MR-Guided Focused Ultrasound, Thermotheraphy & Thermometry
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Thursday May 12th
Room 511A-C  10:30 - 12:30 Moderators: Chrit Moonen and Rudolf Stollberger

10:30 521.   Hybrid referenceless and multi-baseline thermometry for MRgFUS brain applications 
Viola Rieke1, Beat Werner2, Nathan McDannold3, William Grissom4, Ernst Martin2, and Kim Butts Pauly1
1Department of Radiology, Stanford University, Stanford, CA, United States, 2MR-Center, University Children's Hospital Zurich, Zurich, Switzerland, 3Department of Radiology, Brigham and Women's Hospital, Boston, MA, United States, 4Imaging Technologies Laboratory, GE Global Research, Munich, Germany

Even in a non-moving organ such as the brain, temperature errors can be problematic when brain motion occurs. In this study, we investigate if reconstruction methods developed for moving organs can be beneficial for brain applications. We compared the methods in volunteers without heating and a patient undergoing MRgFUS ablation for neuropathic pain management. The results show that the combination of referenceless and multi-baseline thermometry into a hybrid image model accurately measures temperature in the brain with less artifacts and errors due to motion than single baseline subtraction.

10:42 522.   Dynamic study of tissue penetration for MR contrast agents of different sizes following ultrasound induced Blood Brain Barrier disruption in rodent models 
Benjamin Marty1, Benoit Larrat1, Caroline Robic2, Mathieu Pernot3, Mickael Tanter3, Marc Port2, Philippe Robert2, Denis Le Bihan1, Franck Lethimonnier1, and Sébastien Mériaux1
1CEA/DSV/I2BM/Neurospin, Gif-sur-Yvette, France, 2Research Division, Guerbet, Roissy Charles de Gaulle, France, 3Institut Langevin, Paris, France

Lately, many studies have shown the ability to disrupt transiently the Blood Brain Barrier using ultrasound sonication of intravascular microbubbles. However, BBB opening mechanism is not properly known, especially the maximum gap reachable in safe conditions. We used contrast agents of different size to study the closure mechanism of BBB and the maximum molecule size able to penetrate cerebral tissues. BBB opening was obtained in vivo for contrast agents of sizes up to 65nm and its closure exhibits a fast initial closure of largest gaps. Those findings are valuable information in the framework of high molecular weight drug delivery.

10:54 523.   Pressure and Microbubble-Size Dependence of the FUS-Induced Blood Brain Barrier Opening Reversibility In Vivo 
Gesthimani Samiotaki1, Yao-Sheng Tung1, Fotios Vlachos1, and Elisa Konofagou1,2
1Department of Biomedical Engineering, Columbia University, New York, NY, United States, 2Department of Radiology, Columbia University, New York, NY, United States

The purpose of this study was to use CE-T1 weighted MR imaging to evaluate the reversibility of focused ultrasound-induced blood-brain barrier opening in vivo, and its dependence on the acoustic pressures and microbubble sizes used. Duration and volume of the opening region were found to increase with pressure amplitude and microbubble diameter. The shortest opening duration was (24hours) at 1-2μm microbubbles and 0.45MPa, and the longest was (5 days) at 4-5μm and 6-8μm and 0.60MPa. In most cases no histological damage was noted, when it was, it was found to be highly correlated with residual gadodiamide in the opening area.

11:06 524.   ARFI-prepared MR-guided transcostal HIFU in sheep liver in vivo using a high resolution hybrid ARFI/MRT GRE-EPI sequence 
Vincent Auboiroux1, Magalie Viallon1, Jean-Noël Hyacinthe1, Joerg Roland2, Lorena Petrusca1, Thomas Goget1, Patrick Gross2, Christoph D. Becker1, and Rares Salomir1
1Radiology Dept, Geneva University Hospital, Geneva, Switzerland, 2Siemens Healthcare, Erlangen, Germany

High resolution Acoustic Radiation Force Imaging (voxel size: 1x1x5mm) was achieved in sheep liver in vivo using a respiratory triggered hybrid sequence (displacement and temperature sensitive). Accurate detection of HIFU focal point in situ by ARFI was used for the preparation of transcostal ablative HIFU treatment. Respiratory gated CW HIFU sonication induced a sharply localized thermal lesion. Ablated area was characterized by 7 days post-operative Gd-T1w MRI and post-mortem histology.

11:18 525.   Real Time Respiration Based Steering for High Intensity Focused Ultrasound in the Liver 
Andrew B. Holbrook1,2, Charles L Dumoulin3, Juan M Santos4, Yoav Medan5, and Kim Butts Pauly1
1Radiology, Stanford University, Stanford, CA, United States, 2Bioengineering, Stanford University, Stanford, CA, United States, 3University Cincinnati College of Medicine, Imaging Research Center, Cincinnati, OH, United States, 4HeartVista, Palo Alto, CA, United States, 5InSightec, Tirat Carmel, Israel

High Intensity Focused Ultrasound (HIFU) treatment of the liver during free breathing requires maintenance of the ultrasound focus on the desired target. We propose a model-based method utilizing a respiratory belt to provide the respiratory position, which is used to find the target and transducer positions from a lookup table acquired before treatment. The method was tested in a gel phantom moving back and forth over a fixed external transducer and compared to ablations without steering and ablations without motion. The steered ablation produced a much tighter focus compared to the one not steered.

11:30 526.   Three-Dimensional Motion Analysis of Hepatic Tissue for Focal Spot Tracking based on Portal Vain Structure 
Etsuko Kumamoto1,2, Yoshie Takao3, Daisuke Kokuryo4, Toshiya Kaihara2, and Kagayaki Kuroda5,6
1Information Science and Technology Center, Kobe University, Kobe, Japan, 2Graduate School of System Infomatics, Kobe University, Kobe, Japan, 3Graduate School of Engineering, Kobe University, Kobe, Japan, 4Molecular Imaging Center, National Institute of Radiological Sciences, Chiba, Japan, 5Graduate School of Engineering, Tokai University, Hiratsuka, Japan, 6Medical Device Development Center, Foundation for Biomedical Research and Innovation, Kobe, Japan

This study was performed to extend the two-dimensional target tracking technique for MRgFUS of liver to three-dimensional. To analyze translation and deformation of a portal vein tree induced by respiration, we acquired series of multi-slice balanced SSFP images in sagittal plane of a healthy volunteerprime or minutes liver. The rate of the translation and deformation were different by location of branching vessels. The deformation function of the respiratory phase was defined for estimating out-plane displacement. The experimental results demonstrated the three-dimensional translate and deformation of the hepatic tissue could be measured and the estimation method of out-plane displacement will be useful for the three-dimensional target tracking technique.

11:42 527.   Reference-less PRFS MR thermometry of the whole liver based on near-harmonic calculation: Clinical evaluation from LITT ablation data 
Antje Kickhefel1, Christian Rosenberg2,3, Joerg Roland4, Patrick Gross4, Fritz Schick5, Norbert Hosten2, and Rares Salomir6
1Diagnostic and Interventional Radiology, Eberhard-Karls-University Tübingen, Tübingen, Baden-Württemberg, Germany, 2Diagnostic Radiology and Neuroradiology, Ernst-Moritz-Arndt-Universität Greifswald, Greifswald, Germany, 3Diagnostic Radiology and Neuroradiology, Greifswald, Germany, 4Siemens Healthcare, Erlangen, Bavaria, Germany, 5Diagnostic and Interventional Radiology, Eberhard-Karls-University Tübingen, Tübingen, Baden-Würtemberg, Germany, 6Radiology, University Hospitals of Geneva, Geneva, Switzerland

A novel implementation of the reference-less PRFS method for MR thermometry is described here. The method is based on near-harmonic reconstruction of GRE 2D phase background and enables no-user-interaction temperature calculations over the whole liver. Alternatively, it may be used with an arbitrarily thin border (unheated). The current implementation offers high flexibility and robustness under clinical workflow. The actual reference-less calculations were compared to the standard time-referenced respiratory triggered MR thermometry, using clinical data from a liver LITT ablation protocol in 6 patients. The average precision of baseline measurements using the standard reference-method was 4°C, the reference-less calculation greatly improved this precision by reducing it to 0.5°C.

11:54 528.   Feasibility of Temperature Imaging of Fat and Water based on Methylene T1 and Water Proton Resonance Frequency 
Kagayaki Kuroda1,2, Mie Kee Lam3, Taku Iwabuchi1, Makoto Obara4, Masatoshi Honda5, Kensuke Saito1, and 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

Based on the temperature dependence of T1 of methylene (CH2) or methyl (CH3) protons, we have proposed a temperature imaging technique using multiple flip angle, multipoint Dixon acquisitions and a least square estimation. This technique can be combined with the water temperature imaging technique based on the proton resonance frequency (PRF) shift, because the intra-voxel signal fractions of water and fat protons can be obtained once the proton components are separated. In this paper, feasibility of such an integrated temperature imaging technique is demonstrated with phantom experiments at 3T.

12:06 529.   Frequency-selective asymmetric spin-echo EPI with parallel imaging for fast internally referenced MR Thermometry 
Markus Nikola Streicher1, Andreas Schäfer1, Dirk Müller1, Carsten Kögler1, Enrico Reimer1, Bibek Dhital1, Robert Trampel1, Debra Rivera1, André Pampel1, Dimo Ivanov1, and Robert Turner1
1Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany

The proton resonance frequency shift MR thermometry method is inherently very sensitive to magnetic field perturbations in time. We simulated and tested a new referenced spin-echo (SE) EPI sequence which solves these problems reliably, efficiently and quickly. Frequency-selectivity of the SE sequence is achieved by using different slice-select gradient amplitudes for excitation and refocusing, making it easy to image water and a reference substance separately. The sequence alternately images each species, and thereby allows fast voxel-wise correction for magnetic field changes in a working range of ±1ppm and excitation flip angles from 0° to 130°.

12:18 530.   Multi-shot high-speed 3D-EPI thermometry using a hybrid method combining 2DRF excitation, parallel imaging, and UNFOLD 
Chang-Sheng Mei1,2, Onur Afacan2,3, Jing Yuan4, Bruno Madore2, Lawrence Panych2, and Nathan McDannold2
1Physics, Boston College, Chestnut Hill, MA, United States, 2Radiology, Harvard Medical School, Brigham and Women's Hospital, Boston, MA, United States, 3ECE, NortheasternUniversity, Boston, MA, United States, 4The Chinese University of Hong Kong

High-speed MR thermometry has been achieved with many 2D sequences, such EPI, and spiral. 3D temperature mapping is needed for some clinical application, such as transcranial FUS treatment. A hybrid method combining 2DRF excitation, parallel imaging, and UNFOLD incorporated in a 3D EPI sequence is proposed. With only GRAPPA and UNFOLD, temporal resolution achieved 1 s for matrix size 64x64x50 with noise of 0.2¢XC during focused ultrasound sonication in a gel phantom. 2DRF was able to further reduce echo-train-length by 58%.