Viola Rieke¹, Beat Werner², Nathan McDannold³, William Grissom⁴, Ernst Martin², and Kim Butts Pauly^1
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.

Benjamin Marty¹, Benoit Larrat¹, Caroline Robic², Mathieu Pernot³, Mickael Tanter³, Marc Port², Philippe Robert², Denis Le Bihan¹, Franck Lethimonnier¹, and Sébastien Mériaux^1
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.

Gesthimani Samiotaki¹, Yao-Sheng Tung¹, Fotios Vlachos¹, and Elisa Konofagou^1,2
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.

Vincent Auboiroux¹, Magalie Viallon¹, Jean-Noël Hyacinthe¹, Joerg Roland², Lorena Petrusca¹, Thomas Goget¹, Patrick Gross², Christoph D. Becker¹, and Rares Salomir^1
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.

Andrew B. Holbrook^1,2, Charles L Dumoulin³, Juan M Santos⁴, Yoav Medan⁵, and Kim Butts Pauly^1
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.

Etsuko Kumamoto^1,2, Yoshie Takao³, Daisuke Kokuryo⁴, Toshiya Kaihara², and Kagayaki Kuroda^5,6
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 volunteers 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.

Antje Kickhefel¹, Christian Rosenberg^2,3, Joerg Roland⁴, Patrick Gross⁴, Fritz Schick⁵, Norbert Hosten², and Rares Salomir^6
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.

Kagayaki Kuroda^1,2, Mie Kee Lam³, Taku Iwabuchi¹, Makoto Obara⁴, Masatoshi Honda⁵, Kensuke Saito¹, and Yutaka Imai^5
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.

Markus Nikola Streicher¹, Andreas Schäfer¹, Dirk Müller¹, Carsten Kögler¹, Enrico Reimer¹, Bibek Dhital¹, Robert Trampel¹, Debra Rivera¹, André Pampel¹, Dimo Ivanov¹, and Robert Turner^1
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°.

Chang-Sheng Mei^1,2, Onur Afacan^2,3, Jing Yuan⁴, Bruno Madore², Lawrence Panych², and Nathan McDannold^2
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%.