ISMRM 21st Annual Meeting & Exhibition ○ 20-26 April 2013 ○ Salt Lake City, Utah, USA
ELECTRONIC POSTER SESSION • ENGINEERING
4338 -4349 | MR Systems Engineering
4350 -4361 | RF Array Coil Coupling & RF Coils for Multinuclear & Hybrid Systems
4362 -4373 | RF Coils & Concepts
4374 -4385 | Dielectrics & Novel RF Concepts
4386 -4397 | Receive Arrays
4398 -4409 | Transmit Arrays
4410 -4421 | MRI Safety 1
4422 -4433 | MRI Safety 2
ELECTRONIC POSTER SESSION • ENGINEERING Thursday, 25 April 2013 (10:30-11:30) Exhibition Hall
MR Systems Engineering
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4338. | 25 | NIST/ISMRM MRI System Phantom T1 Measurements on Multiple MRI Systems Kathryn E. Keenan1, Michael A. Boss1, Edward F. Jackson2, Seon-joo Kown3, Dominique L. Jennings3, and Stephen Russek1 1National Institute of Standards and Technology, Boulder, CO, United States, 2Imaging Physics, The University of Texas M.D. Anderson Cancer Center, Houston, TX, United States, 3Massachusetts General Hospital, Boston, MA, United States An MRI system phantom was developed through collaboration between the ISMRM and NIST. We used this phantom to answer: 1) how does measured T1 compare to the known T1; and 2) is there variation in the measured T1 across multiple MRI systems? For more information on the NIST/ISMRM phantom, please visit: http://collaborate.nist.gov/mriphantoms/bin/view/MriPhantoms/MRISystemPhantom.
4339. | 26 | A Novel fMRI-Compatible Device to Quantify the Cortical Response to Walking-Related Foot Sole Pressures Ying Hao1,2, Kai Zhang1, Ye Wang1, Xiaoying Wang1,3, Jing Fang1,4, Jue Zhang1,4, and Brad Manor1,2 1Academy for Advanced Interdisciplinary Studies, Peking University, Beijing, Beijing, China, 2Gerontology Department, Beth Israel Deaconess Medical Center, Boston, MA, United States, 3Radiology Department, Peking University First Hospital, Beijing, Beijing, China, 4College of Engineering, Peking University, Beijing, Beijing, China This novel foot sole stimulator elicited more simulated walking pressure stimulus to the foot sole compared to the former version, meanwhile, it remains no interfered with image quality and did not cause severe motion artifacts. This system is thus feasible for fMRI studies to explore functional brain networks involved in the perception and modulation of the real foot sole somatosensation. Combination of this new tool with functional MRI (fMRI) will afford insight into the functional brain networks underlying the afferent feedback under walking.
4340. | 27 | Motion Phantom for Real-Time MRI Sebastian Schaetz1, Markus Untenberger1, Aaron Niebergall1, and Jens Frahm2 1Biomedizinische NMR Forschungs GmbH, Max Planck Institute for Biophysical Chemistry, Göttingen, Lower Saxony, Germany, 2Biomedizinische NMR Forschungs GmbH, Max Planck Institute, Göttingen, Lower Saxony, Germany A novel metal-free motion phantom based on a simple pneumatic rotary motor with optical rotational speed measurement is presented. The phantom facilitates the simulation of various motion speeds from 0.05 to 0.5m/s by air-pressure adjustment. It is a suitable tool for for both qualitative and quantitative evaluation of real-time MRI methods.
4341. | 28 | A Single-Magnet Fast Field-Cycling Whole-Body MRI System with Detection at 0.2 T Gareth R. Davies1, Kerrin J. Pine1, and David J. Lurie1 1Aberdeen Biomedical Imaging Centre, University of Aberdeen, Aberdeen, Scotland, United Kingdom Fast Field-Cycling (FFC) MRI systems differ from conventional scanners by their ability to adjust rapidly the magnetic field strength B0 during the pulse sequence. This offers unique image contrast, based on the field-dependence of the spin-lattice relaxation time (T1-dispersion) giving, for example, increased sensitivity to changes in protein. We have built a whole-body FFC-MRI system with a detection field of 0.2 T. This has required novel designs of magnet, power supplies, and control hardware and software. Design issues and solutions and initial results are presented. The scanner will allow clinical applications of FFC to be explored.
4342. | 29 | Construction of a 1.5 T Cryogen Free MRI System Sergei Obruchkov1 and Robin Dykstra1 1Victoria University, Wellington, New Zealand A 260 mm bore 1.5T MRI system was designed around a cryogen-free superconducting magnet. The system was designed for small animal imaging applications in cancer research, to be located were cryogen availability and costs are prohibitive for conventional magnet systems.
4343. | 30 | PNS Safety of the Composite Gradient System K Craig Goodrich1, Seong-Eun Kim1, Joshua D. Kaggie1, J. Rock Hadley1, William B. Handler2, Blaine A. Chronik3, and Dennis L. Parker1 1UCAIR, University of Utah, Salt Lake City, Utah, United States, 2Physics and Astronomy, Univ of Western Ontario, London, Ontario, Canada, 3Physics and Astronomy, Western University, London, Ontario, Canada This work was done to establish PNS limits for simultaneous operation of a 3 axis head/neck gradient insert and standard gradient system (composite mode operation). PNS thresholds were measured for each gradient system as well as combined operation for each axis separately and combined. Experimental results suggest that body and insert gradient thresholds are independent of each other, allowing for increased combined gradient field strength and slew rates in composite mode until either constituent threshold is reached. These results show a definite safety advantage for composite gradient mode operation allowing larger gradients and slew rates.
4344. | 31 | Design Study for Making Split Gradient Coils More Robust Michael S. Poole1, Nadim Jon Shah1,2, and Rob Hawkes3 1INM-4, Forschungszentrum Juelich, Juelich, Nordrhein-Westfalen, Germany, 2Neurologische Klinik, Universitaetsklinikum Aachen, Aachen, Nordrhein-Westfalen, Germany, 3Wolfson Brain Imaging Centre, Addenbrookes Hospital, Cambridge, Cambridgeshire, United Kingdom The redesign of split gradient coils for a hybrid MR-PET system is considered. Numerous changes in the coil design are assessed for their performance with the aim of making the coil more robust. New design strategies and a slackening of design constraints are also assessed for their ability to mitigate any performance loss from making the coils more robust. A linking annulus was found to be essential, but we enforce radial connections for simplifying the construction. A complex relationship exists between the design constraints and the coil performance, which needs to be considered carefully before a final design is constructed.
4345. | 32 | Simple, Accurate and Efficient Multilayer Integral Method for Eddy Current Simulation in Thin Volumes of Arbitrary Geometry Produced by MRI Gradient Coils Hector Sanchez Lopez1, Fabio Freschi2, Adnan Trakic1, Elliot Smith1, Jeremy Herbert1, Miguel Fuentes1, Stephen Wilson1, Limei Liu1, Maurizio Repetto2, and Stuart Crozier1 1ITEE, The University of Queensland, Brisbane, QLD, Australia, 2Department of Energy, Politecnico di Torino, Torino, Torino, Italy We present a new accurate and efficient eddy current simulation method capable of calculating induced currents in finite thickness conducting volumes of arbitrary geometry induced by arbitrary arrangements of gradient coils. The method has been experimentally validated using a z-gradient coil and its performance tested against COMSOL and the Fourier Network method. We present an example to demonstrate the capabilities of the method in terms of predicting the induced currents, power losses and pre-emphasis simulations using the excited eigenvalue corresponding to the surrounding structure. The method is accurate and fast enough to be performed in a laptop Intel corei7 CPU.
4346. | 33 | Theoretical Design of Shim Arrays with Irregular Coil Geometry Peter T. While1 and Jan G. Korvink1,2 1Department of Microsystems Engineering (IMTEK), Laboratory for Simulation, University of Freiburg, Freiburg im Breisgau, Baden-Württemberg, Germany, 2Freiburg Institute for Advanced Studies (FRIAS), University of Freiburg, Freiburg im Breisgau, Baden-Württemberg, Germany Conventional shim systems are comprised of a set of dedicated coils for inducing low-order spherical harmonic fields. In contrast, shim arrays consist of multiple simple coil structures, such as circular loops, arranged on a uniform grid. These elements generate an alternative set of non-orthogonal basis fields that offer the potential for high-order shimming. In this study, a design concept is presented for generating shim arrays with irregular element geometry that afford field accuracy and efficiency advantages over the use of regular circular loops for inducing low-order fields.
4347. | 34 | Flanged-Edge Transverse Gradient Coil Design for a Hybrid LINAC-MRI System Limei Liu1, Hector Sanchez-Lopez1, Feng Liu1, and Stuart Crozier1 1The University of Queensland, Brisbane, Queensland, Australia Combined Linear accelerator (LINAC) - MRI systems can provide image-guided radiotherapy treatment. These systems require splitting of the MRI scanner to provide a central gap large enough to ensure dual access for the accelerator and the patient. This raises technical difficulties for maintaining high gradient coil performance. In this research, a dedicated split transverse gradient coil was designed with a flange connected to the central coil end and compared to existing coil designs. It was found that a flanged-edge coil design produced manageable coil performance and eddy currents.
4348. | 35 | Very Low Field MRI with Giant Magnetoresistance Based Sensors Quentin Herreros1, Hadrien A. Dyvorne2, Paolo Campiglio1, Amala Demonti1, Guenaelle Jasmin-Lebras1, Myriam Pannetier-Lecoeur1, and Claude Fermon1 1CEA, Gif-sur-Yvette, France, 2Mount Sinai School of Medicine, New York, NY, United States Avoiding numbers of high field drawbacks, very low field MRI requires sensitive detection devices .We have developed a novel magnetic sensor based on a combination of spin electronics and superconductors, labelled mixed sensor, and reaching sensitivities in the fT range at low frequencies down to 1kHz. This mixed sensor was inserted in a small scale prototype system and in vivo images were successfully acquired at 7mT, showing high performance and versatility of the sensor for very low field MRI.
4349. | 36 | Low Acoustic RF Coil Design Saikat Saha1 and Washington De Lima2 1GE, Waukesha, WI, United States, 2GE, Florence, SC, United States During high field MR scans, patients become uncomfortable due to the high acoustic noise and vibration produced inside the patient bore. This noise can be as high as ~125dBA depending on the field strength of the scanner and PSD being used. The main source of noise inside the scanner is due to the gradient coil (when pulsed) vibrating in a static magnetic field generated by the magnet. This noise is transmitted through the RF body coil to the patient ears. Another major source of noise is vibration of the RF body coil itself. RF body coil vibrates due to the eddy current generated by the gradient coil pulsing on the copper sections of the RF coil. Some of the previous work, which addresses the issue of acoustic noise and vibration have been documented in [1-2]. The design described here addresses the issue of acoustic noise by significantly reducing the vibration which in turn reduces the noise by upto 9 dBA in a conventional Birdcage RF coil without compromising the RF performance.
ELECTRONIC POSTER SESSION • ENGINEERING Thursday, 25 April 2013 (10:30-11:30) Exhibition Hall
RF Array Coil Coupling & RF Coils for Multinuclear & Hybrid Systems
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4350. | 37 | Comparison of Arrays with Various Mutual Impedances: Noise Correlation, SNR and Parallel Imaging Performance Adam Maunder1, Mojgan Daneshmand1, Pedram Mousavi1, B. Gino Fallone2, and Nicola De Zanche2 1Electrical and Computer Engineering, University of Alberta, Edmonton, Alberta, Canada, 2Oncology, University of Alberta, Edmonton, Alberta, Canada In arrays, mutual resistance is the source of intrinsic noise correlation, which has been assumed to be unalterable using preamplifier decoupling and lossless decoupling networks. By using inter-element capacitors cancellation of both mutual resistance and reactance is achieved between adjacent coils. Array performance comparisons are made using two-and four-coil arrays in the presence of preamplifier decoupled a) with the mutual impedance removed, b) only the mutual reactance removed and c) with no additional decoupling. On average, the differences in SNR and parallel imaging g-factor are minimal.
4351. | 38 | Evaluation of Capacitive and Transformer Decoupling Methods Using in Non-Overlapped Array at 7.0T Hongbae Jeong1, Kyoung-Nam Kim1, Suk-Min Hong1, Joshua Haekyun Park1, Myung-Kyun Woo1, Young-Bo Kim1, and Zang-Hee Cho1 1Neuroscience Research Institute, Gachon University, Incheon, Korea We have conducted research on comparison between capacitive decoupling network and transformer decoupling methods with 8-channel transceive array. Three coils were desing including hybrid version of two decoupling methods, in terms of SNR and noise correlation matrix on 7T.
4352. | 39 | Analysis of Imaged Object's Permittivity, Conductivity, Size and Position Effects on Optimal Capacitive, Inductive and Transformer Decoupling Schemes in RF Coil Arrays Volkan Emre Arpinar1 and L. Tugan Muftuler1,2 1Department of Neurosurgery, Medical College of Wisconsin, Milwaukee, WI, United States, 2Center for Imaging Research, Medical College of Wisconsin, Milwaukee, WI, United States Although transformer, capacitive and inductive decoupling techniques have been widely used in transmit or receive coil arrays, a comparative analysis of their tolerances to load variances were not reported. In this study full wave electromagnetic simulations with realistic coil models are used to understand the robustness of each decoupling method to the variations in size and electrical properties of the loading object.
4353. | 40 | Mutual Coupling Study Using a Pair of Fractal Loop RF Coils Seunghoon Ha1 and Orhan Nalcioglu1,2 1Tu & Yuen Center for Functional Onco-Imaging, University of California Irvine, Irvine, California, United States, 2Department of Cogno-Mechatronics Engineering, Pusan National University, Pusan, Korea In this work, we introduced a fractal loop RF coil keeping the lower radiation loss than the corresponding loop RF coil, which may provide more adjustment of the coil positioning. With designed a pair of fractal loop RF coils, we investigated optimizing overlap locations and the magnetic vector field propagation on the position. In parallel with the simulation study, we built the pair of the fractal loop coil, measureed the isolation, and scanned phantom images. The results proved that the fractal loop RF coil had an alternative in designing RF coil by comparing with other circular loop coils.
4354. | 41 | A Five Channel Receive Array for Cardiac Imaging Using Hyperpolarized 13C at 3T. William Dominguez-Viqueira1, Angus Z. Lau1, Albert P. Chen2, and Charles H. Cunningham1,3 1Imaging, Sunnybrook Research Institute, Toronto, Ontario, Canada, 2GE Healthcare, Toronto, Ontario, Canada, 3Medical Biophysics, University of Toronto, Toronto, Ontario, Canada Hyperpolarized-13C substrates have become a promising tool to study real-time cardiac-metabolism in-vivo. Multi-channel receiver systems can provide similar SNR performance to a single surface coil, but with increased coverage. A single channel and a 5-channel array 13C receive coil were simulated in Matlab and compared with in-vivo measurements. SNR improvements at the base of the heart, were achieved by using the 5-channel coil array. This coil array may be suitable for human cardiac 13C studies and parallel imaging reconstruction in the near future.
4355. | 42 | 23Na/1H In-Vivo Renal MRI of Rodent Kidney at 3T by Using a Double-Tuned Transceiver Resonator System Raffi Kalayciyan1, Matthias Malzacher1, Sabine Neudecker2, Norbert Gretz2, and Lothar R. Schad1 1Computer Assisted Clinical Medicine, Heidelberg University, Mannheim, Germany, 2Medical Research Center, Heidelberg University, Mannheim, Germany 23Na-MRI at high-field strengths (>3T) has proven to be a unique modality for monitoring renal function non-invasively after pharmacological interventions in animal models. Nevertheless, performing in vivo studies on clinical MR-systems simplifies transferring newly-developed 23Na-MRI methods to clinical diagnostic imaging, although the lower field strengths represent a major drawback. In this work we developed a transceiver double-resonant (23Na/1H) RF resonator system, and integrated it using an RF interface at 3T human scanner in order to monitor furosemide-induced 23Na signal changes in renal tissue.
4356. | 43 | An Improved Surface Coil Design for Proton Decoupled Carbon-13 Magnetic Resonance Spectroscopy Eulalia Serés Roig1, Guillaume Donati1, Martin Meyerspeer2, Lijing Xin1,3, Rolf Gruetter4,5, and Arthur W. Magill1,3 1Laboratory of Functional and Metabolic Imaging, Ecole Polytechnique Fédérale de Lausanne, Lausanne, Vaud, Switzerland, 2Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Vienna, Austria, 3Department of Radiology, University of Lausanne, Lausanne, Vaud, Switzerland, 4École Polytechnique Fédérale de Lausanne, Lausanne, Vaud, Switzerland, 5Department of Radiology, Universities of Lausanne and Geneva, Lausanne, Geneva, Switzerland Carbon-13 MRS is an inherently low-sensitivity technique, making detection signal-to-noise ratio (SNR) critical. An important step in the optimization of SNR is the design of the RF coil. The probe must be capable of simultaneous transmission at the 1H frequency while receiving at the 13C frequency for J-decoupling. Especially when operating at high-field, this makes SAR limitations challenging. In this abstract we demonstrate a quadrature-13C/quadrature-1H surface coil, using traps to decouple the 13C loops from the 1H loops. This design increases the 13C detection sensitivity without increasing power deposition at the 1H frequency. We compare the performance to a standard linear-13C/quadrature-1H coil using glycogen detection in the human calf at 7T. An improvement in SNR by a factor of 1.8 was shown.
4357. | 44 | Numerical Optimization of a 3-Channel Array Coil for 31P Functional Spectroscopy at 7T Andre Kuehne1,2, Ewald Moser1,2, and Elmar Laistler1,2 1Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria, 2MR Centre of Excellence, Medical University of Vienna, Vienna, Austria A 3-channel 31P coil array for 7 T brain spectroscopy of the visual cortex is optimized numerically. The coil size & distance to the head are varied to find the optimum coil geometry. For each configuration, the whole 2D excitation phase parameter space is evaluated w.r.t. B1 and local SAR using a fast SAR calculation routine based on local power correlation matrices. Three different excitation modes are compared w.r.t. B1+/(P), B1+/(SAR) and field homogeneity.
4358. | 45 | Analysis of Tissue Properties and MRI Signals in the Head for PET/MRI Attenuation Correction H. Michael Gach1, Julie C. Price2, Denise K. Davis2, Sungkyu Jung3, Jonathan P. Carney2, James A. Ruszkiewicz2, Brian J. Lopresti2, Charles M. Laymon2, and Chester A. Mathis2 1Radiology & Bioengineering, University of Pittsburgh, Pittsburgh, PA, United States, 2Radiology, University of Pittsburgh, Pittsburgh, PA, United States, 3Statistics, University of Pittsburgh, Pittsburgh, PA, United States Positron emission tomography (PET) requires photon attenuation correction to accurately reconstruct the PET images. PET-MR systems use MRI to image and differentiate tissue and generate attenuation or mu-maps. Tissues are typically delineated into four categories (air, bone, fat, and water) using Dixon fat/water or ultra-short TE (UTE) pulse sequences and then assigned the applicable mu-value. Unfortunately, these sequences have limitations in differentiating the tissue types and cannot image air (due to its negligible mass and proton densities) and compact bone (due to its T2 < 20 µs). A regression analysis based on brain tissue physical parameters and MRI signals indicates that tissue mu values can be accurately calculated for all brain tissues based on a combination of the data, particularly the tissue’s proton density and magnetic susceptibility.
4359. | 46 | Novel and Compact PET Insert for Simultaneous PET/MR Imaging of Small Animals Konrad Lankes1, Hans Post1, Hans Wehrl2, Chih-Chieh Liu2, Mosaddek Hossain2, Bernd Pichler2, and Sven Junge1 1Bruker BioSpin MRI, Ettlingen, Germany, 2Preclinical Imaging and Radiopharmacy, University of Tuebingen, Tuebingen, Germany Over the last view years combined, simultaneous PET and MR imaging has become more importance, especially in the domain of monitoring metabolic processes. and has been developed as an excellent tool in the area of clinical and preclinical research. This work discusses the development of a highly efficient and compact PET/MR imaging system for small animals, allowing studies of rats and mice. The performances with respect of imaging quality, temporal and special resolution of PET- and MR-imaging have been carefully measured on the bench and phantoms. In-vivo studies are presented to show the possibilities of PET/MR imaging in small animal research.
4360. | 47 | Development of a Novel RF Body Coil Integrated with MR-Compatible PET Detector Gary H. Glover1, Craig S. Levin1, Anton Linz2, William T. Peterson2, and Sri Harsha Maramraju2 1Stanford University School of Medicine, Stanford, CA, United States, 2GE Healthcare, Waukesha, WI, United States A hybrid PET/MR prototype for simultaneous PET/MR imaging has been developed. The scanner integrates a high performance Time-of-Flight MR-compatible PET system with a modified widebore MR scanner. A novel RF body coil design enables installation of the 25 cm axial length PET detector inside a conventional gradient coil with negligible impact on B1 homogeneity. Other measurements of signal-to-noise ratio, image temporal stability and geometric distortion parameters with the PET system powered off and on demonstrate negligible image degradation. Furthermore, PET energy and timing resolution measurements were not affected by MRI and confirm bilateral compatibility of the two modalities.
4361. | 28 | MRI Compatible Orthotopic Breast Cancer Window Chamber Model for Multi-Modality Imaging Arthur F. Gmitro1, Rachel L. Schafer2, and Huimin Leung3 1Medical Imaging, University of Arizona, Tucson, Arizona, United States, 2Biomedical Engineering, University of Arizona, Tucson, Arizona, United States, 3College of Optical Sciences, University of Arizona, Tucson, Arizona, United States A new orthotopic breast cancer window chamber animal model system for multi-modality imaging is described and presented. This platform system can be used for MRI, nuclear, photoacoustic, and optical imaging of breast cancer xenografts. High-resolution optical imaging allows cancer processes to be studied at the cellular/molecular level and correlated with observations obtainable with MRI at the tissue level. The new model system is especially applicable to the study of cancer processes such as growth, invasion, metastasis, and therapeutic response. The system is also useful for the validation and application of imaging biomarkers for therapeutic development.
ELECTRONIC POSTER SESSION • ENGINEERING Thursday, 25 April 2013 (11:30-12:30) Exhibition Hall
RF Coils & Concepts
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4362. | 25 | Distribution of RF Traps to Reduce RF Heating with Endoluminal Coils: An Experimental Study Jean-Marie Verret1, Frank Pilleul2, Olivier Beuf3, and Cecile Rabrait4 1CREATIS, Villeurbanne, France, Metropolitan, 2Hospices Civils de Lyon, Lyon, France, Metropolitan, 3CREATIS, Lyon, France, Metropolitan, 4General Electric Healthcare, Velizy, France, Metropolitan There are many techniques considered in the literature to reduce RF heating. A small number of passive RF traps incorporated in the reception cable present excellent results in the case of an endoluminal coil at 3T. The historical design of RF trap such as LC filters is efficient. Due to the distribution of induced currents in the cable, a close attention should be paid to the location of the RF traps along the cable. Optimal placememt can also narrow down the number of RF traps to a minimum.
4363. | 26 | Investigation of the Transition from Travelling Wave to Near Field Excitation Using Crossed Dipole Antennas Karthik Lakshmanan1, Martijn A. Cloos2, and Graham C. Wiggins1 1NYU, Newyork, Newyork, United States, 2New York University School of Medicine, Newyork, Newyork, United States Crossed Dipoles have been used to create travelling waves in the bore of the magnet which can be used for MR imaging. Travelling wave excitation is relatively inefficient compared to conventional volume resonators. If the crossed dipole is placed close to the object, however, efficiency increases while excitation pattern changes. In this study we compared the excitation profile and efficiency of a crossed dipole antenna pair as a function of distance between the antenna and the object imaged. The efficiency of the antenna configuration showed an inverse proportionality to the distance between the antenna and the Imaging object. When the distance between the antenna pair and the imaging object was less than quarter wavelength the excitation pattern changed from a travelling pattern with peak low in the head and with neck excitation to more of a near field excitation with the excitation primarily confined to the top of the head.
4364. | 27 | A Numerical Approach to the Development of MRI Radiofrequency Coils Gemma R. Cook1, Martin John Graves1, and David J. Lomas1 1Department of Radiology, University of Cambridge, Cambridge, United Kingdom This educational presentation is aimed at scientists interested in radiofrequency coil design. It details the steps involved in the simulation of coils and the ways the results aid in the development of optimised designs. General methods to arrange a model geometry with appropriate boundary conditions and approximations are included and the ways in which performance metrics such as SNR, g-factor and SAR are calculated from electromagnetic field results explained. The Finite Element Method for EM field solutions will be described to assess the benefits of a simulation-based assessment of coil designs; examples use COMSOL Multiphysics (COMSOL Inc., Sweden).
4365. | 28 | 3T Transceiver Quadrature Surface Coil Design for Cervical Spine Spectroscopy Wonje Lee1, Oded Gonen2, Daniel Sodickson1, and Graham Wiggins1 1Radiology, NYUMC, New York, NY, United States, 2Radiology, New York University, New York, NY, United States MRS in the cervical spinal cord is particularly challenging because of the small size and deep anatomical location, limiting the signal available and placing stringent demands on the accuracy of spatial localization. Due to the use of high bandwidth refocusing pulses and the inclusion of additional water suppression the body coil transmission with a receive only coil may impose limitations. Motivated by the need of a local transceiver coil aiming for the C-spine spectroscopy a new design of 3T TR quad surface coil is presented, and its efficiency performance is evaluated, compared to the commercial head-neck receive coil.
4366. | 29 | A Transceive RF Coil for Imaging Tissue Specimen at 3T Based on PCB Design Roland Müller1, André Pampel1, Toralf Mildner1, Henrik Marschner1, and Harald E. Möller1 1Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany Goal of the project was to design a transceive RF coil for imaging small tissue specimen on a human-scale 3T MR scanner. Besides high SNR, high homogeneity and stability of the B1+ field, a major objective was to minimize RF heating. Two perpendicular Helmholtz coil pairs were combined to obtain a quadrature coil. To achieve a high degree of accuracy during coil fabrication, the whole 3D design was made from printed circuit board material. Differential-mode sheath waves were easily and aperiodically suppressed by connecting the coax cable shields with a few resistors.
4367. | 30 | A New UHF Transceiver Antenna Design: Modified Folded Dipole Wonje Lee1, Daniel Sodickson1, and Graham Wiggins1 1Radiology, NYUMC, New York, NY, United States The linear electric dipole antenna has been suggested in favor of its current distribution by electrodynamics, reporting potential benefits of better penetration depth and efficiency at 7T. However, it exhibits strong loading sensitivity when close proximity to the conductive object due to its open structure, which hampers applications in subject dependent body imaging. To aim for practical transceiver body array implementation at 7T, a new antenna design, calling “modified folded dipole (mf-dipole)” is presented. The evaluation of the proposed antenna exhibits less loading sensitivity, and favorable B1 patterns, proposing a solution for challenging 7T body imaging.
4368. | 31 | 7T Tx Body Coil with Rx-Only Insert: Primarily Results Shailesh B. Raval1, Yujuan Zhao1, Tiejun Zhao2, Narayanan Krishnamurthy1, Sossena Wood1, and Tamer S. Ibrahim1 1University of Pittsburgh, Pittsburgh, PA, United States, 2Siemens Medical Solutions, Pittsburgh, PA, United States . The goal of this study is to use multi-channel transmit coil to target and excites the nuclei in spatially uniform manner in conjunction with a receive-only insert. In this preliminary study, we utilized 7 Tesla human MRI scanner with a 12-channel transmit array combined with 16-channel receive-only body array that target kidney and liver
4369. | 32 | Transmit-Only Receive-Only Operation of a Switch-Tuned 13C-1H Radiofrequency Coil for Improved in Vivo 13C Spectroscopy Heeseung Lim1, Kundan Thind1, Francisco M. Martinez-Santiesteban1, and Timothy J. Scholl1,2 1Medical Biophysics, Western University, London, Ontario, Canada, 2Imaging Research Laboratories, Robarts Research Institute, Western University, London, Ontario, Canada This work reports the integration of a 13C surface receive coil with a switched-tuned 13C-1H birdcage RF coil to enable combined transmit-only receive-only (TORO) operation to improve sensitivity for in vivo 13C spectroscopy. The 13C-1H birdcage coil is operated in 1H mode as a transmit-receive (TR) volume coil for anatomical imaging. Those images are subsequently co-registered with chemical shift imaging data obtained from 13C TORO operation. The TORO combination produces four times higher 13C signal-to-noise ratio than the switched-tuned RF coil alone operating in TR mode.
4370. | 33 | Development of Cross-Pole RF Tx Array for Breast Imaging at 7T Junghwan Kim1, Narayan Krishnamurthy1, Yujuan Zhao1, Tiejun Zhao2, Kyongtae Ty Bae1, and Tamer S. Ibrahim1 1University of Pittsurgh, pittsburgh, PA, United States, 2Siemens Medical Solutions, pittsburgh, PA, United States We have developed a two-sided RF resonator based on 8-channel array design for breast MR imaging at 7T. The RF resonator was evaluated by means of modeling and simulations as well as successful empirical testing involved with a breast phantom and two normal volunteers. Future studies include optimization of phases and amplitudes for B1 shimming and combination with Rx array insert.
4371. | 34 | Feasibility Numerical Study of the Travelling Wave MRI at 3T Fabian Vazquez1 and Alfredo O. Rodriguez2 1Fac Ciencias, UNAM, Mexico, DF, Mexico, 2Dep Ing. Elec, UAM Iztapalapa, Mexico, DF, Mexico The travelling wave magnetic resonance imaging (twMRI) approach has been proved successful at 3T and 7T for large magnet bores. However, there is still some controversy regarding the feasibility of the twMRI being able to generate images a lower frequency than 300 MHz. To study this, we chose the parallel-plate waveguide because it is able to propagate any frequency for the principal mode, and its cut-off frequency is zero. Then, the PPWG Poynting vector fields with a human phantom and the magnetic fields for the principal mode were numerically computed at 3T.
4372. | 35 | Characterizing Bazooka Baluns M. Arcan Erturk1,2 and AbdEl-Monem M. El-Sharkawy2 1Department of Electrical & Computer Engineering, Johns Hopkins University, Baltimore, Maryland, United States, 2Russell H. Morgan Department of Radiology and Radiological Sciences, Johns Hopkins University, Baltimore, MD, United States Baluns or cable traps are used to suppress common mode currents on the outer shield of coaxial cables connecting MRI coils. Their main function is to enhance the SNR performance of coils, reduce coupling and ensure RF safety. Here, we demonstrate a method to calculate the expected impedance and resonance frequency of bazooka baluns. The method is verified experimentally where bench measurements agree with our calculations from 50MHz up to at least 150MHz.
4373. | 36 | Demonstration of High Efficiency on Coil RF Amplifier for 7 Tesla MRI Hugo Kroeze1, Jeroen Stroeve1, Michel Italiaander1, Ingmar Voogt1, Giel Mens1, Peter R. Luijten1, and Dennis W. J. Klomp1 1Radiology, UMC Utrecht, Utrecht, Utrecht, Netherlands At high field MRI it is usefull to place the RF amplifiers directly on the coil. To avoid excessive heat in the bore, these amplifiers must be very efficient. A class-E amplifier was constructed with an efficiency of 80%. Class-E amplifiers can not amplify amplitude modulated signals, a modulator was added. This modulator was driven from a gradient waveform board. The amplifier was directly connected to a 50 mm loop coil. Images of a phantom and a wrist were made using this setup. This demonstrates that efficient on coil amplifiers can be connected to MRI scanners without major hardware modification.
ELECTRONIC POSTER SESSION • ENGINEERING Thursday, 25 April 2013 (11:30-12:30) Exhibition Hall
Dielectrics & Novel RF Concepts
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4374. | 37 | Near-Field Wave Impedance Matching with High-Permittivity Dielectric Materials for Optimum Transmittance in MRI Systems Giuseppe Carluccio1, Sukhoon Oh1, Qing Yang2, Danilo Erricolo3, Ray Weiluo2, and Christopher Michael Collins1 1Radiology, New York University, New York, New York, United States, 2Radiology, Pennsylvania State University, Hershey, Pennsylvania, United States, 3Electrical and Computer Engineering, University of Illinois at Chicago, Chicago, Illinois, United States A method to find the optimum permittivity of the dielectric pads that maximizes the matching by analyzing with a simple 1D analytical model the near field wave impedance of the fields generated by a magnetic loop which propagate through different materials. The permittivity values that maximize the matching in this simplified model are compared with the permittivity values that maximize the B1 field in 3D simulations to investigate the correlation between matching and high permittivity dielectric pads.
4375. | 38 | Electromagnetic Analysis of Dielectric Shimming Using High Permittivity Materials Wyger M. Brink1 and Andrew Webb1 1Radiology, Leiden University Medical Center, Leiden, Netherlands, Zuid-Holland, Netherlands In this work the field patterns resulting from a high permittivity pad have been analyzed and a theoretical framework for describing these effects has been evaluated.
4376. | 39 | A Novel 7T Transmit Array Using TE 01 Mode Dielectric Resonators Jonathan Y. Lu1, Xiaoliang Zhang2,3, and Brian K. Rutt4 1Electrical Engineering Department, Stanford University, Stanford, CA, United States, 2Department of Radiology and Biomedical Imaging, University of California-San Francisco, San Francisco, CA, United States, 3UC Berkeley/UCSF joint graduate group in Bioengineering, San Francisco, CA, United States, 4Radiology Department, Stanford University, Stanford, CA, United States We propose a novel transmit array coil design for use at 7T employing an array of dielectric resonators. Our design is composed of cylinders filled with deionized water, which after excitation by copper loops can function as transmit array elements. Using FDTD simulations, we have found that this design is easy to tune to high frequency, uses low cost material, and shows improved decoupling and B1+ efficiency compared to a loop array of matched dimension.
4377. | 40 | In-Vivo Evaluation of a New High Dielectric Constant Material for Local Enhancement of B1+ and SNR at 3T Christopher T. Sica1, Sebastian Rupprecht1, Ray Luo2, Zhipeng Cao2, Raffi Sahul3, Seongtae Kwon3, Michael T. Lanagan4, Christopher Collins5, and Qing Yang1,6 1Radiology, Penn State College of Medicine, Hershey, Pennsylvania, United States, 2Bioengineering, Pennsylvania State University, University Park, Pennsylvania, United States,3TRS Technologies Inc, State College, Pennsylvania, United States, 4Engineering Science and Mechanics, Pennsylvania State University, University Park, Pennsylvania, United States, 5Radiology, New York University, New York, New York, United States, 6Neurosurgery, Penn State College of Medicine, Hershey, Pennslyvania, United States A new high dielectric constant material, in the form of monolithic blocks of relative permittivity ~800, is evaluated for local enhancement of B1+ and SNR at 3T. Phantom studies show up to a two fold increase in SNR close to the blocks along with gains in transmit efficiency. An in-vivo study of the brain showed SNR gains up to 40% in a localized region close to the blocks, a reduction of transmission power by 50%, and local gains in transmit efficiency. Parallel imaging performance in the brain was evaluated and was minimally affected by the presence of the HDC blocks.
4378. | 41 | Analytical Study on the Effects of High Dielectric Material Surrounding Spherical Sample with Coil Array for Parallel Imaging Wei Luo1,2, Giuseppe Carluccio3, Zhipeng Cao4,5, Yang X. Qing1, and Christopher Michael Collins1,3 1Radiology, The Pennsylvania State University, Hershey, PA, United States, 2Engineering Science & Mechanics, The Pennsylvania State University, University Park, PA, United States, 3Radiology, New York University, New York, NY, United States, 4Radiology, Pennsylvania State University, Hershey, PA, United States, 5Bioengineering, The Pennsylvania State University, University Park, PA, United States Effects of high dielectric material (HDM), that has a size larger than the coil element of a parallel receive array, are theoretically studied at 3T. The results suggest that the gain from receive sensitivity of the array brought by the HDM overcomes the enhanced g-factor, which can promise to improve signal-to-noise ratio even when the HDM has a size which is larger than the coil element of a parallel receive array.
4379. | 42 | Manipulating B1 Spatial Distribution at 7 Tesla with Dielectric Pads at a Distance from a Transmit Surface Coil Manushka V. Vaidya1,2, Sukhoon Oh1, Christopher Michael Collins1,2, Daniel K. Sodickson1,2, and Riccardo Lattanzi1,2 1Bernard and Irene Schwartz Center for Biomedical Imaging, New York University School of Medicine, New York, NY, United States, 2Sackler Institute of Graduate Biomedical Sciences, New York University School of Medicine, New York, NY, United States The use of dielectric pads between the radiofrequency (RF) coil and sample has been proposed to “focus” the B1 field into the sample to improve transmit efficiency. In this study, we investigated how dielectric pads placed at a distance from the RF coil affect the B1+ spatial distribution inside the sample. We performed numerical simulations of the B1+ distribution inside a uniform cylinder at 7T for various positions of the dielectric pad with and without a surrounding shield. Manipulating B1 spatial distribution with dielectric pads can be advantageous for various MR applications, including improving RF homogeneity at ultra-high fields.
4380. | 43 | Analysis of the Effect of an External High Dielectric Sleeve on the Performance of a Head Coil at 128 MHz Bu S. Park1, Joshua W. Guag1, Leonardo M. Angelone1, and Sunder S. Rajan1 1CDRH/DP, FDA, Silver Spring, MD, United States We present experimental and numerical simulation results showing that high dielectric materials (HDMs) located outside of a RF head coil decrease the electric field (E-field, |E|) with minimum change of the RF magnetic field (B1+) at 3T MRI imaging. Compared to previous research using HDMs located between the RF coil and sample, our method locating the HDM outside the coil allowed an increased sample size and more flexibility of HDM thickness optimization. Numerical simulation results showed more than 30% decrease in the local SAR at the boundary region of the head model. Validating experimental results showed a 21% decrease in the maximum |Etotal| using a HDM made of distilled water.
4381. | 44 | Maximized Local B1+ Using Optimized Dielectric Pad at 7 T: Numerical Optimization and Experimental Validation Sukhoon Oh1, Wei Luo2, Bei Zhang1, Cem Murat Deniz3, Michael T. Lanagan4, Graham C. Wiggins1, and Christopher Michael Collins1 1Center for Biomedical Imaging, School of Medicine, New York University, New York, New York, United States, 2Center for NMR Research, Radiology, College of Medicine, The Pennsylvania State University, Hershey, Pennsylvania, United States, 3New York University, New York, New York, United States, 4Engineering Science and Mechanics, The Pennsylvania State University, University Park, Pennsylvania, United States Dielectric materials with high permittivity have been used to improve signal homogeneity in high field MR images and enhance SNR near the pad. Permittivity, geometry, dimension, and location of dielectric pad are variables to be optimized to maximize the effect of a dielectric pad. In this study, we report the permittivity optimization of dielectric pad to maximize the local B1+ in a phantom with electromagnetic field simulations at 7T and verification with flip angle mapping experiments at 7T when the dielectric pad is present with different permittivity values.
4382. | 45 | Dipole Antenna Without Ceramic Substrate and Still Low SAR: The Fractionated Dipole Antenna. Alexander Raaijmakers1, Ingmar Voogt1, Dennis W. J. Klomp1, Peter R. Luijten1, and Nico van den Berg1 1Imaging Division, UMC Utrecht, Utrecht, Netherlands RF coil array elements for body imaging at ultra-high field strengths need to be designed as antennas. An example of such a design is the single-side adapted dipole antenna (SiSiAD). Its drawback: it is heavy. In this study, we present another type of array element that has been designed according to radiative principles: the fractionated dipole antenna. It consists of a 30 cm dipole where the legs are split into 3 segments, interconnected by 20-50 nH inductors. Simulations and measurements show that the fractionated dipole antenna has similar or better B1+/SAR performance than the SiSiAD, while being lighter and cheaper.
4383. | 46 | A 16-Element Highly Flexible RF Array Coil for 3T MRI Yunsuo Duan1, Bradley S. Peterson1, Feng Liu1, and Alayar Kangarlu1 1MRI Research, Department of Psychiatry, NYSPI/Columbia University, New York, NY, United States The SNR of array coils depend on the filling factor of the coils because the sensitivity of each coil element dramatically attenuates with the increase of the separation between the coil element and the object to be imaged. A desirable array coil therefore is expected to be positioned closest to the object. This requires that the array coil must be highly flexible in order to fit for objects of variable dimensions and the coil built in a way that its flexibility does not affect its performance. Although some adjustable array coils have been proposed, their flexibility is limited because of the extreme difficulty in decoupling between coil elements with the change of coil geometries. We present a 16-element array coil with high flexibility and provide a comparison study between the highly flexible array coil and a rigid cylindrical coil based on our research on high decoupling. The flexible array coils are able to significantly improve the SNR and homogeneity of images.
4384. | 47 | A Novel Alternating Impedance Transceiver Coil for 7T MRI James F. Stack, Jr.1 1Remcom, Inc., State College, PA, United States Particle Swarm Optimization (PSO) and finite difference time domain (FDTD) simulations are employed to design a novel alternating impedance microstrip resonator (MSR) transceiver array for 7T MRI. The resulting design uses non-uniform spacing of impedance elements to control the B1+ field distribution and improve the peak B1+ value. Comparisons are shown between the optimized geometry, a traditional straight MSR and an alternating impedance MSR with uniformly spaced circular impedance elements.
4385. | 48 | Current-Line Solution for Understanding and Predicting B1 / B1+ Behavior and Investigating Central Focusing Gianluigi Tiberi1, Mauro Costagli1, Riccardo Stara1,2, James Tropp3, and Michela Tosetti1,4 1Fondazione Imago7, Pisa, PI, Italy, 2Univerisity of Pisa, Pisa, PI, Italy, 3GE Healthcare Technologies, Fremont, CA, United States, 4Stella Maris Scientific Institute, Pisa, Pi, Italy We introduce a novel analytical approach based on the theory of cylindrical waves radiated by a filament of a-c current. The approach permits to calculate B1/ B1+ inside volume resonators loaded with cylinders. Moreover, it permits to separate the solution to single line source problem (primordial solution) and the composite one (the summations of primordial solutions accordingly to the resonator driving). This feature is of fundamental importance, because only by looking at single line solution it is possible to have insight into central focusing, investigating and discriminating among phenomena of dielectric resonance, standing wave and multi-source interference.
ELECTRONIC POSTER SESSION • ENGINEERING Thursday, 25 April 2013 (10:30-11:30) Exhibition Hall
Receive Arrays
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4386. | 49 | Brain Arrays for Neonatal and Premature Neonatal Imaging at 3T Azma Mareyam1, Duan Xu2, Jonathan R. Polimeni1,3, Eli Siskind1, Vijay Alagappan4, James N. Blau1, Boris Keil1,3, Nan Tian2, Wei Zhao1,3, and Lawrence L. Wald1,3 1A.A. Martinos Center for Biomedical Imaging, Department of Radiology, Charlestown, Massachusetts, United States, 2UCSF School of Medicine, San Francisco, California, United States, 3Harvard Medical School, Boston, Massachusetts, United States, 4GE Healthcare, Cleveland, Ohio, United States Imaging premature and neonatal babies in incubators is challenging due to time constraints, motion artifacts and the need for high resolution. These issues call for increased detector sensitivity to achieve high spatial resolution and highly-parallelized array image acquisition. In this work we have constructed and tested two 16-channel brain arrays sized for roughly 32 and 36 weeks gestational age as well as a 32-channel array for term neonates. The SNR and g-factors of these arrays are compared to each other and to an adult sized coil.
4387. | 50 | The Dual Purpose CAPTAIN (Cardiac Adult / Pediatric Torso Assembly for in-vivo Imaging) Modhurin Banerjee1, Clyve Konrad Follante1, Aleksey Zemskov1, Rodney Bills1, Kolman Juhasz1, Steven G. Lee1, Victor Taracila1, and Fraser Robb1 1MRI, GE Healthcare, Aurora, Ohio, United States It is current practice to use adult coil systems for pediatric imaging, which is problematic due to a variety of difficulties encountered in workflow/preparation, emergency egress, coil sensitivity-anatomy mismatch, and the necessity to anesthetize the patient. A 32 channel thoracic coil system with application to the 0-7 year old patient population was developed from a prototype originally created by Shreyas Vasanwalla at Stanford/Lucinda Bell Children’s Hospital. A uniform array was found (both through simulation and experiment) to give the best SNR and g factor performance, offering a significantly improved scan time and patient experience relative to existing coil systems.
4388. | 51 | A Scalable Constellation Coil Design for 3T Body Imaging Xing Yang1, CemMurat Deniz1, Ye Li1, Ryan Brown1, and Yudong Zhu1 1Center for Biomedical Imaging, Department of Radiology, NYU School of Medicine, New York, NY, United States Based on the field equivalence principles of electrodynamics, a previous study1 introduced a unifying solution to RF coil, suggesting that a single surface structure and a surface current driving mechanism may enable not only emulations of but higher performance than any externally applied RF coil. A full-wave EM simulation included therein further demonstrated a particular 128-port constellation coil structure’s potential as a unifying solution. In an effort to leverage these results and possibly improve today’s clinical MR systems that have varying numbers of parallel RF channels, the present study explored a constellation coil design that was adapted to suit a small as well as a large number of channels. MR imaging experiments on a clinical 3T scanner were conducted to quantify SNR behavior of the same coil as the number of implemented ports increases. Commercial phased array coils were used as comparison references.
4389. | 52 | 8 Channel Transmit and 16 Channel Receive Constellation Coil for 7T MRI Ye Li1, Xing Yang1, Cem Murat Deniz2, and Yudong Zhu1 1NYU School of Medicine, New York, New York, United States, 2New York University, New York, New York, United States In this work, we propose a novel 8-channel transmit and 16-channel receive constellation coil for 7T MRI. The gradient-echo images were acquired with phase shimming. The SNR was calculated and then normalized by flip angle. Transmit power to achieve 90 degree flip angle on central coronal plane was measured. Transmit and reception performance of the constellation coil were compared with that of two commercial coils that is each composed of a birdcage transmit coil and a high-density receive-only phased array. Our results show that the constellation coil can achieve excellent SNR and transmit efficiency with a single structure.
4390. | 53 | High Filling Factor Vs. High Channel Count: Which One Wins in 3T Breast Imaging? Luca Marinelli1, Eric Fiveland1, Keith Park1, Kenneth Rohling1, and Ileana Hancu2 1GE Global Research Center, Niskayuna, NY, United States, 2GE Global Research, Niskayuna, NY, United States The tradeoffs between high filling factor and high number of coils in 3T breast imaging were considered. Experiments performed in vitro and in vivo indicate better performance (higher SNR and lower g-factor) for the cases in which the receive array is allowed to conform to a woman's anatomy. Results also suggest that flexible, high channel count breast arrays may be one of the most promising avenues to increase the SNR of breast images.
4391. | 54 | 31 Channel, Flexible Breast Coil for 3T Imaging Ileana Hancu1, Eric Fiveland2, Keith Park2, Kenneth Rohling2, Seung-Kyun Lee2, and Luca Marinelli2 1GE Global Research, Niskayuna, NY, United States, 2GE Global Research Center, Niskayuna, NY, United States A novel, 31 channel, flexible breast coil for 3T imaging is presented. The performance of this coil, in vitro and in vivo is demonstrated. A comparison with the GE, 8 channel coil is also performed.
4392. | 55 | A Dedicated 8-Channel Flexible Array Coil for Ocular fMRI Marcos Alonso Lopez Terrones1,2, Markus Düring1,3, Daniel Gareis1, and Peter M. Jakob3,4 1NORAS MRI products, Höchberg, Bavaria, Germany, 2Health Services of Durango, Durango, Durango, Mexico, 3Experimental Physics 5, University of Wuerzburg, Wuerzburg, Bavaria, Germany, 4Research Center Magnetic Resonance Bavaria, Wuerzburg, Bavaria, Germany In ocular imaging, the development of dedicated MRI coils is useful to monitoring the visual cortex and to determinate the damage in the visual pathway before a surgery. We developed an 8-channel flexible array for ocular fMRI. The coil is comprised of two pieces with four channels each. SNR-maps and in-vivo images were compared with a conventional head-coil at 1.5T. The 8-channel flexible array shows 200% SNR improvement at the surface and 25% at the center of the phantom. In-vivo images acquired with the 8-channel flexible array have also shown better image quality throughout the whole visual pathway.
4393. | 56 | A 12-Channel Dorsal Receive-Only Body Array for 7 Tesla. Ria Pradhan1, Andreas K. Bitz1, Stefan Maderwald1, Oliver Kraff1, Mark E. Ladd1, and Stephan Orzada1 1The Erwin L. Hahn Institute for Magnetic Resonance Imaging, Universität Duisburg - Essen, Essen, Nord Rhein Westfalen, Germany A 12-channel dorsal receive-only array was built for use with an 8-channel transmit/ receive coil. The 12 elements were geometrically decoupled. The array was evaluated through measurements with a vegetable oil phantom and a volunteer. The g-factor was calculated from the SNR of the images using the pseudo multiple replica method. Maps of the g-factor using only the 8-channel transmit/ receive body coil were compared to those obtained using both the 8-channel coil and the 12-channel array. As expected, the parallel imaging capability was enhanced by the 12-channel array.
4394. | 57 | MR Spectroscopic Imaging (MRSI) Study Using the Diaper Shaped RF Coil Array. Seunghoon Ha1 and Orhan Nalcioglu1,2 1Tu & Yuen Center for Functional Onco-Imaging, University of California Irvine, Irvine, California, United States, 2Department of Cogno-Mechatronics Engineering, Pusan National University, Pusan, Korea MRI and MR spectroscopic imaging (MRSI) is used for detailed anatomic and metabolic evaluation of the prostate. Especially, for successful MRSI acquisition, the research about RF coil, non-invasive, enable to provide both competitive SNR and large FOVs on prostate MRI may be a prerequisite. In this study, we proposed a new non-invasive coil with a competitive SNR for prostate MRSI and compare its performance with other commercial coils. The proposed coil showed MR spectra having a competitive SNR when comparing with the endorectal coil as well as generated more stable spectra than endorectal coil on the overall prostate phantom area.
4395. | 58 | Unilateral 8ch Receiver Array for Ultra High Resolution Time-Resolved 3D CE-MRA of the Hand Paul T. Weavers1, Thomas C. Hulshizer1, Phillip J. Rossman1, Phillip M. Young2, and Stephen J. Riederer1 1MR Research Laboratory, Mayo Clinic, Rochester, Minnesota, United States, 2Radiology, Mayo Clinic, Rochester, Minnesota, United States Hand and arm MR angiography presents a particular challenge due to the spatial and temporal resolution demands. When unilateral vs. bilateral imaging is clinically indicated, unilateral acquisition allows not only reduced FOV but also reduced patient discomfort in positioning. A modular, eight-channel receiver coil is described which provides the high SNR necessary for highly accelerated (R=8) 2D SENSE time-resolved contrast-enhanced MRA, allowing very high (0.6 mm isotropic) spatial resolution, arterial phase imaging.
4396. | 59 | High Temporal and Spatial Resolution Breast MR Imaging at 7T; Feasibility Study Using 8-To-1 Channel Tx-Only Array Combined with 8 Channel Rx-Only Insert Junghwan Kim1, Yujuan Zhao1, Narayan Krishnamurthy1, Tiejun Zhao2, Kyongtae Ty Bae1, and Tamer S. Ibrahim1 1University of Pittsurgh, pittsburgh, PA, United States, 2Siemens Medical Solutions, pittsburgh, PA, United States We have developed the eight Tx only array combined with eight Rx only array insert based on TTT design for breast MR imaging at 7T. RF coil was tested on three normal volunteers with and without the Rx only insert. T1W with fat-saturation breast MRI was successfully acquired and demonstrated.
4397. | 60 | 7-Channel Half-Cylinder Shaped Transmit Coil with 32-Channel Receiver Array for Multipurpose Head Imaging at 7T Johanna J. Bluemink1, Martijn Lunenburg2, Wouter Koning2, Ingmar J. Voogt2, Michel Italiaander2, Peter R. Luijten2, Natalia Petridou2, and Dennis W.J. Klomp2 1Radiotherapy, UMC Utrecht, Utrecht, Utrecht, Netherlands, 2Radiology, UMC Utrecht, Utrecht, Netherlands A half-cylinder coil array is presented that combines 7 detunable transmit coil elements with a high density receiver array of 32 detunable elements. The setup allows optimized focused B1+ and B1- in for instance cerebellum or visual cortex, while providing maximized space for visual stimulation. Being independently flexible with B1 steering, the setup also allows scanning with standard immobilization devices as used in radiotherapy.
ELECTRONIC POSTER SESSION • ENGINEERING Thursday, 25 April 2013 (11:30-12:30) Exhibition Hall
Transmit Arrays
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4398. | 61 | Z-Shim RF Coil Design Enhances Parallel Transmit Performance in Body Imaging at 3T Xiaoping Wu1, Jinfeng Tian1, Sebastian Schmitter1, Brian Hanna1, Joseph Pfeuffer2, Michael Hamm2, Juergen Nistler2, University of Minnesota University of Minnesota Vaughan1, Kamil Ugurbil1, and Pierre-Francois Van de Moortele1 1CMRR, Radiology, University of Minnesota, Minneapolis, MN, United States, 2Siemens Healthcare, Erlangen, Germany There has been an increasing interest in designing RF arrays with coil elements distributed in all three dimensions so as to also allow B1+ manipulation along the Z direction. Such Z-shim coils have been shown to provide improved RF transmit efficiency for brain imaging, as compared to a conventional coil which has only in-plane encoding capability. In this study, we evaluate the performance of a Z-shim RF array designed for body imaging at 3T and compare it to a conventional array, by designing parallel transmit (pTX) RF pulses with power and SAR regularizations based on electromagnetic simulations of the two coils. Our results show that the Z-shim RF array can give rise to large improvement of flip angle homogenization and/or reduction of SAR for pTX when used for body imaging at 3T, as compared to the conventional coil without Z-encoding capability.
4399. | 62 | Simultaneous Excitation of Distinct Electromagnetic Modes Using a Tx Array Yujuan Zhao1, Sossena Wood1, Tiejun Zhao2, Narayanan Krishnamurthy1, and Tamer S. Ibrahim1 1University of Pittsburgh, Pittsburgh, Pennsylvania, United States, 2Siemens Medical Solutions, Pittsburgh, Pennsylvania, United States The inhomogeneous distribution of the magnetic field B1+ at ultrahigh field imaging (≥7T MRI) is a significant challenge for the RF coil design. In this work, a new excitation paradigm is presented utilizing 20-channel Tic-Tac-Toe (TTT) based RF transmit array design where the 20 elements are combined into 5 different groups in order to excite 20 distinct modes with longitudinal spatial selectivity. Any 5 of these modes can be simultaneously excited. The optimization shimming method has been used to find a uniform excitation pattern under SAR constraints. The results are successfully tested on a 7T MRI scanner using phantoms and in-vivo (7 human subjects.)
4400. | 63 | Densely-Populated Transceiver Surface Coil Array for the Human Brain Studies at 7 T. Nikolai I. Avdievich1, Jullie W. Pan1, and Hoby P. Hetherington1 1Neurosurgery, Yale University, New Haven, CT, United States Transceiver surface coil arrays improve transmit performance and B1 homogeneity for head imaging up to 9.4T. Arrays with larger number of smaller elements further improve SNR and parallel imaging. Overlapping adjacent elements optimizes both the loading and the penetration depth, but complicates the decoupling. First, the adjacent coils generate substantial mutual resistance and cannot be decoupled using common methods, which compensate only for the mutual reactance. Second, in a densely-populated overlapped array, coupling exists between non-adjacent elements. We have developed a single-row (1x16) overlapped surface coil transceiver head array with decoupling of both the adjacent and the next-to-one neighboring elements.
4401. | 64 | Construction of a 4-Channel Transmit Neck Array for PCASL Tagging at 7 Tesla and Comparison with a Head Coil. Konstantinos Papoutsis1, James A. Meakin1, Aaron T. Hess2, Jamie Near3, Stephen J. Payne4, David Edwards4, and Peter Jezzard1 1FMRIB Centre, University of Oxford, Oxford, Oxfordshire, United Kingdom, 2Department of Cardiovascular Medicine, University of Oxford, Oxford, Oxfordshire, United Kingdom,3McGill Univeristy, Montreal, Quebec, Canada, 4Department of Engineering Science, University of Oxford, Oxford, Oxfordshire, United Kingdom In this study, a 4-channel neck array has been constructed and used at 7 Tesla as a tagging coil for the pCASL sequence. A comparison of the tagging efficiency and SAR was made between tagging with a 1Tx/32Rx head coil vs tagging with the neck array. Electromagnetic characterization of the neck coil helped to address local SAR risk by estimating the worst case transmission pattern. The neck array provided 70% tagging efficiency with 80% SAR whereas tagging with the head coil generated a tagging efficiency of 30% and a global SAR of approximately 60%. Tagging with the neck coil is the preferable method as long as the SAR is supervised at all times.
4402. | 65 | An Algorithm for Automatic Optimisation of Transmit Array Coil Tune and Match Applied in a Cardiac TEM Coil at 7T Christopher T. Rodgers1, Graeme A. Keith1, Aaron T. Hess2, Carl Snyder3, University of Minnesota University of Minnesota Vaughan3, and Matthew D. Robson1 1Univ Oxford, Oxford, United Kingdom, 2University of Oxford, Oxford, United Kingdom, 3CMRR, Univ Minnesota, Minneapolis, MN, United States 7T body MRI requires transmit array coils. The popular TEM resonator design requires time consuming ~30min manual adjustments for each subject. This can be mechanised using piezo-actuators to drive the adjustment capacitors. We implement a system for monitoring coil RF characteristics in situ using RF pulses from the scanner. We characterise 4 potential optimisation metrics before introducing a simple, robust, efficient algorithm that automates coil tuning in less than 5 minutes. We close by explaining how auto-tuning may give not just faster, but actually superior coil tuning by optimising at isocentre and by monitoring power reflected through all RF channels.
4403. | 66 | Imaging the Kidneys at 7T Using 8Tx/32Rx Abdominal Coil and RF Shimming of Individual Slices Niravkumar Darji1, Martin Haas2, Gopesh Patel1, Oliver Speck1, Inge Brinkmann2, and Michael Bock2 1Department for Biomedical Magnetic Resonance, magdeburg, Sachsen anhalt, Germany, 2Department of Radiology, Freiburg, Baden-Württemberg., Germany B1 field inhomogeneity become increasingly problematic in ultrahigh-field (UHF) strengths (7T). Parallel transmition is introduced to reduce B1 inhomogeneity. In abdominal imaging region like Kidney or spine shows more structural visibility after performing RF shimming on individual channels of the 8Tx/32Rx abdominal RF coil. The T2* maps also reflect the more homogeneous signal distribution after RF shim perfomance.
4404. | 67 | Parallel Transmission Experiments Using an Extensible RF Pulse Generator Andre Kuehne1,2, Patrick Waxmann2, Werner Hoffmann2, Harald Pfeiffer2, Reiner Seemann2, Frank Seifert2, and Bernd Ittermann2 1Medical University of Vienna, Vienna, Vienna, Austria, 2Department for Medical Metrology, Physikalisch-Technische Bundesanstalt, Berlin, Germany An extensible multichannel small signal chain and its application to transmit SENSE experiments at 3T is presented. Up to 20 channels can be driven by a 2x4HE 19" units, with the possibility of interconnecting and synchronizing multiple of these nodes.It is capable to work with any scanner, given a clock and trigger signal is provided, and can be used for a wide range of frequencies up to 300 MHz. The obtained images are indistinguishible from images generated with the manufacturer's small signal chain, proving its feasibility.
4405. | 68 | New Results for Digital Beamforming in MRI Emad Ebbini1, Lance DelaBarre2, University of Minnesota University of Minnesota Vaughan3, and Anand Gopinath4 1University of Minnesota, Minneapolis, Minnesota, United States, 2Radiology, University of Minnesota, Minneapolis, Minnesota, United States, 3CMRR, Radiology, University of Minnesota, Minneapolis, Minnesota, United States, 4ECE, University of Minnesota, Minneapolis, Minnesota, United States Recent novel results on digital beam forming of MRI signals are presented. These show that digital beam forming has gain, enhances contrast and reduces signal to noise ratio.
4406. | 69 | Effect of Shielding on Surface Coil Loops at 7T Gillian Haemer1 and Graham Wiggins1 1The Bernard and Irene Schwartz Center for Biomedical Imaging, NYU Medical Center, New York, NY, United States Radiation power loss, or the radiated power of a coil that is not absorbed into the sample, is assumed to be a problem at high field in MRI, as it is known to increase with the frequency (ω) and coil-bounding area (A): RLOSS α A2 * ω4 [1,2]. Various authors suggest that the effects of radiation loss, such as decreased SNR and coil Q, can be mitigated by adding RF shielding to coils used at high field.
4407. | 70 | Integration of 2-Channel Parallel Transmission with Forced Current Excitation for Improved B1 Homogeneity in Breast Imaging at 7T Sergey Cheshkov1,2, Ivan E. Dimitrov1,3, Wouter Koning4, Joseph Rispoli5, Mary P. McDougall5,6, Steve Wright5,6, and Craig R. Malloy1,2 1Advanced Imaging Research Center, University of Texas Southwestern Medical Center, Dallas, TX, United States, 2Radiology, University of Texas Southwestern Medical Center, Dallas, TX, United States, 3Philips Medical Systems, Cleaveland, OH, United States, 4UMC Utrecht, Utrecht, CX, Netherlands, 5Biomedical Engineering, Texas A&M University, College Station, TX, United States, 6Electrical Engineering, Texas A&M University, College Station, TX, United States Ultra-high field MR offers the promise of higher spatial/temporal resolutions in imaging, and improved sensitivity and quantification in MRS. Capitalizing on these advantages requires resolving the issues of decreased B1 homogeneity. We report on improved B1 homogeneity at 7T achieved by combining the flexibility of 2-channel parallel transmission with the insensitivity to loading of Forced Current Excitation breast coil. The overall transmit design is favorable for high quality breast imaging at high static magnetic field. Additionally, because of its insensitivity to coil loading this approach may allow for better patient throughput since breast size and composition vary widely across population.
4408. | 71 | 20-To-8 Channel Tx Array with 32-Channel Adjustable Receive-Only Insert for 7T Head Imaging Tamer S. Ibrahim1, Yujuan Zhao1, Narayanan Krishnamurthy1, Shailesh B. Raval1, Tiejun Zhao2, Sossena Wood1, and Junghwan Kim1 1University of Pittsburgh, Pittsburgh, PA, United States, 2Siemens Medical Solutions, Pittsburgh, PA, United States The use of multi-channel arrays at 7T is currently common for alleviating RF inhomogeneities and addressing RF safety concerns. In this work we integrate 32-channel Rx-only insert with 20-to-8 channel Tx array in order to achieve safe and robust 3D homogeneous excitation across different subjects.
4409. | 72 | A Shielded 8 Channel TxRx Head Array with Triangular Elements and Second Order Decoupling Gang Chen1, Martijn A. Cloos2, Karthik Lakshmanan3, Daniel Sodickson3, and Graham Wiggins3 1The Sackler Institute of Graduate Biomedical Sciences, New York University School of Medicine, New York, NY, United States, 2The Bernard and Irene Schwartz Center for Biomedical Imaging, New York University School of Medicine, New York, NY, United States, 3The Bernard and Irene Schwartz Center for Biomedical Imaging, New York University Langone Medical Center, New York, NY, United States As more advanced Parallel Transmit (PTx) technology at high field continues to emerge, the development of compatible Transmit-Receive(TxRx) arrays with good transmit and receive sensitivity as well as decoupling has become a greater priority. We describe here a shielded version of the 8 channel PTx suitable triangular array for head imaging at 7T MRI designed to increase B1+ coverage along z direction as well as keeping diverse B1 profiles for the individual elements. In-vivo experiments demonstrated the benefits and potential of using this Triangular array with PTx system.
ELECTRONIC POSTER SESSION • ENGINEERING Thursday, 25 April 2013 (10:30-11:30) Exhibition Hall
MRI Safety 1
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4410. | 73 | Improving B1-Based SAR Determination Via Iterative Determination of Missing Field Components Ulrich Katscher1 and Karim Djamshidi1 1Philips Research Europe, Hamburg, Germany The additional degrees of freedom available in parallel transmission hamper straight-forward SAR estimations as applied for single channel transmission. As an alternative to the usually applied model-based SAR estimation, SAR can be estimated from individually measured B1 maps. Overall, the accuracy of this B1-based SAR determination is satisfying, however, could be further increased if the hitherto unknown longitudinal component of B1 can be determined. This study investigates an iterative estimation of this component and its impact on the resulting local SAR determination, based on spherical and realistic patient models for an eight-element RF transmit array at 3 T.
4411. | 74 | A Low-Power, Offline Prescreen to Detect and Suppress Dangerous Currents Christopher W. Ellenor1, Pascal P. Stang1, John M. Pauly1, and Greig C. Scott1 1Electrical Engineering, Stanford University, Stanford, CA, United States We demonstrate the feasibility of “offline” screening of patients for dangerous interactions between imaging fields and implanted wires. We show that using a standard imaging coil outside the MRI environment, and only a few milliwatts of power, we can measure the impedance spectra of the coil, which shows characteristic distortions in the case of a resonant interaction. Furthermore, we show that this same spectral information can be used to determine the phasing of the drive ports which can null the induced current during a subsequent scan.
4412. | 75 | Parallel Transmit Pulse Design with Implant-Friendly Modes Yigitcan Eryaman1,2, Bastien Guérin3, Elfar Adalsteinsson4,5, and Lawrence L. Wald2,5 1Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, MA, United States, 2Martinos Center for Biomedical Imaging, Dept. of Radiology, MGH, Charlestown, MA, United States, 3Martinos Center for Biomedical Imaging, Dept. of Radiology, Massachusetts General Hospital, Charlestown, MA, United States, 4Dept. of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, MA, United States, 5Harvard-MIT Health Sciences and Technology, Cambridge, MA, United States 8 channel transmit array is used to reduce the SAR around a generic implant model in a uniform phantom. For this purpose, implant friendly modes of the transmit array are generated. Using these modes, the optimum least square 3-spokes pulse design solution is calculated with an optimization approach which explicitly constrains both global and local SAR.
4413. | 76 | Reference-Free Detection of RF Unsafe Conditions and Countermeasures for Implantable MR-Conditional Devices Ingmar Graesslin1, Johannes Achtzehn1, Sascha Krueger1, Peter Vernickel1, Kay Nehrke1, and Steffen Weiss1 1Philips Research, Hamburg, Germany The presence of implants mostly represents a contraindication for MR examinations. Here, a concept based on parallel transmit technology is used to detect potentially RF-unsafe conditions due to implants by monitoring the currents in transmit coils. The original method had required a reference scan without device. Here, the method was improved by exploiting the left-right symmetry of patients to avoid the reference scan. Hence, the method may be applied to patients with implants. Basic feasibility of this concept is shown in pseudo-in vivo and phantom studies by detecting coupling to pacemaker leads. Tip heating could be reduced by a factor of 6 by changing the transmit phases.
4414. | 77 | Evaluation of Virtual Observation Points for Local SAR Monitoring of Multi-Channel Transmit RF Coils at 7 Tesla Andreas K. Bitz1, Rene Gumbrecht2,3, Stephan Orzada1, Hans-Peter Fautz2, and Mark E. Ladd1,4 1Erwin L. Hahn Institute for MRI, University of Duisburg-Essen, Essen, Germany, 2Siemens Healthcare, Erlangen, Germany, 3Department of Physics, Friedrich-Alexander University, Erlangen, Germany, 4Department of Diagnostic and Interventional Radiology and Neuroradiology, University Hospital Essen, Essen, Germany SAR monitoring for multi-Tx approaches in high-field MRI is a challenging task, since several channels have to be supervised simultaneously and the local SAR has to be considered. For computationally efficient online local SAR supervision, the concept of virtual observation points (VOPs) has been proposed. Here, VOP models are evaluated for realistic exposure configurations with two 7T RF coils, an 8-channel head and an 8-channel body coil, and for three body models. For all configurations and for a reasonable maximum overestimation of about 10%, the number of VOPs is smaller than 500, for which online monitoring has been successfully tested.
4415. | 78 | Imaging Healthy Volunteers and Patients with Tattoos or Permanent Make-Up at 7T: A Retrospective Study Yacine Noureddine1,2, Andreas K. Bitz1,3, Markus Thürling1,4, Gregor Schaefers2, Mark E. Ladd1,3, and Oliver Kraff1,3 1Erwin L.Hahn Institute for MRI, University Duisburg-Essen, Essen, NRW, Germany, 2MR:comp GmbH, MR Safety Testing Laboratory, Gelsenkirchen, NRW, Germany, 3Department of Diagnostic and Interventional Radiology and Neuroradiology, University Hospital Essen, Essen, NRW, Germany, 4Department of Neurology, University Duisburg-Essen, Essen, NRW, Germany In this study we describe our experience with scanning 77 subjects with tattoos or permanent make-up at 7T. Only local transmit RF coils were used in the individual measurements. The results indicate safe imaging and no adverse events.
4416. | 79 | In Silico and in Vitro Investigation of Temperature Elevation Close to an Aneurysm Clip at 7T Yacine Noureddine1,2, Oliver Kraff1,3, Mark E. Ladd1,3, Karsten Wrede4, Gregor Schaefers2, and Andreas K. Bitz1,3 1Erwin L.Hahn Institute for MRI, University Duisburg-Essen, Essen, NRW, Germany, 2MR:comp GmbH, MR Safety Testing Laboratory, Gelsenkirchen, NRW, Germany, 3Department of Diagnostic and Interventional Radiology and Neuroradiology, University Hospital Essen, Essen, NRW, Germany, 4Clinic for Neurosurgery, University Hospital Essen, Essen, NRW, Germany For safety assessment of metallic aneurysm clips, RF-induced heating resulting from electric field elevations in the tissue is the major concern with respect to patient safety. In this study, RF and thermal simulations were conducted to determine RF heating around an aneurysm clip at 7T using a simplified model of the head. Validation of the simulations was supported by RF field measurement.
4417. | 80 | Circuit Model for Implant Electrode and Lead-Electrode Impedance Matching Volkan Acikel1,2 and Ergin Atalar1,2 1Electrical and Electronics Engineering, Bilkent University, Ankara, Turkey, 2National Magnetic Resonance Research Center (UMRAM), Ankara, Turkey In our previous studies we modeled the lead of the implant using Modified Transmission Line Method (MoTLiM) and solve the Radio Frequency (RF) induced currents on the leads. In this study we propose an electrode model that completes our electromagnetic model of active implants under MRI. Also with this model electrode and lead impedances are defined considering their RF scattering and tissue interaction properties. It is shown that although putting series inductor between lead and electrode is a working technique to prevent heating, failure in choosing inductance value can cause increase in the heating.
4418. | 81 | Application of Rotating RF Coil Array in B1 Shimming with Strict Local SAR Constraints Jin Jin1, Feng Liu1, Adnan Trakic1, Ewald Weber1, and Stuart Crozier2 1University of Queensland, St Lucia, Queensland, Australia, 2The University of Queensland, St Lucia, Queensland, Australia This work investigated the possibility of using a four-channel mechanically rotating RF coil array (RRFCA) to shim the transmit magnetic fields for high-field MRI, while strictly controlling local specific absorption rate (SAR). Since the numerous available degrees of freedom in both the temporal and the spatial domain are exploited, a notably higher excitation accuracy was achieved compared with the stationary eight-channel phased-array coil. The results of this primarily theoretical study also signify that, since only a low channel count is required, the geometry of RRFCA can be optimised more flexibly to improve field penetration and therefore excitation efficiency and performance.
4419. | 82 | Safety Evaluation of Algorithms to Optimize Transmit Efficiency for Local Excitation with a Transmit Array Giuseppe Carluccio1 and Christopher Michael Collins1 1Radiology, New York University, New York, New York, United States Recently methods have been presented to provide optimum driving currents for transmit array which maximize the circularly polarized component of the B1 field in a small region of interest and minimize the overall power transmitted. In this work we evaluate safety parameters, such as the 10g local average SAR and temperature increase, when some of these methods are applied for two different regions of interest in a body-sized transmit array.
4420. | 83 | Online Local SAR Supervision for Transmit Arrays at 7T Rene Gumbrecht1,2, Ulrich Fontius1, Holger Adolf1, Thomas Benner1, Franz Schmitt1, Elfar Adalsteinsson3,4, Lawrence L. Wald4,5, and Hans-Peter Fautz1 1Siemens Healthcare, Erlangen, Germany, 2Department of Physics, University of Erlangen, Erlangen, Germany, 3Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, MA, United States, 4Harvard-MIT Division of Health Sciences and Technology, Massachusetts Institute of Technology, Cambridge, MA, United States, 5Department of Radiology, A. A. Martinos Center for Biomedical Imaging, Charlestown, MA, United States Local SAR and its safe supervision are dominant limiting factors for high performance pTX applications. Safety concepts typically provide a SAR prediction strategy based on numerical simulations. Only sequences that will not exceed SAR limits are allowed to be executed. To capture system fault during runtime, an additional online supervision was proposed to ensure the correct execution of the RF pulses. In this study, an online local SAR calculation and supervision system using measured RF pulse shapes was built. Local SAR is calculated in near real-time based on a compressed electric field model of the current coil and patient.
4421. | 84 | On Patient-Specific Models for Accurate SAR Estimations at 7 T Jin Jin1, Feng Liu1, Ewald Weber1, and Stuart Crozier2 1University of Queensland, St Lucia, Queensland, Australia, 2The University of Queensland, St Lucia, Queensland, Australia To more effectively predict the patient SAR values for high-field MRI applications, a novel approach of creating patient-specific tissue model is demonstrated in this study. First, a matching model from a high-resolution image- and tissue-library is selected for the target patient. The library tissue distribution is then warped to match the patient’s geometry as the corresponding library image is registered to the low-resolution scans of the patient. Results from studying the models’ 1-gram SAR distribution using finite-different time-domain method suggest that the developed patient model can predict regions of elevated SAR within the patient with remarkable accuracy.
ELECTRONIC POSTER SESSION • ENGINEERING Thursday, 25 April 2013 (11:30-12:30) Exhibition Hall
MRI Safety 2
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4422. | 85 | Functional MRI Using Implanted Stereotactic EEG Electrodes --- Heating Investigation for Safety Pallab K. Bhattacharyya1, Jorge A. Gonzalez-Martinez2, Mark J. Lowe1, Dileep Nair1, Richard Prayson1, Myron Zhang1, and Stephen E. Jones1 1Cleveland Clinic, Cleveland, OH, United States, 2Cleveland Clinic Foundation, Cleveland, OH, United States As a safety measure of performing MRI with implanted stereotactic EEG (SEEG) electrodes, we investigated the effect on electrode heating by the geometry and configuration of the electrodes and associated connections by measuring radio frequency induced heating of a SEEG electrode embedded within a phantom inside an intraoperative MRI suite, with the electrode directly connected to stimulus hardware located in the control room. Once the safety of the procedure was ensured, fMRI scans were performed on human subjects with implanted SEEG electrodes as well. No damage to brain slice was confirmed by pathology.
4423. | 86 | Safe Online Local SAR Calculation for Transmit Arrays Using Asynchron Data Processing Rene Gumbrecht1,2, Thomas Benner1, Ulrich Fontius1, Holger Adolf1, Andreas K. Bitz3, and Hans-Peter Fautz1 1Siemens Healthcare, Erlangen, Germany, 2Department of Physics, Friedrich-Alexander University, Erlangen, Germany, 3Erwin L. Hahn Institute for Magnetic Resonance Imaging, University Duisburg-Essen, Essen, Germany A RF supervision concept that considers local SAR is an essential pre-requisite for high performance pTX applications. It needs to provide at least one online RF supervision component that detects violation of local SAR limits in real-time. Using the MR signal processing unit for that fails to match real-time requirements. In this study, an online local SAR calculation was implemented on the image reconstruction PC of a MRI system. To overcome latency issues, a real-time logic in conjunction with a real-time global SAR supervision unit is used to guarantee patient safety at all times
4424. | 87 | A Novel Method for Experimental Assessment of Antenna Safety Using MR Thermometry Cem Murat Deniz1,2, Leeor Alon2,3, Xing Yang3, Gene Young Cho1,2, Christopher Michael Collins2,3, Daniel K. Sodickson2,3, and Yudong Zhu2,3 1Department of Radiology, Bernard and Irene Schwartz Center for Biomedical Imaging, New York University, New York, NY, United States, 2Sackler Institute of Graduate Biomedical Sciences, New York University School of Medicine, New York, NY, United States, 3Department of Radiology, Bernard and Irene Schwartz Center for Biomedical Imaging, New York University School of Medicine, New York, NY, United States Even though simulations have been commonly used for safety evaluation of antenna structures, often complex antenna-body structures are difficult to simulate and the simulations do not align with the experimental results. In this work, we propose an alternative method of monitoring RF safety by experimentally measuring the temperature change using MR thermometry. We show good agreement between optical temperature measurements and MR thermometry and simulation studies. Heating pattern, |E| and SAR fields from a simulated simple dipole antenna matches well with experimental results both in pattern and in magnitude. Strength of this method is in its simplicity, accuracy and speed.
4425. | 88 | Predicting Long-Term Temperature Increase from Time-Dependent SAR Levels with a Single Short-Term Temperature Response Giuseppe Carluccio1, Zhipeng Cao2, and Christopher Michael Collins1 1Radiology, New York University, New York, New York, United States, 2Bioengineering, Pennsylvania State University, Hershey, Pennsylvania, United States In a patient exam typically a series of pulse sequences with very different power levels and SAR levels are applied. Temperature increase caused by SAR absorption may damage tissues, and development of fast temperature computation methods could be useful. We propose a rapid method to predict temperature increase over an entire patient exam with time-varying SAR levels applied, after characterizing the temperature tissue response to a short SAR pulse.
4426. | 89 | Safely Assessing RF Heating Potential of Conductive Devices Using Image-Based Current Measurements Greg Griffin1, Kevan Anderson2, and Graham A. Wright1,2 1Medical Biophysics, University of Toronto, Toronto, Ontario, Canada, 2Imaging Research, Sunnybrook Research Institute, Toronto, Ontario, Canada This study presents a technique to safely assess the RF heating potential of a conductive device in the MR bore. RF artifacts acquired with a low power sequence are analyzed and used to predict heating induced by a higher power sequence. Experimental validation in a phantom is presented for several configurations.
4427. | 90 | Scanner Specific Relationship Between Displayed SAR and Heating Adjacent to Deep Brain Stimulation Leads: An in Vitro Study Robert Dawe1 and Leo Verhagen Metman1 1Rush University Medical Center, Chicago, IL, United States The guideline for head specific absorption rate (SAR) during MRI of patients with implanted deep brain stimulation (DBS) leads is difficult to interpret because SAR estimation techniques vary among scanner manufacturers. The purpose of this study was to establish a relationship between displayed head SAR and local tissue heating in our particular scanner. Heating of approximately 4.9˚ C per 1.0 W/lb. of displayed head SAR was observed, confirming that potentially dangerous heating of DBS leads is possible. At the same time, the results suggest that the SAR guideline for implanted DBS leads may be overly conservative.
4428. | 91 | Mobile Phone RF Safety Testing Using Magnetic Resonance Imaging Leeor Alon1,2, Cem Murat Deniz1,2, Gene Young Cho1,2, Xing Yang1, Christopher Collins1, Yudong Zhu1,2, and Daniel Sodickson1,2 1Department of Radiology, Bernard and Irene Schwartz Center for Biomedical Imaging, New York University, New York, NY, United States, 2Sackler Institute of Graduate Biomedical Sciences, New York University, New York, NY, United States Local specific absorption rate (SAR) quantification is important for ensuring safe usage of RF transmitting devices. Regulatory bodies around the world mandate RF safety testing and more than $1B is spent annually on testing. In contrast to the gold-standard measurement schemes that mechanically move a probe and measure the electric field generated by the wireless devices, this work utilizes MR thermometry to quantify power deposition from mobile phones, allowing rapid acquisitions with higher resolution than before. The results indicate that safety testing of RF emitting devices such as mobile phones can be robustly conducted using MRI.
4429. | 92 | B1-Based SAR Estimation for Human Brain Imaging with Average Brain Property Values Substitution Xiaotong Zhang1, Jiaen Liu1, Sebastian Schmitter2, Pierre-Francois Van de Moortele2, and Bin He1 1Department of Biomedical Engineering, University of Minnesota, Minneapolis, MN, United States, 2Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN, United States Recently proposed Electrical Properties Tomography technique, which aims to reconstruct the electrical properties of biological tissues via measured B1, provides a feasible way for quantitative subject-specific SAR estimation. However, Laplacian over B1 is involved in the inverse algorithm, which may severely suffer from noise-contamination in measured B1, and deteriorate the reliability of SAR estimation. In this study, by using multi-channel coil at 7T for brain imaging, the performance of local SAR calculation has been evaluated when literature-reported average electrical property and mass density values are employed as a substitution, which intends for a more robust and reliable SAR estimation approach.
4430. | 93 | A Novel MRI Based Electrical Properties Measurement Technique Volkan Acikel1,2, Oytun Ulutan1, Ali Caglar Ozen1,2, Burak Akin2, Yigitcan Eryaman3,4, and Ergin Atalar1,2 1Electrical and Electronics Engineering, Bilkent University, Ankara, Turkey, 2National Magnetic Resonance Research Center (UMRAM), Ankara, Turkey, 3Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, MA, United States, 4Martinos Center for Biomedical Imaging, MGH, Charlestown, MA, United States Most of the Magnetic Resonance Imaging studies require accurate knowledge of electrical properties of the phantoms. There are several techniques for measuring electrical properties of phantoms but there is lack of accuracy analysis. A new method to measure electrical properties of gel phantom was proposed based on the lead tip heating phenomena and used for verification of home made coaxial transmission line measurement fixture. Electrical properties of 3 different gel phantoms were measured using both methods and results are compared. Although the proposed method requires long MRI experiment, it can be used for verification of other electrical properties measurement techniques.
4431. | 94 | Efficient Method to Evaluate the Heating Risk of Coils Lin Liu1, Liang Xuan2, and Qiong Zhang3 1MR, GE Company, Beijing, Beijing, China, 2MR, GE company, Waukesha, WI, United States, 3MR, GE company, Beijing, Beijing, China Safety requirements, has been as MRI system first and foremost of indicators. In direct contact with patients or volunteers parts, the coil is undoubtedly the most in need of extra attention. Thermal test is one of the important coil integrated tests and coil security evaluation. In order to effectively assess the performance of the coil, engineers usually use worse clinical protocol scanning coils up to 2.5 hours; and during the entire testing process, the highest coil surface temperature should not be higher than 41 degrees. To save test time , evaluate and avoid damage caused by overheating of the coil in the testing process, we have designed a new method that is based on using the 1st one hour measured data for fitting and extrapolation, thus, the whole test can be shorten to only one hour, and also the risk of damaging coil is reduced. Validation against 44coils with 52 modes using two scanners has proved that this method can effectively assess coil characteristics and reduce overheating risk.
4432. | 95 | Development of a Patient-Specific, Three-Dimensional, Heterogeneous, Radio Frequency Thorax Phantom Clifton Haider1, David Holmes1, Robert Sainati1, Daniel Schwab1, Daniel V. Litwiller2, Desmond Yeo3, and Barry Gilbert1 1Biomedical Engineering, Mayo Clinic, Rochester, MN, United States, 2Global Applied Science Laboratory, GE Healthcare, Rochester, MN, United States, 3GE Global Research, GE, Niskayuna, NY, United States Methods were developed to create phantoms with specific and highly repeatable conductivity and permittivity matching those of desired tissue. Numerical models results were highly similar with experimental results. Complex 3D organ models accurately represented the target anatomy and RF material properties.
4433. | 96 | A Simple and Conservative Method to Include Variation of Core Blood Temperature with Pennes’ Bioheat Equation Giuseppe Carluccio1 and Christopher Michael Collins1 1Radiology, New York University, New York, New York, United States Pennes’ bioheat equation is one of most used models to predict temperature increase in body tissues. We present a simple and conservative method to include the variation of blood temperature increase in the Pennes’ bioheat equation due to the whole-body SAR absorption. Plots are provided showing the core blood temperature over time, and the spatial temperature increase distribution for a cross-section of the body obtained with both the Pennes’ bioheat equation having constant value of blood temperature, and the method with the time dependent blood temperature here presented.