MR-Guided Focused Ultrasound

Tuesday 2 June 2015

Samuel Fielden¹, Xue Feng¹, Wilson Miller², Kim Butts Pauly³, and Craig Meyer^1,2
1Biomedical Engineering, University of Virginia, Charlottesville, Virginia, United States, ²Radiology, University of Virginia, Charlottesville, Virginia, United States, ³Radiology, Stanford University, Palo Alto, California, United States

For focused ultrasound procedures, the ability to perform thermometry on the entire heated volume is desirable in order to ensure focal spot location and to monitor for off-focus, spurious heating. Here, we have developed a rapid volumetric thermometry sequence based on a stack-of-spirals gradient echo acquisition, with a redundant-in/out method used to impart improved off-resonance performance. This sequence was tested and validated with a real-time reconstruction during focused ultrasound sonication of a gelatin phantom.

Samuel Fielden¹, John Mugler, III², Wilson Miller², Kim Butts Pauly³, and Craig Meyer^1,2
1Biomedical Engineering, University of Virginia, Charlottesville, Virginia, United States, ²Radiology, University of Virginia, Charlottesville, Virginia, United States, ³Radiology, Stanford University, Palo Alto, California, United States

Monitoring bone heating during focused ultrasound procedures is desirable. The popular PRF shift technique for MR thermometry cannot be performed in bone due to its short T2. However, T1 and T2 are temperature dependent, and so an alternative method is to use signal intensity changes, detected by ultra-short echo time (UTE) sequences, as a method by which bone thermometry can be performed. Here, we have used a rapid 3D spiral UTE sequence to image a heated bone sample as it cools down in the bore of the MRI and have detected signal intensity changes consistent with T1-lengthening of heated tissue.

Pierre Bour¹, Fabrice Marquet¹, Solenn Toupin^1,2, Matthieu Lepetit-coiffé², and Bruno Quesson^1
1L'Institut de RYthmologie et de Modélisation Cardiaque, Bordeaux, Aquitaine, France, ²SIEMENS-Healthcare, Saint-Denis, Île-de-France, France

MR guided HIFU allows non-invasive thermal ablation of soft tissues. This abstract proposes to monitor simultaneously temperature and displacement induced at the focus with sub-second sequence integrating a bipolar gradient with alternating polarities and a synchronized blank of the HIFU sonication. This method has been validated ex vivo and applied in vivo on swine liver: During sonication a decrease of measured displacement along with an increase of temperature was measured. This method allows measurements of changes of mechanical properties of targeted tissue that could give additional relevant information on the extent of the induced lesion.

Maya Barbara Müller-Wolf¹, Mathieu Burtnyk², Valentin Ionel Popeneciu³, Gencay Hatiboglu³, Michele Billia⁴, Cesare Romagnoli⁵, Joseph Chin⁴, Sascha Pahernik³, Heinz-Peter Schlemmer⁶, and Matthias C Roethke^1
1Radiology, German Cancer Research Center, Heidelberg, Baden-Wuerttemberg, Germany, ²Profound Medical, Toronto, Ontario, Canada, ³Urology, University Hospital Heidelberg, Heidelberg, Baden-Wuerttemberg, Germany, ⁴Urology, Western University UWO London Victoria Hospital, London, Ontario, Canada, ⁵Radiology, Western University UWO London Victoria Hospital, London, Ontario, Canada, ⁶Radiology, German Cancer Research Center, Baden-Wuerttemberg, Germany

Local disease control and low morbidity are goals of minimally-invasive, image-guided therapies for localised prostate cancer. MRI-guided transurethral ultrasound ablation constitutes an attractive treatment alternative to active surveillance and radical treatments. Real-time MR-thermometry and active temperature feedback control enable assessment of treatment success through thermal dosimetry and visualization of immediate post-interventional contrast-enhanced MRI. A prospective phase I trial was conducted to determine targeting accuracy of conformal heating to predefined acute ablation boundary (T2-planning) using linear and volumetric metrics including Dice Similarity Coefficient. Thermal coagulation was confirmed by visually comparing the MR-thermometry images to the non-perfused volume on CE-MRI.

Martijn Hoogenboom¹, Dylan Eikelenboom², Martijn H den Brok², Erik Dumont³, Gosse J Adema², Arend Heerschap¹, and Jurgen J Futterrer^1,4
1Department of Radiology and Nuclear medicine, Radboud University Medical Center, Nijmegen, Gelderland, Netherlands, ²Department of Tumor Immunology, Radboud University Medical Center, Nijmegen, Gelderland, Netherlands, ³Image Guided Therapy, Pessac, France, ⁴MIRA Institute for Biomedical Technology and Technical Medicine, University of Twente, Enschede, Overijssel, Netherlands

Boiling histotripsy is a focal ablation technique for fragmentation of the tissue using high intensity focused ultrasound. Until now ultrasound imaging is used for guidance of the treatment. This study shows MR guided HIFU treatment (boiling histotripsy and thermal ablation) with different MR response imaging techniques (T2w, PD, T1w, DCE) to evaluate the lesion immediately after treatment in mouse tumors. It is shown that immediately after boiling histotripsy a hyperintense lesion is visualized on T2w imaging which highly correlates with sharp delineated liquefied lesion found on pathologic slices. No contrast enhancement is measured within the lesion using DCE imaging.

Wen Yen Chai^1,2, Po Chun Chu², Chih Hung Tsai², and Hao Li Liu^2
1Department of Medical Imaging and Intervention, Chang Gung Memorial Hospital, Guishan, Taoyuan, Taiwan, ²Department of Electrical Engineering, Chang Gung University, Guishan, Taoyuan, Taiwan

Two different frequency focus ultrasound exposures were used to induce BBB opening in this study. BBB opening kinetics can be evaluated via dynamic contrast-enhanced MRI (DCE-MRI) and the correlation between MI and the kinetic change will be investigated.

Maria Eleni Karakatsani¹, Gesthimani Samiotaki¹, Matthew Downs¹, Vincent Ferrera², and Elisa Konofagou^1,3
1Department of Biomedical Engineering, Columbia University, New York, NY, United States, ²Department of Neuroscience, Columbia University, New York, NY, United States,³Department of Radiology, Columbia University, New York, NY, United States

The application of focused ultrasound (FUS) coupled with the systemic administration of microbubbles has been proved to open the Blood-Brain Barrier locally, transiently and non-invasively in non-human primates. This study provides evidence for a linear correlation between the incidence angle, the FUS pressure and the induced opening size. The parametric optimization of the experimental setup inducing the desired opening and the reproducibility of the experiment are achieved. Results also indicate that the opening-to-targeting-shift is gray-to-white-matter ratio dependent. For both tasks 3D T1 weighted pre- and post-contrast images were acquired based on which an automated intensity-based algorithm was designed.

Yuexi Huang¹, Nir Lipsman², Michael L. Schwartz³, Vibhor Krishna², Francesco Sammartino², Andres M. Lozano², and Kullervo Hynynen^1,4
1Sunnybrook Research Institute, Toronto, ON, Canada, ²Division of Neurosurgery, Toronto Western Hospital, Toronto, ON, Canada, ³Division of Neurosurgery, Sunnybrook Health Sciences Centre, Toronto, ON, Canada, ⁴Department of Medical Biophysics, University of Toronto, Toronto, ON, Canada

Magnetic resonance guided focused ultrasound has shown promising results in the treatment of essential tremor. MR temperature and thermal dose measurement plays a crucial role in monitoring and guiding acoustic parameters. In general, the size of the lesion can be detected by MR imaging immediately after the treatment is significantly smaller than the size on the following day while the lesion continues to develop over hours. Therefore, it would be useful if thermal dose can be used to predict the ultimate lesion size and thus determine the end point of the treatment. In this study, we correlated the size of the thermal dose to the lesion size at the follow-up imaging on the second day and found the lesion sizes were between 240 and 17 EM thermal doses.

Silke M. Lechner-Greite¹, Nicolas Hehn¹, Beat Werner², Eyal Zadicario³, Matthew Tarasek⁴, and Desmond T.B. Yeo^4
1Diagnostics, Imaging and Biomedical Technologies Laboratory, GE Global Research Europe, Garching n. Munich, Germany, ²Center for MR-Research, Children’s Hospital Zurich, Zurich, Switzerland, ³InSightec Ltd., Tirat Carmel, Israel, ⁴Diagnostics, Imaging and Biomedical Technologies Laboratory, GE Global Research Niskayuna, Albany, NY, United States

To minimize image artifacts caused by gradient-induced eddy currents in a transducer electrode ground plane of a transcranial MR guided focused ultrasound applicator during multi-shot echo-planar imaging for fast multi-plane temperature tracking. With this study we demonstrate that segmentation of the transducer ground plane by horizontal and vertical disruption would enable fast multi-plane EPI imaging for accurate MR thermometry in tcMRgFUS with geometric distortions comparable to a scenario where no copper ground plane is present, i.e. in the absence of the FUS transducer.

Raag D Airan¹, Gregory T Clement², Ari Partanen³, Martin G Pomper¹, and Keyvan Farahani^1,4
1Radiology and Radiological Science, Johns Hopkins Medical Institutions, Baltimore, Maryland, United States, ²Biomedical Engineering, Cleveland Clinic Lerner Research Institute, Cleveland, Ohio, United States, ³Clinical Science MR Therapy, Philips Healthcare, Andover, Massachusetts, United States, ⁴National Cancer Institute, National Institutes of Health, Bethesda, Maryland, United States

MR-guided high intensity focused ultrasound (MR-HIFU) has demonstrated great promise for brain applications. As currently implemented, MR-HIFU has a treatment envelope limited to the center of the brain. We demonstrate in silico that a 256-element non-hemispherical clinical MR-HIFU transducer could develop spatially compact sonication foci transcranially in the brain, at clinically relevant locations in the superficial cortex (superior temporal and inferior frontal gyri) as well as near the skull base (hippocampus, amygdala, nucleus accumbens, BA25, and pons). These results are most relevant for applications requiring lower sonication powers such as blood brain barrier disruption and neuromodulation.

Bryant T. Svedin^1,2, Michael J. Beck^1,3, J. Rock Hadley^1,4, Robb Merrill^1,4, Bradley D. Bolster Jr.⁵, and Dennis L. Parker^1,4
1Utah Center for Advanced Imaging Research, Salt Lake City, Utah, United States, ²Physics, University of Utah, Salt Lake City, Utah, United States, ³Electrical Engineering, University of Utah, Utah, United States, ⁴Radiology, University of Utah, Salt Lake City, Utah, United States, ⁵Siemens HealthCare, Salt Lake City, Utah, United States

Treatment planning and patient safety in MR guided focused ultrasound treatment require accurate knowledge of the location of the ultrasound beam focus. Typical methods of locating the focus (low power heating, ARFI) require time and sonication. The proposed method uses 3 tracker coils rigidly attached to the transducer to predict the location of the focus. The six degrees of freedom transformation is calculated that realigns their current locations to their calibration locations. This transform is applied to the calibration focus location to estimate its current position. This method provides real-time determination of the focus location without the need to sonicate.

Megan E Poorman^1,2, Vandiver L Chaplain^2,3, Ken Wilkens², Shantanu Majumdar², William A Grissom^1,2, and Charles F Caskey^1,2
1Biomedical Engineering, Vanderbilt University, Nashville, TN, United States, ²Institute of Imaging Science, Vanderbilt University, Nashville, TN, United States, ³Computational and Physical Biology, Vanderbilt University, Nashville, TN, United States

An open-source small-animal MR guided focused ultrasound system is described that is capable of delivering accurate, precise, and controllable heating over an extended period of time, as well as mechanical ultrasound. This system will lower the barrier for the increasing number of researchers who wish to enter the evolving field of focused ultrasound

Emilee Minalga¹, Robb Merrill¹, Dennis L Parker¹, Josh DeBever¹, J. Rock Hadley¹, and Allison Payne^1
1UCAIR, University of Utah, Salt Lake City, UT, United States

Temperature error is correlated to signal to noise ratio. SNR is important when performing Magnetic Resonance guided Focused Ultrasound treatments.This abstract investigates the differences in anatomy and temperature images at both 1.5T and 3 T field strengths. Two identical coils were tuned and matched to both field strengths and the results of anatomy scans, Temperature imaging, and SNR plot were obtained.

Thermotherapy & Thermometry

Tuesday 2 June 2015

Han-Joong Kim¹, Suchit Kumar¹, Jong-Hoon Han¹, Jong-Min Kim¹, Jun-Sik Yoon¹, Seung-Koo Lee², Chulhyun Lee³, and Chang-Hyun Oh^1
1Korea University, Seoul, Seoul, Korea, ²Unionmedical Corporation, Uijeongbu, Gyeonggi-do, Korea, ³The MRI Team, Korea Basic Science Institute, Cheongju, Chungcheongbuk-do, Korea

The radio-frequency hyperthermia treatment with capacitive driving is now emerging as a noninvasive cancer treatment method. The tumorous tissue having higher ionic concentration have higher electric conductivity than the normal tissue. When the RF electric field is applied, the more electric current is drawn by the tumor cell resulting in the increased temperature around the tumor. This process could be carried out more safely with accuracy if we can monitor the treatment process including the temperature. We have studied the technical feasibility of developing MR compatible electrodes which can be used for RF hyperthermia in the MR systems with proper switching mechanism without affecting MR signal reception. A prototype animal 13.56 MHz capacitive RF hyperthermia system was operated with MR image acquisition capability using a 3.0-T MRI system (Achieva 3.0 T, Philips). We have designed, constructed, and tested experimentally a new RF electrode with switching resonant circuits working at 13.56 MHz without affecting the MR image acquisition at 128 MHz.

M.Arcan Erturk^1,2, Shashank Sathyanarayana Hegde¹, and Paul A Bottomley^1
1Radiology, Johns Hopkins University, Baltimore, Maryland, United States, ²Center for Magnetic Resonance Research, University of Minnesota Medical School, Minnesota, United States

We demonstrate a single interventional antenna that combines high-resolution image-guided targeting, RF ablation therapy, high-resolution thermometry, and quantitative relaxation time mapping. Standard, thermometric, and quantitative T₁ and T₂ MRI were performed in tissue samples in vitro and a rabbit in vivo, before and after ablation using a 3T loopless antenna. Spatial resolution was 200-300µm with 6-8s temporal resolution for thermometry. During ablation, the probe delivered local heating of >85°C resulting in irreversible thermal injury and up to two-fold changes in relaxation times post-ablation. The device could serve as a complete detection, thermal therapy and monitoring vehicle for MRI-guided intervention.

Isabel Dregely¹, Kyung Sung¹, Ferdnand Osuagwu¹, Dong Jin Chung¹, Charles Lassman², David Lu¹, and Holden H Wu^1
1Radiological Sciences, University of California Los Angeles, Los Angeles, CA, United States, ²Pathology and Laboratory Medicine, University of California Los Angeles, Los Angeles, CA, United States

Irreversible electroporation (IRE) is a new technique for minimally invasive local tissue ablation. Multi-contrast MRI has potential to non-invasively monitor IRE procedures. The purpose of this study was to evaluate multi-contrast (T2w, T1w pre and post contrast agent, and diffusion weighted imaging (DWI)) MRI for characterizing tissue ablation zones created by irreversible electroporation (IRE) in normal pig liver and correlate with histopathology. We found that IRE ablation zones were clearly visualized with multiple MRI contrasts and lesion short axis from both T2w and T1w MRI were correlated with pathology.

Etsuko Kumamoto¹, Tastuhiko Matsumoto², Daisuke Kokuryo³, and Kagayaki Kuroda^4,5
1Information Science and Technology Center, Kobe University, Kobe, Hyogo, Japan, ²Graduate School of System Informatics, Kobe University, Kobe, Hyogo, Japan, ³Molecular Imaging Center, National Institute of Radiological Sciences, Chiba, Japan, ⁴Graduate School of Engineering, Tokai University, Hiratsuka, Kanagawa, Japan, ⁵Center for Frontier Medical Engineering, Chiba University, Chiba, Japan

3D deformation of the liver under slow breathing was analyzed on the basis of the branching structure of the portal veins. A series of sagittal, multi-slice fast steady-state (FIESTA) images was acquired from a healthy volunteer�fs liver under slow-paced free respiration and was reconstructed to 4D MR images based on diaphragm positions. Regions of interest, including branching vessels, were set and tracked with the 3D template matching method. The extracted branching vessels showed that the anterior tissue of the liver was extended, and the posterior tissue of the liver was contracted against the superior tissue of the liver, which was compressed as the diaphragm fell.

Eugene Ozhinsky¹, Misung Han¹, Serena J. Scott², Chris J. Diederich², and Viola Rieke^3
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, ³University of California San Francisco, San Francisco, CA, United States

We have calibrated T2-based thermometry in adipose tissue and yellow bone marrow at 3T and investigated its dependence on pulse sequence parameters.

Pooja Gaur^1,2, Beat Werner³, Pejman Ghanouni⁴, Rachelle Bitton⁴, Kim Butts Pauly⁴, and William A Grissom^2,5
1Chemical and Physical Biology, Vanderbilt University, Nashville, TN, United States, ²Institute of Imaging Science, Vanderbilt University, Nashville, TN, United States, ³Center for MR-Research, University Children's Hospital, Zurich, Switzerland, ⁴Radiology, Stanford University, Stanford, CA, United States, ⁵Biomedical Engineering, Vanderbilt University, Nashville, TN, United States

MR thermometry measurements used during thermal treatments such as focused ultrasound are subject to heat-induced chemical shift (CS) distortions, which cause errors in images and temperature maps if left uncorrected. A CS-correction method has been previously demonstrated in simulation and phantom studies. In this work, we apply the method to data from clinical sonications in the brain and in soft tissue tumors in the leg. Results show that CS temperature errors can be reliably corrected in patient data, in 0.6 s per map, suggesting that corrections could be performed during the time of treatment.

Fuyixue Wang¹, Zijing Dong¹, Yuxin Hu¹, Feiyu Chen¹, Shuo Chen², Bingyao Chen³, Jiafei Yang³, Xing Wei³, Shi Wang², and Kui Ying^2
1Department of Biomedical Engineering, Tsinghua University, Beijing, China, ²Key Laboratory of Particle and Radiation Imaging, Ministry of Education, Department of Engineering Physics, Tsinghua University, Beijing, China, ³Department of Orthopedics, First Affiliated Hospital of PLA General Hospital, Beijing, China

Microwave ablation for bone tumor requires large volume coverage of the diseased tissue and the surrounding healthy tissues, especially spinal nerves. We developed an accelerated dynamic 3D MR temperature estimation method based on the 2D CAIPIRINHA in order to obtain better temperature estimation accuracy while significantly reducing the acquisition time. Finally, we validate the advantages and feasibility of this method for monitoring the temperature change of spinal cord. Generally, this method also allows researchers to extend it to all common 3D parallel imaging for MR temperature monitoring to obtain higher temperature estimation accuracy.

Henrik Odéen^1,2 and Dennis L Parker^1
1Utah Center for Advanced Imaging Research, Department of Radiology, University of Utah, Salt Lake City, Utah, United States, ²Department of Physics and Astronomy, University of Utah, Utah, United States

Dynamically adjusted model parameters lead to increased measurement accuracy in model based reconstruction methods of MR thermometry.

Juan Plata^1,2, Kristin Granlund², Brian Hargreaves², and Kim Butts Pauly^2
1Bioengineering, Stanford University, Stanford, CA, United States, ²Radiology, Stanford University, Stanford, CA, United States

Monitoring thermal treatments using a double echo steady state (DESS) sequence can allow for real-time lesion visualization. Proton resonant frequency changes from the first echo can be used to compute changes in temperature, while associated changes in signal intensity of the second echo are related to changes in T1, T2, and ADC. All these parameters have been previously associated with irreversible changes in tissue viability. Our work focused on empirically determining how these parameters changed in an egg-white phantom, and then using this information to simulate and validate signal changes for our DESS signal during heating of an egg.

Mingming Wu^1,2, Pauline Ferry³, Tim Sprenger^1,2, Desmond Teck Beng Yeo⁴, Axel Haase¹, and Silke Lechner-Greite^2
1IMETUM, Technische Universität München, Garching, Germany, ²GE Global Research, Garching, Germany, ³IADI, Nancy, Lorraine, France, ⁴GE Global Research, Niskayuna, New York, United States

The presented work examines the potential of combining fast and accurate T1 mapping for temperature quantification in fat applying fast inversion recovery or saturation recovery bSSFP and jointly using phase maps for PRFS based thermometry in water-based tissue. Bloch simulations of the steady state phase demonstrate the feasibility of PRFS quantification with bSSFP phase images. First experimental T1 maps at a constant temperature of ex vivo pork lard are illustrated. The magnitude data of the steady-state phase image can be used for the T1 mapping as the magnitude with long or infinite inversion time.

Yuan Zheng¹ and G. Wilson Miller^2
1Physics, University of Virginia, Charlottesville, VA, United States, ²Radiology and Medical Imaging, University of Virginia, Charlottesville, VA, United States

We have developed a proton resonance frequency shift (PRFS) based MR thermometry technique that collects temperature-sensitive phase images using a balanced steady-state free precession (bSSFP) pulse sequence. Our technique makes use of the sharp phase transition of bSSFP images over a narrow frequency range near resonance. Although the phase transition is non-linear, the phase change can be accurately mapped to PRFS (and thus temperature) using a pre-scanned phase transition curve. We performed phantom experiments using MR-guided focused ultrasound, to demonstrate the advantages of our bSSFP technique over conventional GRE-based methods for measuring small, fast temperature changes at the ultrasound focus.

Christiaan G. Overduin¹, Eva Rothgang², Jurgen J. Fütterer¹, and Tom W.J. Scheenen^1
1Radiology, Radboud University Medical Center, Nijmegen, Netherlands, ²Siemens Corporate Research, Erlangen, Germany

This study is the first to explore the feasibility of 3D ultrashort TE (UTE) MR thermometry of frozen tissue during cryoablation on a clinical MR system at 3T. We demonstrated 3D UTE imaging to achieve measurable MR signal from frozen tissue down to temperatures as low as -40°C within a clinically realistic time-frame (~1min.) and with clinically sufficient spatial resolution (1.63mm isotropic). Using a calibration curve, this allowed the 3D estimation of temperatures inside the iceball during cryoablation. In vivo application of this technique could allow interventionalists feedback on the effective treatment zone during MR-guided cryoablation procedures, however a robust calibration method will be needed.

MR-Guided Interventions

Tuesday 2 June 2015

Ethan K. Brodsky^1,2, Miles E. Olsen², and Walter F. Block^1,2
1Medical Physics, University of Wisconsin, Madison, WI, United States, ²Biomedical Engineering, University of Wisconsin, Madison, WI, United States

Real-time imaging is useful for many diagnostic and interventional procedures. While the most basic morphological imaging techniques are adequate in many cases, there is an increasing need for more sophisticated imaging sequences. Spectral decomposition techniques like IDEAL would be used to image a ceramic biopsy trocar in fatty areas of the breast, or for monitoring the delivery of therapeutic agents tagged with lipid or SPIO markers. By eliminating closely coupled and vendor specific integration between the image processing layers, the development and deployment of new imaging techniques is simplified and accelerated. We present an implementation of IDEAL on the HeartVista RTHawk real-time imaging platform, showing phantom studies for both a Cartesian and spiral acquisition, with per-frame imaging time on the order of seconds.

Reza Monfaredi^1,2, Emmanuel Wilson¹, Bamshad Azizi Koutenaei¹, Raymond Sze¹, Karun Sharma¹, and Kevin Cleary^1
1Sheikh Zayed Institute, Children's National Medical Center, Washington, DC, District Of Columbia, United States, ²Industrial department, Azad University- South Tehran Branch, Tehran, Iran

In this abstract, we are introducing an MRI compatible robot for needle placement for shoulder arthrography. Gold standard for this procedure is a two-stage procedure, i.e. an intra-articular contrast injection typically guided by fluoroscopy followed by an MRI. The current two-step workflow can result in prolonged sedation time when sedation is needed for younger patients, radiation exposure, and may increase cost due to the use of both the fluoroscopy and MRI suite. In this abstract new version of our MRI compatible robot is introduced. We aimed to reduce backlash and friction to increase the positioning accuracy of this new system.

Tatsuya J Arai¹, Joris Nofiele², Yam Ki Cheung¹, Rajiv Chopra², and Amit Sawant^1
1Radiation Oncology, UT Southwestern Medical Center, Dallas, Texas, United States, ²Radiology, UT Southwestern Medical Center, Dallas, Texas, United States

Respiratory motion management during the thoracoabdominal tumor treatment is one of the biggest challenges in modern image-guided radiation therapy (RT). MRI enables the long-term, dose-free, soft-tissue monitoring, representing clear advantages over x-ray-based imaging modalities. Given unique requirements of RT guidance-quality (high temporal resolution, and modest spatial resolution and SNR), we have been investigating the adaptation of k-t BLAST. We have also developed MRI-compatible, programmable, and externally and internally deformable lung motion phantom, which replicates respiratory motion traces acquired from lung cancer patients. To our knowledge, this is the first report of using k-t BLAST for lung cancer radiotherapy motion management.

Guan Wang^1,2, M. Arcan Erturk³, Shashank Sathyanarayana Hegde², and Paul A. Bottomley^1,2
1Dept. of Electrical & Computer Engineering, Johns Hopkins University, Baltimore, MD, United States, ²Russell H. Morgan Dept. of Radiology & Radiological Sciences, Johns Hopkins University, Baltimore, MD, United States, ³Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN, United States

The ability to characterize atheroma components is central to assessing the status of vessel disease, its progression and response to interventions, diet, etc, but is poorly served by existing modalities. To test whether high-field, high-resolution intravascular MRI (IVMRI) combined with quantitative T1, T2, proton density and mobile lipid mapping could be used to stage vessel disease, we applied 200µm resolution multi-parametric 3T MRI to diseased human artery specimens. The results were used to train an automatic machine-learning-based classifier to classify disease, and the performance was compared with histology.

Barret Daniels¹, Ronald Pratt², Randy Giaquinto^1,2, and Charles Dumoulin^1,2
1Biomedical Engineering, Univsersity of Cincinnati, Cincinnati, Ohio, United States, ²Imaging Research Center, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio, United States

MR active tracking suffers from less efficient signal detection, poorer accuracy, and a complicated phase sensitivity profile when MR signals detected by the tracking coil arise only from regions outside of the coil. Hadamard Multiplexing and Phase Field Dithering have been proposed to improve tracking accuracy in these low SNR conditions. We developed a strategy to further increase MR tracking accuracy in these conditions by improving upon the conventional “max pixel” approach to MR tracking peak detection in the power spectrum. Furthermore, we quantified the combined benefit in accuracy and precision of all three methods through electromagnetic simulation and experimentation.

Adrienne E Campbell-Washburn¹, Toby Rogers¹, Burcu Basar^1,2, Merdim Sonmez¹, Ozgur Kocaturk^1,2, Robert J Lederman¹, Michael S Hansen¹, and Anthony Z Faranesh^1
1Cardiovascular and Pulmonary Branch, Division of Intramural Research, National Heart Lung and Blood Institute, National Institutes of Health, Bethesda, MD, United States,²Institute of Biomedical Engineering, Bogazici University, Istanbul, Turkey

Clinical translation of MRI-guided cardiovascular catheterizations has been limited by the unavailability of MRI visible and safe devices, particularly rigid metallic guidewires. Here, we use gradient echo spiral imaging to reduce RF-induced heating compared to Cartesian bSSFP (0.47°C vs. 37.2°C). Guidewire visualization was enabled using through-slice dephasing in alternating frames to generate positive contrast images where the guidewire appears bright compared to the background. Imaging ran at 6.25 frames/s and guidewire signal was overlaid onto anatomical images in real-time during left-heart catheterization in swine. This method shows promise to enable the safe use of commercial guidewires during MRI-guided cardiovascular catheterizations.

Axel Joachim Krafft^1,2, Simon Reiß¹, Klaus Duering³, and Michael Bock^1
1Radiology - Medical Physics, University Medical Center Freiburg, Freiburg, Germany, ²German Cancer Consortium (DKTK), Heidelberg, Germany, ³MaRVis Medical GmbH, Hannover, Germany

Recently, dedicated passive MR-compatible guidewires were introduced that employ embedded iron particles to generate a local artifact for device visualization. The generated artifact depends in particular on the echo time (TE) and on the orientation of the guidewire marker relatively to the main magnetic field. In conventional gradient-echo imaging, the guidewire exhibits a wide artifact for orientations perpendicular to the main magnetic field and a narrow one parallel to it. Here, we present a radial acquisition scheme to realize a uniform, orientation-independent artifact for improved guidewire visualization.

Job G. Bouwman¹, Bram A Custers¹, Chris J.G. Bakker², and Peter R Seevinck^1
1Image Sciences Institute, University Medical Center Utrecht, Utrecht, Netherlands, ²Image Sciences Institute, University Medical Center, Utrecht, Netherlands

A novel positive contrast method to depict pointine, strong magnetic markers, based on their phase saddles; locations where the encoding gradient is cancelled by the marker induced gradient.