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1810. Tissue Acoustic Properties Using MRI Temperature Measurements of Low Powered Ultrasound Heating Pulse. Urvi Vyas 1 , Nick Todd 2 , Allison Payne 3 , Douglas Christensen, Dennis L. Parker 4 1 Bioengineering, University of Utah, Salt Lake City, UT, United States; 2 Physics, University of Utah; 3 Mechanical Engineering, University of Utah; 4 Radiology, University of Utah An inverse parameter estimation technique that non-invasively determines ultrasound tissue properties ( speed of sound, attenuation) using MRI temperature maps of low level ultrasound heating pulses is presented. The properties determined by the new technique are compared to ultrasound tissue properties measured using the transmission-substitution technique. 1811. MR-Guided Unfocused Ultrasound Disruption of the Rat Blood-Brain Barrier Kelly Ann Townsend 1 , Randy L. King 1 , Greg Zaharchuk 2 , Kim Butts Pauly 1,2 1 Bioengineering, Stanford University, Stanford, CA, United States; 2 Radiology, Stanford University, Stanford, CA, United States The purpose of this study was to investigate the effects of unfocused ultrasound on blood-brain barrier opening across the whole brain using contract enhanced-MRI. T1-weighted FSE images of the brain were acquired in rats for several minutes after gadolinium administration and unfocused ultrasound whole brain treatment. Signal increased immediately after sonication, and continued to increase in the brain as time passed, while muscle signal decreased due to washout. Our findings demonstrate that unfocused ultrasound sonication can disrupt the blood-brain barrier across the whole brain, including cortex and deep grey matter nuclei. This can be observed using contrast-enhanced MRI. 1812. Simultaneous Monitoring of Temperature and Magnetization Transfer During HIFU Transmission: In Vivo Rabbit Investigations Hsu-Hsia Peng 1 , Teng-Yi Huang 2 , Hsiao-Wen Chung 3 , Shiun-Ying Ju 2 , Yao-Hao Yang 2 , Po-Cheng Chen 4 , Yu-Hui Ding 4 , Wen-Shiang Chen 4 , Wen-Yih Isaac Tseng 5 1 Department of Biomedical Engineering and Environmental Sciences, National Tsing Hua University, Hsinchu, Taiwan; 2 Department of Electrical Engineering, National Taiwan University of Science and Technology, Taipei, Taiwan; 3 Department of Electrical Engineering, National Taiwan University, Taipei, Taiwan; 4 Department of Physical Medicine and Rehabilitation, National Taiwan University Hospital, Taipei, Taiwan; 5 Center for Optoelectronic Biomedicine, Medical College of National Taiwan University, Taipei, Taiwan In this study, an imaging sequence, which simultaneously monitors temperature change and magnetization transfer (MT) contrast at 2- sec temporal resolution, was applied on rabbit thigh muscle during HIFU sonicaiton to verify in vivo feasibility. The characteristics of better immunity to phase variance (in contrast to temperature mapping derived from phase images) and clear distinction between heated spot (4.29%¡Ó0.41%) and non-heated region (-0.19%¡Ó0.30%) of MT, even after turning off HIFU pulse, suggest its usefulness in long-term monitoring. In conclusion, MRI with simultaneous temperature and MT mapping is an effective technique to evaluate tissue damage for HIFU treatment. 1813. A High Precision MR-Compatible Positioning System for Focused Ultrasound Experiments in Small Animal Models Adam Christian Waspe 1,2 , Anthony Chau 1 , Rajiv Chopra 1,2 , Kullervo Hynynen 1,2 1 Imaging Research Discipline, Sunnybrook Health Sciences Centre, Toronto, Ontario, Canada; 2 Department of Medical Biophysics, University of Toronto, Toronto, Ontario, Canada An MR-compatible system was developed for performing focused-ultrasound exposures in preclinical models. A focused-ultrasound transducer attaches to the positioning system and is submerged within a closed water tank. Sonicating a phantom and measuring the thermal focal zone registers ultrasound and MRI coordinates. For each axis, a 5 cm travel and 0.1 mm positioning resolution was achieved. The system was constructed with non-magnetic components and operation of the focused-ultrasound system within the bore during imaging did not result in any mutual interference. This system is used to study the applications of ultrasound energy for novel therapeutic applications in preclinical animal models. 1814. Optimization of a Four-Coil Array Arrangement for Brain Therapy by MR-Guided Transcranial Focused Ultrasounds Line Souris 1 , Najat Salameh 1 , Matthias Korn 1 , Laurent Marsac 2 , Jean-François Aubry 3 , Mathieu Pernot 3 , Mickael Tanter 3 , Luc Darrasse 1 1 Imagerie par Résonance Magnétique Médicale et MultiModalité (UMR 8081), Université Paris-Sud, CNRS, Orsay, France; 2 SuperSonic Imagine, Aix en Provence, France; 3 Institut Langevin, ESPCI ParisTech, CNRS UMR 7587, INSERM U979, Paris, France MRI is a well-suited candidate for temperature monitoring during the heating with transcranial HIFU. For this application, the body coil is usually used because of the constraints due to the large sized of the HIFU system and the stereotactic frame surrounding the patient head. This study showed the improvement of image quality, and therefore temperature sensitivity, by using a dual Flex-coil arrangement. Further improvement is possible by designing dedicated coil arrays with a larger number of coil elements and integrated EMI filters within the coil architecture to reject any interference of the HIFU shots with the MR signal.
1815. MR Guided High Intensity Focused Ultrasound for Tumor Ablation in Brain: Preliminary Results Najat Salameh 1 , Line Souris 1 , Laurent Marsac 2 , Jean-François Aubry 3 , Mathieu Pernot 3 , Benjamin Robert 2 , Mathias Fink 3 , Luc Darrasse 1 , Mickaël Tanter 3 1 Imagerie par Résonance Magnétique Médicale et MultiModalité (UMR 8081), Université Paris-Sud, CNRS, Orsay, Iles-de-France, France; 2 SuperSonic Imagine, Aix-en-Provence, France; 3 Institut Langevin, ESPCI ParisTech, CNRS UMR 7587 INSERM U979, Paris, France A novel prototype for brain therapy with transcranial focused ultrasound is presented here. The first part of this study showed that this new HIFU system was fully MR-compatible. Secondly, we optimized a sequence for MR thermometry, and followed the increase in temperature in a gel heated with increasing power (from 125 to 500 Wac). Finally, we showed it is possible to heat veal brains through a human skull at a high frequency and monitor the heating process with MRI. After validation on cadaver heads, this work will open new horizons to tumor brain therapy in animals and then in humans. 1816. Brain Tissue Flow Measurement Using Arterial Spin Labeling with Flow Discrimination by Cumulative Readout Pulses Yi Wang 1 , Allison Payne 2 , Seong-Eun Kim 2 , Edward DiBella 2 , Dennis L. Parker 2 1 Bioengineering, University of Utah, Salt Lake City, UT, United States; 2 Utah Center for Advanced Imaging Research, University of Utah, Salt Lake City, UT, United States The Pennes' perfusion term in the Pennes bioheat transfer equation depicts the rate at which blood flow removes heat from a point and can play an important role in tissue heat dissipation. Because tissue perfusion is known to change over the course of a thermal therapy treatment, the ability to perform multiple flow assessments to detect perfusion changes during magnetic resonance-guided highintensity focused ultrasound treatment is of high importance. In this work, we present a method to use arterial spin labeling to determine the Pennes' perfusion term in brain tissue and evaluate performance as a function of various imaging parameters, such as flip angle , bandwidth, and resolution. The results indicate that the proposed technique could be applied in MRgHIFU to provide an efficient estimate of the Pennes' perfusion term. Although demonstrated on brain tissue, this technique could be applied to other tissue types. Thermotherapy Hall B Wednesday 13:30-15:30 1817. Dual-Echo Sequence for MR Thermometry in Moving Objects Bruno Madore 1 , Lawrence P. Panych 1 , Chang-Sheng Mei 1,2 , Renxin Chu 1 1 Radiology Department, Brigham and Women's Hospital, Harvard Medical School , Boston, MA, United States; 2 Department of Physics, Boston College, Chestnut Hill, MA, United States An MR thermometry dual-echo sequence is proposed here that offers advantages both in terms of temperature-to-noise ratio and image contrast, as compared to typically-used sequences. For thermometry in moving organs, the contrast properties of the proposed sequence allow blood vessels to be readily detected, for motion tracking purposes. 1818. Fat Temperature Imaging with T1 of Fatty Acid Species Using Multiple Flip Angle Multipoint Dixon Acquisitions Kagayaki Kuroda 1,2 , Taku Iwabuchi, Mie Kee Lam 3 , Makoto Obara 4 , Masatoshi Honda 5 , Kensuke Saito, Marc Van Cauteren 4 , Yutaka Imai 5 1 Graduate School of Engineering, Tokai University, Hiratsuka, Kanagawa, Japan; 2 Medical Device Development Center, Foundation for Biomedical Research and Innovation, Kobe, Hyogo, Japan; 3 Image Sciences Institute, University Medical Center Utrecht, Utrecht, Netherlands; 4 MR Marketing, Philips Electronics Japan Medical Systems, Shinagawa, Tokyo, Japan; 5 Department of Radiology, Tokai University, Isehara, Kanagawa, Japan A fat temperature imaging technique based on multiple flip angle, multipoint Dixon acquisitions and a least square estimation scheme is proposed. Gradient recalled acquisition of 5 echo times with 3 different flip angles were obtained to separate the signals of methylene and methyl protons and to estimate T1's of these fatty acid species. Temperature images of a water-oil phantom were successfully obtained with previously obtained temperature coefficients demonstrating the feasibility of quantitative thermometry of fat. Since the acquisition time was 4-6 second, the technique seemed to be practical for temperature monitoring of fat-water tissues like breast under thermal therapies. 1819. Novel Body Coil Driven Radio Frequency Ablation Device Yik-Kiong Hue 1 , Jerome L. Ackerman 1 , Erez Nevo 2 1 Martinos Center, Department of Radiology, Massachusetts General Hospital, Boston, MA, United States; 2 Robin Medical, Inc., Baltimore, MD, United States A novel body coil driven radiofrequency ablation (RFA) device is proposed. It provides an alternative to commercial available RFA device which required external power generator and large grounding pad. It allowed MR scanner as the sole modality to localize tumor, probe placement, RF power control, temperature mapping and tissue monitoring.
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