Traditional Posters: Interventional



Traditional Posters: Interventional

MR-Guided Focused Ultrasound

Hall B Tuesday 13:30-15:30

1796. MR-Guided Focused Ultrasound Ablation of the Rat Liver

Randy Lee King1,2, Viola Rieke1, Kim Butts Pauly1

1Department of Radiology, Stanford University, Stanford, CA, United States; 2Department of Bioengineering, Stanford University, Stanford, CA, United States

This study investigates the use of a rat model for the MR-guided focused ultrasound treatment of hepatocellular carcinoma. PRF-thermometry, thermal dose calculation and post-ablation imaging are used to determine the ablated liver area and compared to necropsy. Thermal dose reliably predicts the ablated area for single sonications, but care has to be taken to avoid overestimation in lesions resulting from multiple sonications.

1797. Non-Invasive Suppression of Animal-Model Chronic Epilepsy Using Image-Guided Focused Ultrasound

Seung-Schik Yoo1, KwangIk Jung1, YongZhi Zhang1, Nathan McDannold1, Alexander Bystritsky, 12, Ferenc A. Jolesz1

1Radiology, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, United States; 2Psychiatry, David Geffen School of Medicine at UCLA, Los Angeles, CA, United States

We showed the evidence of MRI-guided focused ultrasound can suppress the ictal actvity induced by the chemical kindling of rat brain via kainic acid. This evidence demonstrate that non-invasive suppression of epilepsy may be feasible using pulsed, low-energy focused ultrasound.

1798. Proton Resonance Frequency MRI Shows Focal Spot Shifts Due to Interfaces During MR-HIFU Treatment

Elizabeth Hipp1, Xiaobing Fan1, Ari Partanen2, Gregory S. Karczmar1

1Radiology, University of Chicago, Chicago, IL, United States; 2Philips Healthcare

MR-HIFU is emerging as a treatment modality for a variety of pathologies. Treatments near tissue interfaces can result in unwanted heating caused by an impedance mismatch. This research uses the proton resonance frequency measured by MRI to explore the changes in heating pattern and shift in sonication focus as a result of proximity to an interface in a thermal phantom. Air, acrylic, rubber and a tissue-equivalent gel pad were tested with treatment cells focused at 1, 2 and 4 cm from the interface material revealing 0.7 to 3 mm shifts depending on focal position and interface material.

1799. An MR-Compatible Hydrophone for Ultrasound Monitoring of MRI-Guided Transcranial Focused Ultrasound Therapy

Meaghan Anne O'Reilly1, Yuexi Huang1, Kullervo Hynynen1,2

1Imaging Research, Sunnybrook Research Institute, Toronto, Ontario, Canada; 2Medical Biophysics, University of Toronto, Toronto, Ontario, Canada

Ultrasound monitoring of MR-guided transcranial ultrasound therapy could help identify control parameters to better deliver therapy to the brain. An MR-compatible PVDF hydrophone with a high sensitivity was constructed and characterized. The hydrophone was used to monitor microbubble-mediated ultrasound disruption of the blood-brain barrier in rats. Comparison of captured acoustic emissions with T1w and T2w images demonstrated that the hydrophone was able to detect differences in acoustic emissions in sonications producing different bioeffects. The results show promise for real-time monitoring of MRI-guided transcranial therapy.

1800. MR Guided HIFU in Cadaver Breasts for Pre-Operative Tumor Localization of Non-Palpable Breast Tumors as an Alternative to Needle Wire Tumor Localization

Rachel R. Bitton1, Elena Kaye1,2, Bruce Daniel1, Kim Butts Pauly1

1Radiology, Stanford University, Palo Alto, CA, United States; 2Electrical Engineering, Stanford University, Palo Alto, CA, United States

Physicians are increasingly confronted with non-palpable breast lesions only visible on MRI. This study examined the visibility and palpability of focused ultrasound lesions in fatty human breast tissue. Eighteen sonications were made around the perimeter of an arbitrary prescribed “tumor” square, representing a non-palpable tumor area. Potential stiffness changes were measured using MR-ARFI showing the displacement difference between the pre and post sonication. The lesions were fully registered with images, circumscribing a tumor area in a human cadaver breast, and thus, providing a visible and palpable perimeter for a surgeon as a guide for excision during breast conservation surgery.

1801. Detecting Blood-Brain Barrier Disruption Under Biosafety Regime Using Optimum Transcranial Focused Ultrasound and Improved Contrast-Enhanced MRI

Jun-Cheng Weng1,2, Sheng-Kai Wu3, Win-Li Lin3,4, Wen-Yih Iascc Tseng1,5

1Center for Optoelectronic Biomedicine, National Taiwan University College of Medicine, Taipei, Taiwan; 2Department of Medical Imaging and Radiological Sciences, Chung Shan Medical University, Taichung, Taiwan; 3Institute of Biomedical Engineering, National Taiwan University, Taipei, Taiwan; 4Medical Engineering Research Division, National Health Research Institutes, Miaoli, Taiwan; 5Department 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 micro-bubbles 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 Josan1, Andrew B. Holbrook, 12, Elena Kaye, 1,3, Christine Law, 1,3, Kim Butts Pauly1

1Radiology, Stanford University, Stanford, CA, United States; 2Bioengineering, Stanford University, Stanford, CA, United States; 3Electrical 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 Baboi1, Magalie Viallon1, Sylvain Terraz1, Thomas Goget1, Denis Morel2, Christoph Becker1, Rares Salomir1

1Department of Radiology, University Hospital of Geneva, Geneva, Switzerland; 2Department 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 Viallon1, JN Hyacinthe1, T Goget1, L Baboi1, P Gross2, CD Becker1, R Salomir1

1Radiologie, Hopital Universitaire de Genève, Geneva, Switzerland; 2Siemens 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 Lee1, Kenneth Marro1, Bryan Cunitz1, Michael Bailey1

1University 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 Smet1, Sander Langereis2, Roland van de Molengraaf2, Edwin Heijman2, Nicole Hijnen1, Holger Gruell1,2

1Biomedical NMR, Eindhoven University of Technology, Eindhoven, Netherlands; 2Biomolecular 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 Ries1, Baudouin Denis de Senneville1, Sébastien Roujol1, Chrit Moonen1

1laboratory 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 non-invasive 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 Todd1, Josh De Bever2, Urvi Vyas3, Allison Payne4, Dennis L. Parker5

1Physics, University of Utah, Salt Lake City, UT, United States; 2Robotics, University of Utah, Salt Lake City, UT, United States; 3Bioengineering, University of Utah, Salt Lake City, UT, United States; 4Mechanical Engineering, University of Utah, Salt Lake City, UT, United States; 5Radiology, 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 Peng1, Teng-Yi Huang2, Hsiao-Wen Chung3, Po-Cheng Chen4, Yu-Hui Ding4, Shiun-Ying Ju2, Yao-Hao Yang2, Wen-Yih Isaac Tseng5,6, Wen-Shiang Chen4,7

1Department of Biomedical Engineering and Environmental Sciences, National Tsing Hua University, Hsinchu, Taiwan; 2Department of Electrical Engineering, National Taiwan University of Science and Technology, Taipei, Taiwan; 3Department of Electrical Engineering, National Taiwan University, Taipei, Taiwan; 4Department of Physical Medicine and Rehabilitation, National Taiwan University Hospital, Taipei, Taiwan; 5Center for Optoelectronic Biomedicine, Medical College of National Taiwan University, Taipei, Taiwan; 6Department of Medical Imaging, National Taiwan University Hospital, Taipei, Taiwan; 7Division 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.

1810. Tissue Acoustic Properties Using MRI Temperature Measurements of Low Powered Ultrasound Heating Pulse.

Urvi Vyas1, Nick Todd2, Allison Payne3, Douglas Christensen, Dennis L. Parker4

1Bioengineering, University of Utah, Salt Lake City, UT, United States; 2Physics, University of Utah; 3Mechanical Engineering, University of Utah; 4Radiology, 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 Townsend1, Randy L. King1, Greg Zaharchuk2, Kim Butts Pauly1,2

1Bioengineering, Stanford University, Stanford, CA, United States; 2Radiology, 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 Peng1, Teng-Yi Huang2, Hsiao-Wen Chung3, Shiun-Ying Ju2, Yao-Hao Yang2, Po-Cheng Chen4, Yu-Hui Ding4, Wen-Shiang Chen4, Wen-Yih Isaac Tseng5

1Department of Biomedical Engineering and Environmental Sciences, National Tsing Hua University, Hsinchu, Taiwan; 2Department of Electrical Engineering, National Taiwan University of Science and Technology, Taipei, Taiwan; 3Department of Electrical Engineering, National Taiwan University, Taipei, Taiwan; 4Department of Physical Medicine and Rehabilitation, National Taiwan University Hospital, Taipei, Taiwan; 5Center 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 Waspe1,2, Anthony Chau1, Rajiv Chopra1,2, Kullervo Hynynen1,2

1Imaging Research Discipline, Sunnybrook Health Sciences Centre, Toronto, Ontario, Canada; 2Department 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 Souris1, Najat Salameh1, Matthias Korn1, Laurent Marsac2, Jean-François Aubry3, Mathieu Pernot3, Mickael Tanter3, Luc Darrasse1

1Imagerie par Résonance Magnétique Médicale et MultiModalité (UMR 8081), Université Paris-Sud, CNRS, Orsay, France; 2SuperSonic Imagine, Aix en Provence, France; 3Institut 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 Salameh1, Line Souris1, Laurent Marsac2, Jean-François Aubry3, Mathieu Pernot3, Benjamin Robert2, Mathias Fink3, Luc Darrasse1, Mickaël Tanter3

1Imagerie par Résonance Magnétique Médicale et MultiModalité (UMR 8081), Université Paris-Sud, CNRS, Orsay, Iles-de-France, France; 2SuperSonic Imagine, Aix-en-Provence, France; 3Institut 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 Wang1, Allison Payne2, Seong-Eun Kim2, Edward DiBella2, Dennis L. Parker2

1Bioengineering, University of Utah, Salt Lake City, UT, United States; 2Utah 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 high-intensity 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 Madore1, Lawrence P. Panych1, Chang-Sheng Mei1,2, Renxin Chu1

1Radiology Department, Brigham and Women's Hospital, Harvard Medical School , Boston, MA, United States; 2Department 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 Kuroda1,2, Taku Iwabuchi, Mie Kee Lam3, Makoto Obara4, Masatoshi Honda5, Kensuke Saito, Marc Van Cauteren4, Yutaka Imai5

1Graduate School of Engineering, Tokai University, Hiratsuka, Kanagawa, Japan; 2Medical Device Development Center, Foundation for Biomedical Research and Innovation, Kobe, Hyogo, Japan; 3Image Sciences Institute, University Medical Center Utrecht, Utrecht, Netherlands; 4MR Marketing, Philips Electronics Japan Medical Systems, Shinagawa, Tokyo, Japan; 5Department 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 Hue1, Jerome L. Ackerman1, Erez Nevo2

1Martinos Center, Department of Radiology, Massachusetts General Hospital, Boston, MA, United States; 2Robin 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.

1820. Temperature and B0 Field Measurment Bias of Multi-Echo Fat-Water Fitting Algorithms

Cory Robert Wyatt1, Brian J. Soher2, James R. MacFall2

1Department of Biomedical Engineering, Duke University, Durham, NC, United States; 2Department of Radiology, Duke University Medical Center, Durham, NC, United States

Multi-echo fat-water separation techniques, such as IDEAL, have been shown to be effective in measuring temperature changes in fatty tissue, but often make assumptions that allow them to linearize the model in order to simplify the computation of a solution. This can result in the addition of significant bias to the measurement of the temperature and the B0 field offset, both important parameters to monitor during therapeutic heat applications (tumor ablation, hyperthermia). In this work, the bias of a multi-peak IDEAL algorithm (without T2* decay) and a new nonlinear fitting algorithm is characterized using Monte Carlo simulations.

1821. Optimal Multi-Echo Water-Fat Separated Imaging Parameters for Temperature Change Measurement Using Cramer-Rao Bounds

Cory Robert Wyatt1, Brian J. Soher2, Kavitha Arunachalam3, James R. MacFall2

1Department of Biomedical Engineering, Duke University, Durham, NC, United States; 2Department of Radiology, Duke University Medical Center, Durham, NC, United States; 3Department of Radiation Oncology, Duke University Medical Center, Durham, NC, United States

Multi-echo fat-water fitting techniques that separate the fat and water effects have been shown to be useful in measuring temperature in fat-water phantoms. In this study we explore optimization of echo time selection by minimizing the temperature noise using Cramer-Rao Lower Bound (CRLB) analysis. Accuracy of fitting is improved by including multiple fat peaks and T2* effects. Our approach finds the minimum temperature noise that has the minimum sensitivity to the values of nominally fixed parameters. The CRLB results were then confirmed in experiments with fat-water gelatin phantoms.

1822. Measurement of Human Brain Temperature Changes During Cooling

Jan Weis1, Lucian Covaciu2, Sten Rubertsson2, Mats Allers3, Anders Lunderquist4, Francisco Ortiz-Nieto1, Håkan Ahlström1

1Department of Radiology, University Hospital, Uppsala, Sweden; 2Department of Surgical Sciences, Anesthesiology and Intensive Care, University Hospital, Uppsala, Sweden; 3Department of Clinical Sciencies, University Hospital, Lund, Sweden; 4Department of Clinical Sciences, University Hospital, Lund, Sweden

Decrease of the human brain temperature (1-2 oC in 15 minutes) was induced by intranasal cooling. The purpose of this study was to verify the cooling technique on the volunteers and to compare two methods for noninvasive monitoring of the relative brain temperature: MRSI with high spatial and reduced spectral resolution and PRF shift technique. Ability of the proposed brain cooling technique to induce moderate hypothermia was confirmed. Good agreement was found between relative temperatures measured by MRSI and PRF method. Both temperature mapping techniques can be used for monitoring the brain temperature changes during hypothermia.

1823. Measurement of the Temperature Dependence of the Susceptibility of Human Breast Fat Tissue

Sara Maria Sprinkhuizen1, Chris J. Bakker1, Johannes H. Ippel2, Rolf Boelens2, Lambertus Wilhelmus Bartels1

1Radiology, Image Sciences Institute, Utrecht, Netherlands; 2Bijvoet Center for Biomolecular Research, NMR Spectroscopy Research Group, Utrecht, Netherlands

In fat tissue, large susceptibility-related PRFS-based temperature errors can be expected, due to temporal changes in tissue susceptibility (χ) which lead to non-local magnetic field changes. This affects the PRF (hence, the measured temperature) of all water protons that experience this magnetic field change, leading to temperature errors. In order to conclusively assess the impact of temperature-induced χ changes on PRFS-based MRT, accurate and precise susceptibility measurements in human tissue are a prerequisite. We therefore measured dχ/dT of fat tissue of the human breast on a 14 T NMR spectrometer. A dependence of 0.0051 ppm/°C was found.

1824. PRFS-Based MR Thermometry Is Hampered by Susceptibility Changes Caused by the Heating of Fat: Experimental Demonstration

Sara Maria Sprinkhuizen1, Chris J. Bakker1, Lambertus Wilhelmus Bartels1

1Radiology, Image Sciences Institute, Utrecht, Netherlands

Susceptibility (χ) related field changes are commonly ignored in the application of proton resonance frequency shift (PRFS)-based MR thermometry (MRT) during thermal interventions, even though the temperature dependence of the χ of fat is in the same order of magnitude as the temperature dependence of the chemical shift of water. Its influence on PRFS-based MRT maps was investigated experimentally. The results showed that changes in χ fat hamper the PRFS-based MRT method nonlocally. The measured errors were ranging between -4.6 °C and +4.1 °C. Important to stress is the fact that fat suppression is not a solution for this effect.

1825. Modified Balanced SSFP Sequence for Better Temperature Sensitivity

Mahamadou Diakite1, Nick Todd1, Dennis L. Parker2

1Physics, University of Utah, Salt lake, UT, United States; 2Radiology, Utah Center for Advanced Imaging Research (UCAIR), Salt lake, UT, United States

Safety and efficacy of tumor treatment using high intensity focus ultrasound requires accurate temperature measurement throughout the thermal procedure. In this work, we investigate how the noise in temperature measurements can be reduced by variations to this new ub-SSFP sequence.

1826. Hyperthermia Induced Gadodiamide Release from Thermosensitive Liposomes in Solid Tumors and Muscle Tissue

Michael Peller1, Martin Hossann2, Tungte Wang2,3, Steven Sourbron1, Lars H. Lindner2,3

1Institute of Clinical Radiology, University Hospital of Munich, Munich, Germany; 2Department of Internal Medicine III, University Hospital Munich; 3CCG-Hyperthermia, Helmholtz Zentrum München, German Research Center for Environmental Health, Germany

Purpose was to investigate the dynamics of mild temperature induced contrast agent release from phosphatidylglyc-eroglycerol containing thermosensitive liposomes with encapsulated Gd-DTPA-BMA (Gd-TSL) in tumor tissue. Tumor bearing mice were investigated at 1.5T after intravenous injection. The temperature induced release of contrast agent at 42°C caused a fast and strong increase of T1-weighted signal. Immediately after i.v. injection heated tumor tissue was distinguishable from unheated tumor and muscle tissue. Unheated muscle tissue may thus be less affected by a potential anti tumor therapy based on TSL.

1827. MRgRFA: Physical Model and First Order Correction of PRFS Thermometry Corrupted by Magnetic Susceptibility-Mediated Cavitation’s Effects

Rares Salomir1, Magalie Viallon1, Sylvain Terraz1, Christoph D Becker1

1Radiologie, Hopital Universitaire de Genève, Geneva, Switzerland

MR thermometry based on the proton resonance frequency (PRF) method (1) has gained good acceptance for guiding RF ablation of liver tumors (2). Major artifacts in the PRFS thermometry have recently been reported related to per-operatory changes of the tissue bulk susceptibility during RF heating (3). They are originating from gas bubbles formation, known as white cavitations’ artifacts in US imaging. We propose here a theoretical description of the effects and a first order correction that confirm the source of the spatially related errors in temperature maps and TD during power application.

1828. MR Thermometry in Moving Objects Using a Novel Referenceless and User-Independent Approach

Bruno Madore1, Renxin Chu1, Chang-Sheng Mei1,2, Lawrence P. Panych1

1Radiology Department, Brigham and Women's Hospital, Harvard Medical School , Boston, MA, United States; 2Department of Physics, Boston College, Chestnut Hill, MA, United States

MR thermometry in moving organs is a challenging application, as fairly subtle temperature-induced changes must be accurately measured in the presence of often much larger motion-induced changes. A novel approach at doing so is proposed here, which is both referenceless (does not require a baseline reference image) and user-independent.

1829. Air Susceptibility Effects on Proton Resonance Frequency Temperature Mapping

Markus Nikola Streicher1, Andreas Schäfer1, Dimo Ivanov1, Robert Turner1

1Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany

MR thermometry is usually based on the temperature dependence of the proton resonance frequency (PRF), thus any magnetic field changes might be misinterpreted as temperature changes. Here we report on the effects of changes of susceptibility of surrounding air on the magnetic field inside an object. When the air was heated by 46 ºC, its susceptibility changed from χ air = 3.6×10-7 to χ air = 2.7×10-7, inducing an apparent additional temperature change of 1.9°C inside the object. For a more realistic surrounding air temperature increase of 10°C this could result in an error of 0.75°C.

1830. Real-Time MR-Thermometry and Dosimetry for Interventional Guidance on Abdominal Organs

Sébastien Roujol1,2, Mario Ries1, Bruno Quesson1, Chrit Moonen1, Baudouin Denis de Senneville1

1laboratory for molecular and functional imaging: from physiology to therapy, CNRS/ University Bordeaux 2, Bordeaux, Aquitaine, France; 2LaBRI, University Bordeaux 1, Talence, Aquitaine, France

A computationally efficient pipeline for 2D motion compensated PRF-thermometry and thermal dose measurements on moving abdominal organs is presented. The method is designed to address both, inter-scan and intra-scan artifacts by applying high frame-rate MRI coupled with a real-time image processing. The proposed MR-thermometry method was evaluated in both liver and kidney of 11 healthy volunteers and achieved a precision of less than 2 °C in 70 % of the pixels. The ability to perform MR-Thermometry and Dosimetry in-vivo was demonstrated on one HIFU-heating experiment on a porcine kidney.

1831. A Self-Reference MR Thermometry Method Utilizing the Phase Gradient

Jason A. Langley1,2, Qun Zhao1,2

1Department of Physics and Astronomy, The University of Georgia, Athens, GA, United States; 2Bioimaging Research Center (BIRC), The University of Georgia, Athens, GA, United States

A modified self-reference MR thermometry method is presented in this abstract. We circumvent the phase unwrapping procedure in the self-reference MR thermometry procedure by utilizing the phase gradient to estimate the baseline phase map. In the method proposed in this abstract, the phase map is modeled as a 2D polynomial. The components of the gradient of the model are then fitted to the components of the phase gradient using 2D weighted least squares. The proposed procedure is evaluated using two simulated MR thermometry data sets.

1832. First Clinical Experience with Navigated RF Ablations of the Liver in a Closed-Bore 1.5T MRI

Daniel Seider1, Harald Busse1, Nikita Garnov1, Gregor Thörmer1, Susann Heinig1, Tim Riedel1, Thomas Kahn1, Michael Moche1

1Diagnostic and Interventional Radiology, Leipzig University Hospital, Leipzig, Germany

MRI is well suited to guide percutaneous interventions of liver lesions that are hardly visible with ultrasound or CT. Dedicated open MR systems are often used because they provide good patient access. This work presents first clinical experience with a new navigation solution that was used during RF ablation of liver tumors in a standard closed-bore scanner environment. After a special breathhold training, even double oblique access paths could be realized. RFA probe and thermally induced lesion could be reliably visualized with a VIBE sequence. While technical efforts are higher the times for needle placement and thermal ablation are comparable to those under CT guidance.

1833. Highly Accelerated Temperature Mapping Using Nonlocal Regularized Parallel Imaging

Sheng Fang1, Xinyi Pan1, Kui Ying1

1Department of Engineering Physics, Tsinghua University, Beijing, China

Model-based MR thermometry method based on the proton resonance frequency shift (PRFS) can effectively improve the temperature estimate accuracy of conventional phase different method. However, its temporal resolution need be improved for real-time temperature monitoring. To solve the problem, we applied highly accelerated PI to temperature mapping and used nonlocal regularization that extracts the prior from the acquired data themselves to stabilize the reconstruction. The method was demonstrated using whipping cream phantom. The results show that the nonlocal regularization can effectively increase the temporal resolution of PRFS while avoiding the introducing the bias to quantification, due to its data-driven property.

1834. Quantitative Analysis for Optimizing the MRI Temperature Monitoring Using Keyhole Technique

Yong hee Han1, Kang soo Kim1, Dong Hyuk Kim1, Kwang sik Lee2, Jae Ryang Juhn3, Choong ki Eun3, Chi woong Mun1,4

1Bio medical engineering, Inje University, Gimhae, Gyeongsangnam-do, Korea, Republic of; 2Medical Image Science, Pusan Paik hospital, Korea, Republic of; 3Diagnostic of Radiology Medical School, Pusan Paik hospital, Korea, Republic of; 4Medical Image Research Center, Inje University, Korea, Republic of

This study proposes the keyhole method in order to improve the time resolution of the proton resonance frequency (PRF) MR temperature monitoring technique. To evaluate proposed method, the values of Root Mean Square (RMS) error were compared with full phase encoded temperature images. And the paired t-test was performed for optimization at Keyhole technique. As a result of this study, >32 encoded images were reasonable in 95% confidence level whereas ................
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