Electronic poster

Thursday 13:30-15:30 Computer 63

13:30 4116. Direct Comparison of Dynamic Susceptibility Weighted MR Perfusion with CT Perfusion in Brain Tumors

Hassan Bagher-Ebadian^1,2, Jayant Narang³, James Russel Ewing¹, Siamak Pourabdollah Nejad-Davarani^1,4, Mohammad Hossein Asgari¹, Sona Saksena³, Rajan Jain<sup>3

1</sup>Neurology, Henry Ford Hospital, Detroit, MI, United States; ²Physics, Oakland University, Rochester, MI, United States; ³Radiology, Henry Ford Hospital, Detroit, MI, United States; ⁴Biomedical Engineering, University of Michigan, Ann Arbor, MI, United States

The purpose of this study is comparison of Dynamic susceptibility contrast enhanced MR perfusion (DSC-MRP) and CT Perfusion (CTP) in brain tumors patients in normal as well as abnormal regions. CTP maps were calculated using the Johnson and Wilson Model and DSC-MRP maps were calculated based on conventional singular value decomposition (SVD) technique. The results imply that there is underestimation of all perfusion parameters by SVD technique as compared to CTP mostly due to the fact that DSC-MRP only measures CBV from the microvasculature as well as due to the non-linearity of arterial input function with Contrast Agent (CA) concentration.

14:00 4117. Measuring CBV by the Recirculation Part of Dynamic Susceptibility Contrast MRI on Rat Model

Yi-Ling Wu¹, Chien-Chung Chen¹, Yi-Chun Wu¹, Chia-Hao Chang¹, Fu-Nien Wang<sup>1

1</sup>Biomedical Engineering and Environmental Sciences, National Tsing Hua University, Hsin-Chu, Taiwan, Taiwan

Measuring Relative CBV from the recirculation part of concentration time curve is investigated on rat model. Since the first pass of DSC method is relative fast on rat, more data points could be recruited for CBV quantification in the recirculation part. The results showed better regression lines between MION CBV and recirculation CBV, and therefore the feasibility is proved in this study.

14:30 4118. Quantification of Systematic Error in Standard Formula for Computing Transverse Relaxation Rates in DSC–MRI. Implications for Blood Volume and Flow Calculations

José Rufino Solera Ureña¹, Salvador Olmos<sup>1

1</sup>Aragon Institute of Engineering Research, Universidad de Zaragoza, Zaragoza, Spain

In dynamic susceptibility contrast (DSC) MRI experiments, the increase in the tissue transverse relaxation rate due to the passage of a bolus of intravascular paramagnetic contrast agent is routinely calculated (up to a constant) as the logarithm of the tracer dependent MR intensity normalised to baseline intensity, assuming that T1 effects are negligible. This assumption is revisited by developing the enhancement condition for a typical GE pulse sequence and the associated enhancement angle. The systematic error associated with the usual formula is analysed. Error expressions for the blood volume and flow calculations in DSC–MRI experiments are also presented and their implications discussed.

15:00 4119. Comparison of Four Techniques That Directly Use Residue Function Characteristics When Estimating Cerebral Blood Flow During DSC MRI Studies

Michael R. Smith^1,2, Juan Qiao¹, Marina Saluzzi^1,3, Richard Frayne, <sup>1,3

1</sup>Electrical and Computer Engineering, University of Calgary, Calgary, Alberta, Canada; ²Radiology, University of Calgary, Calgary, Alberta, Canada; ³Seaman Family MR Research Centre, Foothills Hospital, Calgary, Alberta, Canada

Current filtering techniques used in dynamic susceptibility contrast (DSC) studies to remove deconvolution noise are based on characteristics of the arterial signal C_a (t) and lead to CBF maps that decrease in accuracy as the tissue mean transit time (MTT) gets smaller. Our hypothesis is that greater CBF accuracy and CBF precision can be achieved by using techniques based on characteristics of the residue function; either in the time domain R(t) or in the frequency domain R(f). Of the four techniques investigated, one approach shows the most promise. This technique uses multiple points along the tissue residue function in time and frequency domains to obtain MTT estimates, and then derives CBF using CBF = CBV / MTT where CBV is the cerebral blood volume.

MR-Guided Focused Ultrasound

Hall B Monday 14:00-16:00 Computer 64

14:00 4120. Multislice Treatment Planning and Control for Real Time MR-Guided Prostate Ablation with Transurethral Multisectored Ultrasound Applicators

Andrew B. Holbrook^1,2, Punit Prakash³, Peter Jones³, Catherine Planey², Juan M. Santos^4,5, Chris J. Diederich³, Kim Butts Pauly², F. Graham Sommer<sup>2

1</sup>Bioengineering, Stanford University, Stanford, CA, United States; ²Radiology, Stanford University, Stanford, CA, United States; ³Radiation Oncology, UCSF, San Francisco, CA, United States; ⁴HeartVista, Los Altos, CA, United States; ⁵Electrical Engineering, Stanford University, Stanford, CA, United States

Targeted prostate ablation with transurethral multisectored ultrasound applicators could be improved with an integrated imaging platform that minimizes procedural setup and treatment time. The purpose of this work was to integrate device localization, prostate-specific planning tools, and multi-slice MR thermometry into a single imaging platform. Various phantom experiments were performed to validate each of these steps. Device localization and MR tracking was validated in a phantom, and an ablation was performed in another phantom with multi-slice thermometry and ROI feedback. The platform successfully measured temperature rises and relayed that data to external power control software that regulated the ablation.

14:30 4121. Towards Real-Time Tracking of Anatomic Features for HIFU Beam Steering

David A. Hormuth^1,2, Brian J. Zappia², Andrew B. Holbrook³, Kim Butts-Pauly³, Charles L. Dumoulin<sup>2

1</sup>Biomedical Engineering, Rose Hulman Institute of Technology, Terre Haute, IN, United States; ²Imaging Research Center, Cincinnati Children's Hospital Medical Center, Cincinnati, OH, United States; ³Radiology, Stanford University, Stanford, CA, United States

Software for identifying and following anatomic features during real-time imaging was developed. This software was tested in real-time images of the liver during free breathing. It was able to successfully locate and follow the diaphragm and selected blood vessels within the liver during free breathing. These feature locations were used to generate the coordinates of an arbitrary target within the liver with sufficient speed and robustness to provide real-time offsets to a HIFU beam. It is anticipated that these algorithms will permit real-time ablation of liver lesions using HIFU during free-breathing and overcome the difficulties associated with breath held approaches.

15:00 4122. MRI-Based Temperature Analysis of Transcranial MRI-Guided Focused Ultrasound Surgery for Functional Neurosurgery

Nathan McDannold¹, Beat Werner², Daniel Jeanmonod³, Eyal Zadicario⁴, Rita Schmidt⁴, Ernst Martin<sup>2

1</sup>Radiology, Brigham & Women's Hospital/Harvard Medical School, Boston, MA, United States; ²MR-Center, University Children’s Hospital Zurich, Zurich, Switzerland; ³Department of Functional Neurosurgery, University Hospital Zurich, Zurich, Switzerland; ⁴InSightec, Ltd., Tirat Carmel, Israel

This work used MR temperature imaging (MRTI) to evaluate focal and skull-induced heating in nine patients treated for neuropathic pain in order to characterize the safety profile of a Transcranial MRI-guided Focused Ultrasound system. The ratio between focal and skull-induced heating was 11.3 using a conservative approach, approximately 2.7 times higher than in previous tests of an earlier ver-sion in glioblastoma patients, presumably due to improvements in the system, MRTI, and differences in target location. These results suggest an improved treatment window that can potentially increase the volume of the brain that can be safely targeted by the system.

15:30 4123. Focal Spot Visualization in MRgFUS of the Breast: MR-ARFI Vs. T1-Weighted FSE

Elena Kaye^1,2, Rachel Rinat Bitton¹, Kim Butts Pauly<sup>1

1</sup>Radiology, Stanford University, Palo Alto, CA, United States; ²Electrical Engineering, Stanford University, Palo Alto, CA, United States

The goal of this study was to compare MR-ARFI and T1-w FSE approaches to focal spot visualization during breast MRgFUS. An ex vivo human breast tissue sample was imaged on a 3T MRI scanner equipped with an InSightec HIFU system. MR-ARFI displacement were compared with the magnitude difference images obtained by subtraction of FSE images with ultrasound on and off. The results of the study showed that both T1-w imaging and MR-ARFI allow visualization of the FUS focal spot., however, the MR-ARFI approach deposits 10 times less ultrasound energy and gives 3 times greater SNR than an FSE-based approach.

Tuesday 13:30-15:30 Computer 64

13:30 4124. Integrated MRI and HIFU Control System: Towards Real Time Treatment of the Liver

Andrew B. Holbrook^1,2, Chuck L. Dumoulin³, Juan M. Santos^4,5, Yoav Medan⁶, Kim Butts Pauly<sup>2

1</sup>Bioengineering, Stanford University, Stanford, CA, United States; ²Radiology, Stanford University, Stanford, CA, United States; ³Imaging Research Center, University of Cincinnati College of Medicine, Cincinnati, OH, United States; ⁴HeartVista, Los Altos, CA, United States; ⁵Electrical Engineering, Stanford University, Stanford, CA, United States; ⁶InSightec Ltd, Tirat Carmel, Israel

We have developed an integrated MRI and high intensity focused ultrasound (HIFU) real time system. The system allows for both flexible control and monitoring of both systems, from device localization utilizing MR tracking to treatment planning and therapy monitoring utilizing MR thermometry pulse sequences. Additionally, the software allows for prescription of complex sonication spots, including treatment paths and regions. The system was tested both in a phantom and in vivo to assess its effectiveness in guiding HIFU therapy. Prescribed treatment plans were achieved in both experiments.

14:00 4125. In Vivo Characterization of Tissue Thermal Properties of the Kidney by HIFU Local Hyperthermia Under MR-Thermometry with Modulation of the Arterial Flow

François Cornelis^1,2, Nicolas Grenier^1,2, Chrit Moonen¹, Bruno Quesson<sup>1

1</sup>UMR 5231, Laboratory for molecular and functional imaging, CNRS/ Université Bordeaux 2, Bordeaux, France; ²Radiology Department, CHU de Bordeaux, Bordeaux, France

The purpose was to evaluate in vivo quantitatively the tissue thermal properties (perfusion, absorption, thermal diffusivity). A total of 42 localized HIFU heating were performed in the kidney of 6 pigs monitored by MR thermometry. Arterial flow was modulated by an angioplasty balloon in the aorta. The resulting temperature data were analyzed with the Bio Heat Transfer model and an excellent correspondence was observed. Absorption and thermal diffusivity were found independent from the flow, whereas perfusion was directly linked to arterial flow. This method could improve the quality of the planning of the non invasive therapy with MR guided HIFU.

14:30 4126. Mechanical Focal Spot Scanning with a Robotic Assistance System for MRgFUS Therapy

Axel Joachim Krafft¹, Jürgen Walter Jenne^2,3, Florian Maier¹, Peter E. Huber³, Wolfhard Semmler¹, Michael Bock<sup>1

1</sup>Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany; ²Mediri GmbH, Heidelberg, Germany; ³Clinical Cooperation Unit Radiation Oncology, German Cancer Research Center (DKFZ), Heidelberg, Germany

Magnetic Resonance imaging guided Focus Ultrasound Surgery (MRgFUS) is a highly precise method for non-invasive tissue ablation. Existing MRgFUS systems are mostly integrated into the patient table of the MR scanner. The objective of this ongoing project is to establish an MRgFUS therapy unit combining a commercial robotic assistance system with a fixed focus transducer as add-on. The combined system’s targeting precision was evaluated during focal spot scanning procedures. The system proved to allow for accurate and highly flexible focus positioning, and thus, might enable novel FUS treatment access.

15:00 4127. Navigator Based FUS Transducer Tracking Without the Micro-RF Coil Setup

Naveen Bajaj<sup>1

1</sup>GE Healthcare, Bangalore, Karnataka, India

Focused ultrasound transducer tracking is of great significance in various new Magnetic Resonance guided Focused Ultrasound (MRgFUS) applications like in pain palliation of bone metastases and prostate tumor treatment. In this work, a navigator based novel method is described to demonstrate the feasibility of transducer tracking without the micro RF-coil setup. The algorithm is verified experimentally and provides highly accurate estimates, thereby making it suitable for the new applications. A novel tracking pulse sequence is also developed for the same, which is interleaved within the main thermal imaging pulse sequence.

Wednesday 13:30-15:30 Computer 64

13:30 4128. Effect of Water Resonance Thermal Shift on Methylene T1 Estimation with Multiple Flip Angle Multipoint Dixon Technique for Fat Temperature Imaging

Mie Kee Lam^1,2, Taku Iwabuchi¹, Kensuke Saito¹, Kagayaki Kuroda<sup>3,4

1</sup>School of Engineering, Tokai University, Hiratsuka, Kanagawa, Japan; ²Image Sciences Institute, University Medical Center Utrecht, Utrecht, Netherlands; ³Graduate School of Engineering, Tokai University, Hiratsuka, Kanagawa, Japan; ⁴Medical Device Development Center, Foundation for Biomedical Research and Innovation, Kobe, Hyogo, Japan

Numerical simulations were performed to investigate the effect of thermal shift of water proton resonance on the accuracy of methylene T1 estimation for fat temperature quantification with multiple flip angle, multipoint Dixon acquisitions and a least square estimation scheme. The performance of separating methylene and methyl, and estimating T1's of those species were successful as far as the frequency separations between those species and water was exact. The results with incomplete setting of the frequency separations showed that the error in methylene T1 would be controlled and an accuracy of ±4°C can be achieved by adjusting the separation within an error of ±0.05 ppm.

14:00 4129. MR Guidance, Monitoring and Control of Brain Focused Ultrasound Therapy: In Vivo Demonstration in
Rats at 7T

Benoit Larrat¹, Mathieu Pernot¹, Elvis Dervishi², Danielle Seilhean², Yannick Marie², Anne-Laure Boch², Jean-François Aubry¹, Mathias Fink¹, Mickael Tanter<sup>1

1</sup>ESPCI Paristech - Institut Langevin, CNRS UMR 7587, Paris, France; ²Hôpital de la Pitié Salpêtrière

A complete therapeutic workflow is developed to induce necrosis in the rat brain using a focused ultrasonic transducer under the guidance and monitoring of a 7T MR system. Three sequences are combined to monitor the procedure at different steps. Before the treatment, acoustic radiation force imaging shows the ability to accurately locate the focal spot in vivo. Furthermore, the MR signal is shown to provide a reliable quantification of the maximum acoustic pressure in situ. Then, the heating step is followed up via MR-thermometry. Finally, MR-Elastography.is evaluated as a tool to assess necrosis. 15 rats with and without injected tumors are treated. Induced lesions are confirmed at histology.

14:30 4130. Polyethylene Glycol (PEG) Labeled Liposomal Drug Delivery Systems as a Source for Dynamic Absolute MR Thermometry

Roel Deckers¹, Sara M. Sprinkhuizen¹, Bart J. Crielaard², J H. Ippel³, R Boelens³, Twan Lammers^2,4, C. J. Bakker¹, L W. Bartels<sup>1

1</sup>Image Sciences Institute, University Medical Center Utrecht, Utrecht, Netherlands; ²Department of Pharmaceutics, Utrecht University, Utrecht, Netherlands; ³Department of NMR Spectroscopy, Bijvoet Center for Biomolecular Research, Utrecht University, Utrecht, Netherlands; ⁴Department of Experimental Molecular Imaging, RWTH Aachen, Aachen, Germany

Dynamic absolute MR thermometry may be of great interest for the precise and accurate spatio-temporal control of hyperthermia in local drug delivery applications using MR guided HIFU. In this study we evaluate the use an mFFE sequence in combination with polyethylene glycol (PEG) labeled liposomes for dynamic absolute MR thermometry. PEG provides a temperature insensitive proton resonance frequency (PRF) that can serve as reference for the temperature sensitive PRF of water. The frequency difference between the PRFs of PEG and water, and thus the absolute temperature, can be deduced from the signal evolution in time over 32 echoes acquired with the mFFE sequence.

15:00 4131. Volumetric Ablation of Tissue Using Magnetic Resonance Imaging Guided High Intensity Focused Ultrasound (MRgFUS) with Feedback Control and Multi-Slice Thermal Monitoring: Initial Experience in a Pig Model

Jiming Zhang¹, Ann Marie Marciel², Tiina Karjalainen³, Ari Partanen⁴, Charles Mougenot, Amol Pednekar³, Gil Costas⁵, Jesse Rios⁵, Fredd Clubb⁵, John Fischer², Robert Zurawin⁶, Pei Hor¹, Raja Muthupillai<sup>2

1</sup>Dept of Physics, University of Houston, Houston, TX, United States; ²Diagnostic and Interventional Radiology, St. Luke's Episcopal Hospital, Houston, TX, United States; ³Clinical Science, Philips Medical Systems, Cleveland, OH, United States; ⁴Clinical Science, Philips Healthcare, Cleveland, OH, United States; ⁵Texas Heart Institute; ⁶Baylor College of Medicine

Preliminary results from a pig model suggest that it is feasible to create volumetric thermal lesions within in-vivo tissue using dynamic movement of the focal point of a High-Intensity Focused Ultasound beam with real-time multi-slice monitoring, and feedback control. The measured thermal dose diameters and lengths correspond closely with planned dose diameters for treatment cell sizes ranging from 4-16 mm in diameter.

Thursday 13:30-15:30 Computer 64

13:30 4132. SNR Trade-Offs in MR-ARFI of Focused Ultrasound in the Brain

Elena Kaye^1,2, Kim Butts Pauly<sup>1

1</sup>Radiology, Stanford University, Palo Alto, CA, United States; ²Electrical Engineering, Stanford University, Palo Alto, CA, United States

MRgFUS is of interest in the treatment of various brain pathologies, such as tumors and neuropathic pain. One way to visualize the focal spot prior to the treatment relies on MR acoustic radiation force imaging. A recent implementation of MR-ARFI used a diffusion-weighted 2DFT sequence with a low b-value. The goal of this work was to find the optimum b-value for the displacement sensitizing gradient in MR-ARFI, relevant to in vivo human imaging. The optimal b-value of 33 s/mm2 was found to minimize the ghosting artifacts in vivo human brain images, and maximize displacement in the focal spot of ex vivo porcine brain, while keeping ultrasound energy minimal.

14:00 4133. Therapeutic MRI-Guided High Intensity Focused Ultrasound Ablation of Uterine Fibroids with Volumetric Heating Technique: Early Clinical Experience in South Korea

Bilgin Keserci^1,2, Young-sun Kim³, Max Oskar Köhler⁴, Hyunchul Rhim³, Hyo Keun Lim<sup>3

1</sup>Philips Healthcare, Seoul, Korea, Republic of; ²Samsung Medical Center,Department of Radiology, Sungkyunkwan University School of Medicine, Seoul, Korea, Republic of; ³Samsung Medical Center, Department of Radiology, Sungkyunkwan University School of Medicine, Seoul, Korea, Republic of; ⁴Philips Healthcare, Finland

As an alternative sonication method in magnetic resonance guided high intensity focused ultrasound treatment, volumetric sonication method with feedback control under volumetric MRI thermometry for the ablation of uterine fibroids was presented. This method efficiently utilizes the inherent heat diffusion by electronically switching the focal point between a number of predetermined locations situated at outwards-moving concentric circles with diameters of upto 16 mm. A significant improvemet in symptom severity score at 1month follow-up over baseline was observed. Volumetric treatment allows for complete and uniform cell coverage, and the delivery of optimal thermal dose significantly minimizing the risk of overtreatment.

14:30 4134. Optimal Ultrasonic Focusing Through Strongly Aberrating Media Using Radiation Force Magnetic Resonance Guidance

Benoit Larrat¹, Mathieu Pernot², Laurent Marsac³, Benjamin Robert³, Gabriel Montaldo¹, Jean-François Aubry¹, Mathias Fink¹, Mickael Tanter<sup>2

1</sup>ESPCI Paristech - Institut Langevin, CNRS UMR 7587, Paris, France; ²ESPCI Paristech - Institut Langevin, INSERM, Paris, France; ³SuperSonic Imagine, Aix en Provence, France

The non invasive correction of phase aberrations of ultrasonic waves is mandatory in the framework of human transcranial brain High Intensity Focused Ultrasound (HIFU) therapy at relatively high frequency (> 500 kHz). This study proposes an adaptive focusing technique based on the measurement of the acoustic intensity at the focus via MRI. The main objective is here to demonstrate the ability of acoustic radiation force MR imaging to learn experimentally how to correct strong medium aberrations with a few ultrasonic transmissions. Sharp focal spots and optimal acoustic energies are restored through several aberrating layers.

15:00 4135. Continuous Liver Tracking During Free Breathing MRI Guided Focused Ultrasound

Yuval Zur<sup>1

1</sup>GE Healthcare Haifa, Tirat Carmel, Israel

MRI guided focused Ultrasound (FUS) tissue ablation of the liver during free breathing requires continuous tracking of all the points to be treated (target points) throughout the treatment so that the FUS transducer can deliver energy to the right position. We present a tracking method using the liver blood vessels. The tracking is done with a restricted FOV single shot EPI suitable for temperature measurement. At first the landmarks are assigned to the blood vessels. These landmarks are then tracked during heating. The location of the target point is found by 2D interpolation of the landmarks coordinates.