Traditional Posters: Interventional - ismrm

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1801. Detecting Blood-Brain Barrier Disruption Under Biosafety Regime Using Optimum Transcranial Focused Ultrasound and Improved Contrast-Enhanced MRI Jun-Cheng Weng 1,2 , Sheng-Kai Wu 3 , Win-Li Lin 3,4 , Wen-Yih Iascc Tseng 1,5 1 Center for Optoelectronic Biomedicine, National Taiwan University College of Medicine, Taipei, Taiwan; 2 Department of Medical Imaging and Radiological Sciences, Chung Shan Medical University, Taichung, Taiwan; 3 Institute of Biomedical Engineering, National Taiwan University, Taipei, Taiwan; 4 Medical Engineering Research Division, National Health Research Institutes, Miaoli, Taiwan; 5 Department of Medical Imaging, National Taiwan University Hospital, Taipei, Taiwan Focused ultrasound (FUS) along with an ultrasound contrast agent (UCA) can induce transient and local increase in the permeability of blood vessel wall or cell membrane, and the change in blood-brain barrier (BBB) permeability can be appropriately indicated by contrast-enhanced MRI. Recently, most studies have used optimum FUS parameters with intravascular injection of pre-formed microbubbles to produce BBB disruption with minimum damage to the neurons. However, there are no studies reporting that under biosafety regime BBB disruption could still be predicted by MR contrast enhancement. The purpose of this study was to see if the traditional T1-weighted (T1W) imaging sequences, spin echo (SE) and gradient echo (GE), can discern the difference in the BBB disruption in lower dose regime or not. A high sensitivity R1 mapping was used as a gold standard and absolutely quantification. The quantitative analysis indexing the degree of BBB disruption and the correlation against Evans blue (EB) staining were also demonstrated. Our results suggest that, in the absence of hemorrhage, contrast-enhanced T1W gradient echo and spin echo sequence were equally reliable in quantifying the BBB disruption. 1802. Analysis of Focused Ultrasound Hotspot Appearance on EPI and Spiral MR Imaging Sonal Josan 1 , Andrew B. Holbrook, 12 , Elena Kaye, 1,3 , Christine Law, 1,3 , Kim Butts Pauly 1 1 Radiology, Stanford University, Stanford, CA, United States; 2 Bioengineering, Stanford University, Stanford, CA, United States; 3 Electrical Engineering, Stanford University, Stanford, CA, United States MR thermometry relies on the proton resonance frequency shift with temperature, which can produce off-resonance artifacts in EPI and spiral sequences. This work analyzed the appearance of the focused ultrasound (FUS) hotspot on several EPI and Spiral trajectory designs through simulations and FUS experiments. The distortion of the FUS spot with single shot EPI or Spiral imaging can be severe for the high temperature changes used in ablation, and may lead to under-estimation of the peak temperature. Multi-shot sequences can be used to reduce the shifts/distortion to a tolerable level. 1803. Preventing Far-Field Bone-Reflection of HIFU Beam by Selective Elements De- Activation Is a Sub-Optimal Approach Loredana Baboi 1 , Magalie Viallon 1 , Sylvain Terraz 1 , Thomas Goget 1 , Denis Morel 2 , Christoph Becker 1 , Rares Salomir 1 1 Department of Radiology, University Hospital of Geneva, Geneva, Switzerland; 2 Department of Anesthesiology, Pharmacology and Surgical Intensive Care, University Hospital of Geneva, Geneva, Switzerland MRgHIFU is a hybrid technology which aims to offer efficient and safe thermal ablation of targeted tumors or other pathological tissues, while preserving the normal surrounding structures unaltered. Theoretically MRgHIFU has no limitation on lesion size [1]. The main challenge is to avoid near and far field heating [2]. We demonstrate here that beam reflection on bones is a major problem whenever bone is situated in the proximity of the prescribed region for sonication, even laterally from the main beam axis. This study evaluates selective de-activation of phased-array transducer’s elements as a potential strategy to reduce bone reflection. 1804. Simultaneous Acoustic Radiation Force Imaging and PRFS Thermal Monitoring at 3T for MRgHIFU Focusing M Viallon 1 , JN Hyacinthe 1 , T Goget 1 , L Baboi 1 , P Gross 2 , CD Becker 1 , R Salomir 1 1 Radiologie, Hopital Universitaire de Genève, Geneva, Switzerland; 2 Siemens Medical Solutions, Erlangen, Germany One challenge in MRgHIFU is to provide safe and thermally neutral focusing of HIFU beam pattern using acoustic radiation force imaging (ARFI). The radiation force is localized and highly directional (along the main propagation axis of the HIFU beam) while negligible outside the focal zone. This force initiates a tissue displacement correlated to the amplitude of the acoustic field and thus a phase shift that can be encoded in the MR signal using a motion encoding gradient (MEG) [1]. In addition, ARFI also provide ‘stiffness weighted’ images that may allow one to assess for pre- versus post- therapy changes in tissue. Since HIFU also causes tissue heating, temperature elevation and RFI effects are always associated, at various degree. We propose here to obtain a precise localization of the HIFU focal point by subtracting GRE phase images from two independent acquisitions, where ARF-induced phase shift is sequentially encoded with positive and, respectively, negative monopolar MEG pulse. For illustration, the MEG was implemented here along the slice-select direction. 1805. Does Proton Resonance Frequency Linearly Change with Temperature? Donghoon Lee 1 , Kenneth Marro 1 , Bryan Cunitz 1 , Michael Bailey 1 1 University of Washington, Seattle, WA, United States To improve the accuracy in temperature measurements over a wide temperature region (20 – 95 C), we designed and fabricated a test sample holder and conducted temperature measurements over the temperature range. The test sample holder comprised a reference chamber for temperature reference and a heating chamber. Both chambers, filled with water, were in well thermal insulation.
Nonlinear relationship between proton resonance frequency shift and temperature was observed for the wide temperature region. Accurate information of temperature variations over a wide temperature region would be valuable to thermal therapy for a temperature region that could reach the water boiling temperature. 1806. Temperature Sensitive Liposomes for Drug Delivery with MRI-HIFU Mariska de Smet 1 , Sander Langereis 2 , Roland van de Molengraaf 2 , Edwin Heijman 2 , Nicole Hijnen 1 , Holger Gruell 1,2 1 Biomedical NMR, Eindhoven University of Technology, Eindhoven, Netherlands; 2 Biomolecular Engineering, Philips Research Eindhoven, Eindhoven, Netherlands Temperature sensitive liposomes (TSL) incorporating both a chemotherapeutic drug, i.e. doxorubicin, and a clinically approved MRI contrast agent, [Gd(HPDO3A)(H2O)] were prepared and evaluated for MR image guided drug delivery. A gel phantom was prepared containing spots of agarose gel mixed with the liposomes. Before and after heating with High Intensity Focused Ultrasound (HIFU), a T1 map was obtained with a Look-Locker EPI-sequence. When heated above the phase transition temperature, the TSLs showed a rapid release of both the drug and contrast agent. The spots with liposomes which were heated with HIFU clearly showed a lower T1 after ultrasound application. 1807. Latency Compensation for Real-Time 3D HIFU Beam-Steering on Moving Targets Mario Ries 1 , Baudouin Denis de Senneville 1 , Sébastien Roujol 1 , Chrit Moonen 1 1 laboratory for molecular and functional imaging: from physiology to therapy, CNRS/ University Bordeaux 2, Bordeaux, Aquitaine, France Dynamic beam-steering of high intensity focused ultrasound (HIFU) based on MR-guidance is a promising technology for the noninvasive ablation of pathological tissue in abdominal organs such as liver and kidney. A particular problem of this technique remains the intrinsic latency between the position measurement and the beam update, which leads to undesired energy dispersion and potentially to the destruction of non-pathological tissue. In this study, dynamic beam-steering using a robust Kalman-predictor for 3D motion anticipation is evaluated experimentally. 1808. Retrospective Reconstruction of High Spatial and Temporal Resolution Temperature Maps for Tissue Property Determination Nick Todd 1 , Josh De Bever 2 , Urvi Vyas 3 , Allison Payne 4 , Dennis L. Parker 5 1 Physics, University of Utah, Salt Lake City, UT, United States; 2 Robotics, University of Utah, Salt Lake City, UT, United States; 3 Bioengineering, University of Utah, Salt Lake City, UT, United States; 4 Mechanical Engineering, University of Utah, Salt Lake City, UT, United States; 5 Radiology, University of Utah, Salt Lake City, UT, United States For certain MR thermometry applications, such as tissue property determination or total accumulated thermal dose calculations, retrospectively reconstructed temperature maps are acceptable. For such purposes, we have implemented a temporally constrained reconstruction method. The technique uses the entire dynamic imaging data set and an iterative cost function minimization algorithm to create 3-D temperature maps with high spatial resolution (~1 - 2mm3), high temporal resolution (~1 sec), and large field of view coverage (~26x16x3cm3). We present the TCR method and applications to retrospective determination of tissue thermal conductivity, ultrasound power deposition, and total accumulated thermal dose. 1809. Three-Slice MR Pre-Treatment Temperature Mapping and Spherical Model Estimation for Accurate Localization of the Heating Focus Before High-Intensity Focused Ultrasound Treatment Hsu-Hsia Peng 1 , Teng-Yi Huang 2 , Hsiao-Wen Chung 3 , Po-Cheng Chen 4 , Yu-Hui Ding 4 , Shiun-Ying Ju 2 , Yao-Hao Yang 2 , Wen-Yih Isaac Tseng 5,6 , Wen-Shiang Chen 4,7 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; 6 Department of Medical Imaging, National Taiwan University Hospital, Taipei, Taiwan; 7 Division of Medical Engineering Research, National Health Research Institutes, Miaoli, Taiwan During HIFU treatment, the focus of ultrasound (US) is arranged to the targeting region determined in advance. In practical treatments, however, the focus might be deviated due to the complex path (tissue-bone interface or tissue-air interface) of US beams. For safety considerations, accurate localization of heating focus is important before performing HIFU treatment. In this study, a spherical model is proposed to estimate the real position of US focus. A low power pre-treatment experiment was performed on ex vivo porcine muscle. The estimated focus position was verified via magnetization transfer ratio images after a high power HIFU transmission.
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Traditional Posters: Interventional - ismrm

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