Junichi Tokuda¹, Kemal Tuncali¹, Gang Li², Nirav Patel², Tamas Heffter³, Gregory S Fischer², Iulian I Iordachita⁴, Everette Clif Burdette ³, Nobuhiko Hata¹, and Clare M Tempany^1
1Department of Radiology, Brigham and Women's Hospital, Boston, MA, United States, ²Department of Mechanical Engineering, Worcester Polytechnic Institute, Worcester, MA, United States, ³Acoustic MedSystems Inc., Savoy, IL, United States, ⁴Department Of Mechanical Engineering, Johns Hopkins University, Baltimore, MD, United States

We present the clinical feasibility of our MRI-compatible 4-DOF needle-guide manipulator for in-bore MRI-guided transperineal prostate biopsy. Total 11 men were biopsied in a 3T MRI scanner using this manipulator. All 11 procedures were successfully performed in 102.6±24.5 minutes with targeting errors of 4.9±2.9 mm. The targeting errors were consistent with other clinical studies. Pathology results confirmed prostate cancer with Gleason score ≥ 6 in 5/6 men with previous negative TRUS biopsies, and upgraded 2/5 men on active surveillance to clinically significant cancer with Gleason score 7. In conclusion, In-bore MRI-guided prostate biopsy using the manipulator was feasible.

Ravi Teja Seethamraju¹, Jayender Jagadeesan², Vera Kimbrell², Aida Faria², Thomas C Lee², and Daniel T Ruan^3
1MR R&D, Siemens Healthcare, Boston, MA, United States, ²Radiology, Brigham and Women's Hospital, Boston, MA, United States, ³Endocrine Surgery, Brigham and Women's Hospital, Boston, MA, United States

Diagnostic imaging of the recurrent laryngeal (RLN) and vagus nerves (VN) could help in surgical planning and in minimizing the risk of damage to the nerves. However, imaging these nerves is technically challenging due to their size, location, and physiological motions such as breathing and swallowing. The RLN and VN can be visualized on the CISS and T2 TSE, however with a novel phase navigator, the nerves are better delineated on the motion-compensated T2 TSE compared to the CISS which is un-navigated.

Carsten Stueber^1,2, Alexey Dimov¹, Kofi Deh¹, David Pitt², and Yi Wang^1
1Weill Cornell Medical College, New York, NY, United States, ²Yale School of Medicine, Yale University, New Haven, CT, United States

Quantitative susceptibility mapping (QSM) provides a quantitative MRI contrast, which reflects the local iron concentration. Thus, QSM allows to determine the geometries of iron-rich deep grey matter nuclei including substantia nigra (SN) and subthalamic nucleus (STN). These basal nuclei are of particular interest in Parkinson’s disease. However, the measured dimensions need to be validated in histology using post-mortem human brain tissue. In this work, we show the concordance of the geometries measured in QSM and histology using Perls’ iron stain, which opens the door to use QSM as a pre-surgical mapping for deep brain stimulation targeting the STN.

Ivan E Dimitrov^1,2 and Strahinja Stojadinovic^3
1Philips Medical Systems, Dallas, TX, United States, ²Advanced Imaging Research Center, UT Southwestern Medical Center, Dallas, TX, United States, ³Radiation Oncology, UT Southwestern Medical Center, Dallas, TX, United States

Radiation therapy aims to maximize dose delivery to tumor areas while minimizing the exposure to healthy tissue. Quality control is required to ensure that the delivered dose closely matches the calculated dose.   We performed a patient-specific quality assurance for cranial radiotherapy using MRI to visualize delivered radiation dose. We utilized an anthropomorphic 3D printed head phantom filled with polymer gel that was scanned before and after exposure to Gamma Knife irradiation. Irradiation changed the polymerization state of the gel and multi-parametric (T1, T2, MR Spectroscopy, CEST) quantitative dose-imaging maps were generated that may lead to optimized patient-specific dose delivery planning.

Heling Zhou¹, David Wilson², Jason Lickliter³, Jeremy Ruben⁴, Natarajan Raghunand⁵, Michael Sellenger⁶, Ralph P Mason⁷, and Evan Unger^2,8
1UT Southwestern Medical Center, Dallas, TX, United States, ²NuvOx Pharma, Tucson, AZ, United States, ³Nucleus Networks, Melbourne, Australia, ⁴William Buckland Radiotherapy Centre, Melbourne, Australia, ⁵Moffitt Cancer Center, Tampa, FL, United States, ⁶Alfred Hospital, Prahran, Australia, ⁷Radiology, UT Southwestern Medical Center, Dallas, TX, United States, ⁸Medical Imaging, The University of Arizona, Tucson, AZ, United States

Glioblastoma multiforme (GBM) is known to be a hypoxic tumor and hypoxia adversely affects response to radiation therapy. Dodecafluoropentane emulsion (DDFPe) can improve oxygenation. Tissue oxygen level dependent (TOLD) MRI is an oxygen sensitive imaging technique which is used in this study to assess the improvement of oxygenation after administration of DDFPe. Two different doses were tested and each showed decreased T₁ indicating improved oxygenation. 

Elena A Kaye¹, Kristin L Granlund², Stephen B Solomon², and Majid Maybody^2
1Medical Physics, Memorial Sloan Kettering Cancer Center, New York, NY, United States, ²Radiology, Memorial Sloan Kettering Cancer Center, New York, NY, United States

Acquisition of a viable tissue sample is critical to success of a biopsy. DWI could help differentiate between viable and necrotic tissue during the procedure, however, EPI-DWI is not suitable in a percutaneous-biopsy setting due to geometric distortions. DW Dual Echo Steady State (DESS) sequence allows acquisition of 3D undistorted DWI images. This study evaluated the application of DW-DESS during an MR-guided liver biopsy in two patients. Using single breath-hold acquisition, DW-DESS image depicted a liver lesion sharper and less distorted than EPI-DWI. DW-DESS also allowed DWI in the presence of a biopsy needle without distortions of EPI.  

Frank Preiswerk¹, Cheng-Chieh Cheng¹, Sanjay S. Yengul^1,2, Lawrence P. Panych¹, and Bruno Madore^1
1Radiology, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, United States, ²Mechanical Engineering, Boston University, Boston, MA, United States

MRI can provide favorable image quality for image-guided interventions, but both magnetic field of the scanner and limited patient access inside the bore impose many limitations on image-guidance endeavors. The aim of this work was to estimate MRI of respiratory organ motion outside the scanner, which allows for a wider range of interventional applications. A single-element ultrasound transducer was used as a surrogate for the MR scanner outside the bore, after the correlation between both signals had been learned in a preceding training phase. Validation of estimated MR images outside the bore was performed using tracked 2D ultrasound.

Samantha Mikaiel^1,2, Thomas Boyd Martin^1,2, Kyung Sung^1,2, and Holden H Wu^1,2
1Radiological Sciences, University of California, Los Angeles, Los Angeles, CA, United States, ²Biomedical Physics, University of California, Los Angeles, Los Angeles, CA, United States

Real-time visualization is crucial to the success of MRI-guided minimally invasive cancer interventions. In this work we combine iSSFP with a golden-angle(GA) ordered radial trajectory and non-Cartesian parallel imaging to create a new real-time MRI sequence with good tissue contrast while suppressing bSSFP banding artifacts. Phantom and volunteer data were acquired and reconstructed using a combined sliding-window SPIRiT algorithm, at different frame rates, showing the capability of the sequence to achieve real-time imaging.  These advantages of GA Radial iSSFP show its potential for improving real-time MRI-guided interventions.

Peter Andrew Hardy¹, Christopher J Norsigian², Walter Witschey³, and Luke H Bradley^2
1Radiology, University of Kentucky, Lexington, KY, United States, ²Anatomy & Neurobiology, University of Kentucky, Lexington, KY, United States, ³Smilow Center for Translational Research, University of Pennsylvania, Philadelphia, PA, United States

Developing tissue mimicking materials can be helpful in reducing the cost and duration of experiments which otherwise require animals. We tested a variety of agarose gels of different gel strength as suitable tissue mimicking material for convection enhanced delivery. The results demonstrate a significant difference in infusion volume and we relate that, through MR measurements, to the mechanical stiffness of the gels. 

Aapo Nummenmaa¹ and Matti Stenroos^2
1Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, MA, United States, ²Department of Neuroscience and Biomedical Engineering, Aalto University, Espoo, Finland

MRI-guided targeting and dosing has the potential increase the consistency and efficacy of transcranial magnetic stimulation (TMS). We propose a boundary element method (BEM) approach for estimating the TMS-induced cortical electric fields (E-fields). The method can be applied based on standard T1/T2-weighted MRI data and can incorporate the cerebrospinal fluid (CSF) as a separate conductivity compartment. Our results show that the CSF layer may increase the estimated E-field amplitudes up to 25%. The effect of the CSF depends on the location and orientation of the TMS coil/target in a rather intricate manner, highlighting the importance of individualized, realistically shaped models.

Katharina E. Schleicher¹, Stefan Kroboth¹, Klaus Düring², Michael Bock¹, and Axel Joachim Krafft^1,3,4
1Dept. of Radiology - Medical Physics, University Medical Center Freiburg, Freiburg, Germany, ²MaRVis Medical GmbH, Hannover, Germany, ³German Cancer Consortium (DKTK), Heidelberg, Germany,⁴German Cancer Research Center (DKFZ), Heidelberg, Germany

A simulation framework is presented to optimize radial acquisition schemes with variable echo times which are designed to minimize the directional anisotropy of the artifact of an MR-safe guidewire. The simulation results are compared to measurements. We could theoretically and experimentally verify that the homogeneity of the artifact can be improved via the variable-TE method.

Robert Darrow¹, Mauricio Castillo-Effen¹, Eric Fiveland¹, Elizabeth Morris², and Ileana Hancu^1
1GE Global Research Center, Niskayuna, NY, United States, ²Memorial Sloan Kettering Cancer Center, New York City, NY, United States

Tissue motion during MR guided interventional procedures leads to the desire to perform simultaneous high speed tracking of the surgical instrument and imaging. In this work, a novel approach for concurrent tracking and imaging, based on an inertial measurement unit (IMU) and technology from plane/missile tracking, is presented. While using infrequent position updates for the IMU (that could be provided by MR tracking), we have showed fast tracking (166Hz) of the IMU sensor with ~2mm rms error.

Francesco Padormo¹, Arian Beqiri¹, Joseph V Hajnal¹, and Shaihan Malik^1
1Division of Imaging Sciences and Biomedical Engineering, King's College London, London, United Kingdom

We propose a novel method to visualise guidewires in interventional MRI procedures using the coupling mode of a PTx array.

Ellis Beld ¹, Marinus A. Moerland¹, Frank Zijlstra², Jan J.W. Lagendijk¹, Max A. Viergever², and Peter R. Seevinck^2
1Department of Radiotherapy, UMC Utrecht, Utrecht, Netherlands, ²Image Sciences Institute, UMC Utrecht, Utrecht, Netherlands

In order to verify the positions of a high-dose-rate (HDR) brachytherapy source during treatment, fast imaging and post-processing are needed. To get high temporal resolutions, the use of lower spatial resolutions in combination with subpixel source localization and the use of parallel imaging were introduced. MR artifacts were simulated and correlated to the experimentally obtained artifacts (by phase-only cross correlation) to determine the position of the HDR source. It was shown that the described method was fast enough for localization of an HDR brachytherapy source in real-time and high accuracy and precision (submillimeter scale) were achieved. 

Allegra Conti^1,2, Rémi Magnin^1,3, Matthieu Gerstenmayer¹, François Lux⁴, Olivier Tillement⁴, Sébastien Mériaux ¹, Stefania Della Penna², Gian Luca Romani², Erik Dumont³, Denis Le Bihan¹, and Benoît Larrat^1
1CEA/DSV/I2BM/NeuroSpin, Gif Sur Yvette, France, ²Department of Neuroscience, Imaging and Clinical Sciences, G. D'Annunzio, University of Chieti and Pescara, Chieti, Italy, ³Image Guided Therapy, Pessac, France, ⁴Université Lyon 1, Lyon, France

We present here a new method to study the diffusion process of Gadolinium-based Contrast Agents within the brain extracellular space after the artificial Blood-Brain Barrier opening induced by ultrasound. Four compounds were tested (MultiHance, Gadovist, Dotarem and AGuIX). By estimating the Free Diffusion Coefficients from in vitro studies, and the Apparent Diffusion Coefficients from in vivo experiments, an evaluation of the tortuosity (λ) in the right striatum of 11 Sprague-Dawley rats has been performed. The values of λ are in agreement with literature and demonstrate that the chosen permeabilization protocol maintains the integrity of brain tissue.

HAO FU^1,2, Chenxia Li¹, Rong Wang¹, Jianxin Guo¹, Bilgin Keserci³, and Jian Yang^1
1Department of Radiology, the First Affiliated Hospital of Xi'an Jiaotong University, xi'an, China, People's Republic of, ²MR Marketing, Philips Healthcare, xi'an, China, People's Republic of, ³MR Therapy Clinical Science, Philips Healthcare, Seoul, Korea, Republic of

The aim of the study was to investigate the variation among screening fibroids through analysis of ADC histogram, in order to predict fibroids residual NPV proportion (residual NPV%=NPV at 6 months follow up/ NPV immediately after treatment ) and patients Symptom Severity Score (SSS). Thirty five patients who accepted MRgHIFU ablation were divided into group 1 (residual NPV%≥20%) of 19 patients and group 2 (residual NPV%<20%) of 16 patients, respectively. The SSS of patients were obtained at two time-point, screening and 6 months follow up. ADCmean, ADCq, kurtosis and skewness are derived from ADC histogram. The results showed that values of ADCmean, ADCq and kurtosis were significant difference between two groups. The average SSS reduction of group 1 between pre and post treatment was more obvious than that of group 2. Therefore, histogram analysis of ADC maps can provide the quantitative information to predict fibroids ablation outcome and patients symptom relief, which may be indicated as a useful screening tool to guide patients selection for MRgHIFU ablation.

Samantha Mikaiel^1,2, James Simonelli³, David Lu¹, Kyung Sung^1,2, Tsu-Chin Tsao³, and Holden H Wu^1,2
1Radiological Sciences, University of California, Los Angeles, Los Angeles, CA, United States, ²Biomedical Physics, University of California, Los Angeles, Los Angeles, CA, United States, ³Mechanical and Aerospace Engineering, University of California, Los Angeles, Los Angeles, CA, United States

In this work we investigate a new rolling-diaphragm-based hydrostatic actuator design to achieve smooth remote manipulation without fluid leakage for MR-compatible robotic systems. We show that the actuators exhibit negligible impact on MR image fidelity and SNR, the actuator provides a linear displacement response over the fluid lines, and we were able to use the master/slave actuator pair to insert and retract the needle in a phantom with no leakage and no noticeable friction issues. Our new rolling-diaphragm hydrostatic actuators can potentially enable physicians to remotely perform real-time MRI-guided interventions.

Matthew Alexander MacDonald^1,2, Adam C. Waspe^3,4, Joao Amaral^3,4, and Samuel Pichardo^1,2
1Electrical Engineering, Lakehead University, Thunder Bay, ON, Canada, ²Thunder Bay Regional Research Institute, Thunder Bay, ON, Canada, ³Medical Imaging, University of Toronto, Toronto, ON, Canada, ⁴Hospital for Sick Children, Toronto, ON, Canada

An experiment demonstrates a simple technique for a clinician operator to interactively align scan planes to an interventional device within the scan room during an MRI guided procedure. Input is collected using foot pedal switches to select axial/device intersection points to specify a virtual line of best fit about which auxiliary views are aligned automatically. Volunteer operators position a biopsy needle within an ex vivo porcine specimen while interactively tracking the needle position and measurements are taken to assess the technique's efficiency.

Han-Joong Kim¹, Jong-Min Kim¹, Young-Seung Jo^1,2, Suchit Kumar¹, Seong-Dae Hong¹, Chulhyun Lee², and Chang-Hyun Lee^1
1Electronics and Information Engineering, Korea University, Seoul, Korea, Republic of, ²The MRI Team, Korea Basic Science Institute, Cheongju, Korea, Republic of

  Many reports suggest that hyperthermia is very effective treatment for tumor therapy. In this work, MR compatible RF hyperthermia system is presented for a 3.0 T MRI. Phantom and animal experiments have been conducted and the results compared with the simulations results for tumor and tissue model. They are in very good coincidence with each other, which confirms the utility and feasibility of the MR compatible RF hyperthermia system with capacitive driving.  

Junmo An¹, Eftychios G. Christoforou², Karen Chin³, Jeremy Hinojosa³, Dipan J. Shah³, Andrew G. Webb⁴, and Nikolaos V. Tsekos^1
1University of Houston, Houston, TX, United States, ²University of Cyprus, Nicosia, Cyprus, ³Houston Methodist, Houston, TX, United States, ⁴Leiden University Medical Center, Leiden, Netherlands

Integrated control system of the manipulator and marker control is important for localization and tracking of multiple optically detunable MR markers on MR-compatible manipulators. Selecting which markers are visible on MR images by the motion of the maneuvering portion of the MR-compatible manipulators allows unambiguous identification of a combination of markers and simplifies both the data acquisition and the post processing. This proposed technique can be employed to track multiple marker positions on interventional devices such as the steerable catheters and the end-effectors of the MR-compatible manipulator.

Frank C Eibofner¹, Hansjörg Graf¹, and Petros Martirosian^1
1University Hospital Tübingen, Tübingen, Germany

A technique for the visualization of interventional devices by use of transient, local magnetic field alterations and bSSFP sequences is presented. It allows the generation of distinct artifacts with controllable dimension. The instrument is visualized in the phase image obtained in the same scan as the undisturbed anatomical image. Localization is done by subsequent superposition.

Samuel Pichardo^1,2, Charles Mougenot³, Steven Engler^1,4, Adam C. Waspe^5,6, and James Drake^5,6
1Thunder Bay Regional Research Institute, Thunder Bay, ON, Canada, ²Electrical Engineering, Lakehead University, Thunder Bay, ON, Canada, ³Philips Healthcare, Toronto, ON, Canada, ⁴Computer Science, Lakehead University, Thunder Bay, ON, Canada, ⁵University of Toronto, Toronto, ON, Canada, ⁶The Hospital For Sick Children, Toronto, ON, Canada

For dynamic studies, it is often desirable to adjust parameters in “real time” depending on decisions made by user-defined algorithms. We performed a modification to the software tool MatMRI to develop a method that allows changing on demand multiple MR sequence parameters. We present results of this new method when applied to the modification of sequence parameters for MR-Acoustic Radiation Force Imaging. Our results demonstrate that it is feasible to reprogram MR sequence parameters dynamically using existing technology for the control of scanners.

Sascha Krueger¹ and Tim Nielsen^1
1Philips GmbH, Innovative Technologies, Research Laboratories, Hamburg, Germany

4D image data are used in radiation therapy planning to estimate motion of the tumor or regions at risk. Today 4D CT is commonly used for this purpose. Due to better soft tissue contrast and quantitative and functional imaging, a clinical demand for MRI in therapy planning exists. Consequently, there is also a growing interest in 4D MRI techniques. A scan-time-efficient 4D MRI method utilizing the MRI Navigator as motion sensor with high geometric fidelity is proposed.

Juan C Camacho¹, Courtney Moreno¹, Peter Harri¹, and Pardeep Mittal^1
1Department of Radiology and Imaging Sciences, Emory University School of Medicine, Atlanta, GA, United States

Cholangiocarcinoma may demonstrate typical imaging manifestations and common patterns of organ involvement, guiding diagnosis, and facilitating imaging follow up after therapy. Adequate knowledge of tumoral biology in cholangiocarcinoma and current image-guided therapeutic approaches, along with imaging appearance of cholangiocarcinoma before and after image-guided interventions is crucial for adequate diagnosis and surveillance .MR imaging plays a key role for patient management, assessing therapy response and patient surveillance.

Chen-Hua Wu¹, Shih-Tsung Kang¹, Chih-Kuang Yeh¹, Wen-Shiang Chen², and Hsu-Hsia Peng^1
1Biomedical Engineering and Environmental Sciences, National Tsing Hua University, Hsinchu City, Taiwan, ²Physical Medicine and Rehabilitation, National Taiwan University Hospital, Taipei, Taiwan

This study aims to real-time monitor inertial cavitation on microbubbles (MBs) while transmitting focused ultrasound (FUS) with various duty cycle and pulse repetitive frequency (PRF) by gradient echo MRI. For in vitro experiments, with increasing duty cycle, more significant signal intensity (SI) changes or prolonged SI drop duration were shown. For in vivo experiment, two SI drop peaks were observed, reflecting the two IC events. In conclusion, FLASH has been proved to be a useful technique for real-time monitoring of IC when transmitting FUS pulses to MBs for in vitro and in vivo experiments.

Philippa Krahn^1,2, Haydar Celik³, Venkat Ramanan², Jennifer Barry², and Graham A Wright^1,2
1Medical Biophysics, University of Toronto, Toronto, ON, Canada, ²Physical Sciences, Sunnybrook Research Institute, Toronto, ON, Canada, ³Sheikh Zayed Institute for Pediatric Surgical Innovation, Washington, DC, United States

In this work we evaluated the quality and accuracy of myocardial RFA lesion visualization using the MCLE sequence. To compare MCLE to the standard LGE, we imaged 29 acute lesions in 11 pigs. Lesion sizes measured from each set of images were highly correlated, yet MCLE consistently achieved higher CNR than LGE. Our relaxometry maps from MCLE suggested a dramatic variation in T₁ after contrast injection, which will alter the optimal TI for LGE. Therefore, we demonstrated that MCLE, with the varied TIs in each acquisition, is a more robust sequence for visualizing even the most subtle lesions.

Yuval Zur^1
1GE Healthcare, Haifa, Israel

A time shifted Fast Spin Echo (FSE) thermometry sequence which is insensitive to B0 inhomogeneity is used in conjunction with restricted FOV module and parallel imaging to reduce scan time and increase the number of slices. Up to 5 slices are acquired in 3 sec. This sequence works well on a clinical Focused Ultrasound brain system. The temperature signal to noise ratio (TSNR) of this FSE sequence is approximately 2 times higher than the conventional Gradient Echo (GRE) sequence used today. 3 to 5 slices are acquired in 3 sec, rather than 1 slice with GRE.

Alexander Squires¹, Sheng Xu², Reza Seifabadi², Yue Chen¹, Harsh Agarwal³, Marcelino Bernardo², Ayele Negussie², Peter Pinto², Peter Chokye², Bradford Wood², and Zion Tsz Ho Tse^1
1College of Engineering, University of Georgia, Athens, GA, United States, ²National Institutes of Health, Bethesda, MD, United States, ³Philips Research North America, Briarcliff Manor, NY, United States

MRI-guided focal laser ablation (FLA) shows promise as an effective treatment for prostate cancer, but presents challenges related to accurate catheter positioning and ablation monitoring. A catheter positioning robot was designed to overcome these problems by positioning the catheter optimally for ablation and monitoring the ablation via MRI thermometry. A remote insertion guide allows the surgeon to perform the procedure without removing the patient from the MRI bore, saving time and increasing accuracy. Treatment planning software iteratively plans optimal catheter positioning. Preliminary tests show the robot can greatly improve efficiency and accuracy without sacrificing image quality.

Tetiana Dadakova¹, Axel Joachim Krafft^1,2,3, Jan Gerrit Korvink⁴, Stephan Meckel⁵, and Michael Bock^1
1Dept. of Radiology - Medical Physics, University Medical Center Freiburg, Freiburg, Germany, ²German Cancer Consortium (DKTK), Heidelberg, Germany, ³German Cancer Research Center (DKFZ), Heidelberg, Germany, ⁴Institute of Microstructure Technology, Karlsruhe Institute of Technology, Karlsruhe, Germany, ⁵Department of Neuroradiology, Neurocenter, University Medical Center Freiburg, Freiburg, Germany

Proton resonance frequency shift thermometry uses phase MR images to calculate temperature change in tissue during thermal therapies. Temporal and spatial changes of local magnetic field influence the phase images and can mimic temperature change. In order to correct for temperature errors due to magnetic field drift with time the FID navigators were used before and after imaging readout. Field-drift related phase slope during each repetition was calculated and used to correct the imaging data. This correction method is especially useful for the long thermometry procedures during which the temperature change is small and high temperature precision is needed.

Joyce GR Bomers¹, Christiaan G Overduin¹, Sjoerd FM Jenniskens¹, Michiel Sedelaar², and Jurgen J Futterer^1
1Radiology, Radboud University Medical Center, Nijmegen, Netherlands, ²Urology, Radboud University Medical Center, Nijmegen, Netherlands

Focal therapy offers great hopes in terms of cancer control and decreased morbidity (i.e. impotence and incontinence) for patients with localized for low- and intermediate grade prostate cancer (PCa). Transrectal MR-guided focal laser ablation of newly diagnosed PCa was successfully performed in 5 patients. It was technically feasible and safe. PSA level decreased in all patients and follow-up MRI showed no residual or recurrent cancer; indicating local cancer control, without compromising with increased morbidity or a decrease in quality of life. Initial results are promising and more patients have to be included with longer follow-up.

Eugene Ozhinsky¹, Vasant A. Salgaonkar², Chris J. Diederich², and Viola Rieke^1
1Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, CA, United States, ²Radiation Oncology, University of California San Francisco, San Francisco, CA, United States

We have developed and evaluated a real-time MR thermometry-guided system for acoustic power output and beam pattern control for prostate hyperthermia therapy. It was designed to be integrated with a commercial focused ultrasound ablation system and supports real-time ultrasound phase pattern switching and MR thermometry for monitoring and automated power adjustment.

Silke Lechner-Greite¹, Matthew Tarasek², Desmond Teck Beng Yeo², and Florian Wiesinger^1
1GE Global Research, Munich, Germany, ²GE Global Research, Albany, NY, United States

Monitoring temperature changes in the human skull is important in clinical transcranial MR-guided focused ultrasound, as it can absorb a large amount of energy during sonication and thereby produce heat. We propose to extract relative temperature information from proton density weighted zero TE imaging and additionally calibrate the T₁ signal contamination effect.

Cyril J Ferrer¹, Clemens Bos¹, Marijn van Stralen¹, Baudoin Denis de Senneville², Chrit T.W Moonen¹, and Lambertus W Bartels^1
1University Medical Center Utrecht, Utrecht, Netherlands, ²Mathematical Institute of Bordeaux, Talence, France

MR-guided High Intensity Focused Ultrasound has recently been suggested to provide non-invasive alternative treatment options for pancreatic cancer patients. To successfully apply PRFS MR Thermometry in the pancreas motion correction techniques have to be applied. For other moving organs, several solutions have already been proposed to this end: gating, multibaseline and referenceless. However, due to specific properties of the pancreas, there was still a need to evaluate the performance of these methods in this organ. Our results show that all the evaluated techniques improved thermometry in the pancreas to a level that is sufficient to monitor thermal ablation.

Michael Simonson¹, Peng Wang², Christopher Brace^1,2,3, and Walter Block^1,2,3
1Biomedical Engineering, UW - Madison, Madison, WI, United States, ²Radiology, UW - Madison, Madison, WI, United States, ³Medical Physics, UW - Madison, Madison, WI, United States

Monitoring microwave ablation with thermometry could extend the application of this clinical procedure into territories where greater control is necessary to protect healthy tissue, such as the spine. MRI thermometry could also provide useful insights to generate and validate new thermal models based on the fundamentally different mode of dielectric heating utilized by microwave ablation.  We present here a platform consisting of 1) a high power MR compatible microwave ablation system based on a FDA-approved design, 2) real-time applicator guidance during applicator insertion and 3) high frame rate MR thermometry and tissue monitoring.

Eugene Ozhinsky¹, Matthew D. Bucknor¹, and Viola Rieke^1
1Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, CA, United States

Current clinical protocols for bone treatments rely on measurement of the temperature change of adjacent muscle to estimate the temperature of the bone. In this study we have demonstrated for the first time that T2-based thermometry can be used in vivo to measure the heating in the marrow during bone ablation. The ability to monitor the temperature within the bone marrow allowed visualization of the heat penetration into the bone, which is important for local lesion control and treatment of osteoid osteomas.

Cheng-Tao Ho¹, Chen-Hua Wu¹, Shih-Tsung Kang¹, Chih-Kuang Yeh¹, Wen-Shiang Chen², Hau-Li Liu³, and Hsu-Hsia Peng^1
1Biomedical Engineering and Environmental Science, National Tsing Hua University, Hsinchu, Taiwan, ²Physical Medicine and Rehabilitation, National Taiwan University Hospital, Taipei, Taiwan,³Electrical Engineering, Chang-Gung University, Taoyuan, Taiwan

Gas-filled microbubbles (MBs) can be locally cavitated by spatially focused ultrasound (FUS) to trigger stable cavitation (SC) and inertial cavitation (IC) to induce blood–brain barrier (BBB) opening ; therefore, magnetic resonance imaging (MRI) may provide useful imaging information to real-time monitor the process of FUS cavitation on MBs. In this study, a HASTE (Half Fourier Acquisition Single Shot Turbo Spin Echo) sequence was used to observe the signal changes during SC for in vitro experiments. Experiments with different acoustic pressure, pulse repetitive frequency, and duty cycle were performed to clarify the SC effect on MR images.

Matthew Bucknor¹, Rutwik Shah¹, Eugene Ozhinsky¹, and Viola Rieke^1
1Radiology and Biomedical Imaging, University of California, San Francisco, San Francisco, CA, United States

One challenge in magnetic resonance guided focused ultrasound ablation of bone lesions is extending the ablation zone deep to the cortical surface in order to cover the full intramedullary extent of the lesion. Extension of the ablation zone is important for complete treatment of for example, osteoid osteomas, and improved local control of metastatic bone disease. This study used a swine model to compare differences in the depth of the ablation zone between two protocols using short versus longer sonications, respectively, while maintaining the same overall sonication energy (by adjusting acoustic power).

Zhe-Wei Wu¹, Wu Chen-Hua², Hsu Po-Hong³, Hao-Li Liu³, Yeh Chic-Kuang², and Peng Hsu-Hsia^2
1Biomedical Engineering and Environmental Sciences, Nation Tsing Hua University, Hsinchu, Taiwan, ²Biomedical Engineering and Environmental Sciences, National Tsing Hua University, Hsinchu, Taiwan,³Electrical Engineering, Chang-Gung University, Taoyuan, Taiwan

The aim of this study was to real-time assess flow velocity changes in the neighboring pixels of acoustic radiation force (ARF) aggregated bubbles by using phase-contrast MRI (PC-MRI). The flow velocity increased with the increase of microbubbles (MBs) concentrations, which might be attributed to the increase of aggregated bubbles size, narrowing the chamber diameter and thus presenting higher flow velocity. In conclusion, we verified the feasibility of using PC-MRI to assess flow velocity changes on pixels near ARF aggregated bubbles. In the future, a systematic investigation shall be conducted to comprehend the association between bubble size and the flow velocity.  

Jaya Prakash¹, Nick Todd², and Phaneendra K Yalavarthy^3
1Institute for Biological and Medical Imaging, Helmholtz Zentrum Munich, Munich, Germany, ²Wellcome Trust Centre for Neuroimaging, UCL Institute of Neurology, University College London, London, United Kingdom, ³Supercomputer Education and Research Centre, Indian Institute of Science, Bangalore, India

Prior image based temporally constrained reconstruction (PITCR) algorithm was found to obtain accurate temperature maps with better volume coverage, and spatial, and temporal resolution than other algorithms using highly undersampled data in magnetic resonance (MR) thermometry. PITCR method is compared with the standard temporally constrained reconstruction (TCR) algorithm using ex-vivo pork muscle sample. It was seen that the PITCR method showed superior performance compared to the TCR approach with highly undersampled datasets. 

Tetiana Dadakova¹, Ali Caglar Özen¹, Axel Joachim Krafft^1,2,3, Jan Gerrit Korvink⁴, and Michael Bock^1
1Dept. of Radiology - Medical Physics, University Medical Center Freiburg, Freiburg, Germany, ²German Cancer Consortium (DKTK), Heidelberg, Germany, ³German Cancer Research Center (DKFZ), Heidelberg, Germany, ⁴Institute of Microstructure Technology, Karlsruhe Institute of Technology, Karlsruhe, Germany

MR-guided acoustic radiation force imaging (ARFI) is used for the focal spot localization during high intensity focused ultrasound (HIFU) therapies. The acoustic radiation force related tissue displacement is measured with help of motion encoding gradients (MEG). While MEGs are sensitive enough to detect micrometer-scale displacement, the images acquired using MR-ARFI pulse sequences are often corrupted with artifacts. The method described uses very short FID navigator readout for correction of ARFI images without any manual interaction. ARFI displacement maps corrected by FID navigator have substantially less artifacts, 2.5 times higher SNR, and clearly visible HIFU focal spot.

Pejman Ghanouni¹, Sirish Kishore¹, Matthew Lungren¹, David Mohler², Raffi Avedian², and David Hovsepian^1
1Radiology, Stanford University, Stanford, CA, United States, ²Orthopaedic Surgery, Stanford University, Stanford, CA, United States

Low flow vascular malformations are typically treated with ultrasound-guided percutaneous sclerotherapy, but not all of these lesions are visible sonographically. MR guided focused ultrasound (MRgFUS) combines the ability of MRI to delineate these tumors with the use of FUS to ablate the tumor non-invasively. We report our technical and clinical results after using MRgFUS to treat four patients with small intramuscular low flow vascular malformations in the lower extremities. 

Valéry Ozenne¹, Solenn Toupin^1,2, Pierre Bour¹, Baudouin Denis de Senneville³, Alexis Vaussy², Matthieu Matthieu Lepetit-Coiffé², Pierre Jaïs^1,4, Hubert Cochet^1,4, and Bruno Quesson^1
1Institut Hospitalier Universitaire : LIRYC Institut de Rythmologie et Modélisation Cardiaque, Bordeaux, France, ²Siemens France, Saint Denis, France, ³Mathematical Institute of Bordeaux, Bordeaux, France, ⁴Centre Hospitalier Universitaire de Bordeaux, Bordeaux, France

Catheter ablation using radiofrequency is commonly used to treat cardiac arrhythmia. However, direct assessment of lesion formation with MRI thermometry during RF delivery may improve safety and efficiency of the therapeutic procedure. Despite recent studies demonstrating the feasibility on volunteers or animal models, there are no reports regarding the possibility of doing cardiac thermometry on patient in the context of arrhythmias. The purpose of the present study was to evaluate the uncertainty of temperature estimate on patients depicting potential arrhythmic episodes, which may alter the precision of the method relying on an ECG-triggered acquisition.

Pim Borman¹, Clemens Bos², Sjoerd Crijns¹, Bas Raaymakers¹, and Chrit Moonen^2
1Radiotherapy, UMC Utrecht, Utrecht, Netherlands, ²Imaging Division, UMC Utrecht, Utrecht, Netherlands

PRFS thermometry is important for guidance of thermal therapies. Here we show that the thermometry sequence can be accelerated by the novel parallel imaging technique SMS-CAIPIRINHA and we compare it to an unaccelerated sequence and a SENSE accelerated sequence. Heating was applied by means of HIFU and LITT. A good agreement was seen between temperature curves from SMS-CAIPIRINHA and those from the unaccelerated sequence. Furthermore, the noise level was significantly lower compared to temperature curves from the SENSE accelerated sequence.

Frank Zijlstra¹, Job G Bouwman¹, Marinus A Moerland², and Peter R Seevinck^1
1Image Sciences Institute, UMC Utrecht, Utrecht, Netherlands, ²Department of Radiotherapy, UMC Utrecht, Utrecht, Netherlands

We present a method which can accurately localize brachytherapy seeds in MRI using fast MR simulations and template matching. In 5 patients we correctly detected and localized 298 out of 307 seeds. Using this method an MRI-only approach to post-implant dosimetry will be possible, which should increase accuracy by not requiring CT to MRI image registration.

Samuel Fielden¹, Matthew Geeslin², Xue Feng¹, Wilson Miller², Kim Butts Pauly³, and Craig Meyer^1,2
1Biomedical Engineering, University of Virginia, Charlottesville, VA, United States, ²Radiology & Medical Imaging, University of Virginia, Charlottesville, VA, United States, ³Radiology, Stanford University, Palo Alto, CA, United States

A rapid volumetric MR thermometry sequence, using a stack-of-spirals acquisition, was implemented on a real-time platform in order to support animal model experiments. The performance of the sequence, as measured by the maximum and mean recorded temperature as well as the sequence accuracy, was assessed against a clinically used 2DFT sequence in vivo. The use of efficient spiral trajectories supports rapid generation of volumetric thermometry maps and allows the visualization of the entire insonication as well as correlation with post-ablation imaging of lesion size and location.

Steffen Weiss¹, Jochen Keupp¹, and Edwin Heijman^2
1Tomographic Imaging, Philips Research, Hamburg, Germany, ²Oncology Solutions, Philips Research, Eindhoven, Netherlands

MR-HIFU therapies require stable PRFS-based temperature monitoring over the treatment duration (>30min). Drift effects may be corrected using independent temperature information e.g. based on T2 or T1 maps and simultaneously obtained using fast interleaved sequences. As interleaves may impact PRFS-accuracy, a dynamic on-off-interleaved sequence pattern is introduced to selectively measure their influence on the PRFS phase. The mechanism of the phase variations is explored using multiple variants of the interleaved sequence. It is shown that eddy currents induced during the interleaved sequences represent the main cause of the phase variation. The spatio-temporal characteristics of the effect are explored as a first step towards compensation.

Valery Ozenne¹, Thibaud Troadec¹, Pierre Bour¹, Solenn Toupin^1,2, Erik Dumont³, and Bruno Quesson^1
1Institut Hospitalier Universitaire : LIRYC Institut de Rythmologie et Modélisation Cardiaque, Bordeaux, France, ²Siemens France, Saint Denis, France, ³Image Guided Therapy, Bordeaux, France

Although catheter-based radiofrequency (RF) ablation is increasingly used to treat cardiac arrhythmia, insufficient temperature increase may lead to incomplete treatment whereas excessive local energy deposition may result in severe adverse effects (e.g. esophageal fistulas or tamponade due to steam pop). Since MR thermometry can monitor in real-time the temperature distribution in the cardiac muscle, automatic regulation of RF energy deposition from temperature images, using well established proportional, integral controller algorithms, may improve safety and efficiency of the therapeutic procedure.

Pejman Ghanouni¹, Sirish Kishore¹, David Mohler², Matthew Lungren¹, Raffi Avedian², and Nishita Kothary^1
1Radiology, Stanford University, Stanford, CA, United States, ²Orthopaedic Surgery, Stanford University, Stanford, CA, United States

Osteoid osteoma is currently most frequently treated with CT guided radiofrequency ablation (CTgRFA), which is effective, but invasive and exposes the typical young patient population with osteoid osteomas to radiation. Our preliminary results are presented describing MR guided focused ultrasound (MRgFUS) for the treatment of patients with osteoid osteomas. As also reported in two European studies, in our experience, MRgFUS is effective at eliminating pain in these patients. These data form the basis for a proposed clinical trial directly comparing the safety and efficacy of MRgFUS and CTgRFA for treatment of osteoid osteoma.