Ethan K. Brodsky^1,2, Benjamin Grabow¹, Martin L. Brady³, Raghu Raghavan³, Chris D. Ross⁴, and Walter F. Block^1,2
1Medical Physics, University of Wisconsin, Madison, WI, United States, ²Biomedical Engineering, University of Wisconsin, Madison, WI, United States, ³Therataxis, LLC, Baltimore, MD, United States, ⁴Engineering Resources Group, Inc., Pembroke Pines, FL, United States

Convection-enhanced delivery (CED) is a neurosurgical procedure for delivering large molecular and viral vectors into the brain. Its effectiveness has been somewhat limited, however, by unexplained variability, with two identical infusion protocols sometimes generating very different drug distributions. We have completed a comprehensive study on the use of real-time MR monitoring to unravel often conflicting recommendations on the design of infusion catheters, flow rates, and other techniques to minimize variance in drug distribution. Specifically, we present results here regarding an investigation to minimize variations in drug distribution due to unwanted loss of infusate through a low pressure escape route along the exterior of the catheter, termed “backflow”.

Tie-Qiang Li¹, Yanlu Wang¹, Rolf Hallin², and Jan-Erik Juto^3
1Department of Medical Physics, Karolinska University Hospital, Huddinge, Stockholm, Sweden, ²Department of Neurophysiology, Karolinska University Hospital, Huddinge, Stockholm, Sweden, ³Department of CLINTEC, Karolinska Institute, Huddinge, Stockholm, Sweden

The purpose of the study was to investigate the dynamical functional response in hypothalamus to a novel therapeutic intervention which has been shown to be extraordinarily effective for treating migraine headache and narcolepsy. BOLD fMRI experiments were carried out under a non-invasive intervention for clinical patients with acute migraine headache attack. The BOLD responses under different interventional conditions indicate that restoring the physiological homeostasis in hypothalamus and associated functional network at the basal of the brain, which is the control center of the autonomic nervous system (ANS), provides an efficient approach for the treatment of central nervous system disorders.

Delphine Elbes¹, Julie Magat¹, Assaf Govari², Yaron Ephrath², Delphine Vieillot³, Christopher Beeckler², Pierre Jais¹, and Bruno Quesson^1
1CRCTB/IHU LIRYC, University of Bordeaux, Pessac, Gironde, France, ²Biosense Webster, Israel, ³PTIB, University of Bordeaux, Pessac, Gironde, France

Cardiac electrical dysfunction can be assessed by mini-invasive electrophysiological (EP) mapping. Being able to collect electrical data simultaneously to MR acquisition would simplify the interventional procedure, allow for reduction of examination duration for the patients and clinicians, and reduce registration errors. This study presents simultaneous MR-EP using a 10 poles, circular, EP catheter. Evaluation of the MR-compatibility is presented, together with simultaneous MR-EP measurements obtained in vivo on a large animal model. The electrograms obtained in the MR scanner operating at 1.5 T were compared to measurement performed under identical conditions in the adjacent catheter lab under X-Ray fluoroscopy.

Ming Zhao^1,2 and Jerome L. Ackerman^2
1University of Massachusetts Lowell, Lowell, MA, United States, ²MGH/MIT Athinoula A. Martinos Center for Biomedical Imaging, Charlestown, MA, United States

As part of a project to develop MR coagulation (MR-induced RF heating of a coagulable biomaterial) for minimally invasive repair of vascular lesions, we investigate the relationship between the heat coagulation behavior and MR relaxation properties of egg white. This protein solution is a good model for the analogous behavior of human serum albumin solution, an optimal (but expensive) biomaterial for MR coagulation. We find that large changes in both T2 and T1rho clearly indicate the temperature at which the coagulation process occurs, as validated by light scattering measurements.

Adrienne E Campbell-Washburn¹, Toby Rogers¹, Hui Xue¹, Michael S Hansen¹, Robert J Lederman¹, and Anthony Z Faranesh^1
1Division of Intramural Research, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, Maryland, United States

In order to perform MR-guided cardiovascular interventions, imaging must be fast, interactive and provide good visualization of devices. A dual echo bSSFP sequence is implemented to image commercially available passive devices. This sequence generates a positive contrast device image and an anatomical reference image in a single acquisition (3 frames/second), and reduces SAR using a variable flip angle scheme. Graphical color overlay of the device is provided as visual feedback to operator. In vivo data of a nitinol guidewire in a pig shows utilization of this technique for improved visualization of commercially available passive devices without device modification.

Taner Demir¹, Ali Caglar Ozen², Emre Kopanoglu³, and Ergin Atalar^1,4
1Umram, Bilkent University, Ankara, Ankara, Turkey, ²University of Freiburg, Freiburg, Baden-Wurttemberg, Germany, ³Yale University, Connecticut, United States, ⁴Dept. of EE Engineering, Bilkent University, Ankara, Ankara, Turkey

The cylindrical encoding as a novel method for high resolution imaging without requiring the use of high strength gradients is introduced. Phase encoding in the circumferential direction is obtained by alternating transmission using a loopless catheter antenna and a birdcage coil in two shot fast spin echo pulse sequence. The readout is carried out in the direction of main magnetic field. The MR signal is received as the radial projection of the spins. The image is reconstructed by inverse Fourier transforming the rearranged projection data.

Adrienne E Campbell-Washburn¹, Hui Xue¹, Robert J Lederman¹, Anthony Z Faranesh¹, and Michael S Hansen^1
1Division of Intramural Research, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, Maryland, United States

Spiral MRI is fast and low SAR, and therefore has potential utility for MR-guided interventions. To remove distortions in spiral MR images, gradient waveform imperfections must be corrected. In this abstract, the measured gradient system impulse response function is used to correct k-space trajectories in real-time for arbitrary image orientations and is demonstrated to remove image distortions in a phantom. In addition, an interactive off-resonance reconstruction is used to de-blur image regions of interest. In vivo, spiral imaging is performed with 10-15 frames/second. The introduction of these real-time distortion corrections will make spiral MR-guided interventions feasible.

James Box¹, T. Stan Gregory¹, Alexander Squires¹, Yabiao Gao¹, and Zion Tse^1
1College of Engineering, The University of Georgia, Athens, Georgia, United States

Microscopic medical robots capable of translating in a bloodstream or similar liquid represents a new type of therapeutic technology for endo-vascular interventions. Local drug delivery of diagnostic and chemotherapeutic agents could be delivered to tumors, blood clots, and infections. Microcapsule control in such a situation presents a barrier for the implementation of this technology. Magnetohydrodynamic (MHD) voltages are created in major vasculature when blood ejected into the aortic arch during early systole interacts with the strong magnetic field of the MRI. By utilizing the MHD effect within the strong magnetic field of the MRI (Fig. 1), the opportunity to propel a device and provide imaging is presented simultaneously. We hypothesized that a wireless MHD-driven thruster could be developed for the application of controlling microscopic endo-capsules within the strong magnetic field of the MRI scanner.

Nicholas C von Sternberg¹, Junmo An¹, Karen Chin², Dipan J Shah², and Nikolaos V Tsekos^1
1University of Houston, Houston, Texas, United States, ²Houston Methodist, Houston, Texas, United States

This work briefly describes the purpose, implementation and results of a new method of linear force transmission that has been developed to address the specific needs of MR compatible actuation. Described within are the strengths and weaknesses of current actuation techniques and how a novel new technology can better fulfill the actuation needs of image guided interventions without sacrificing image quality. The described method of force transmission can be used to transform standard robotic actuators and control hardware solutions into MR compatible solutions and has been developed using only off-the-shelf hardware.

Yue Chen¹, Ka-Wai Kwok¹, Thomas CP Chau², Wayne Luk², Kent Ronald Nilsson¹, Ehud J. Schmidt³, and Zion Tsz Ho Tse^1
1Engineering, University of Georgia, Athens, GA, United States, ²Computing, Imperial College London, London, United Kingdom, ³Radiology, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, United States

A catheter control device is developed, which is capable to simulate force and tactile feeling of interaction between the cardiovascular structure and catheter tip. The objective is to improve radiofrequency ablation (RFA) safety and reliability for MR-guided cardiac electrophysiological (EP) therapy. This MR-conditional haptic interface can be integrated with the clinically-used catheters and kits for MR-guided EP. Detailed validation was conducted in simulated RFA tasks performed by 12 subjects to evaluate the effect of such haptic feedback on improved catheter manipulation and lesion RFA. The task improvement in terms of in safety, accuracy and RFA sufficiency demonstrates the clinical potential.

Santhi Elayaperumal¹, Juan Camilo Plata², Andrew Holbrook³, Bruce Daniel³, Mark Cutkosky¹, and Kim Butts Pauly^3
1Mechanical Engineering, Stanford University, Stanford, CA, United States, ²Bioengineering, Stanford University, CA, United States, ³Radiology, Stanford University, CA, United States

We present a feasibility study of a system for MR-guided interventions including a passive manipulator to steer a needle from outside a closed bore scanner, demonstrated by a prostate biopsy in a canine. The system comprises of a shape sensing needle with fiber optic strain sensors such that the full 3D shape of the needle can be reconstructed and used to inform the physician about the tool trajectory in real-time. Real-time imaging, tracking and tool annotation is integrated with a web browser based guided user interface, which allows the physician visualization and scanner control intraoperatively from inside the MRI suite.

Akihiro Takahashi¹, Etsuko Kumamoto², Yuichiro Matsuoka³, Yoshinori Morita⁴, Hiromu Kutsumi⁵, Takeshi Azuma⁵, and Kagayaki Kuroda^6,7
1Graduate School of System Informatics, Kobe University, Kobe, Hyogo, Japan, ²Information Science and Technology Center, Kobe University, Kobe, Hyogo, Japan,³Center for Information and Neural Networks, National Institute of Information and Communications Technology, Suita, Osaka, Japan, ⁴School of Medicine, Kobe University, Kobe, Hyogo, Japan, ⁵Graduate School of Medicine, Kobe University, Kobe, Hyogo, Japan, ⁶Kobe International Frontier Medical Center, Kobe, Hyogo, Japan,⁷Graduate School of Engineering, Tokai University, Hiratsuka, Japan

A multi-planar reconstruction (MPR) technique based on the endoscope tip tracking information for MR-endoscope system is proposed. Cross sectional images of arbitrarily extracted sagittal, coronal, axial and oblique planes are readily reconstructed from the MR volume data according to the endoscope tip location and orientation detected by a gradient magnetic field sensor. The geometry data are annotated in the endoscope images as a digital watermark. The proposed technique enables smooth presentation of the region of interest in the MR images simultaneously superimposed on the endoscope images during operation.

Felix V. Güttler¹, Andreas Heinrich¹, Michael Sonnabend¹, and Ulf Teichgräber^1
1Department of Radiology, University Hospital Jena, Jena, Thuringia, Germany

The purpose of the study is to evaluate the suitability of a novel RFID-based tracking system for intraoperative MRI. Therefore the spatial accuracy and SNR according to the NEMA standard MS 1-2008 was quantified. The installation of an RFID system including transponders and receivers in the magnet room in close distance to the magnet has low of non-relevant influence on MRI. However the spatial accuracy have to be improved for an application as tracking system in intraoperative MRI.

Junmo An¹, Nicholas von Sternberg¹, Karen Chin², Dipan J. Shah², Andrew G. Webb³, and Nikolaos V. Tsekos^1
1University of Houston, Houston, Texas, United States, ²Houston Methodist, Texas, United States, ³Leiden University, Leiden, Netherlands

The aim of this work is to investigate localization and tracking techniques to automatically select which MR-visible markers are required to be visible on the MR image by the robot control module. To unambiguously distinguish the markers, each marker can be selectively visible or invisible on the MR image for monitoring the motion of the MR-compatible manipulators. The described technique can be used for robust and fast tracking with two-dimensional images or one-dimensional projections of multiple markers on an interventional device, such as the shaft of steerable catheters and the end-effectors of MR-compatible manipulators.

Bradford RH Thorne¹, Prasheel Lillaney¹, Aaron Losey¹, Xiaoliang Zhang¹, Yong Pang¹, and Steven Hetts^1
1Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, California, United States

The purpose of this study was to design and manufacture a miniature resonant structure for use as a bright marker on endovascular catheters for use in interventional magnetic resonance imaging (iMRI) procedures. Resonant markers were positioned Parallel with B₀ in a water phantom and imaged using a spoiled gradient echo sequence with a low flip angle. Prior to imaging, a network analyzer was used to tune the markers to the desired frequency of 127.72 MHz for operation at 3T. The marker provides an opportunity to safely and accurately perform MR guided procedures with smaller devices than previously possible.

Xinyang Liu¹, Kemal Tuncali¹, William M Wells III¹, and Gary P. Zientara^1
1Radiology, Brigham and Women's Hospital and Harvard Medical School, Boston, MA, United States

The purpose of this study is to develop an automatic approach to detect multiple 3D probes in 3T abdominal HASTE images obtained during MRI-guided cryoablation. The detected probes can be used to guide automatic iceball segmentation during the freeze cycles of the procedure. We introduced a novel template to model the probe artifact, and an extra local refinement process to improve accuracy of the detection. Retrospective experiments based on 13 MRI-guided cryoablation cases show that our automatic probe detection method with local refinement is accurate and robust, compared with results determined manually, and is feasible for clinical use.

Peng Wang¹ and Orhan Unal^1,2
1Medical Physics, University of Wisconsin - Madison, Madison, Wisconsin, United States, ²Radiology, University of Wisconsin - Madison, Madison, Wisconsin, United States

MRI-guided RF ablation is a promising method for guiding and conducting thermal therapies such as electrophysiology (EP) procedures and relies on accurate temperature monitoring. Proton resonance frequency (PRF) shift MR thermometry, which is the choice of method, is very sensitive to motion. In this work, a novel method that employs active tip tracking coils and Extended Kalman Filter is proposed for motion prediction and compensation. Compared with previously described MR thermometry methods, the proposed method can be particularly advantageous for correcting through-plane motion.

Ronald D Watkins¹, Rachelle Bitton¹, and Kim Butts Pauly^1
1Radiology, Stanford University, Stanford, CA, United States

A volume brain coil has been developed that allows the upper half of the coil to reside inside a focused ultrasound brain transducer. The upper half is inductively driven by the lower coil half obviating the need for electrical wire connections across the membrane into the acoustic water path. The coil transmits in the local region of the head reducing total SAR from a whole body coil and improves signal to noise ratio and temperature uncertainty by 300%

Kim Butts Pauly¹, Ron Watkins², Rachelle Bitton², Wyger Brink³, Andrew Webb³, Beat Werner⁴, and Pejman Ghanouni^2
1Radiology, Bioengineering, Electrical Engineering, Stanford University, Stanford, CA, United States, ²Radiology, Stanford University, Stanford, CA, United States, ³Radiology, Leiden University Medical Center, Leiden, Netherlands, ⁴University Children’s Hospital Zurich, Zurich, Switzerland

During MRgFUS neurosurgery at 3T, dielectric resonances occur in the integrated water bath that is required for coupling and to cool the scalp. These resonances result in heterogeneous MR signal intensity across the brain. Here, we investigate RF shimming with a high permittivity material to mitigate this effect. Simulations and experiments for pads of barium titanate, placed outside but in contact with the water bath, show that the pads improve the homogeneity of the B1+ field significantly.

Yuexi Huang¹, Alec Hughes², Michael L. Schwartz³, Andres M. Lozano⁴, and Kullervo Hynynen^1,2
1Sunnybrook Research Institute, Toronto, ON, Canada, ²Department of Medical Biophysics, University of Toronto, Toronto, ON, Canada, ³Division of Neurosurgery, Sunnybrook Health Sciences Centre, Toronto, ON, Canada, ⁴Division of Neurosurgery, Toronto Western Hospital, Toronto, ON, Canada

Magnetic resonance guided focused ultrasound has shown promising results in the treatment of essential tremor. MR-based targeting and temperature monitoring ensured precise lesioning of the ventral intermediate nucleus (VIM) in the thalamus. However, although the centres of VIM were precisely targeted, oblique lesion volumes angled to the main acoustic axes were observed in our initial patients, with the two most severe ones close to 45 degrees in the coronal plane. In this study, we investigated the reason for this oblique focus, reproduced results in a skull phantom, and demonstrated solutions for correcting the obliqueness using MR thermometry.

Wen Yen Chai^1,2, Po Chun Chu², Yu Chun Lin¹, Jiun Jie Wang³, Yau Yau Wai¹, and Hao Li Liu^2
1Department of Medical Imaging and Intervention, Chang Gung Memorial Hospital, Linkou, Taiwan, ²Department of Electrical Engineering, Chang Gung University, Taoyuan, Taiwan, ³Department of Medical Image and Radiological Sciences, Chang Gung University, Taoyuan, Taiwan

The purpose of this study is to evaluate perfusion change caused by FUS-BBB opening, and evaluate the correlation with the permeability change. And the result is that permeability increase after BBB opening highly correlates with the cerebral blood volume increase, and independent of the cerebral blood flow. This information provides useful insights in understanding the pharmacodynamic behavior when intending to apply this approach to deliver drugs into the brain.

Po-Chun Chu¹, Hong-Yu Chiu², Wen-Yen Chai^1,3, Yu-Cheng Pei^4,5, You-Yin Chen⁶, and Hao-Li Liu^1
1Department of Electrical Engineering, Chang-Gung University, Taoyuan, Taiwan, Taiwan, ²Department of Life Sciences, National Yang-Ming University, Taipei, Taiwan, Taiwan, ³Department of Diagnostic Radiology, hang-Gung University and Memorial Hospital, Taoyuan, Taiwan, Taiwan, ⁴Department of Physical Medicine and Rehabilitation, Chang-Gung University and Memorial Hospital, Taoyuan, Taiwan, Taiwan, ⁵School of Medicine, Chang Gung University, Taoyuan, Taiwan, Taiwan, ⁶Department of Biomedical Engineering, National Yang-Ming University, Taipei, Taiwan, Taiwan

This study is to observe the effect and the relationship between the diffusion imaging (ADC mapping) and neuroactivity (SSEP waveform) after blood brain barrier opening by focus ultrasound with microbubbles. The result showed that the lower exposure make both ADC value and the SSEP waveform decrease but recovered in two days. However, the higher exposure make them both significant decrease and come back slower. We want to reveal more details need to be considered in the future neurophysiological, neuromodulation, or BBB issues.

Benjamin Goggio Cohn¹, Patrick Ye², and Kim Butts Pauly^3
1Electrical Engineering, Stanford University, Stanford, CA, United States, ²Bioengineering, Stanford University, Stanford, CA, United States, ³Radiology, Stanford University, CA, United States

MR guidance of transcranial FUS using MR-ARFI allows for precise targeting of specific brain regions and visualization of the focal region. The target location itself can strongly affect focal intensity and size; assuming constant intensity and spot size can result in ultrasound dose error. MR-ARFI enables more accurate quantification of ultrasound physical effects for ultrasound neuromodulation and other transcranial FUS applications.

Feiyu Chen¹, Kangrong Zhu², Urvi Vyas³, Rachelle Bitton³, Karen Ying⁴, John M Pauly², and Kim Butts Pauly^3
1Center for Biomedical Imaging Research, Department of Biomedical Engineering, Tsinghua University, Beijing, China, ²Department of Electrical Engineering, Stanford University, Stanford, California, United States, ³Department of Radiology, Stanford University, Stanford, California, United States, ⁴Department of Engineering Physics, Tsinghua University, Beijing, China

We validate the feasibility of simultaneous multi-slice EPI to monitor the volumetric temperature of the target tissue with high temperature accuracy during MRgFUS treatment. The average uncertainty of the measured temperature is less than 0.4°C for an ex-vivo porcine tissue. This approach allows researchers to monitor the temperature of the whole brain, especially the brain surface and scalp. It can be used to prevent undesired heating during MRgFUS treatment of the brain.

Gesthimani Samiotaki¹, Sachin Jambawalikar², and Elisa E Konofagou^1,2
1Biomedical Engineering, Columbia University, New York, NY, United States, ²Department of Radiology, Columbia University, NY, United States

Allison Payne¹, Matthias Koopmann², Jill Shea³, Joshua de Bever⁴, Jose Reyes², Emilee Minalga⁵, Robb Merrill⁵, J. Rock Hadley⁵, Dennis L. Parker⁵, and Nassir Marrouche^2
1Radiology, University of Utah, Salt Lake City, UT, United States, ²Cardiology, University of Utah, Utah, United States, ³Surgery, University of Utah, Utah, United States,⁴Computer Science, University of Utah, Utah, United States, ⁵Radiology, University of Utah, Utah, United States

Renal sympathetic denervation has been shown to be effective in reducing drug-resistant hypertension. Presented is a feasibility study performing renal denervation using MR guided focused ultrasound in a porcine model. Two animals were underwent unilateral renal denervation. A mean systolic and diastolic blood pressure change of -11.5±13.4 and -23.5±0.7 mmHg was observed. There were distinct differences in the histological appearance of the nerve bundles between the treated and non-treated sides and no indication of damage to either arterial wall demonstrating that MRgFUS can be effectively and safely used to perform renal denervation in a porcine model.

Rachelle R Bitton¹, Taylor Webb², Pejman Ghanouni¹, and Kim Butts Pauly^1
1Radiology, Stanford University, Stanford, CA, United States, ²Electrical Engineering, Stanford University, Stanford, CA, United States

MRgFUS treatment efficacy is quantified during treatment using PRF thermometry calculated dose, and immediately after treatment by measuring the non-perfused volume (NPV) of contrast-enhanced (CE) images. However, conventional PRF thermometry dose volume often under-predict treatment, when compared with NPV. The purpose of this work was to investigate how much of the under-prediction was due to errors in baseline temperature assumption of PRF thermometry. We propose the use of a prior baseline method to better predict MRgFUS treatment volume. The method searches previously acquired baselines images to determine a match based on magnitude and phase similarity criteria. Using prior baselines, we calculated thermal dose volumes that were more similar to post treatment CE non-perfused volume than the immediate baseline method.

Joost Wijlemans¹, Martijn de Greef², Gerald Schubert³, Maurice van den Bosch¹, Chrit Moonen², and Mario Ries^2
1Dept. Radiology, UMC Utrecht, Utrecht, Netherlands, ²Image Sciences Institute, UMC Utrecht, Utrecht, Netherlands, ³Philips Healthcare, Vantaa, Finland

During MR-HIFU ablation, heat accumulation in near-field tissues (i.e. between transducer and target) can cause thermal damage to healthy tissues. In seven porcine liver ablation experiments we studied a strategy for managing this risk. Active external tissue cooling was used to reduce the risk of thermal damage, while T2 thermometry was used to monitor heat accumulation in near-field tissues. This method can be used to adjust the re-sonication intervals during the procedure, reducing the risk of thermal damage while optimizing ablation speed. Unlike modeling methods, this strategy is effective regardless of ultrasound beam geometry, near-field tissue composition, and perfusion variations.

Tatsuhiko Matsumoto¹, Etsuko Kumamoto^1,2, Daisuke Kokuryo³, and Kagayaki Kuroda^4,5
1Kobe university, Kobe, Hyogo, Japan, ²Information Science and Technology Center, Kobe, Japan, ³Molecular Imaging Center, National Institute of Radiological Sciences, Chiba, Japan, ⁴Tokai University, Hiratsuka, Japan, ⁵Kobe International Frontier Medical Center, Kobe, Japan

Three-dimensional (3D) deformation of the liver under free breathing was analyzed using branching structure of portal veins. A series of sagittal, multi-slice fast steady-state (FIESTA) images were acquired in a healthy volunteer�fs liver under slow-paced free respiration and were reconstructed to isotropic volume data. Branching points of the portal veins included in the volume were extracted by using our in-house 3D image processing software. The software-extracted branching points exhibited that the liver constricts in right-left (RL) direction for about 12 mm when came down to inferior with maximum inhalation.

Nick Todd¹, Allison Payne², and Dennis L Parker^2
1Wellcome Trust Centre for Neuroimaging, London, United Kingdom, ²Radiology, UCAIR, Salt Lake City, UT, United States

A hybrid PRF/T1/T2* sequence is used to measure tissue temperature and the relaxation parameters T1 and T2* in real time during MR-guided focused ultrasound (MRgFUS) heating of in vivo and ex vivo rabbit thigh muscle. T1 and T2* are analyzed as functions of temperature and thermal dose to investigate whether they are sensitive to the various processes that occur during the onset and progression of tissue thermal damage.

Patrick Winter¹, Matthew Lanier¹, Ari Partanen², and Charles Dumoulin^1
1Radiology, Cincinnati Children's Hospital, Cincinnati, OH, United States, ²Philips Healthcare, Cleveland, OH, United States

MR-HIFU uses MRI to precisely target a HIFU beam to heat small areas of tissue and to monitor tissue temperature at the target and surrounding regions. A novel application of MR-HIFU is the ablation of fat depots to reverse the progression of obesity and other associated diseases. However, typical MRI thermometry methods cannot monitor temperature changes in fat because there is no shift in the proton resonance frequency. As an alternative, we utilized T2 mapping to assess HIFU ablation of fat under MRI guidance.

Taylor D Webb¹, Rachelle Bitton², Pejman Ghanouni², and Kim Butts Pauly^2
1Electrical Engineering, Stanford University, Stanford, CA, United States, ²Radiology, Stanford University, Stanford, CA, United States

We investigated the impact of heat radiation from bone during the high intensity focused ultrasound treatment of a patient with metastatic tumor in the bone. Extra images were acquired post sonication to allow for better understanding of the temporal characteristics of the temperature in the soft tissue. We show that temperature rise in the soft tissue adjacent to the bone is delayed with respect to the sonication. Additionally, our spatial analysis of the temperature over time reveals that radiation from bone causes slower temperature decay, leading to higher dose accumulations and necessitating longer cooling times between sonications.

Chen-Hua Wu¹, Chih-Kuang Yeh¹, Chung-Hsin Wang¹, Shih-Tsung Kang¹, Wen-Shiang Chen^2,3, and Hsu-Hsia Peng^1
1Department of Biomedical Engineering and Environmental Sciences, National Tsing Hua University, Hsinchu, Taiwan, ²Department of Physical Medicine and Rehabilitation, National Taiwan University Hospital, Taipei, Taiwan, ³Division of Medical Engineering Research, National Health Research Institutes, Miaoli, Taiwan

In this study, a gradient echo based sequence was used to observe the signal intensity (SI) changes during FUS cavitation for in vitro gel phantom experiments. We investigated SI changes under different concentrations of MBs, FUS powers, and imaging slice thicknesses. Even with conditions of diluted MBs of 0.001X, low FUS power of 2W in a burst mode, or thicker slice of 8 mm, reduced SI still can be observed. The pulse sequence of gradient echo has been proved to be a useful technique for real-time monitoring of SI changes when transmitting FUS to MBs.

Samuel Fielden¹, Li Zhao¹, Wilson Miller², Xue Feng¹, Max Wintermark², Kim Butts Pauly³, and Craig Meyer^1,2
1Biomedical Engineering, University of Virginia, Charlottesville, VA, United States, ²Radiology, University of Virginia, Charlottesville, VA, United States, ³Radiology, Stanford University, Palo Alto, CA, United States

MRgFUS is a promising non-invasive technique with a wide range of applications; however, acquiring fully sampled 3D volumetric data with sufficient spatial and temporal resolution for adequate dose monitoring and guidance is difficult. Here, we present initial results using a 3D spiral sequence for MR thermometry and accelerate imaging in order to improve temporal resolution through the application of a Kalman filter.

Andrew Webb^1
1Radiology, C.J.Gorter Center for High Field MRI, Leiden, Zuid Holland, Netherlands

The standard setup for MR-guided FUS includes a transducer, water bath integrated into the patient table, and either a specialized RF coil placed close to the patient, or else the body coil is used as the receiver. However, the body coil has low sensitivity and a local RF coil can interfere with ultrasound irradiation. Here a completely new approach is presented in which an RF coil is not needed at all: the dimensions of the water bath are adjusted so that a high order dielectric mode is excited, resulting in efficient MR excitation and reception at the transducer focal point.

Mathew Carias^1,2, Kevan Anderson¹, Graham Wright^1,2, and Kullervo Hynynen^1,2
1Physical Sciences, Sunnybrook Research Institute, Toronto, Ontario, Canada, ²Medical Biophysics, The University of Toronto, Toronto, Ontario, Canada

In this study we propose the use of therapeutic ultrasound as a therapy delivery technique combined with a local asymmetrical loopless antenna for treatment monitoring. It was determined that a 10 mm distal whip length and 80 mm proximal whip length would be best suited for such a catheter. These asymmetrical designs show a decreased SNR when compared to symmetrical loopless antennas, however, SNR measurements are still adequate which enables one to place a transducer on the device. These results suggest that such a catheter can provide a minimally invasive platform for both therapy delivery and treatment monitoring for cardiac ablation therapies.

Mehmet Arcan Erturk^1,2, AbdEl-Monem M. El-Sharkawy², and Paul A. Bottomley^1,2
1Department of Electrical and Computer Engineering, Johns Hopkins University, Baltimore, Maryland, United States, ²Department of Radiology, Johns Hopkins University, Baltimore, Maryland, United States

Active interventional loopless antenna may heat locally during MRI, or when they are used for thermal ablation therapy. Here we develop a novel MRI-less thermometry method employing the internal MRI detector as an RF radiometer at the 3T MRI frequency. Local temperature is monitored by a loopless antenna, based on the magnitude of its RF noise voltage. The radiometer is calibrated in a gel phantom to an accuracy of <0.3°C at two measurements/sec. The radiometer tracks the temperature probe with high local sensitivity. RF radiometry provides thermometry without MRI’s confounding factors or the need for additional sensor probes.

Henrik Odéen^1,2, Nick Todd¹, Josh de Bever³, Scott Almquist³, Allison Payne¹, MarJanna Dahl⁴, Kurt Albertine⁴, Douglas Christensen^5,6, and Dennis L Parker^1
1Utah Center for Advanced Imaging Research, Department of Radiology, University of Utah, Salt Lake City, Utah, United States, ²Department of Physics and Astronomy, University of Utah, Salt Lake City, Utah, United States, ³School of Computing, University of Utah, Salt Lake City, Utah, United States, ⁴Department of Pediatrics, University of Utah, Salt Lake City, Utah, United States, ⁵Department of Bioengineering, University of Utah, Salt Lake City, Utah, United States, ⁶Department of Electrical and Computer Engineering, University of Utah, Salt Lake City, Utah, United States

Methods for 3D intracranial treatment envelope evaluations for magnetic resonance guided focused ultrasound applications are described. A 3D segmented echo planar imaging pulse sequence is used to acquire k-space data that is subsampled in the ky-phase encode direction with a reductions factor of R=4. The data is reconstructed with a temporally constrained reconstruction algorithm and temperature maps are created with the proton resonance frequency shift method. The 3D treatment envelope is evaluated in terms of relative near-field heating, and hydrophone scans are used to investigate amount of phase aberration and intensity loss due to US-focusing through the skull bone.

Pooja Gaur^1,2 and William A Grissom^2,3
1Chemical and Physical Biology, Vanderbilt University, Nashville, Tennessee, United States, ²Institute of Imaging Science, Vanderbilt University, Nashville, Tennessee, United States, ³Biomedical Engineering, Vanderbilt University, Nashville, Tennessee, United States

Single echo scans with low bandwidth are commonly used in guiding thermal therapies, but are susceptible to distortions caused by both heating-induced and static off-resonance effects, resulting in distorted temperature maps. We show that multi-echo scans with higher bandwidths can alleviate distortions without sacrificing temperature SNR. A penalized-likelihood temperature reconstruction algorithm is also proposed for multi-echo thermometry, that produces more accurate temperature maps than previous methods, and does not require phase unwrapping.

Tetiana Dadakova¹, Johanna Gellermann², Otilia Voigt², John Matt Pavlina¹, and Michael Bock^1
1Medical Physics, Department of Diagnostic Radiology, University Medical Center Freiburg, Freiburg, Germany, ²Department of Radiation Oncology, University Hospital Tübingen, Tübingen, Germany

Regional hyperthermia is used as a supplementary therapy during cancer treatment to improve chemotherapy and radiotherapy effect. The temperature of the cancerous and healthy tissue is typically monitored with temperature probes inserted into catheters. MR thermometry with the proton resonance frequency method allows for a non-invasive temperature monitoring, and often conventional gradient echo techniques (FLASH) are used to measure the phase changes during heating. In this work, a double echo segmented EPI sequence (DEPI) for MR thermometry during hyperthermia was developed. The higher acquisition speed of DEPI can be exploited to localize unwanted thermal focal spots in the body of the patient, which can make the hyperthermia procedure safer and more reliable.

Florian Maier¹, Christopher J. MacLellan¹, Ken-Pin Hwang^1,2, David Fuentes¹, John D. Hazle¹, and R. Jason Stafford^1
1Department of Imaging Physics, The University of Texas M. D. Anderson Cancer Center, Houston, TX, United States, ²Global Applied Science Laboratory, GE Healthcare Technologies, Waukesha, WI, United States

Real-time multi-parametric MR temperature imaging using a multi-echo gradient-echo (MGE) can simultaneously provide temperature information from PRF as well as information on tissue damage. This work is focused on an extended MGE sequence. By using echo-shifting, higher spectral resolution data can be accumulated over multiple time points to provide higher resolution PRF and R2* measurements and un-aliasing capabilities along with dynamic PRF, R2* and T1 mapping for interventions.

Aliya Gifford^1,2, Theodore F Towse^1,3, Malcolm J Avison^1,4, and E Brian Welch^1,5
1Institute of Imaging Science, Vanderbilt University, Nashville, TN, United States, ²Chemical and Physical Biology Program, Vanderbilt University, Nashville, TN, United States, ³Department of Physical Medicine and Rehabilitation, Vanderbilt University, Nashville, TN, United States, ⁴Department of Pharmacology, Vanderbilt University, Nashville, TN, United States, ⁵Department of Radiology & Radiological Sciences, Vanderbilt University, Nashville, TN, United States

This work aims to apply a novel fat-water MRI (FWRMI)-based thermometry method to observations of both activated and non-activated brown adipose tissue (BAT) in adult human subjects, to demonstrate the method’s ability to distinguish between the two states of BAT. This FWMRI-based thermometry method explicitly models the frequency shift of the water peak due to temperature changes in regions with both fat and water, such as BAT. FWRMI and PET-CT scans were performed twice for each subject, after cold and warm exposure. FWMRI mFFE scans were able to detect temperature increase in BAT regions of subjects with PET-confirmed BAT activation.

Yuxin Hu¹, Feiyu Chen¹, Dan Zhu¹, Chenguang Peng², Shi Wang², and Kui Ying^2
1Department of Biomedical Engineering, Tsinghua University, Beijing, China, ²Department of Engineering Physics, Tsinghua University, Beijing, China

We validate the feasibility of currently-used parallel imaging methods (GRAPPA, SPIRiT and ESPIRiT) for the reconstruction of temperature maps using model-based PRF methods. All of GRAPPA, SPIRiT and ESPIRiT result in temperature errors lower than 2¡æ and ESPIRiT has the best temperature accuracy with a value of 1.55¡æ at a reduction factor of 4.

Feiyu Chen¹, Xinwei Shi², Shuo Chen³, Bingyao Chen⁴, Gang Ren⁴, Xing Wei⁴, Shi Wang³, and Kui Ying^3
1Center for Biomedical Imaging Research, Department of Biomedical Engineering, Tsinghua University, Beijing, China, ²Department of Electrical Engineering, Stanford University, Stanford, CA, United States, ³Department of Engineering Physics, Tsinghua University, Beijing, China, ⁴Department of Orthopedics, First Affiliated Hospital of PLA General Hospital, Beijing, China

In this research, we proposed an acceleration method for model-based PRF temperature mapping using Echo-based GRAPPA. The method can accelerate the MR temperature monitoring at a net reduction factor of 2.3. The temperature uncertainty and temperature RMSE is less than 1.4°C based on the ex-vivo goose liver experiment. This technique is also insensitive to inter-frame motion compared with other MR temperature measurement methods. When combined with other traditional methods, the combined method can measure the temperature of tissue with multiple composition.

Dengrong Jiang¹, Dan Zhu², Shuo Chen², Shuo Chen¹, and Kui Ying^1
1Engineering Physics, Tsinghua University, Beijing, Beijing, China, ²Biomedical Engineering, Tsinghua University, Beijing, Beijing, China

Goal of this work is to correct intra-frame motion induced errors in model-based MR temperature mapping. Model-based temperature mapping exploits multi-echo signal model to estimate temperature information, thus eliminates the effects of field drifting and inhomogeneity, and is robust to inter-frame motion. However, it is sensitive to intra-frame motion due to its relatively long acquisition time. We addressed this problem by incorporating motion models into multi-echo image reconstruction to compensate for motion induced phase distortions and image artifacts. A prototype framework of motion correction was proposed in this work, and simulations were performed to validate its efficiency.

Ron Instrella¹, Michael Marx¹, and Kim Butts Pauly^2
1Electrical Engineering, Stanford University, Stanford, CA, United States, ²Stanford University, Stanford, CA, United States

This study presents a simple, preliminary, real-time temperature processing method for determining pre-treatment baseline library size recommendations for Hybrid MB+R Thermometry. Temperature data collected from 3 volunteer brain scans are analyzed using the real-time method to produce recommendations that are consistent with retrospective analysis. If implemented clinically, this method shows promise as a practical approach to ensuring sufficient baselines are collected pre-treatment to improve temperature estimates, while minimizing the amount of time spent scanning.

Christiaan G. Overduin¹, Yi Sun¹, Tom W.J. Scheenen¹, and Jurgen J. Fütterer^1
1Radiology, Radboud University Medical Center, Nijmegen, Gelderland, Netherlands

Our study investigates the relation between MR signal intensity and tissue temperature using ultrashort TE imaging and demonstrates feasibility of a high-resolution MR temperature map of frozen tissue at 11.7T. For subzero temperatures, the signal decay is fitted by SI = 0.47e^0.04T+1.16e^0.24T. Mean temperature error of the fit is 3.9°C. Using the fit, SI values are converted to temperatures to construct temperature maps of the frozen tissue. MR thermometry of frozen tissue using signal intensity is feasible, allowing assessment of temperatures within the cryoablation iceball as low as -40°C. Further work into the accuracy and consistency of this method is required.

Henrik Odéen^1,2, Nick Todd¹, Chris Dillon³, Allison Payne¹, and Dennis L Parker^1
1Utah Center for Advanced Imaging Research, Department of Radiology, University of Utah, Salt Lake City, Utah, United States, ²Department of Physics and Astronomy, University of Utah, Salt Lake City, Utah, United States, ³Department of Bioengineering, University of Utah, Salt Lake City, Utah, United States

The effect of errors in the thermal properties (thermal conductivity and power density) in the previously described model predictive filtering (MPF) algorithm for reconstruction of magnetic resonance temperature change maps is investigated. Simulations and focused ultrasound heatings in ex-vivo pork muscle are performed, using a 3D segmented EPI pulse sequence. Effects of k-space reduction factor (ranging from 4 to 12) and temperature rise rates (ranging from 0.28 to 0.75 °C/s) on the temperature measurement accuracy are also investigated. Both simulations and experiments show that the accuracy decreases with increasing R and increasing temperature rise rates.

Roel Deckers¹, Baudouin Denis de Senneville^1,2, Gerald Schubert³, Laura G. Merckel¹, H. H.B. Vaessen⁴, Maurice A.A.J. van den Bosch¹, Chrit T.W. Moonen¹, and Lambertus W. Bartels^1
1Imaging Division, University Medical Center Utrecht, Utrecht, Utrecht, Netherlands, ²IMB, UMR 5251 CNRS/Université Bordeaux 1/INRIA, France, ³Philips Healthcare, Vantaa, Finland, ⁴Department of Anesthesia, University Medical Center Utrecht, Utrecht, Utrecht, Netherlands

When using PRFS-based MR thermometry for temperature monitoring respiration induced magnetic field fluctuations can cause significant temperature errors for organs close to the lungs such as the breast. Here we evaluate the performance of a LUT-based and a model-based correction method for MR thermometry in healthy free-breathing volunteers and in breast cancer patients under conscious sedation. Both methods showed significantly improved temperature precision compared to the uncorrected case for volunteers. In contrast, in patients both correction methods resulted only in minor or no improvement of the temperature precision. In conclusion, conscious sedation improved the quality of MR thermometry.

Pooja Gaur^1,2 and William A Grissom^2,3
1Chemical and Physical Biology, Vanderbilt University, Nashville, Tennessee, United States, ²Institute of Imaging Science, Vanderbilt University, Nashville, Tennessee, United States, ³Biomedical Engineering, Vanderbilt University, Nashville, Tennessee, United States

A temperature reconstruction algorithm that compensates for chemical-shift distortions that result from heating is presented for proton resonance frequency-shift thermometry. A hybrid multibaseline and referenceless temperature change model is fit directly to k-space data and iteratively updated to determine the heating-induced phase shift at the echo time while compensating for off-resonance phase accrual throughout the readout. The method is evaluated in simulation and phantom experiments. It is able to correctly reconstruct the simulated temperature and has a large impact on thermal dose measurements.