MR-Guided Focused Ultrasound

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

Randy Lee King^1,2, 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 Hynynen^1,2

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 Kaye^1,2, 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 Weng^1,2, Sheng-Kai Wu³, Win-Li Lin^3,4, Wen-Yih Iascc Tseng^1,5

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 Gruell^1,2

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 Tseng^5,6, Wen-Shiang Chen^4,7

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 Pauly^1,2

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 Waspe^1,2, Anthony Chau¹, Rajiv Chopra^1,2, Kullervo Hynynen^1,2

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

                  1817.     Dual-Echo Sequence for MR Thermometry in Moving Objects

Bruno Madore¹, Lawrence P. Panych¹, Chang-Sheng Mei^1,2, 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 Kuroda^1,2, 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 Wang^2,3, Steven Sourbron¹, Lars H. Lindner^2,3

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 Mei^1,2, 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 Roujol^1,2, 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. Langley^1,2, Qun Zhao^1,2

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 Mun^1,4

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 <32 encoded images showed statistically significant difference.

                  1835.     Convection Enhanced Delivery of Drugs to the CNS

Peter Andrew Hardy¹, Zhiming Zhang¹, Don Gash¹, Doug U. Gwost², David Stiles², Brian D. Nelson², Pei Ge³, Dinah Sah³

¹Anatomy & Neurobiology, University of Kentucky, Lexington, KY, United States; ²Medtronic Neurological, Minneapolis, MN, United States; ³Alnylam Pharmaceuticals, Inc., Cambridge, Massachussets, United States

Convection Enhanced Delivery is a powerful method of delivering drugs to the CNS. We tested CED hardware and imaging methods by delivering Magnevist at three flow rates to the putamen in rhesus monkeys over a period of 7 days. T1-weighted images were acquired at three time points and from these the volume of distribution was characterized. Results demonstrate a compact distribution to the putamen with a flow rate-dependent volume.

                  1836.     Gd-Labelled Polylysine as a Tracer for Convective Enhanced Delivery

Peter Andrew Hardy¹, Luke H. Bradley¹, Zhiming Zhang¹, Don Gash¹, Dan Keeley², Brian Kramer³, Greg Schorn⁴

¹Anatomy & Neurobiology, University of Kentucky, Lexington, KY, United States; ²Advanced Technologies and Regenerative Medicine, Rayntham, MA, United States; ³Advanced Technologies and Regenerative Medicine, Somerville, NJ, United States; ⁴Advanced Technologies and Regenerative Medicine, Rayntham, Massachussets, United States

Convection Enhanced Delivery is a powerful method of delivering drugs to the CNS. MR-visible tracers co-infused with drug will be useful to assess drug distribution. We tested four compounds (Magnevist and three Gd-labeled polylysines) with molecular weights between 0.5k Da and 200 kDa as potential tracers for CED. Compounds were tested in vitro to model CED parameters used to plan delivery into four rhesus monkeys. In vitro results demonstrated MW dependent CED distribution. In vivo results demonstrated distribution of the Magnevist in the putamen but little distribution of the polylysine as a result of binding and digestion of the polylysine.

Clinical & Pre-clinical Interventions (Non-thermal)

                  1837.     Novel Delivery System for Minimally Invasive MR Guided Neurological Interventions

Alastair Martin¹, Mark Richardson², Adrian Kells², John Bringas², Pete Piferi³, Lisa Tansey³, Geoffrey Bates³, Philip Starr², Paul Larson², Krystof Bankiewicz²

¹Radiology and Biomedical Imaging, University of California - San Francisco, San Francisco, CA, United States; ²Neurological Surgery, University of California - San Francisco; ³SurgiVision, Inc, Irvine, CA

A novel delivery system for MR guided precision minimally invasive access to deep brain structures is presented.  A targeting accuracy of 0.5 mm at depths of 85-90mm is achieved in a phantom model.  The delivery system is also used to insert cannula’s for infusing therapeutic agents via convection-enhanced delivery (CED).  CED is demonstrated in a non-human primate with infusions to the thalamus, putamen and sub-thalamic nucleus.  Accurate delivery of infusion cannula’s was achieved and CED infusions extending up to 10mm in diameter are demonstrated.

                  1838.     Retrograde Drilling of Osteochondral Lesions of the Knee with MRI Guidance

Christian Jürgen Seebauer¹, Hermann Josef Bail², Jens Christian Rump³, Ulf Teichgräber³

¹Center for Musculoskeletal Surgery, Charité, Berlin, Germany; ²Department of Trauma and Orthopedic Surgery, Clinic Nuremberg, Nuremberg, Germany; ³Department of Radiology, Charité, Berlin, Germany

Osteochondritis Dissecans (OD) of the knee is a common articular lesion in adolescents and young adults. Retrograde drilling is an alternative in surgical treatment before more invasive and complex procedures are necessary; however drilling under fluoroscopic guidance via the epiphyses is technically challenging in terms of maintaining drill depth and accuracy of drill placement. The purpose of this study was to evaluate applicability and accuracy of a passive navigation method by drilling a simulated OD target at the knee with MRI guidance. Interactive MR navigation allowed precise drilling of OCD of the knee. Targeting was possible with a single drilling.

                  1839.     Implementation of an Interactive Real-Time MRI Acquisition and Display for Improving Efficiency and Accuracy of MR-Guided Breast Interventions

Matt Smith¹, Ethan Brodsky^1,2, Steve Kecskemeti¹, Xu Zhai¹, Sean Fain^1,3

¹Medical Physics, University of Wisconsin, Madison, WI, United States; ²Radiology, University of Wisconsin, Madison, WI, United States; ³Biomedical Engineering, University of Wisconsin, Madison, WI, United States

During an MR-guided breast intervention, placement of a needle or probe requires accurate localization of the target. To allow rapid identification of these errors, avoid unnecessary trauma to the patient, and minimize scanner time, a real-time MR acquisition and display was implemented to allow the physician to monitor both the progress of the insertion and the procedure itself, such as core needle biopsy or tumor ablation. Flexibility was added to adjust the scan plane in real-time and make tradeoffs between update display rate and image quality.

                  1840.     A Passive, Image-Based Navigation Tool for Real-Time MR-Guided Percutaneous Interventional Procedures

Wilhelm Strehl¹, Eva Rothgang^1,2, Wesley Gilson², Klaus J. Kirchberg³, Joachim Hornegger¹, Christine Lorenz²

¹Pattern Recognition Lab, Department of Computer Science, University of Erlangen-Nuremberg, Erlangen, Bavaria, Germany; ²Center for Applied Medical Imaging, Siemens Corporation, Corporate Research, Baltimore, MD, United States; ³Center for Applied Medical Imaging, Siemens Corporation, Princeton, NJ, United States

Percutaneous interventions involve the navigation of a needle or probe to a target location. MRI is well-suited to guide these procedures as it offers good soft tissue target visualization and no ionizing radiation. High field wide bore MRI has stimulated interest in performing more of these procedures, but workflow and procedure speed are significant hurdles for full adoption.  Here, a navigation tool for guiding and tracking the needle in real-time under MRI is presented.

                  1841.     Navigated Liver Biopsies in a Closed-Bore MR Scanner: First Clinical Experience

Michael Moche¹, Gregor Thörmer¹, Nikita Garnov¹, Jochen Fuchs¹, Susann Heinig¹, Tim Riedel¹, Thomas Kahn¹, Harald Busse¹

¹Leipzig University Hospital, Leipzig, Germany

MRI has been shown to be of great clinical utility for the guidance of various procedures. In a closed-bore scanner, the simplest approach is to manipulate the instrument outside the bore and move the patient inside for control imaging only. Potential benefits for percutaneous biopsies in the liver have been investigated in 15 patients by using a flexible add-on navigation solution which even allowed interventions in obese patients. Real time navigation was provided by following the virtual instrument on properly reformatted images of a 3D roadmap. In combination with a specific breathhold protocol, punctures could be reliably performed in reasonable times.

                  1842.     Evaluation of a Real Time MR-Guided Interactive Navigation Device: Phantom and Animal Experiments

Steffi Valdeig¹, Barry Fetics², Li Pan, ^1,3, Clifford R. Weiss¹, Erez Nevo², Dara L. Kraitchman¹, Frank K. Wacker¹

¹Department of Radiology and Radiological Science, Johns Hopkins University, Baltimore, MD, United States; ²Robin Medical Inc., Baltimore, MD, United States; ³Center for Applied Medical Imaging, Siemens Corporation, Corporate Research, Baltimore, MD, United States

Purpose: To test the feasibility and accuracy of a tool that allows for interactive adjustments of the needle plane during a MR guided puncture Method: Experiments were performed in vivo and in phantoms using a gradient based navigation system for real time MR guided punctures in a wide bore MR imager. To assess for accuracy of the system the distance of the needle tip (virtual and real) to the target was determined on MR control scans. Result: The mean 3D total error was 4.9 ±2.8mm in the phantom. The system error was less than 2 mm. In the animal, successful punctures of the target structures could be confirmed in all punctures. Conclusion: The combination of image overlay with real time adjustment of the virtual needle and real-time imaging feedback provides an accurate and intuitive means to perform percutaneous interventions in a wide bore MR imager.

                  1843.     Fast and Precise: Real Time MR-Guided Prostate Biopsy at 3 Tesla in Animal Experiment.

Patrik Zamecnik¹, Axel j. Krafft², Florian Maier³, Jaane Rauschenberg², Michael Bock²

¹DKFZ German Cancer Research Center), Heidelberg, Baden-Württemberg, Germany; ²DKFZ (German Cancer Research Center); ³DKFZ (German Cancer Resaerch Center)

Real time MR-guided prostate biopsy at 3 Tesla in animal experiment proved to be a fast an precise method to perform prostate biopsies.

                  1844.     Development of a Pneumatic Robot for MRI-Guided Transperineal Prostate Intervention

Sang Eun Song¹, Nathan Bongjoon Cho¹, Iulian Iordachita², Gregory Scott Fischer³, Junichi Tokuda⁴, Nobuhito Hata⁴, Gabor Fichtinger⁵, Clare Tempany⁴

¹Engineering Research Center, The Johns Hopkins University, Baltimore, MD, United States; ²Department of Mechanical Engineering, The Johns Hopkins University, Baltimore, MD, United States; ³Mechanical Engineering Department, Worcester Polytechnic Institute, Worchester, MA, United States; ⁴Brigham and Women’s Hospital, Boston, MA, United States; ⁵School of Computing,, Queen’s University, Kingston, Ontario, Canada

As accurate needle positioning helps the prostate cancer detection and treatment, a number of MRI-compatible robots have been introduced. However, problems exist due to the strong magnetic field and limited workspace. Pneumatic actuator has the minimum distraction in the environment. However, it has poor controllability. To overcome the controllability problem, a simple external damping mechanism that can enhance accuracy was developed. Based on the actuator mechanism and workflow optimized modular design approaches, a new pneumatically actuated 4-DOF parallel robot for MRI-guided prostate intervention was developed. A preliminary evaluation was conducted with satisfying actuator average position error of 0.2mm.

                  1845.     Development and Preliminary Evaluation of a MRI-Guided Transrectal Prostate Intervention

Axel Krieger^1,2, Sang Eun Song³, Nathan Bongjoon Cho³, Peter Guion⁴, Iulian Iordachita¹, Gabor Fichtinger⁵, Louis L. Whitcomb¹

¹Department of Mechanical Engineering, The Johns Hopkins University, Baltimore, MD, United States; ²Sentinelle Medical Inc., Toronto, Canada; ³Engineering Research Center, The Johns Hopkins University, Baltimore, MD, United States; ⁴National Institute of Health, Bethesda, MD, United States; ⁵School of Computing,, Queen’s University, Kingston, Ontario, Canada

This paper reports the design, development and MRI compatibility evaluation of a transrectal prostate robot for MRI-guided intervention. The robot employs an automated needle guide with the goal of increasing needle placement accuracy and reducing interventional procedure times. The design of the robot, employing piezo-ceramic-motor actuated needle guide and manual needle insertion, is reported. Results of a MRI compatibility study show no reduction of MRI image SNR with the motors disabled and a 40% to 60% reduction with the motors enabled. The addition of RF shielding is shown to significantly reduce SNR degradation to the presence of the robotic device.

                  1846.     A Device to Facilitate the Performance of Magic Angle Studies on the Wrist and Elbow

Marc Rea^1,2, Zion Tsz Ho Tse³, Haytham Elhawary³, Michael Lampérth², Graeme Bydder⁴, Ian Young⁵

¹Radiological Sciences Unit, Imperial College London, London, UK, United Kingdom; ²Mechanical Engineering, Imperial College London, London, England, United Kingdom; ³Brigham Womens Hospital, Boston, United States; ⁴Radiology, University of California San Diego, San Diego, CA, United States; ⁵Electrical Engineering, Imperial College London, London, United Kingdom

A limb-positioning mechanical platform device was developed for remote orientation of the arm to make use of the magic angle effect for imaging tendons. The platform is MR-compatible and actuated by rotary air-driven motors. Clinical trials are imminent.

                  1847.     Intra-Procedural MRI-Monitoring of Irreversible Electroporation of Liver Tissues in Rodent Model

Yue Zhang^1,2, Yang Guo², Ann B. Ragin², Robert J. Lewandowski^2,3, Guang-yu Yang, ^3,4, Grace M. Nijm⁵, Alan V. Sahakian⁵, Reed A. Omary^2,3, Andrew C. Larson^2,3

¹Bioengineering, University of Illinois at Chicago, Chicago, IL, United States; ²Radiology, Northwestern University, Chicago, IL, United States; ³Robert H. Lurie Comprehensive Cancer Center, Northwestern University, Chicago, IL, United States; ⁴Pathology, Northwestern University, Chicago, IL, United States; ⁵Electrical Engineering and Computer Science, Northwestern University, Evanston, IL, United States

MRI permits immediate depiction of ablated tissue zones for intra-procedural monitoring during irriversible electroporation (IRE) ablation procedures. MRI monitoring offers the potential to permit intra-procedural optimization of IRE procedures to ensure complete ablation of targeted tissue volumes.

                  1848.     Early Visualization of the Irreversible Electroporation Ablated Tissue Margin by Contrast Enhanced Imaging in Rodent Model

Yang Guo¹, Yue Zhang^1,2, Grace Nijm³, Alan Sahakian³, Guang-Yu Yang⁴, Reed Omary^1,5, Andrew Larson^1,5

¹Department of Radiology, Northwestern University, Chicago, IL, United States; ²Department of Bioengineering , University of Illinois at Chicago, Chicago, IL, United States; ³Department of Electrical Engineering and Computer Science, Northwestern University, Evanston, IL, United States; ⁴Department of Pathology, Northwestern University, Chicago, IL, United States; ⁵Department of Biomedical Engineering , Northwestern University, Chicago, IL, United States

Electroporation involves targeted delivery of electrical pulses to permeabilize cell membranes, either reversible or irreversible. Irreversible electroporation (IRE), as a new tissue ablation technique, induces tissue necrosis due to permanent cell membrane defects. Assessment of tissue response to IRE may be critical. For our study, we demonstrate that inversion recovery prepared contrast enhancement imaging, with TI adjusted to null the signal intensity from the reversible zone, can visualize the IRE ablated tissue margin (differentiating reversible/irreversible zones) to provide an accurate prediction of ablation. This technique can early detect tissue response to IRE and might be helpful to guide further treatments.

                  1849.     MRI-Guided Focused Ultrasound for Local Delivery of Anti-Aβ Antibodies in a Mouse Model of Alzheimer’s Disease

Jessica F. Jordao^1,2, Carlos A. Ayala-Grosso^3,4, Yuexi Huang¹, JoAnne McLaurin², Isabelle Aubert, ^2,4, Kullervo Hynynen^1,5

¹Imaging Research, Sunnybrook Health Sciences Centre, Toronto, ON, Canada; ²Laboratory Medicine & Pathobiology, University of Toronto, Toronto, ON, Canada; ³Unidad de Biología Molecular, Universidad Central de Venezuela, Los Chaguaramos, Venezuela; ⁴Brain Sciences Research, Sunnybrook Health Sciences Centre, Toronto, ON, Canada; ⁵Medical Biophysics, University of Toronto, Toronto, ON, Canada

The use of antibodies to target toxic amyloid-beta peptides (Aβ) in the brain of Alzheimer’s patients has shown promise in clinical trials but still faces some difficulties.  The blood-brain barrier remains a major obstacle; preventing intravenously delivered antibodies from reaching the brain.  In this study, we use transcranial MRI-guided focused ultrasound to efficiently deliver antibodies to the brain of a mouse model of Alzheimer’s disease and evaluate the efficacy of this treatment.  We found that delivery of the antibody is localized to targeted regions and yields a rapid and significant reduction of Aβ plaque load from a single treatment.

                  1850.     4D Transcatheter Intra-Arterial Perfusion MR Imaging for Monitoring Uterine Artery Embolization in the Rabbit VX2 Tumor Model

Johnathan C. Chung¹, Robert K. Ryu¹, Dingxin Wang², Richard Tang¹, Reed A. Omary^2,3, Andrew C. Larson^2,3

¹Department of Radiology, Northwestern University, Chicago, IL, United States; ²Department of Radiology and Biomedical Engineering, Northwestern University, Chicago, IL, United States; ³Robert H. Lurie Comprehensive Cancer Center, Northwestern University, Chicago, IL, United States

Four-dimensional (4D) transcatheter intra-arterial perfusion (TRIP) MRI is a monitoring technique that involves targeted intra-arterial (IA) injections of gadolinium (Gd) (<0.001 mmol/kg) to help quantify volumetric tissue-perfusion changes over time. This technique can be used to objectively monitor tumor perfusion changes after UAE in VX2 rabbits. The technique may have future clinical application in optimizing endpoints during UAE.

Technical Developments for MR-Guided Interventions

                  1851.     Tuning and Amplification Strategies for Intravascular Imaging Coils

Nicolas Yak¹, Kevan Anderson², Graham Wright^1,2

¹Imaging Research, Sunnybrook Health Sciences Centre, Toronto, ON, Canada; ²Medical Biophysics, University of Toronto, Toronto, ON, Canada

The manufacturing of intravascular imaging coils poses several challenges.  Due to their size, it can be difficult to incorporate local matching networks and signal amplifiers. This study investigates tuning and amplification strategies for intravascular coils and to assess the signal-to-noise benefits of incorporating a matching network and/or miniature amplifier into catheter-based intravascular imaging devices at various locations in the signal chain.  Results suggest that the use of a LNA close to the receiving coil allows for miniature coax cables to be used despite being noisy.  Therefore, designing devices for intravascular applications capable of generating high-SNR images becomes much more feasible.

                  1852.     Three Concepts for Tuning and Matching Intravascular Catheter Coils

Celine Pitsaer¹, Reiner Umathum¹, Ann-Kathrin Homagk¹, Cengizhan Ozturk², Michael Bock¹

¹Medical Physics in Radiology, German Cancer Research Center, Heidelberg, Germany; ²Institute of Biomedical Engineering, Bogazici University, Istanbul, Turkey

Over the past years, the benefit of intravascular coils has been demonstrated providing a local SNR gain in comparison with external coils. Although matching and amplifying directly at the catheter tip could enhance signal quality, it could not be done due to space limitations. In this work we compared three coil concepts that bring matching and preamplifying to the catheter tip. Despite possible limitations due to space restrictions and artefacts from magnetic components, the results show that a significant SNR gain of up to 3 can be achieved with local matching and pre-amplification at the tip of the catheter.

                  1853.     Evaluation of RF Heating of a Multi-Mode Intravascular MRI Coil

Peng Wang¹, Krishna Kurpad¹, Orhan Unal¹

¹Medical Physics, University of Wisconsin - Madison, Madison, WI, United States

Intravascular MRI coils are investigated in our research group to develop a 3D real-time interventional MRI guidance platform with unique imaging and device tip-tracking capabilities. For safety considerations a model is proposed to predict temperature rise in the vicinity of a multimode intravascular coil due to SAR as well as thermal conduction from the heated wire. Numerical simulations are applied to study the current induction, SAR distribution and thermal conduction. The mechanisms for temperature rise around the coil are evaluated and compared for safe interventional MRI operations.

                  1854.     Guidewire Tip Design with Selectively Enabled Magnetic Field Perturbation

Wilfred W. Lam¹, Charles H. Cunningham^1,2

¹Imaging Research, Sunnybrook Health Sciences Centre, Toronto, Ontario, Canada; ²Dept. of Medical Biophysics, University of Toronto, Toronto, Ontario, Canada

One challenge in the placement of guidewires has been tracking the devices as they are moved within the body.  In MR imaging, the marker is a material with a sufficiently large magnetic susceptibility relative to tissue that creates a hypointense region in the surrounding tissue.  However, the resulting black hole obscures the region that must be seen.  A device is presented which can create a susceptibility marker that can be mechanically turned on and off.  Hypointensity in an image of water ahead of the device was only evident when the device was configured to create the marker.

                  1855.     Use of Saline Coolant and Alumina to Facilitate Heat Transfer from Conductive Wires in Interventional MRI

Fabio Settecase¹, Anthony F. Bernhardt², Lee Evans², Vincent Malba², Alistair J. Martin¹, Mark Wilson¹, Steven Hetts¹

¹Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, CA, United States; ²Lawrence Livermore National Laboratory, Livermore, CA, United States

Microcoils can be used to steer catheter tips in the interventional MRI setting. Resistive heating due to currents necessary to achieve tip deflections, however, in addition to RF heating of conductive wires, can cause clinically significant temperature increases. This study investigates the use of alumina at the catheter tip to facilitate heat transfer to saline coolant flowing in the catheter lumen to mitigate temperature increases. The use of saline coolant and high heat conductivity material to facilitate heat dissipation are feasible strategies for other microcoil-catheter devices using nonferromagnetic conductive wires designed for interventional MRI.

                  1856.     Post-Mortem In-Situ Vs in Vitro and in Vivo RF Safety Evaluation of a Two-Channel Intravascular Active Guidewire for Cardiovascular Interventional MRI

Christina E. Saikus¹, Merdim Sonmez¹, Israel M. Barbash¹, Vincent Wu¹, Jamie A. Bell¹, Christopher J. Yeung¹, Robert J. Lederman¹, Ozgur Kocaturk¹

¹Translational Medicine Branch, Division of Intramural Research, National Heart Lung and Blood Institute, National Institutes of Health, Bethesda, MD, United States

Devices for interventional MRI must be evaluated for potential radiofrequency induced heating but phantom heating tests can be difficult to relate to intended uses in vivo.    We examined in vivo and post-mortem in situ device heating in swine and more realistic phantom in vitro testing of an actively visualized guidewire for interventional cardiovascular MRI.

                  1857.     An Integrated CMOS Detector for MR Image Guided Interventions

Jens Anders¹, Paul SanGiorgio¹, Giovanni Boero¹, Xenia Deligianni², Sunil Patil², Klaus Scheffler²

¹Ecole Polytechnique Federale de Lausanne (EPFL), Lausanne, Switzerland; ²University of Basel, University Hospital, Basel, Switzerland

In this work, standard CMOS technology is used to miniaturize highly integrated active tracking devices in MR image guided interventions. The presented microsystem contains a detection coil, a tuning capacitor, a low-noise amplifier, a downconversion mixer and a low-frequency gain stage on a single integrated circuit. Downconverting the NMR signal to a few kilohertz on chip significantly reduces losses in the cables and thereby facilitates the use of the system in small catheters. The feasibility of the approach is demonstrated with phantom experiments in a standard 1.5 T clinical scanner.

                  1858.     A Method to Eliminate Motion-Related Ghosting Artifacts from Images of Active Devices During Parallel Imaging

Ashvin Kurian George¹, Christina E. Saikus¹, Ozgur Kocaturk¹, Robert J. Lederman¹, Anthony Z. Faranesh¹

¹National Institutes of Health, Bethesda, MD, United States

We present a method to remove the ghosting artifact from images formed from under-sampled active device data such as in multi-slice, parallel imaging systems for MR-guided interventions. Ghosting is caused by discontinuities in Fourier space along the phase-encoding direction. The method works by first forming an image from temporally-local, under-sampled Fourier data. This image contains periodically repeated copies in the phase-encoding direction. The non-ghost period of each column is determined by using the view-shared image and exploiting the correlation of the active device image across columns.

                  1859.     Automatic Device Tracking in a Closed-Bore MRI: Principle and Initial Experimental Results on a Robotically Driven Needle

Gregor Thörmer¹, Nikita Garnov¹, Jürgen Haase², Thomas Kahn¹, Michael Moche¹, Harald Busse¹

¹Diagnostic and Interventional Radiology, Leipzig University Hospital, Leipzig, Germany; ²Physics and Geosciences Department, Leipzig University, Leipzig, Germany

Localization and tracking of devices in a closed-bore scanner may improve the accuracy and workflow of MR-guided interventions and also reduce a potential user bias. The goal was to evaluate the performance of a novel image-based approach for device tracking which is demonstrated in a phantom experiment with a robotically driven needle inside the magnet. The presented method is based on the automatic localization of wireless MR-visible markers in poorly resolved MR images. Integration of the localization algorithm into a custom-made pulse sequence with interleaved anatomical imaging would provide a relatively simple and safe alternative to other tracking approaches.

                  1860.     A Multi-Slice Interactive Real-Time Sequence Integrated with the EndoScout Tracking System for Interventional MR Guidance

Kun Qing^1,2, Li Pan^1,3, Barry Fetics⁴, Frank K. Wacker⁵, Steffi Valdeig⁵, Mathew Philip⁴, Amir Roth⁴, Erez Nevo⁴, Dara L. Kraitchman⁵, Andre J. van der Kouwe⁶, Christine H. Lorenz^1,7

¹Center for Applied Medical Imaging, Siemens Corporation, Corporate Research, Baltimore, MD, United States; ²Department of Biomedical Engineering, University of Virginia, Charlottesville, VA, United States; ³Department of Radiology and Radiological Science,  Johns Hopkins University, Baltimore, MD, United States; ⁴Robin Medical Inc., Baltimore, MD, United States; ⁵Department of Radiology and Radiological Science, Johns Hopkins University, Baltimore, MD, United States; ⁶Department of Radiology, Harvard Medical School, Brookline, MA, United States; ⁷ Department of Radiology and Radiological Science, Johns Hopkins University, Baltimore, MD, United States

The purpose of the present work was to integrate the EndoScout tracking technique into a multi-slice interactive real-time sequence to assist MR guided interventions.  The sequence was modified to provide the excitation gradients fed into the Endodoscout system for sensor tracking.  The position and orientation of the surgical device is real-time updated and superimposed either on pre-acquired images or real-time images during the procedures.  The multi-slice real-time images were displayed to enable both surgical device guidance and underlying tissue monitoring.  Animal study suggests that MR guidance using the integrated system is feasible and effective at performing interventional procedures.

                  1861.     Phase Only Cross-Correlation Tracking of a Passive Marker for MR-Guided Interventions

Roger Jason Stafford¹, Florian Maier², Axel Joachim Krafft², Michael Bock², Axel Winkel³, Kamran Ahrar⁴

¹Department of Imaging Physics, The University of Texas M. D. Anderson Cancer Center , Houston, TX, United States; ²Department of Medical Physics in Radiology, Cancer Research Center Heidelberg (DKFZ), Heidelberg, Germany; ³Invivo GMBH, Schwerin, Germany; ⁴Department of Diagnostic Radiology, The University of Texas M. D. Anderson Cancer Center, Houston, TX, United States

Real-time MR-guidance of percutaneous procedures may benefit from methods for automatically adjusting the scan prescription to the needle trajectory, as well as visual delineation of the trajectory, in real-time.  In this work, the feasibility of using a phase only cross correlation tracking algorithm for automated identification of a contrast filled needle sleeve with real-time adjustment of the scan prescription for continuous delineation of the needle trajectory during manipulation was investigated in phantom and patients for MR-guidance of percutaneous procedures in a closed bore 1.5T clinical scanner.

                  1862.     Targeted Magnetic Delivery of Cells with an MRI Scanner

Johannes Riegler^1,2, Jack A. Wells¹, Panagiotis Kyrtatos¹, Anthony N. Price¹, Mark F. Lythgoe¹

¹Centre for Advanced Biomedical Imaging (CABI), Department of Medicine and Institute of Child Health, University College London (UCL), London, United Kingdom; ²Centre for Mathematics and Physics in the Life Sciences and Experimental Biology (CoMPLEX), UCL, London, United Kingdom

Targeted delivery of cells or drugs is a technique that could increase the efficacy of medical treatments. One possibility for that is using magnetic fields to drag labelled entities to the site of interest. MRI systems are particular interesing for this purpose due to their ability to generate uniform magnetic field gradients across the whole body. We demonstrated the feasibility of steering magnetically labelled cells to one exit tube of a bifurcation phantom by applying MR imaging gradients. This technique could potentially be used for localised cell delivery in the vascular system.

                  1863.     Simultaneous Wireless Fast Scan Cyclic Voltammetry and Amperometry with 3T MRI

Kendall Lee¹, Jonathan Bledsoe¹, Kiaran McGee², John Huston², Chris Kimble³, Filippo Agnesi, Kevin Bennet³, Charles Blaha⁴, Paul Garris⁵

¹Department of Neurosurgery, Mayo Clinic, Rochester, MN, United States; ²Department of Radiology, Mayo Clinic, Rochester, MN, United States; ³Department of Engineering, Mayo Clinic, Rochester, MN, United States; ⁴Department of Psychology, University of Memphis; ⁵Biological Sciences, Illinois State University

Electroanalytical techniques such as fast-scan cyclic votlammetry (FSCV) and constant-potential amperometry (CPA) have revolutionized neuroscience research by supporting temporally, spatially, and chemically resolved neurotransmitter measurements in the brain. CPA and FSCV were performed by a small, digital-telemetry device called a wireless instantaneous neurotransmitter concentration system (WINCS) specifically developed for neurochemical monitoring. Test measurements were collected during simultaneous 3T imaging using a fast spin echo sequence. WINCS dynamically recorded dopamine electrochemical signatures with sub-second temporal resolution and with high fidelity. We demonstrate proof-of-concept for combining WINCS real-time neurochemical measurements and 3T MRI that may offer simultaneous neurochemical monitoring during fMRI.

                  1864.     Two Channel Interventional Cervix Coil for High Dose Rate Brachytherapy

Nikolay Vladimirovic Viskusenko¹, Emre Kopanoglu², John Jezioranski³, Warren Foltz³, Oktay Algin⁴, Ergin Atalar²

¹UMRAM: National Magnetic Resonance Research Center , Bilkent Universty Elektrical and Elektronic Engineering  , Ankara , Turkey; ²UMRAM: National Magnetic Resonance Research Center, Bilkent Universty Elektrical and Elektronic Engineering, Ankara, Turkey; ³University Health Network, Toronto, Canada; ⁴Radiology, Ataturk Hospital, Ankara, Turkey

Determination of the diseased tissue region is very crucial for brachytherapy treatment. In this study, we propose a new 2-channel coil structure that is embedded on a commercially available HDRT applicator. After MRI imaging of the cervix, brachytherapy procedure can be carried out as normal without moving the applicator, which is essential for the correctness of radiation dose calculations. In-vivo animal experiments have been conducted and good quality images have been obtained.

                  1865.     Esophagus Imaging with Intraluminal RF Coil for Integrated MR-Endoscope System

Yuichiro Matsuoka¹, Hayato Yoshinaka¹, Susumu Aizawa², Makiya Matsumoto², Yoshinori Morita¹, Hiromu Kutsumi¹, Etsuko Kumamoto³, Kagayaki Kuroda^4,5, Takeshi Azuma¹

¹Graduate School of Medicine, Kobe University, Kobe, Hyogo, Japan; ²Graduate School of Engineering, Kobe University, Kobe, Hyogo, Japan; ³Information Science and Technology Center, Kobe University, Kobe, Hyogo, Japan; ⁴Medical Device Development Center, Foundation for Biomedical Research and Innovation, Kobe, Hyogo, Japan; ⁵School of Information Science and Technology, Tokai Univesity, Hiratsuka, Japan

An endoscope shows an interior surface image of organ, but it has difficulty finding the information under tissue surface. To assist endoscopy and endoscopic surgery by providing cross-sectional images, we have developed an integrated MR-endoscope system. An intraluminal RF coil to be inserted into esophagus was designed, and MR imaging using this coil and a tracking system to detect the coil position in MRI was conducted using an excised porcine tissue. The layer structure in esophagus could be distinguished in T1- and T2-weighted images. The feasibility of esophagus imaging by the developed coil having high Q value was demonstrated.