Emilee Shaw Minalga¹, Allison Payne¹, Robb Merrill¹, Dennis L. Parker¹, and J. Rock Hadley^1
1UCAIR, University of Utah, Salt Lake City, Utah, United States

An 11-channel cylindrical ladder coil was built to increase SNR to improve temperature measurement, cancer verification, and tissue characterization for MR guided high intensity focused ultra-sound over a single chest coil. The HIFU coil was found to improve such aspects of temperature measurement by using SNR plots, g-factor maps, human anatomy images, and temperature maps. For future human studies, this coil can add to patient safety and treatment efficacy.

Charles Mougenot¹, Max Köhler², Matti Tillander², Chrit Moonen³, Wilbert Bartels⁴, and Gösta Ehnholm^2
1Philips Healthcare, Suresnes, France, ²Philips Healthcare, Vantaa, Finland, ³IMF, CNRS / Univ. Bordeaux 2, Bordeaux, France, ⁴University Medical Center Utrecht, Utrecht, Netherlands

A novel large aperture transducer design is proposed for MR-HIFU treatment of breast tumors. The phased array is composed of 384 elements placed on a circular structure with a lateral beam direction. This beam path orientation considerably reduces the risk of damaging nearby vital organs. In addition, this transducer shape induces a well delineated sharp focal point with low energy density in the near and far field for safe, accurate and efficient treatment. The performance of the transducer is demonstrated with acoustic field measurements and temperature maps of a phantom sonication.

Max Oskar Köhler¹, Matti Tillander¹, Antti Syrjä¹, Risto Nakari¹, and Mika Ylihautala^1
1Philips Healthcare, Vantaa, Finland

A novel RF coil design for MR-HIFU therapy is presented that enables placing coil elements within the acoustic field without the coil interfering with the HIFU beam. The coil design furthermore allows HIFU beam propagation through the coil elements without causing imaging artifacts in the MR thermometry commonly used for therapy monitoring. This coil design allows a larger acoustic window and improved transducer access while maintaining or improving image quality. The additional coil element(s) also enable acceleration factors for MR thermometry that would otherwise not be possible. Coil performance is evaluated by acoustic field measurements and MR thermometry experiments.

Yoni Hertzberg^1,2, Omer Naor³, Alex Volovick², Shy Shoham³, and Gil Navon^4
1School of Physics and Astronomy, Tel-Aviv University, Tel-Aviv, Israel, ²Insightec Ltd., Tirat Carmel, Israel, ³Faculty of Biomedical Engineering, Technion, Israel, ⁴School of Chemistry, Tel-Aviv University, Israel

A method for generation of continuous acoustic holograms is presented and demonstrated. Goal is to generate efficient and uniform acoustic holograms for the magnetic resonance guided focused ultrasound applications. Acoustic fields simulations and magnetic resonance temperature elevation measurements of the first three English letters holograms are presented. The acoustic holograms were generated on relative small areas of 1.5x1.5cm and in sub-millimeter acoustic field resolution to demonstrate the high accuracy and flexibility of this method. By using this technology, the efficiency and safety of focused ultrasound applications, e.g. hyperthermia and ultrasound neural stimulation, could be further improved.

Silke Hey¹, Baudouin D. de Senneville¹, Charles Mougenot², Max Köhler³, Chrit Moonen¹, and Mario Ries^1
1IMF, CNRS / Univ. Bordeaux 2, Bordeaux, France, ²Philips Healthcare, Suresnes, France, ³Philips Healthcare, Vantaa, Finland

Real time feedback control of the HIFU beam position and the beam power during MR-guided interventions requires continuously updated volumetric information of the thermal dose and temperature over the entire target area. Here, a dynamic volume sweep for volumetric and motion compensated MR-thermometry and dosimetry is presented in combination with a real time adaptation of the ablation trajectory. The feedback control algorithm is based on the target temperature, as it is required for the use of HIFU in local drug delivery applications, or alternatively directly on thermal dose estimates as is preferable for the direct thermal destruction of tumors.

Rachel Rinat Bitton¹, Elena Kaye^1,2, and Kim Butts Pauly^1
1Radiology, Stanford University, Stanford, CA, United States, ²Electrical Engineering, Stanford University, Stanford, CA, United States

Calcifications have the potential to interfere with an MRgHIFU treatment in the brain. Although they may be identified in pre-treatment CT scans, they are not registered to the MR images or the in vivo HIFU focal spot. In this study we present the use MR-ARFI imaging to detect a calcification in ex-vivo swine brain by creating a displacement weighted map of an ROI larger than the focal spot. This technique is proposed as an adjunct to SWI in order to visualize calcifications prior to an MRgHIFU brain treatment.

Elena Kaye¹, and Kim Butts Pauly^2
1Electrical Engineering, Stanford University, Palo Alto, CA, United States, ²Radiology, Stanford University, Palo Alto, CA, United States

In this work we investigate the performance of three displacement encoding configurations that were recently proposed for spin echo based MR-ARFI pulse sequences. Displacement phase images were obtained using three methods in ex vivo brain tissue and tissue mimicking phantom.

Magalie Viallon¹, Lorena Petrusca¹, Sylvain Terraz¹, Thomas Goget¹, Vincent Auboiroux¹, Christoph Becker¹, Patrick Gross², and Rares Salomir^1
1Radiology, Hopital Universitaire de Genève, GENEVE, Switzerland, ²Siemens Healthcare, Erlangen, Germany

Fast volumetric ablation (5 to 6 cubic centimeters per minute) has been investigated in vivo demonstrating that a large and uniform ablation zone may be obtained rapidly. However, no experimental demonstration was provided that such volumetric lesion is indeed centered on a specific predefined target in 3D, i.e. no proof of absence of thermal buildup drift during the sonication. The effective spatial control of the induced thermal lesion during fast volumetric ablation should be considered as a major safety issue. Therefore before clinical trials, it is highly desirable to evaluate in animal models, the accuracy of the spatial control of ablation for a given volumetric HIFU sonication paradigm. We describe here a method to create a user-defined ballistic target as absolute reference marker that is MR-compatible and MR-detectable, while also being a well-established histology staining.

Magalie Viallon¹, Sylvain Terraz¹, Thomas Goget¹, Lorena Petrusca¹, Denis Morel², Vincent Auboiroux¹, Christoph Becker¹, Patrick Gross³, and Rares Salomir^1
1Radiology, Hopital Universitaire de Genève, GENEVE, Switzerland, ²Anesthesiology, Hopital Universitaire de Genève, GENEVE, Switzerland, ³Siemens HealthCare, Erlangen, Germany

MRgHIFU is a hybrid technology which aims to offer efficient and safe thermal ablation of targeted tumors or other pathological tissues, while preserving the normal surrounding structures unaltered. Theoretically MRgHIFU has no limitation on lesion size. The main challenge is to avoid near and far field heating. We demonstrate here that reflection at air-tissue interfaces in the far field is a problem and we evaluate an home-made multi-layer protection against tissue-to-air interface heating.

Silke Hey¹, Mario Ries¹, and Chrit Moonen^1
1IMF, CNRS / Univ. Bordeaux 2, Bordeaux, France

The combination of real time MR thermometry with a proportional, integral, derivative (PID) feedback control has been suggested as a precise solution for controlling high intensity focused ultrasound devices in applications such as local drug delivery. However, depending on the desired target temperature profile and the measurement noise, overshoots and oscillations can occur, which lead to undesired tissue damage. Here an adaptive PID controller algorithm is presented that continuously adjusts the controller gains as a function of the current temperature error and the measurement noise. Its superior performance in comparison to a conventional PID controller with static controller gains is demonstrated experimentally.

Nick Todd¹, Henrik Odeen¹, Allison Payne¹, Laurent Marsac², Dorian Chauvet³, Mathieu Pernot⁴, Anne-Laure Boch³, Jean-Francois Aubry⁴, Mickael Tanter⁴, and Dennis L Parker^1
1University of Utah, Salt Lake City, UT, United States, ²SuperSonic Imagine, Aix en Provence, France, ³Département de Neurochirurgie, Hôpital Pitié Salpêtrière, Paris, France, ⁴Institut Langevin, ESPCI ParisTech, France

New techniques for focusing ultrasound through the skull have made non-invasive heating in the brain possible, paving the way to clinical applications such as tumor ablation and targeted drug delivery via blood-brain barrier opening. However, high bone absorption can lead to undesirable heating outside of the focus and severe consequences if not properly monitored. To realize 3D MR thermometry over the entire volume of interest, we have developed an approach that combines a modified 3-D segmented EPI sequence with data undersampling and a constrained reconstruction method to provide temperature maps with good spatial resolution, large volume coverage, and high temporal resolution.

Meaghan O'Reilly¹, and Kullervo Hynynen^1,2
1Imaging Research, Sunnybrook Research Institute, Toronto, Ontario, Canada, ²Medical Biophysics, University of Toronto

Short pulses have been previously used to eliminate standing waves in the skull cavity in MR-guided transcranial ultrasound disruption of the blood-brain barrier (BBB) and improve treatment consistency. Parameters related to the use of these short pulses to disrupt the BBB were examined. Disruption of the BBB was performed in rats using sonations as short as 3μs in length at a 1Hz PRF. Mean contrast-enhanced T1w enhancement levels showed a reduced level of BBB disruption for short sonations at low PRF. However, the use of short bursts could substantially reduce treatment times when treatment of large volumes is required.

Yuexi Huang¹, Junho Song¹, and Kullervo Hynynen^1,2
1Imaging Research, Sunnybrook Research Institute, Toronto, ON, Canada, ²Department of Medical Biophysics, University of Toronto, Toronto, ON, Canada

Magnetic resonance guided focused ultrasound (MRgFUS) has been demonstrated to reversibly disrupt the blood-brain barrier (BBB) for targeted drug delivery on small animal models. For large animals, however, a precise control of the location and pressure of the ultrasound focus is difficult due to the deflection and absorption of the ultrasound beam by the relatively thicker skull. In this study, a low frequency (230kHz) MRgFUS brain system was used to demonstrate the feasibility of localized BBB disruption in pigs without craniotomies. Cavitation signals from sonicated microbubbles were detected by hydrophones as a mean to monitor the treatment in real-time. The levels of cavitation signals at various acoustic powers showed good correlation to the levels of BBB disruption and tissue damage measured by T1-weighted and T2-weighted MR images.

Urvi Vyas¹, Allison Payne¹, Nick Todd¹, Dennis L Parker¹, Robert B Roemer¹, and Douglas A Christensen^1
1University of Utah, Salt Lake City, Utah, United States

The accuracy of acoustic properties used in beam simulation techniques impacts the accuracy and efficacy of treatment planning and control in Magnetic Resonance Imaging-guided focused ultrasound surgery (MRIgFUS). In this research we use the traditional rate of heating technique with an optimization routine, MR-temperature imaging and a fast beam propagation technique to non-invasively estimate subject-specific tissue acoustic properties.

Frederic Courivaud¹, Airazat M. Kazaryan¹, Alice Lund², Per Steinar Halvorsen¹, Bjørn Edwin¹, and Per Kristian Hol^1
1The Intervention Centre, Oslo University Hospital, Oslo, Norway, ²Department of Pathology, Oslo University Hospital, Oslo, Norway

Colorectal cancer has a high incidence and is a common cause of cancer death. Surgical removal of colorectal cancer metastases in the liver improves survival rate of these patients but cannot be applied in many cases. MR guided High Intensity Focused Ultrasound (HIFU) is a promising minimal invasive alternative to surgery. However, substantial work is still needed to validate this approach. We demonstrate in this survival study a method to apply HIFU ablation using several sonication cycles during mechanically controlled breath-hold periods on anaesthetized pigs. Ablation is confirmed by MRI and histopathology one week after HIFU treatment.

Delphine Elbes¹, Benjamin Robert², Max O Köhler³, Mickael Tanter², Chrit Moonen¹, and Bruno Quesson^1
1Laboratory for Molecular and Functional Imaging, UMR 5231, CNRS/Université Bordeaux 2, Bordeaux, France, ²Inserm U979 physique des ondes pour la médecine, institut Langevin (CNRS UMR 7587), ESPCI ParisTech, Paris, France, ³Philips healthcare, Vantaa, Finland

This study aims to detect and exploit acoustic cavitation for enhancement of High Intensity Focused Ultrasound (HIFU) heating in ex vivo liver. MR acoustic radiation force imaging (MR-ARFI) allowed visualization of the local tissue displacement in absence/presence of cavitation induced by a short and intense HIFU pulse. The temperature increase measured by MR-thermometry was higher in presence of cavitation. The spatial distribution of the acoustic pressure (MR-ARFI) in presence of cavitation was coherent with the observed modifications on MR-thermometry. Enhancement of tissue heating with acoustic cavitation may improve the efficiency of MR guided HIFU ablation in the liver.

Robert Staruch^1,2, Melissa Togtema¹, Rajiv Chopra^1,2, and Kullervo Hynynen^1,2
1Centre for Research in Image-Guided Therapeutics, Sunnybrook Health Sciences Centre, Toronto, Ontario, Canada, ²Department of Medical Biophysics, University of Toronto, Toronto, Ontario, Canada

MRI-controlled focused ultrasound was used to generate mild hyperthermia at a soft tissue-bone interface in 5 rabbit thighs, for the purpose of achieving localized drug delivery with thermosensitive liposomes. FSPGR images perpendicular to the ultrasound beam were used for temperature control in muscle adjacent to bone. Median temperatures in a 10mm target were maintained at 43°C for 20min. Muscle adjacent to heated bone had 18-fold higher drug concentrations as muscle adjacent to unheated bone. The results demonstrate the feasibility of MRI-controlled focused ultrasound hyperthermia at soft tissue-bone interfaces, and its potential for localized drug delivery with thermosensitive liposomes.

Alessandro Napoli¹, Michele Anzidei², Giulia Brachetti², Luisa Molisso², Carlo Catalano², and Roberto Passariello^2
1Radiological Sciences, Policlinico Umberto I, Rome, Rome, Italy, ²Radiological Sciences, Policlinico Umberto I, Rome, Italy

MRgFUS is a new technique that allows non invasive palliation of bone metastases pain with a real-time control of the achieved temperature and consequently necrosis induced.

Heikki Juhani Nieminen¹, Charles Mougenot², Bilgin Keserci³, Jouko Soini¹, Sham Sokka⁴, Max Oskar Köhler¹, and Teuvo Vaara^1
1Philips Healthcare, Vantaa, Finland, ²Philips Healthcare, Bordeaux, France, ³Philips Healthcare, Seoul, Korea, Republic of, ⁴Philips Healthcare, Andover, MA, United States

The most common clinical application of Magnetic Resonance guided High Intensity Focused Ultrasound (MR- HIFU) is the thermal ablation of uterine fibroids. The spatial targeting and thermal dose volume accuracies of the volumetric feedback procedure are here studied based on data acquired in a clinical study with 33 patients and a total of 38 symptomatic fibroids. Based on an analysis of the ablated volumes produced by the 471 sonications performed with the Philips Sonalleve MR-HIFU system, the accuracy appears to be better than the imaging resolution, 2.5×2.5×7.0mm, which is acceptable compared to typical fibroid sizes of 3-15cm in diameter.

Kim Shultz¹, Pascal Stang¹, John Pauly¹, and Greig Scott^1
1Electrical Engineering, Stanford University, Stanford, CA, United States

The process of RF ablation treatment is often imaged with MRI using temperature mapping. MRI has the additional cabability of imaging the RF fields from the ablation currents if the ablation is performed at the Larmor frequency. We demonstrate the feasibility of performing ablation at 64 MHz with temperature and impedance monitoring and show the change in RF field maps from the ablation procedure.

Jerome L Ackerman^1,2, YiK Kiong Hue^1,2, Erez Nevo³, Alexander R. Guimaraes^1,2, Martin Polak^1,4, Kyum S. Lee¹, and Daniel E. Ackerman^1
1Martinos Center/Department of Radiology, Massachusetts General Hospital, Charlestown, MA, United States, ²Harvard Medical School, Boston, MA, United States, ³Robin Medical, Inc., Baltimore, MD, United States, ⁴Children's Hospital, Boston, MA, United States

MR-Mediated Radiofrequency Ablation (MR-RFA) is a novel method for producing thermal lesions in tissue for the purpose of destroying tumors. In this method the scanner not only provides image guidance for placing the RF applicator, it also supplies the RF energy for heating. In gel phantoms MR-mediated RFA yielded temperatures of up to 100 °C and heating rates up to 4 °C/s, somewhat more modest temperatures and heating rates in tissue specimens, and temperatures over 70 °C in live pigs undergoing MR-mediated RFA of the liver. In vivo, thermal lesions 1 cm in diameter were achieved within the liver.

Eva Rothgang^1,2, Wesley D. Gilson², Steffi Valdeig³, Li Pan², Jörg Roland⁴, Aaron Flammang², Christine H. Lorenz², Frank Wacker³, and Bernd Frericks^5
1Pattern Recognition Lab, University Erlangen-Nuremberg, Erlangen, Germany, ²Center for Applied Medical Imaging, Siemens Corporate Research, Baltimore, MD, United States, ³Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University, Baltimore, MD, United States, ⁴Siemens Healthcare, Erlangen, Germany, ⁵Department of Radiology and Nuclear Medicine, Universitätsmedizin Berlin–Charité Campus Benjamin Franklin, Berlin, Germany

For enhanced intra-operative control during cryoablation, we propose to online monitor the procedure using the proton resonance frequency method (PRF). By monitoring temperatures in close proximity to the region being ablated, procedure safety and efficacy can be increased. The purpose of this study was to demonstrate the value of online PRF temperature monitoring to 1) estimate the pattern of ice ball growth between multiple cryoprobes; and 2) prevent injury to adjacent structures. In this study, PRF imaging during in vivo cryoablation of porcine kidney was compared to post-ablation imaging and histopathology.

Viola Rieke¹, Andrew B Holbrook¹, William Grissom², Juan M Santos³, Michael V McConnell⁴, and Kim Butts Pauly^1
1Department of Radiology, Stanford University, Stanford, CA, United States, ²Imaging Technologies Laboratory, GE Global Research, Munich, Germany, ³Heart Vista, Inc., Los Altos, CA, United States, ⁴Division of Cardiovascular Medicine, Stanford University, Stanford, CA, United States

In recent years there has been increased interest to perform cardiac interventions such as EP ablation under MR-guidance. Directly monitoring the temperature rise during these procedures could potentially be helpful to verify successful ablation and predict treatment outcome. In this study, we investigate the feasibility of monitoring temperature changes in the left ventricular myocardium in real-time using spiral imaging at 3T with varying imaging parameters with and without blood suppression. Temperature images based on the proton resonance frequency (PRF) shift are reconstructed using a hybrid method that combines multi-baseline subtraction and referenceless thermometry.

Nelly A. Volland^1,2, Eugene G. Kholmovski^1,2, J. R. Hadley¹, and Dennis L. Parker^1
1Radiology / Utah Center for Advanced Imaging Research, University of Utah, Salt Lake City, UT, United States, ²Comprehensive Arrhythmia Research & Management Center, University of Utah, Salt Lake City, UT, United States

Introduction: Limited FOV MR temperature image acquisition in less than 200 ms with high sensitivity was investigated using a local RF cardiac coil. Methods: Loop coil was designed, coated, and tested to assess the feasibility of measurements. Results: SNR gain attainable with local coil in static phantom compared to surface coils was 26 times. Stable MR phase images were acquired within 230 ms on limited FOV imaging volume without aliasing in moving phantom 4 times faster than surface coils could allow. Conclusions: Local cardiac coil was successfully used to perform MR thermometry in static and moving phantoms.

Baudouin Denis de Senneville¹, Sébastien Roujol¹, Pierre Jaïs², Chrit TW Moonen¹, Gwenaël Herigault³, and Bruno Quesson^1
1Laboratory for Molecular and Functional Imaging: From Physiology to Therapy, CNRS/University of Bordeaux 2, Bordeaux, Gironde, France, ²Hôpital Cardiologique du Haut-Lévèque, Bordeaux, France, ³Philips Healthcare, France

On-line MR-temperature monitoring during radio-frequency ablation of cardiac arrhythmias may improve the efficacy and safety of the treatment. Magnetic Resonance Imaging can provide rapid and quantitative thermometric measurements in addition to a detailed anatomical information. For this purpose, cardiac triggering and dynamic navigator-based slice tracking were combined with image registration and modeling of susceptibility changes with respiration, in order to investigate the precision of PRF thermometry during a RF ablation in-vivo on a sheep heart.

Mahamadou Diakite¹, Rock Hadley², and Dennis L. Parker^2
1Physics, University of Utah, Salt Lake City, Utah, United States, ²Radiology, University of Utah, Salt Lake City, Utah, United States

The goal of the present work is to show the feasibility of proton resonance frequency (PRF) shift based thermometry using a modified Turbo Spin Echo (modified TSE) sequence.. In this work, we present a modified TSE sequence to generate phase maps, in which the proton resonance frequency shift is detected.Although, the proposed modified TSE sequence is in an early development stage, we have shown that this sequence can be used to monitor temperature and could be used to quantify heating effects in suspect TSE studies.

Bruno Madore¹, Renxin Chu¹, Chang-Sheng Mei¹, Jing Yuan², Tzu-Cheng Chao¹, and Lawrence P. Panych^1
1Department of Radiology, Harvard Medical School, Brigham and Women's Hospital, Boston, MA, United States, ²Department of Imaging and Interventional Radiology, the Chinese University of Hong Kong

An MR thermometry method is proposed that offers advantages in terms of temperature-to-noise-ratio (TNR), tissue contrast and temperature accuracy. An interleaved-EPI sequence was modified so that both a gradient-echo and a spin-echo-like magnetization pathway would be sampled every TR. Three main advantages come from sampling both types of signal: 1) Independent temperature measurements can be combined for improved TNR, 2) images of different contrast can be compared to help identify blood vessels and/or regions of thermal damage, and 3) system imperfections, such as sub-optimal shimming, can be detected and corrected for, potentially enabling improvements in temperature accuracy.

Mahamadou Diakite¹, Nick Todd², and Dennis L. Parker^2
1Physics, University of Utah, Salt Lake City, Utah, United States, ²Radiology, University of Utah, Salt Lake City, Utah, United States

Accurate temperature mapping in tumor and surrounding tissue throughout the thermal therapy is essential to ensure the safety and efficacy of thermal treatment. Methods based on the temperature dependency of the water proton resonance frequency (PRF) shift have shown the best ability to quantify temperature rises in soft tissues. Unfortunately, the PRF shift with temperature does not apply to lipid protons, since there is no hydrogen bonding among the methylene protons that supply the bulk of fat signal. However, the temperature sensitivity of the spin-lattice relaxation time, T1, has been measured for a number of fatty tissues and found to obey a linear relationship over a small temperature range [1]. We previously proposed the hybrid PRF-T1 method to combine these two techniques to simultaneously monitor temperature in fat and soft tissues. In this work, we show a sequence implementation and improve the accuracy of T1 measurements for better temperature mapping.

Nigel Paul Davies¹, Maryam Kalantari Saghafi², Xiaoyan Pan³, Theodoros N Arvanitis⁴, and Andrew C Peet^3
1Medical Physics, University Hospitals Birmingham NHS Foundation Trust, Birmingham, United Kingdom, ²School of Physics & Astronomy, University of Birmingham, Birmingham, United Kingdom,³Cancer Sciences, University of Birmingham, Birmingham, United Kingdom, ⁴Department of Electrical, Electronic, and Computer Engineering, University of Birmingham, Birmingham, United Kingdom

In-vivo 1H MRS can be used as a probe of temperature through its observed linear relationship with water chemical shift. However, such measurements are potentially subject to contributions from fast exchange effects that are dependent on factors such as macromolecular content and microstructure. Few if any studies have addressed the impact of these effects on MRS temperature calibrations. In this study, tissue-like phantoms have been constructed and used to test the effects of macromolecular concentration and dynamics on temperature measurements using 1H MRS, showing a significant linear relationship between the temperature calibrations and the agarose concentration.

Lorne Hofstetter¹, Desmond Yeo¹, W Thomas Dixon¹, Cynthia Davis¹, and Thomas K Foo^1
1GE Global Research, Niskayuna, NY, United States

Accurate and stable MR thermometry is critical for interventional procedures such as RF hyperthermia and MR guided focused ultrasound therapy. In this work we present a 3-echo fat-referenced thermometry technique that reduces measurement error caused by time-varying changes in the underlying B0 field. This technique was validated in a cream cooling experiment (T = 8.4°C) where deviations between MR and fiber-optic temperature probe measurements were less than 0.28°C.

William A Grissom¹, Lorne W Hofstetter², Viola Rieke³, Yoav Medan⁴, Kim Butts Pauly³, and Cynthia E Davis^2
1GE Global Research, Munich, Germany, ²GE Global Research, Niskayuna, New York, United States, ³Radiology, Stanford University, Stanford, CA, United States, ⁴Insightec, Ltd, Tirat Carmel, Israel

Proton resonance frequency-shift thermometry is a promising technique to monitor thermal therapies in organs such as the breast and prostate, but is complicated by the presence of fat, organ motion, and the small size of these organs relative to typical hot spot sizes. While thermometry can be performed by suppressing fat, it can also be exploited as a reference to improve the separation of phase shifts caused by time-varying main field changes from temperature-induced phase shifts. We introduce an extension to the hybrid multibaseline subtraction and referenceless thermometry method that exploits the fat image as a reference to yield accurate temperature estimates that are robust to main field changes, large hot spot sizes, and motion in organs such as the prostate and breast that are surrounded by or contain fat.

Paul Baron¹, Roel Deckers¹, Sara M Sprinkhuizen¹, Laura G. Merckel², Ronald L.A.W. Bleys³, Chris J.G Bakker¹, and L W Bartels^1
1Image Sciences Institute, University Medical Center Utrecht, Utrecht, Netherlands, ²Department of Radiology, University Medical Center Utrecht, Utrecht, Netherlands, ³Department of Anatomy, University Medical Center Utrecht, Utrecht, Netherlands

The aim was to assess the T1 and T2 temperature dependence of human adipose breast tissue and compare these with sunflower oil and pig fat. The temperature of tissue samples were increased by heating a water bath from 26.5°C to 72°C and then allowed to cool. During heating and cooling, the temperature was measured with a fiber optic probe and T1 and T2 were mapped. Reversible T1 changes but irreversible T2 changes were found for breast and pig fat. The T1-temperature dependence was similar for all three samples. T2 had a larger temperature dependence for pig than for breast fat.

Eva Rothgang^1,2, Jörg Roland³, Wesley D. Gilson², Joachim Hornegger¹, and Christine H. Lorenz^2
1Pattern Recognition Lab, University Erlangen-Nuremberg, Erlangen, Germany, ²Center for Applied Medical Imaging, Siemens Corporate Research, Baltimore, MD, United States, ³Siemens Healthcare, Erlangen, Germany

PRF-derived temperature measurements are sensitive to patient motion and B0 drifts. The mean phase drift is often calculated from an area which is not heated and thus remains at reference temperature. However, this region can be difficult to place and its location and size highly influence the effectiveness of correction. On the contrary, we introduce a method which automatically corrects for B0 drift by determining the mean phase drift from all voxels which show a standard deviation smaller than a threshold the phase.

Paul Baron¹, Roel Deckers¹, Sara M Sprinkhuizen¹, Chris J.G Bakker¹, and L W Bartels^1
1Image Sciences Institute, University Medical Center Utrecht, Utrecht, Netherlands

The aim was to correct susceptibility errors in Proton Resonance Frequency Shift (PRFS)-based thermometry caused by the heating of fat. The feasibility was shown in an oil/water phantom, cooled from 60 to 35°C . The susceptibility change in oil was calculated using T1-thermometry. The resulting field disturbance was calculated using the Fourier transform technique. The corrected PRFS change was calculated by subtracting the field disturbance from the measured PRFS change. The temperature was monitored with fiber optic probes. For two locations measured for the whole temperature range the mean absolute PRFS temperature error decreased by about one third when corrected.

Jan Weis¹, Lucian Covaciu², Sten Rubertsson², Mats Allers³, Anders Lunderquist³, Francisco Ortiz-Nieto¹, and Håkan Ahlström^1
1Department of Radiology, Uppsala University Hospital, Uppsala, Sweden, ²Department of Surgical Sciences, Anesthesiology and Intensive Care, Uppsala University Hospital, Uppsala, Sweden,³Department of Clinical Sciences, Division of Thoracic Surgry, University Hospital, Lund, Sweden

Brain temperature reductions (1-3 °C) were induced by intranasal cooling. Purpose of this study was to compare MRSI with high spatial and reduced spectral resolution and phase-difference technique that were used in monitoring the brain temperature changes during cooling. Both methods were sensitive to the slight involuntary movement (rotation) of the head. Random (reversible) and systematic (irreversible) movement artifacts were observed. Measurements in the transversal slices were more robust to the movement artifacts than those in sagittal planes.

Weiguo Li¹, Zhuoli Zhang¹, Daniel Procissi¹, Andrew Gordon¹, Jodi Nicolai¹, Reed Omary¹, and Andrew Larson^1
1Department of Radiology, Northwestern University, Chicago, Illinois, United States

Radioembolization with Yttrium-90 (90Y) microspheres is a relatively new form of intra-arterial therapy for Hepatocellular carcinoma. However, visualization and quantification of 90Y microsphere biodistribution using conventional radiologic modalities is challenging. Whereas labeling 90Y microspheres with SPIOs offers the potential to use MRI to visualize in vivo biodistribution, optimization of the amount of SPIO included within these microspheres may be critical. In this study, we have demonstrated the potential to optimize SPIO content for future studies intended to quantify microsphere concentrations in vivo; we found that spheres with relatively low SPIO contents will be ideal candidates for future study.

Samdeep Mouli¹, Noam Belkind¹, Weiguo Li¹, Jason Sandberg¹, David Magill¹, Rachel Klein¹, Daniel Procissi¹, Jodi Nicolai¹, Yang Guo¹, Andrew Larson¹, and Reed Omary^1
1Radiology, Northwestern University, Chicago, Illinois, United States

We describe a novel locoregional technique, termed electro-nanotherapy, to increase the intra-tumoral uptake of dual imaging and therapeutic nanoparticles through tissue electroporation. Our results demonstrate the procedure results in a 6 fold increase in liver tumor nanoparticle uptake over conventional systemic delivery. Furthermore, using high resolution MRI T2 and T2* maps, we are able to assess the real-time biodistribution of these nanoparticles non invasively.

Johannes Riegler^1,2, Baptiste Allain^3,4, Richard J Cook⁴, Quentin A Pankhurst⁵, and Mark F Lythgoe^1
1Centre for Advanced Biomedical Imaging, University College London, London, United Kingdom, ²Centre for Mathematics and Physics in the Life Sciences and Experimental Biology (CoMPLEX), University College London, London, United Kingdom, ³Centre for Medical Image Computing (CMIC), University College London, London, United Kingdom, ⁴KCL Dental Institute, Biomaterials, Biomimetics and Biophotonics Group, Guy’s Hospital Campus, London, United Kingdom, ⁵Davy-Faraday Research Laboratory, The Royal Institution of Great Britain, London, United Kingdom

One of the major challenges for cell transplantation therapies is the spatial localization and tracking of cells over time. MRI has been used for cell tracking while magnetic delivery strategies using permanent magnets have been tested in animal models. MR gradient coils could potentially be used to steer magnetically labeled cells through the vascular system to their target. We show that steering of cells in a flow phantom is feasible. Following this, we derived a simple mathematical model which predicts that cell aggregation is an important factor explaining our results. Additionally we confirmed cell aggregation via confocal endoscopy.

Bradley D Hann¹, and Kevin M Bennett^1
1School of Biological and Health Systems Engineering, Arizona State University, Tempe, Arizona, United States

A technique to noninvasively detect the macromolecular structure in hydrogels could be used to monitor cell viability and migration in vivo, and thus the efficacy of hydrogel-based cell therapies. Here we develop a technique to track structural changes in a biocompatible hyaluronic acid hydrogel doped with functionalized iron oxide nanoparticles. Changes in particle aggregation state can modulate T2. We measured T2 changes over time in vitro consistent with cellular rearrangement of the matrix and demonstrated that this technique can be used to detect cell proliferation in the hydrogel. We further report that these hydrogels can be visualized in vivo.

Yue Zhang^1,2, Haitham M Al-Angari³, Yang Guo², Jodi Nicolai², Rachel A Klein², Alan V Sahakian³, Reed A Omary^2,4, and Andrew C. Larson^2,4
1Bioengineering, University of Illinois at Chicago, Chicago, IL, United States, ²Radiology, Northwestern University, Chicago, IL, United States, ³Electrical Engineering and Computer Science, Northwestern University, Evanston, IL, United States, ⁴Robert H. Lurie Comprehensive Cancer Center, Northwestern University, Chicago, IL, United States

Irreversible electroporation (IRE) has recently been applied as a novel tissue ablation modality; IRE involves application of short-lived electrical fields across the cell membrane to permanently increase membrane permeability leading to cell death. 2D finite element methods (FEM) are used to model anticipated electrical field distributions but these typically assume homogeneous tissue conductivity; heterogeneity could lead to poor approximations of subsequent ablation volume. In this work, we developed a 3D FEM approach using pre-procedural MRI measurements to produce a patients-specific 3D surrogate-conductivity map for simulation of IRE ablation zones in a rat model of hepatocellular carcinoma. Our results showed FEM-simulated ablation zones were well correlated to histology-confirmed ablation zones. Thus pre-procedural MRI and 3D FEM can be used to accurately predict IRE ablation zones.

Burkhard Mädler¹, Kaveh Mehdiani¹, and Volker A. Coenen^1
1Dep. of Neurosurgery, Div. of Stereotaxy and MR-based OR-Techniques, University Bonn, Bonn, Germany

DBS is a technique that delivers continuous electric stimulation through permanently into the brain implanted electrodes. Depending on diagnosis and symptoms, different anatomical targets have been chosen for stimulation in movement disorders, depression or obsessive compulsive disorders. Discussion to date focused mostly on the sole definition of DBS-targets with little debate about their important remote connectivity. We believe that it is this connectivity that might explain clinical improvement and side effects in distinct DBS procedures. Our study indicates that better target areas by means of specific WM-tracts might exist for various DBS-procedures.

Arne Hans¹, Adam Wittek², Grand Joldes², Karol Miller², Neil I Weisenfeld¹, Mark Alexiuk³, John Saunders³, Einat Liebenthal⁴, Garnette R Sutherland⁵, and Simon K Warfield^1
1Radiology, Children's Hospital Boston and Harvard Medical School, Boston, MA, United States, ²University of Western Australia, Perth, Australia, ³IMRIS, Winnipeg, Canada, ⁴National Research Council Canada, Canada, ⁵University of Calgary

We propose to significantly increase the intraoperative utility of data acquired preoperatively by compensating, in real time, for brain shift during surgery. This is demonstrated on craniotomy case data that has been processed using our non-rigid registration pipeline. We have achieved intraoperative visualization of preoperative fMRI and DTI aligned to intraoperative MRI, and we have validated the alignment quality by comparing automatically generated edges. Our study shows that preoperative data can be warped to the current configuration of the patient's brain in real time and with subvoxel accuracy. Such visualization may dramatically improve surgical decision making.

Christian Jürgen Seebauer¹, Jens Rump², Hermann Josef Bail³, Felix Güttler², Bernd Hamm², Carsten Perka⁴, Christian Gross⁴, and Ulf Teichgräber^2
1Center for Musculoskeletal Surgery, Charité-Universitätsmedizin Berlin, Berlin, Berlin, Germany, ²Department of Radiology, Charité-Universitätsmedizin Berlin, Berlin, Berlin, Germany,³Department of Trauma and Orthopedic Surgery, Clinic Nuremberg, Nuremberg, Germany, ⁴Center for Musculoskeletal Surgery, Charité-Universitätsmedizin Berlin

In recent years, a number of minimally invasive nuclear decompression techniques for lumbar disc prolapse have been introduced. Partial removal of the nucleus has been shown to decompress herniated discs, relieving pressure on nerve roots and, in some cases, offering relief from disc pain. Most spine procedures have traditionally been performed using fluoroscopic or CT guidance. With the increasing role of MRI in diagnosis of musculoskeletal conditions, clinicians have been eager to explore the possibility of using MR guidance for musculoskeletal procedures. The aim of this study was to evaluate feasibility and practice of MR-guided percutaneous lumbar mechanical disc decompression in an experimental setting in 3 human cadavers.

Andreas Heinrich¹, Jens Rump¹, Felix Güttler¹, Christian Seebauer², Bernd Hamm¹, and Ulf Teichgräber^1
1Department of Radiology, Charité-Universitätsmedizin Berlin, Berlin, Berlin, Germany, ²Center for Musculoskeletal Surgery, Charité-Universitätsmedizin Berlin, Berlin, Berlin, Germany

For a non-invasive assessment of the birth process under MR control, an MR-compatible cardiotocograph (CTG) was developed and tested for a safe monitoring of physiological parameters (heart rate, uterine contraction). Voltages generated by the MRI led to disturbances of heart rate data, whereas uterine contraction data were minor influenced. The effects of spoiled and balanced gradient-echo sequences on CTG was examined. Disturbances caused by MRI mainly depends on repetition time (TR). In order to overcome this, a MR-noise-filter (TR-dependend frequency comb filter and a low pass filter) was developed and analyzed. As a result, the fetal heart rate as well as the uterine contraction could be assessed clearly during MR image acquisition.