the measured signal. The first echo, Echo1, is effectively a gradient echo dominated by free-induction decay from to the preceding RF pulse. Although there are multiple echo pathway contributions for the second echo, Echo2, it is mainly a spin echo of Echo1 of the previous repetition with an effective echo time of TE2=2TR-TE1.
The purpose of this work was to assess whether DESS imaging can provide lesion formation information during thermal ablation of in vivo porcine muscle. DESS Pulse Sequence Schematic. The Sequence consisted of two echoes a gradient echo (TE = 4 ms) and a spin echo (TE = 46 ms). A spoiler gradients of 60 cycles/cm or 6 cycles/voxel was used Methods In order to assess the DESS sequence in vivo, interstitial ablations were performed within 40–45 kg farm pigs under MRI guidance. All animal experiments were reviewed and approved by our institution’s Administrative Panel on Laboratory Animal Care (APLAC). MRI compatible interstitial ultrasound applicators, consisting of a two element array of 1.5 mm x 10 mm tubular ultrasound transducers, each with independent power control, were used to generate thermal ablative lesions within in vivo porcine muscle.
The ultrasound applicators, with integrated water-cooling, were inserted within 13g (2.4 mm OD) Celcon plastic implant catheters which were placed free-hand 10–12 cm deep into the inner thigh muscles. For each experiment, two distinct thermal lesions were planned.
For the first trial, thermal ablation was performed using the distal transducer only; after imaging and allowing time for the cool-down, the ultrasound applicator was translated back 2 cm within the stationary catheter for repositioning prior to the second trial. A second thermal lesion was then produced using the proximal element.
This translation and sequencing from distal to proximal element were used to isolate the thermal lesions. All ablative sonications (n=4) were 10 min in length, with approximately 5–6 W acoustic power at 7.45 MHz delivered. Applicator and sonication parameters were chosen to generate circumferential lesions with an extent of approximately 1cm away from the active transducer segment.
A Double Echo Steady State (DESS) sequence was developed using HeartVista’s SpinBench and RTHawk platforms in order to monitor thermal lesion development. The phase of the first echo of the image was used to obtain temperature information using PRF thermometry while the magnitude of the second echo was used to detect lesion induced changes in signal intensity DESS magnitude images. At the end of the treatment DESS magnitude images were compared to contrast enhanced (CE-MRI) and gross histology. Results Temperature information was successfully obtained from the first echo, and the lesion was monitored using the second echo (Fig. ). Lesion extent obtained from the magnitude of the second echo correlated well with CE-MRI and gross histology (Fig. ). Lesion Extent Comparison. Magnitude images before and after contrast are compared to the magnitude image of the final Echo 2 image prior to contrast injection and gross histology Conclusions Lesion formation was visible using the proposed DESS sequence, allowing for more direct lesion monitoring during treatment.
Acknowledgements PO1 CA159992, RO1 CA111981, GE Healthcare. References  Chen J, et al. MRM 2008; 59: pp.  Plata J, et al.  Plata J, et al. ISTU Annual Meeting Abstract: 2173929.
Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, California, USA Objectives MR-guided focused ultrasound (MRgFUS) is a non-invasive technique for the treatment of painful bone metastases. Proton resonant frequency shift (PRF) thermometry is the standard method for monitoring temperature during MRgFUS interventions.
It can precisely measure the changes in temperature in water-based tissues, but fails to detect temperature changes in bone and in tissues with high lipid content, such as bone marrow. Current clinical protocols for bone treatments rely on measurement of the temperature change of adjacent muscle to estimate the temperature of the bone. This approach carries a significant risk of overtreatment in that more energy might be used than is needed to ablate the target.
In fact, we observe in HIFU treatments of bone metastases that the highest temperature in soft tissue is only reached 10–15 seconds after the end of the sonication. Collateral treatment of the near-field soft tissues during MRgFUS increases the risk for muscle and vascular injury, which can result in significant perioperative or chronic pain. Deeper penetration of the ablation through the cortical bone into the bone marrow or tumor is often desired for local control of osseous lesions. In the treatment of osteoid osteomas, complete ablation of the nidus is required for pain relief and to avoid recurrence, but the thickened cortical bone makes ultrasound penetration difficult.
Therefore, temperature measurement within the bone is desirable. Previous studies have shown a change in T2 of subcutaneous fat, red and yellow bone marrow in controlled calibration experiments and during treatments with focused ultrasound (Ozhinsky, et al. J Ther Ultrasound 2015; Baron et al. Magn Reson Med 2014).
The goal of this study was to determine if T2 based thermometry could be used to monitor the temperature change in ex-vivo and in-vivo bone marrow during focused ultrasound ablation of intact bone. Methods All experiments were performed using an ExAblate 2100 system (InSighTec, Haifa, Israel) integrated with a 3.0 Tesla MR scanner (GE Healthcare, Waukesha, WI, USA). Bone marrow T2 was quantified with a double-echo fast spin-echo sequence with water suppression (TE = 35/186 ms, TR = 1500 ms, echo train length = 40, FOV = 32 cm, 128 x 128 matrix size, 10mm slice thickness, 15 sec/slice). For ex-vivo validation, we performed MRgFUS ablation in an ex-vivo porcine femur (sonication: 20 sec, acoustic power: 30 W). The focus of the sonication was placed in the middle of the marrow, but due to the high ultrasound absorption of cortical bone most of the energy is absorbed in the cortical bone.
Focused ultrasound ablation was also performed in a swine model. All experimental procedures were done in accordance with NIH guidelines for humane handling of animals and received prior approval from the local Institutional Animal Care and Use Committee.
Each of the three animals received 12–14 sonications on femur and ilium bones (acoustic power: 10-35W, duration: 20–40 sec). As in the ex vivo validation, the focus was placed in the middle of the marrow. At the end of the focused ultrasound, pre- and post-contrast 3D Fast SPGR images were acquired. Results Figure shows the results of the ex-vivo experiment, where we measured a T2 elevation of 269 ms.
Assuming the T2/temp coefficient of 7 ms/°C (Ozhinsky, et al. ISMRM 2014), this corresponds to a temperature rise of 38°. The ex-vivo experiment shows that it takes on the order of 15 minutes for the marrow to return to the baseline temperature. T2 Measurement in ex-vivo bone marrow during and after the heating: a Localizer image showing the ultrasound transducer in the table; b T2 map during heating, showing the ROI; c Plot of T2 values within the ROI over time Figure shows the results of the in vivo experiment in a swine model. We measured a T2 rise of 231 ms within the bone marrow, which corresponds to temperature change of 33°C from baseline.
The in-vivo experiment showed excellent correspondence between the area of T2 elevation in marrow during the ablation and the resulting non-enhancing area in the post-contrast images. T2 Measurement in in-vivo bone marrow: a T2 map during ablation of a single sonication, showing the ROI; b post-contrast 3D Fast SPGR image after ablation (total of six sonications per location) c plot of T2 values within the ROI over time Conclusions In this study we have demonstrated for the first time that T2-based thermometry can be used in vivo to measure the heating in the marrow during bone ablation. The ability to monitor the temperature within the bone marrow allowed visualization of the heat penetration into the bone, which is important for local lesion control and treatment of osteoid osteomas. Therefore, T2 based temperature mapping, in addition to PRF-based thermometry could be used to monitor heating during the bone focused ultrasound treatments and improve safety and efficacy of MRgFUS bone applications. 1Clinical Science MR Therapy, Philips, Andover, Massachusetts, USA; 2Center for Interventional Oncology, Department of Radiology and Imaging Sciences, Clinical Center, National Institutes of Health, Bethesda, Maryland, USA Objectives Tissue mimicking phantoms (TMPs) are routinely used for calibration and quality assurance of medical devices including thermal therapy applicators prior to their use in clinic.
TMPs are also used in thermal therapy research as alternatives to ex vivo soft tissues and organs as they possess several advantages including greater availability and shelf life, high uniformity, and customizability. The efficacy of thermal ablation therapies depends on several factors including targeting accuracy and temperature elevation in the treated tissue.
Thus, an ideal TMP for thermal therapy applications should have the capacity to report ablated volumes and geometries as well as absolute temperatures. Magnetic Resonance Imaging -guided High Intensity Focused Ultrasound (MR-HIFU) is a therapeutic technique that can be used to precisely target and heat tissue non-invasively to induce thermal ablation or mild hyperthermia, among other applications. The objective of this study was to develop a novel, MR compatible tissue-mimicking thermochromic (TMTC) phantom for studying and characterizing HIFU devices, heating methods, and sonication parameters. Specifically, the intent of this work was to develop a phantom that reports on targeting accuracy, thermal energy deposition, and spatial heat distribution following HIFU. Additionally, the objective was to employ the TMTC phantom in characterization of two different HIFU devices, and to assess the temperatures and distribution of heating post-HIFU in relation to the treatment plan. Methods Polyacrylamide gel phantoms containing silica particles (1.0% w/v), bovine serum albumin (BSA, 3% w/v), and thermochromic ink (5.1% v/v, colour change temperature threshold of 60 °C) were produced. Both a preclinical Therapy Imaging Probe System (TIPS, Philips Research, Briarcliff Manor, NY) and a clinical MR-HIFU system (Sonalleve V2, Philips, Vantaa, Finland) were used for HIFU exposures targeted within the TMTC phantoms.
The TIPS system contains an 8 element annular array with an 80 mm focal length, as well as a 2-axis motion control system to move between targets. The Sonalleve system contains a 256-element phased array transducer (focal length = 140 mm), as well as a motion control system with 5 degrees of freedom. HIFU exposure parameters for the TIPS were: frequency 1.0 MHz, acoustic power 30 W, with sonication durations of 60, 120, and 180 s.
HIFU exposure parameters for the Sonalleve were: frequency 1.2 MHz, acoustic power 100 W, and duration 20–70 s, targeted to regions of 4–16 mm in diameter using electronic steering of the focal point. Together with the Sonalleve system, a clinical 1.5T MR scanner (Achieva, Philips Healthcare, Best, the Netherlands) was used for exposure planning and real-time thermometry utilizing the proton resonance frequency shift (PRFS) method. In addition, T2-weighted MR imaging and quantitative T2 mapping were performed to visualize and characterize thermal lesions within the TMTC phantoms after both Sonalleve and TIPS sonications.
Post-MRI, HIFU-induced colour changes within the phantoms were identified, photographed, and compared to the sonication plan as well as to MRI T2 and temperature maps. Results Tissue-mimicking thermochromic phantoms were developed, produced, and validated for use in characterizing HIFU devices and sonication methods.
HIFU thermal ablations (maximum temperature >60 °C) resulted in permanent colour changes at targeted locations within the phantoms. These colour changes corresponded to maximum temperatures recorded using real-time MRI thermometry. A gradual colour change from yellow to magenta was visible between 40 °C and 64 °C. At temperatures above 64 °C, no further colour change was observed.
In addition, heated volumes were visible on T2-weighted MRI and T2 maps as regions of permanent hypointensity and of lower T2 values, respectively, due to BSA coagulation. Increased HIFU energies and target diameters lead to greater colour change and a larger volume of colour change, respectively, as well as, correspondingly, to greater absolute change in T2 and a larger region of T2 change. Conclusions A tissue-mimicking thermochromic phantom was developed to assess the spatial targeting accuracy, maximum temperatures, and temperature uniformity of HIFU exposures. This TMTC phantom changes colour (over a range of temperatures that is relevant to ablative HIFU procedures) upon heating, allowing for quantitative measurements of absolute temperature and delineation of heated regions, and thus may be useful in HIFU device characterization, parameter optimization, quality assurance, and user training.
TMTC phantoms can also provide volumetric temperature information in experiments where MRI-based real-time thermometry is not feasible, as the stepwise nature of the colour change associated with changes in temperature allow for assessment of temperature gradients within and at the periphery of the heated region. 1Philips Healthcare, Vantaa, Finland, 2Imaging Division, University Medical Center, Utrecht, Utrecht, Netherlands Objectives During HIFU ablation of abdominal and pelvic lesions, a balance needs to be established between ablation speed and heat accumulation in the pre-focal subcutaneous layers, resulting in a safe but time-efficient intervention. As the de facto standard form of magnetic resonance thermometry, which is based on the proton resonance frequency shift, is ill-suited for temperature monitoring in the adipose tissues, several alternatives have been proposed. (Baron, MRM, 2014) have demonstrated the feasibility of monitoring heating in adipose tissue layers using apparent T2 mapping based on dual echo fast spin echo imaging. A linear (5.2 ms/○C) and reversible T2 - temperature dependency was shown reproducible over a relevant temperature range. In this study, the strategy developed by Baron et al.
Was combined with reduced field-of-view (FOV) imaging using perpendicular selection gradients, in the literature referred to as zonally-magnified or local-look imaging (Mansfield, J. Of Phys.,1988). Reducing the FOV in phase-encoding (PE) direction while preventing fold-over allows to improve the spatio-temporal resolution of apparent T2-based thermometry. This opens new possibilities such as near-field monitoring during sonication at relevant temporal resolutions using sequence interleaving but also high resolution inter-sonication monitoring of accumulative heating.
Methods All imaging experiments were performed on a 1.5-T MR Scanner (Achieva, Philips Healthcare, Best, The Netherlands) using a research version of the Sonalleve HIFU Platform (Philips Healthcare, Vantaa, Finland) that is supplied with an integrated four-channel loop coil and a 16-channel back coil. Two imaging experiments were performed in this study. Under normothermic conditions, a volunteer was imaged using a dual echo fast spin echo sequence, with a single slice placed at the location of the subcutaneous fat layer (coronal orientation, TE1/TE2: 11/140 ms, train length: 24 lines/excitation, FOV: 400 x 105 mm2, matrix size: 168 x 48). The purpose of these experiments was to demonstrate the feasibility of apparent T2-mapping using a reduced FOV in PE direction. A next experiment aimed at demonstrating the feasibility of resolving a temperature gradient along the subcutaneous fat layer of a volunteer, comparing a cooled and slightly heated state. Heating (37○C skin temperature) and cooling (14○C skin temperature) were achieved using a water-filled cushion together with a circulation unit, which was placed outside of the MR room.
Skin temperatures were monitored using a fibre optic probe (Luxtron, LumaSense, Santa Clara, CA), placed between skin and cushion. Imaging parameters were the following: single slice, sagittal orientation, TE1/TE2: 11.8/130 ms, train length: 20 lines/excitation, FOV: 200 x 52 mm2, matrix size: 200 x 40.
In both imaging experiments, the radio-frequency pulse generating the initial transverse magnetization was implemented as a fat-selective binomial pulse (1-2-1) and the corresponding selection gradient was oriented parallel and perpendicular to the imaging slice, respectively. As a consequence, the volume experiencing the spectrally non-selective refocussing pulses was limited to the subcutaneous tissue layers. This aims at preventing disturbance of the magnetization in the water compartment at the location of the focus. Results An overview of the results of the imaging experiment under normothermic conditions is shown in Fig. (a-c). Reduction of the FOV in phase-encoding direction (left-right in the image) was achieved without apparent fold-over artefacts. Overview of the result obtained in the two imaging experiments.
The results obtained under normothermic conditions are shown in panels a- c, where panel a shows the signal magnitude at the first echo time, panel b the signal magnitude at the second echo. Figure (d-f) shows the signal intensity at the first echo time (panel d), the signal intensity at the second echo time (panel e) and the difference in apparent T2 between the heated and cooled state as an overlay (panel f, background: intensity at the first echo time). A gradual change along the anterior-posterior direction (left-to-right in the image) is observed in the difference of the apparent T2. Conclusions Dual echo fast spin echo imaging in combination with reduced FOV imaging using perpendicular selection gradients was successfully shown to allow for apparent T2-mapping with no/minimal fold-over artefacts under normothermic conditions. Furthermore, comparing a cooled and slight heated state, a gradient in the apparent T2 difference could be resolved at high resolution (~1mm).
Both examples show the potential of reduced FOV apparent T2-mapping, enabling near-field monitoring at improved spatio-temporal resolution. The potential interference in interleaved T2/PRFS imaging scenarios is currently under investigation.
1Biomedical Engineering, Vanderbilt University, Nashville, Tennessee, USA; 2Institute of Imaging Science, Vanderbilt University, Nashville, Tennessee, USA; 3Chemical and Physical Biology, Vanderbilt University, Nashville, Tennessee, USA; 4Radiology, Vanderbilt University, Nashville, Tennessee, USA Objectives Focused Ultrasound (FUS) therapy is a promising approach for treating cancerous lesions in the body. In addition to cell destruction, FUS hyperthermia has been shown to have immunomodulatory effects, increasing dendritic cell infiltration and activating the body's immune response to reduce metastases and future recurrence [1–2]. However, the development and understanding of FUS immunomodulation has been limited by an inability to characterize the immune response in vivo. This ability would enable optimal timing of ex vivo immunophenotyping, resulting in more efficient and more statistically powerful studies with fewer animals. Here we describe and validate a novel double-transgenic murine model of breast cancer that we have developed to meet this need.
Methods A double transgenic PyNGL murine model was bred to express a nuclear factor-kappaB (NF-kB) reporter transgene (NGL) into the polyoma virus middle T oncogene model. This mouse exhibits spontaneous mammary tumour formation comparable to that of human breast cancer as well as a spatially-resolved, detectable change in bioluminescence with NF-kB activation, a key factor in immunomodulatory inflammation. By monitoring bioluminescence with In Vivo Imaging Systems (IVIS) imaging, tissue collection for immunophenotyping can be optimally timed. Experiments were performed to validate the mouse model when treated with FUS. Baseline luminescence maps were first obtained with IVIS prior to treatment. Subsequently, FUS thermal treatment was applied with either hyperthermia (CEM43 200) doses with a custom-designed MRgFUS system built in-house .
IVIS was used to monitor the change in luminescent inflammatory response every 12 hours after undergoing thermal therapy until the collection of tissues. This enabled the time of maximum immune response post-FUS treatment to be localized. Subsequent mice were sacrificed 48 hours post-treatment (the optimum time point based on the IVIS data) and analyzed with flow cytometry for infiltration of immune markers such as T cells (CD3,CD4,CD8), cytokines, and macrophages. Histology sections were taken of the skin, tumours, and spleen to assess cellular damage and composition (results not shown). Results For both treatment groups, a change NF-kB activation was observed with IVIS as soon as 24 hours post-treatment and reached a peak between 48 and 96 hours, consistent with the anticipated timeline for recruitment of inflammatory immune cells. Activation was spatially consistent with the area of MRgFUS treatment (Fig. ) and remained above baseline activation levels for the duration of luminescent imaging.
The varied thermal doses were shown to have different effects on NF-kB activation - hyperthermia resulted in a consistent decrease in activation in the treated tumour (n=3) while ablation resulted in an increase in activation (n = 1) (Fig. ). Additional mouse studies are currently underway to confirm these results.
Immunophenotyping revealed a large influx of T-cells 48 hours post-treatment in response to hyperthermia in comparison to the untreated control. Analysis of the ablated tumour tissue revealed no significant change in immune cell concentration compared to the control. No superficial skin burns were observed on the treated mice in the area of applied MRgFUS treatment. A preliminary cellular analysis of treated tumours excised 48 hours post MRgFUS treatment and analyzed with flow cytometry. CD3+, CD4+, and CD8+ are cellular markers for T-cells that are involved in the in vivo immune response. A substantial difference.
Conclusions The use of a novel transgenic reporter mouse with spontaneous tumor generation enables spatiotemporally-resolved quantification of the immune response to FUS treatment in vivo. Cell analysis from excised tissue was supplemented by spatially-localized monitoring of the in vivo inflammatory immune response.
Preliminary results showed that immune modulation measured by NF-kB activation depends on thermal dose. The increase in infiltrating T cells with hyperthermia, and lack thereof in the ablation case, suggests that the immune response may be more effectively activated by FUS treatment at a lower thermal dose. More experiments are ongoing to further explore the difference between thermal doses varying from hyperthermia to ablation as well as long term studies to investigate the effect of FUS-induced immune activation on metastases outside of the primary tumour. Acknowledgments This work was supported by DoD W81XWH-12-BCRP-IDEA, NIH RO1 CA111981, and a Vanderbilt University Discovery Grant. References  F Wu, Z Hu et al. Journal of Translational Medicine 5(34), 2007  J Unga et al. Advanced drug delivery reviews 72:144–153, 2014  M Poorman et al.
ISMRM 2015 #1642. The Institute of Cancer Research, Department of Physics, Sutton, United Kingdom Objectives Hypoxia is a common feature of radioresistant tumours, resulting in a decreased efficiency of radiotherapy (Harada, 2011). Several approaches have been proposed to overcome this limitation, including the adjuvant use of hyperthermia and chemotherapy. We propose the use of High Intensity Focused Ultrasound (HIFU) to target these hypoxic regions, which lack perfusion and so provide good targets for thermal ablation. One of the challenges when targeting hypoxia is the accurate detection of poorly oxygenated regions, ideally non-invasively, for treatment planning. Several imaging techniques may be used in clinical practice for this purpose. Recently Photoacoustic (PA) imaging has been proposed for distinguishing between oxy- and deoxy-haemoglobin inside tumours.
The technique is based on the generation of acoustic waves by the tissue after being exposed to short pulses of light. These waves can be detected using a transducer and the distribution of optical absorption in tissue is then reconstructed with US spatial resolution. For this study, we used PA imaging to detect hypoxia in a radioresistant head and neck tumour model, implanted subcutaneously in mice. Selected hypoxic regions were targeted with HIFU, under US-guidance, using a dedicated small animal system, and the outcome of the treatment was evaluated histologically. Methods Twelve female NCr nude mice (6 weeks old) were subcutaneously injected with 5x10 5 CAL R cells (head and neck tumour model) in the right flank.
Tumours were measured up to 3 times a week, until they reached a volume of 200–300 mm 3. Animals were imaged using a MultiSpectral Optical Tomography (MSOT, iThera Medical) device with an excitation wavelength range of 660–1350 nm (details in Morscher, 2014). Coupling gel is applied to the tumour and surrounding area, and the animal is placed in a horizontal position in a holder under isoflurane anaesthesia. Furthermore, they are enveloped in a thin polyethylene membrane as it provides acoustic coupling, before being submerged in a water tank.
Multiple transverse 2D slices of the tumour were acquired at 680, 700, 715, 730, 760, 770, 800, 850 and 900nm, in 0.5mm steps (from head to tail), and were reconstructed using interpolated model-matrix inversion (Rosenthal, 2010). The reconstructed data were multispectrally unmixed using a linear regression technique to identify the distribution of oxy and deoxygenated haemoglobin. Animals were US imaged 24h after PA imaging (injectable anaesthesia: mix of hypnovel, fentanyl and medetomidine), using an E-cube scanner with a phased array transducer (f=12MHz). Animals were imaged in the same direction as in the PA experiment, with a 0.5mm step between each image acquisition. For the HIFU exposures, a pre-clinical VIFU2000 (Alpinion) system was used (single element spherical-focused transducer, 1.5MHz).
Although hypoxic regions are not visible in B-mode images, they are generally distributed around areas of necrosis that can be identified by their hypoechogenicity. We compared these regions with those in PA images to define the target regions, which were exposed using the VIFU system at different acoustic power levels in order to define the thermal lesioning threshold for these tumours. Six animals were HIFU-exposed, at 31.1 +/− 3.1 W (N=2), 26.3 +/− 2.6 W (N=3) and 23.0 +/− 2.3 W (N=1), for 8 seconds, one exposure per tumour. In addition, a Passive Cavitation Detection (PCD) system consisting of a Precision Acoustics broadband sensor, 20 mm outer diameter, weakly focused co-aligned to the HIFU focal peak and connected to a data acquisition system (Spectrum MI.2031, 8-bit) via a 1.5MHz notch filter. A 20dB pre amplifier was used to record data at a rate of 12x1.5MHz in 5 of the treatments.
Broadband activity between 3-9MHz was analysed to detect inertial cavitation. Animals were allowed to recover for 24h after HIFU, at which point an i.p. Injection of pimonidazole (a marker for hypoxia) was given and they were sacrificed 45min later.
Tumour samples were collected, snapped frozen in cardice and stored at −80°C for histological analysis, which included pimonidazole and H&E staining. Results PA imaging suggested that this tumour model develops a necrotic core surrounded by hypoxic areas, despite the well vascularised rim around the tumour, when the volumes reaches ~200 mm 3, after ~14-26 days, (Fig. ). This was confirmed by H&E and pimonidazole staining (Fig. ), although the latter did not show as extensive hypoxic regions as did the PA imaging. Pimonidazole staining section, corresponding to the tumour in Fig.. Hypoxic areas are characterised by bright green regions, surrounding a ( darker) necrotic core, as exemplified by the blue arrows US imaging was able to reliably identify the largest necrotic regions, which we used to compare with PA images to identify target areas for treatment. Of the HIFU treatments performed, the lowest acoustic power was interrupted.
The remaining exposures resulted in tissue lesioning, observed after H&E histological analysis, and were identified as further extensive areas of necrosis and haemorrhage. None of the exposures resulted in skin burns. One interesting effect was that treated tumours did not take up the pimonidazole dye, which suggests a significantly reduced tumour perfusion at 24h. Inertial cavitation was detected in both higher power exposures, but not at lower power exposures. Conclusions The hypoxia distribution observed with photoacoustic imaging correlated well with that expected from the literature on this tumour model (Box et al., 2013). For future studies, we intend to co-register the PA and US images for a more precise treatment plan and use a larger cohort of animals to validate the results obtained with both modalities, using the standard histological techniques - pimonidazole and H&E. The pimonidazole results, intended to indicate the oxygen distribution, showed lack of penetration of pimonidazole, probably due to vascular occlusion, within 24 hours after HIFU treatment, whereas uptake in control animals processed at the same time was normal.
Future studies will investigate this effect at different time points after treatment, with both post-exposure PA imaging and histological analysis, and investigating both hypoxia and perfusion staining. The effects of HIFU on vasculature have been studied before, but it is important to understand the time course of these effects in pre-clinical models as this may have a significant impact on the outcome of combined therapies, such as HIFU-chemotherapy and HIFU-radiotherapy.
Radiology and Imaging Sciences, NIH Clinical Center, Bethesda, Maryland, USA Objectives Stem cell therapies are promising regenerative medicine approaches. Pulsed focused ultrasound (pFUS) induces microenvironmental changes in normal and diseased tissues that can enhance local homing and efficacy of intravenously-infused mesenchymal stromal cells (MSC) and further improve disease outcomes.
How pFUS interacts with tissues to produce the necessary molecular changes is unclear. Mouse muscle tissue was sonicated at increasing powers while passive cavitation was measured. Sonicated tissue was harvested for cyclooxygenase-2 (COX2) expression to correlate with physical ultrasound effects, as COX2 expression is critical for molecular signalling cascades that induce MSC homing.
Lastly, mice were given inhibitors of mechanosensitive channels prior to pFUS to investigate their role in propagating physiological effects of pFUS. Methods C3H mice were treated with pFUS to the hamstring using a VIFU 2000 system.
Under ultrasound imaging guidance, pFUS was delivered at 1 MHz, 5 Hz pulse repetition frequency, 5% duty cycle, and varying transducer output powers (ranging from 10–80 W). Passive cavitation detection was performed with a hydrophone. Mice were euthanized 16 hr post-pFUS and harvested muscle was homogenized and analyzed for COX2 expression by ELISA. For drug studies, mice were given GdCl 3 (0.04 mmoles/kg) or ruthenium red (0.01 mmoles/kg) by intravenous injection at the beginning of sonications.
Statistical comparisons were performed by one-way analysis of variance (ANOVA) using Bonferroni post-hoc tests with p values. Radiology and Imaging Sciences, NIH Clinical Center, Bethesda, Maryland, USA Objectives Pulsed focused ultrasound (pFUS) enhances homing of IV-infused mesenchymal stem cells (MSC) to murine kidneys during cisplatin (CIS)-induced acute kidney injury (AKI). PFUS acts as a neo-adjuvant to MSC therapy and the combination leads to better AKI outcomes (renal function and survival) than MSC alone. In wild-type mice, nearly twice as many MSC home to diseased kidneys following pFUS, but >10 times as much interleukin (IL)-10 is produced by MSC that home to pFUS-treated kidneys. This suggests that pFUS sonications modify the renal microenvironment to increase potency of MSC that home to sonicated kidneys. Interferon-g (IFNg) has long been known to increase MSC potency and has been shown to be upregulated in kidneys after pFUS. This study investigates the role of IFNg released by kidneys in response to pFUS improving the therapeutic efficacy of IV-infused MSC.
Methods IFNg knockout (KO) mice received CIS (15 mg/kg ip), kidney pFUS (4 MPa; 5% duty cycle) and/or MSC (10 6 human MSC). Intravenous MSC injections were performed 3–4 hr post-pFUS. Groups included mice that had AKI only, AKI+pFUS, AKI+MSC, AKI+pFUS+MSC, and normal mice. Mice received CIS on Day (D) 0 and pFUS/MSC on D1. Some mice were euthanized on D2 and kidneys were harvested for molecular analyses. Other mice were euthanized on D4 to measure renal function (blood urea nitrogen [BUN]; serum creatinine [SCr]). Statistical comparisons were performed by one-way analysis of variance (ANOVA) using Bonferroni post-hoc tests with p values.
1Mechanical Engineering, University of Dundee, Dundee, Angus, United Kingdom; 2University of Dundee, Dundee, United Kingdom; 3University of Washington, Seattle, Washington, USA Objectives Focused ultrasound can induce shear-wave when certain requirements of acoustic power are met, e.g. Pulse length, amplitude, frequency. Our group recently found that the characteristics of HIFU-induced shear-wave (HiSW) can be manipulated by changing different acoustic pulse-length and amplitude.
By manipulating the HIFU pulse, we could control the wavelength and displacement of the HiSW. Our objective is to demonstrate that HiSW can be manipulated into either i) small and sharp propagating wave, or ii) long wavelength and large displacement propagating wave.
Methods Optical Coherence Tomography with Phase-sensitive technique was utilized for shear-wave imaging. Phase-sensitive Optical Coherence Tomography performs a 256 (time axis) x A-scanlines (depth axis) over the period of 2 milliseconds at the same location for each HIFU pulse.
This PhS-OCT-scan repeats in 256 different locations (width axis), forming a complete B-scan dataset over time (3D-dataset). The camera runs at 46200 kHz A-scan rate, exposure 17.4 μs, sensitivity 450 e/count. Ex-vivo porcine skin is embedded inside 2%-agar phantom to ensure good contact with HIFU transducer.
The HIFU transducer (2.09 MHz, 20 mm diameter, 13 mm focal length) is placed at the bottom of the sample. The scanning plane captures the top surface of the ex-vivo sample, defined by the centre point of the HIFU focus, and the axial- and lateral-direction of the HIFU beam. HIFU-induced shear-wave (HiSW) is captured in reducing number of cycles per pulse, from 100 cycles/pulse to 20 cycles/pulse.
The captured image is then processed offline for quantitative analysis of the HiSW, regarding the wavenumber of the HiSW signal. Results The displacement of HiSW correlates well with the reduction of HIFU cycles per pulse. Lowering HIFU cycles-per-pulse number would reduce HiSW displacement.
A reduction of 80% HIFU cycles-per-pulse number (100 vs. 20 cycles/pulse) results in a reduction of less than 50% HiSW displacement (approximately 140 nm vs. Reducing the HIFU cycles-per-pulse parameter also leads to a sharper HiSW, regarding the peak wavenumber of HiSW (refer to Fig., peak wavenumber of 4.2 mm - 1 in 100 cycles per pulse, as opposed to 3.7 mm −1 in 20 cycles per pulse). However, the sharper HiSW is greatly burdened by the relatively short propagation, as the high-frequency components quickly attenuate over travelling distance. Wavenumber comparison between HIFU-induced shear-wave using 20 cycles per pulse versus 100 cycles per pulse, at constant time frame (85.4 μs after acoustic output pulse) and constant acoustic power of 3.72 W Conclusions Understanding the response of HIFU-induced shear-wave (HiSW) under different acoustic settings, we can adapt HIFU into both diagnostic and treatment regime. In particular, our experimental setup would benefit the diagnostic and treatment of skin cancer at the same time.
PhS-OCT can recover elasticity information from HiSW speed map. The acoustic power output is relatively low, with I sata measuring 23.6 mW.cm −2 maximum (100 cycles per pulse, total acoustic power output of 3.72 W), which is suitable for diagnostic purposes. By manipulating the acoustic settings, we could either a) induce a sharp HiSW for tracking purposes, or b) induce a strong HiSW with long propagating distance for diagnostic purposes, i.e. Elasticity measurement.
1Action-Physics, Pardes-Hanna, Israel; 2CByond ltd., Nesher, Israel Objectives Traditional transducer designs require a half-wavelength resonator, posing a lower bound for the size of the transducer. The Langevin type transducers are common for frequencies of about 30–60 kHz, comprising a stack of piezoelectric rings pressed to a metal resonator. Their size is about 50–100 mm, depending on frequency and speed of sound in the resonator material. This type of transducers is employed in ultrasonic cleaning baths, ultrasonic dental scalers, ultrasonic scalpel and in many other applications. The low frequency and the relatively large displacement-amplitude provided by the transducer make it ideal to generate cavitation, which may be useful, in turn, for the fragmentation of solid structures, plaque removal, tearing and cutting biological material etc. In this paper we describe the development of the Twin Piezo Motor: a miniature low frequency, large displacement-amplitude transducer of a new design, in which the resonating element is a metallic, beam shaped tip, vibrating in a transverse (bending) mode. Geometry of the tip may be adjusted for a resonance in the required frequency range, while preserving small footprint.
The Twin Piezo Motor is assumed to be capable of generating cavitation in applications where space is heavily restricted. One possible application is Ultrasonic Lithotripsy (USL) - breaking kidney stones by cavitation. The required solution should pass through the urinary tract over a ureteroscope or a catheter, achieving full contact or getting very close (. 1School of Medicine, IMSaT, Dundee, United Kingdom; 2Fraunhofer, Mevis, Bremen, Germany Objectives The application of Focussed Ultrasound (FUS) in upper abdominal organs is particularly challenging due to complexity of breathing motion, a multitude of risk structures and possible occlusions through the rib cage. TRANS-FUSIMO Treatment System (TTS) is a newly developed software (MEVIS, Fraunhofer, Bremen) enabling Magnetic Resonance (MR) guided FUS (MRgFUS) in upper abdominal organs. MR organ motion tracking data is used for a model-based motion compensation while monitoring the temperature . Due to the complexity of the system, TTS demands thorough validation before its use in animal trials.
One important system parameter in this evaluation of FUS is the duration of sonication. The delay when starting a sonication, the deviation from the planned sonication time, and the delay in the system after a sonication is stopped, needs to be measured accurately to quantify system performance. Methods The evaluated version of the TTS uses the software interface of Signa 1.5 T MR Scanner (GE Healthcare, UK ) and the transducer of Conformal Bone System 2100 (CBS) (INSIGHTEC, Israel). On the CBS transducer system, steerable sonications are realized by so called subsonications that have an individual focus position, and duration.
Subsonications are organized in sonication banks and the active subsonication can be switched during sonication rapidly (2ms). Starting a sonication on the CBS, however has a considerable delay of approximately 2–3 seconds.
To enable precise control of the sonication time, TTS employs a sonication strategy that exploits the short switching times between subsonications. For example, to start a static sonication, it builds a sonication bank with two subsonications. The first is a subsonication with very low power (0.001 W) and a long duration. It is the default subsonication and used to start the sonication. In the TTS, this step is called arming the transducer. The second subsonication has the actually prescribed sonication focus position and power information. It is activated immediately after the user choses to start the sonication via the TTS execute command.
For safety reasons, the second sonication’s duration is limited to 250 ms and it is actively looped by the software until the prescribed duration of the sonication has passed, or until the user stops the sonication via a stop command (Fig. ). Sonication execution with subsonication bank algorithm using Trans-fusimo Treatment Software The sonication is monitored via single shot EPI MR Sequence of 512 phases, with TE: 26.4, TR: 100, flip angle: 40, freq phase: 128 x 96 parameters on the MR machine. To synchronise the MR to the TTS, the MR is configured to start monitoring after a TTL-Trigger pulse sent from the TTS. Testing To collect data during sonication, fiber optic hydrophone (Pa Ltd, UK) was used. The fiber optic hydrophone works on the principle of interferometric detection of changes in the optical thickness of a thin polymer film at the tip of the optical fiber sensor downlead. Changes in the thickness may be induced acoustically (through the acoustic pressure) or thermally.
The system is capable of differentiating between the two and making simultaneous measurements of both (Morris et al. However, in this study, the main purpose was to record the signal during sonication. Experiment set-up consisted of a water tank filled with degassed water. Gridded surface sensor holder was placed on the top of the water tank (Fig. ). Fibre-optic hydrophone sensor was mounted on the grid surface. MR Scan was used to find the exact location of the tip of the sensor. This data was used to sonicate to the tip of the fibre-optic sensor by using TTS.
Fibre-optic sensor was hard wired to Fibre-optic Hydrophone System control unit. Hydrophone system has its own software to control its hardware. To obtain reading from hydrophone, a computerised scope such as PicoScope (Picotech, UK) was connected via the “AC out” connector on the front panel. The system was designed to have an output impedance of 50 Ohm. PicoScope has two inputs, first is the output of the hydrophone, and second is the monitoring trigger pulse coming from TTS. In order to initiate recording of data, detected by hydrophone, a TTL pulse generated by TTS, was utilised. The time information for the TTL pulse, the ‘execute’ command and ‘stop’ commands were recorded as a tag line in the software (Fig. ).
Deviation during sonication was calculated as t2- t1 (1). Delay after sonication stop button pressed was calculated as shown below (2) length of the signal on PicoScope (t3) minus delay in the start time ( t1) during sonication duration. Time diagram for the execution of the sonication with Trans-fusimo Treatment System Picoscope was programmed using LabView (National Instruments, UK) with 100 ms of time resolution to record the signal simultaneously with the TTL pulse. Results With sonication power of 30W for 30 seconds, the deviation of the actual sonication duration from the planned duration was found smaller than 1 second. The time until the transducer stops sonicating, after the stop button was pressed, was calculated as less than 200 ms.
Conclusions In this study, feasibility of measuring the deviation of the actual sonication and delay after stop button release was tested. The methodology described in this study proves that it is possible to quantify these parameters. With the established methodology, the next step is to quantify the repeatability and reliability of the system with different sonication timings and power values using the Transfusimo Treatment Software (TTS) and the conformal bone system transducer. Transfusimo Treatment System (TTS) is planned to be tested on animals based on these results. References  Schwenke et al.
An integrated model-based software for FUS in moving abdominal organs, Int J Hyperthermia. Vol 31(3): 240–250, 2015.  Morris et aI. A Fabry-Perot fibre-optic ultrasonic hydrophone for the simultaneous measurement of temperature and acoustic pressure”, J. Vol 125(6) pp.
3611–3622, June 2009. Department of Biomedical Engineering, Technion-Israel Institute of Technology, Haifa, Israel Objectives Extracorporeal acute cardiac pacing by high intensity focused ultrasound (HIFU) could be a disruptive technology in the field of cardiology. Two clinical applications in which acute cardiac pacing by HIFU may be valuable are: (1) preoperative patient screening in cardiac resynchronization therapy surgery where currently 20-40% of operations fail; (2) Emergency life support, which may prevent an event of cardiac arrest from causing sudden death.
Both applications may better morbidity and mortality rates in heart failure patients. While ultrasonic cardiac stimulation was first applied 87 years ago, the mechanisms of ultrasonic cardiac pacing are yet unknown. Our work aims to unveil the dominant mechanisms of HIFU cardiac pacing, using a combined experimental and modeling approach. Recently, we published results demonstrating HIFU extra systole induction in whole anesthetized rats.
Sequences of multi harmony HIFU paced extrasystoles were obtained owing to adequate spatiotemporal control, which employed online ultrasound guidance and real-time vital signs signal processing. An illustration of a sequence of HIFU paced premature ventricular contractions (PVCs) is presented in panel A of the figure below. Visual inspection post pacing showed no indication of gross damage or petechia, histological evaluation didn’t show staining or signs of inflammation 24 hours post pacing. Panel B of the figure below shows a heart post HIFU pacing and histological staining results 24 hours post pacing. Extrasystole induction was demonstrated temporally throughout the entire cardiac cycle beyond the absolute refectory period and spatially across the entire left ventricle. Passive Cavitation Detection (PCD) was applied in conjunction with US imaging on a gel phantom, and on rats. The gel phantom was sonicated with a HIFU pacing sequence, PCD positive cavitation indication was correlated with observed hyperechoic imaging.
Similar PCD indications were recorded during in-vivo HIFU pacing, while hyperechoic imaging was not observed. Analysis of these experimental results suggests membrane currents as the dominant cellular level mechanism and cavitation as the dominant ultrasound tissue interaction mechanism. The hypothesis we test here through modeling and simulation is that HIFU induced intramembrane cavitation could induce Premature Action Potentials (PAPs) in a model of a cardiomyocyte by altering the membrane capacitance. Methods The Livshitz & Rudy guinea pig LV cardiomyocyte model and O’Hara et al. Human LV cardiomyocyte model were adapted to include variable capacitance induced ionic currents and membrane voltage alterations. Numerical simulation in Matlab was applied to calculate the temporal membrane capacitance changes due to simulated HIFU insonation, and the resulting ion and membrane voltage dynamics.
The simulated HIFU insonation reconstructed the minimal peak negative pressure that was observed to be required for HIFU pacing in rats. Results Numerical simulation results demonstrated HIFU PAP induction throughout the entire diastole (evaluated by the temporal offset from the preceding AP peak of the membrane voltage trace). An illustration is shown in panels C-E of the figure below. The membrane potential is shown in blue. A baseline sinus rhythm was produced by electrical stimulation at 2Hz, the electrical stimulation is noted by the down facing black bars at 0 and 500ms.
Ultrasonic pacing was applied at different times during the diastole, the ultrasonic pacing is noted by the upward facing red bars. Membrane depolarization was gradual, and the ion dynamics composition was similar to that of normal sinus rhythm. The temporal offset between insonation onset and the resulting PAP replicated the in-vivo observations.
Moreover, PAP induction was demonstrated to occur also during insonation. Conclusions The simulation results of a small animal model reproduced our in-vivo observations. This supports our hypothesis of the suggested dominant mechanisms. The simulation results of a human cardiomyocyte model share similar characteristics and attributes to those of the small animal model, offering the prediction that HIFU pacing could be performed in humans with the same pacing patterns that were applied on whole anesthetized rats. The presented results offer new insights to the study of HIFU pacing and predict that HIFU pacing may be performed in human subjects without membrane disruption. Focal spot observation in 3 orthogonal planes: local maximum pressure is given in arbitrary unit.
Focal spot dimensions: 3x3x10 mm. Cross-sections of the time-reversal cavity and MSM are shown on the right in light green With our real device in a water tank, hydrophone measurements confirmed the spatio-temporal focalisation of the signal. Observations in a plane 10 cm away from the cavity showed a 1.2 x 1.2 mm focal spot, with a temporal peak less than 2 cycles long. At full power, the peak pressure obtained at the focus was about 40 MPa (linearly extrapolated value). These observations were consistent over a large area (−3 dB area 10x6 cm). The negative pressure obtained was sufficient to achieve cavitation. It was even possible to generate bubble clouds in various spots at the same time by emitting the stored signals corresponding to several locations successively at a PRF of 313 Hz between the different signals and between 16 and 260 Hz overall.
Figure shows the bubble clouds formed by the targeting of 2 simultaneous focal spots. We also succeeded in creating lesions in a slice of ham. 1Department of Urology, University of Washington, Seattle, Washington, USA; 2Applied Physics Laboratory, University of Washington, Seattle, Washington, USA; 3Physics Department, M.V.
Lomonosov Moscow State University, Moscow, Russian Federation; 4Department of Medicine, University of Washington, Seattle, Washington, USA Objectives Boiling histotripsy (BH) uses millisecond-long pulses of HIFU shock waves emitted at low duty cycle to induce localized boiling in tissue within each pulse. Further interaction of ultrasound with the vapor cavity for the rest of the pulse results in mechanical fractionation of tissue into subcellular debris. Our group is developing BH as a non-invasive treatment of renal and hepatic masses. The feasibility of producing single BH lesions in vivo in an exposed porcine liver has been demonstrated previously. The goal of the present work was to evaluate the feasibility and safety of transcutaneous, volumetric BH ablation of porcine liver and kidney in acute pig studies.
Methods Pigs (37–40 kg, n=4) were anesthetized and placed on the surgical table in either lateral (for kidney treatment) or supine (for liver treatment) position. A 1.5 MHz HIFU transducer (12-element sector array of 7.5 cm aperture, F#=1.07) with a central opening (2 cm) to allow for ultrasound treatment guidance was attached to a 3D positioning system and submerged in a degassed water bath coupled to the abdomen (Fig. ). The HIFU focus position, pre-recorded with the ultrasound imaging system, was aligned with the targeted region at the depth of 2.5-4.5 cm from the skin surface. The pulse-average power output threshold for initiating BH at each location was measured by sonicating the focal point with BH pulses at gradually increasing amplitude until a hyperechoic region was observed at the focus, indicating boiling. Prior to the in vivo experiments, similar measurements of threshold output power were performed in freshly harvested ex vivo porcine liver and kidney for comparison to the transcutaneous in vivo setting. The subsequent in vivo sonications were performed slightly above the threshold (10-15% increase in driving voltage).
The following treatment parameters were used: pulse duration 5 or 10 ms, pulse repetition frequency (PRF) 1 or 2 Hz (with the duty factor fixed at 1%). A total of 10–30 pulses were delivered per focal point (this number will be further referred to as BH dose), with the focal points spaced 1–1.5 mm apart in a rectangular grid with 0.5-1.5 cm linear dimensions. The BH treatment was not gated by or synchronized with the respiratory motion. Following BH exposure, higher resolution ultrasound assessment of the treated regions was conducted. Necropsy was then performed and the treated portions of the liver and the kidneys were collected for gross and histologic assessment. 12-element 1.5 MHz HIFU sector array transducer integrated with an ultrasound imaging probe (ATL P7-4) Results Kidney treatments.
Lower poles of 7 kidneys were targeted and n=11 volumetric lesions containing cortex, medulla, and renal sinus were created. The transducer driving voltage required to initiate the subcostal transcutaneous treatment in the kidneys was 30 – 50% higher than that observed in the exposed ex vivo tissue; the partially transcostal exposures (30-40% of the beam obstructed by the ribs) required 120-150% larger driving voltage. The respiration-induced motion of the target did not appreciably interfere with the treatment Post-BH, higher resolution ultrasound images revealed well-defined hypoechoic cavities.
At necropsy no gross evidence of collateral damage was appreciated within the beam path and no subjects had gross hematuria. On gross inspection of the kidney, small clots were seen within the collecting system in all treated kidneys with regions of petechial hemorrhage surrounding a centrally located fractionated volume of parenchyma.
Histologically, all BH exposures produced completely fractionated cortex sharply demarcated from histologically normal untreated tissue (Fig. ). In the medulla, blood was noted within the collecting ducts with areas of focally fractionated tissue at higher dose exposures (20–30 pulses per focal spot). Within the wall of the collecting system, focal petechial hemorrhage was visualized only at the higher dose exposures without disruption of the wall.