Traditional Poster Session - Engineering
  Magnets & Systems 2575-2587
  Gradients, Shims & Field Monitoring 2588-2608
  Transmit Arrays 2609-2621
  TX Coils (Non-Array) 2622-2635
  Novel RF Technology 2636-2644
  Receive Arrays 2645-2662
  RF Safety 2663-2676
  RF: Other 2677-2682
  Receive Efficiency & Noise Mitigation 2683-2692
  Travelling Wave & Dielectric Padding 2693-2703
  Safety & Devices 2704-2715
  MR/PET 2716-2725

Magnets & Systems
Click on to view the abstract pdf. Click on to view the poster (Not all posters are available for viewing.)

Monday 7 May 2012
Exhibition Hall  14:15 - 16:15

2575.   Design and construction of a Halbach array magnet for portable brain MRI
Clarisa Zimmerman1, Lawrence L Wald2, Matthew S Rosen3, and James Blau4
1Electrical Engineering, Massachusetts Institute of Technology, Cambridge, MA, United States, 2Department of Radialogy, Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, United States, 3Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, United States, 4Athinoula A. Martinos Center for Biomedical Imaging, United States

A Halbach array magnet was designed, modeled and constructed for a portable brain MRI application. The array consists of 20 radially magnetized NdFeB N42 magnets and is large enough to fit the human head. The modeled field shows a roughly quadratic field profile with a central Larmor frequency sufficient for imaging (~3.3MHz). While the homogeneity is well below that of superconducting magnets, it fits well with our light-weight and portable concept if the inhomogeneities are used in image encoding.

2576.   A practical insert design for dreMR imaging in the human torso
Chad Tyler Harris1, William B Handler1, and Blaine A Chronik1,2
1Physics and Astronomy, University of Western Ontario, London, Ontario, Canada, 2Imaging Research Laboratories, Robarts Research Institute, London, Ontario, Canada

Delta relaxation enhanced magnetic resonance (dreMR) is a relatively new technology that allows for enhanced signal specificity when using targeted MR contrast agents. The method utilizes a supplementary “Bo insert coil” to modulate the main magnetic field within an otherwise unmodified superconducting system. Previously, Bo inserts have been developed for small-animal imaging and recently we have presented a practical insert design for dreMR imaging of the human head. In this work, we present a feasible design for an open-geometry Bo insert coil capable of producing significant dreMR contrast in the human torso.

2577.   Next Generation Delta Relaxation Enhanced MRI with ±0.36T ΔB
Eddy SM Lee1, Ludovic de Rochefort2, Gianni Ferrante3, and Brian K Rutt1
1Lucas Center, Stanford University, Stanford, California, United States, 2Univ. Paris-Sud, CNRS, UMR8081, IR4M, Orsay, Paris, France, 3STELAR s.r.l., Mede, Italy


Delta relaxation-enhanced magnetic resonance (dreMR) imaging is a B0-cycled MR technology that produces contrast from intended targets only. Variable B0 was produced with a next generation, insertable, field-cycling magnet that enabled dreMR imaging with ΔB of up to ±0.36T; the highest achieved to date. dreMR signal was linearly enhanced as ΔB was increased, while physiological background remain suppressed. Our results demonstrate the advantage and proof-of-concept of achieving dreMR imaging at high ΔB.

2578.   Magnetic filed shimming of a high Tc superconducting bulk magnet using a cylindrical single-channel shim coil
Daiki Tamada1, Keisuke Maruyama1, Katsumi Kose1, and Takashi Nakamura2
1Institute of Applied Physics, University of Tsukuba, Tsukuba, Ibaraki, Japan, 2RIKEN, Wako, Saitama, Japan

A cylindrical single-channel shim coil was developed for a high critical temperature (Tc) superconducting bulk magnet (4.7 Tesla) with a 23 mm diameter room temperature bore. The single channel shim coil was designed using circular current loops periodically placed on the cylindrical surface. The magnetic field distribution in a rectangular region (5 mm x 5 mm x 7 mm) was measured for various shim current values. As a result, about 30% homogeneity improvement was achieved for an optimal current value, which demonstrated usefulness of our approach.

2579.   Magnetic field shimming of a 2.0 T permanent magnet using a bi-planar single-channel shim coil
Daiki Tamada1, Katsumi Kose1, and Tomoyuki Haishi2
1Institute of Applied Physics, University of Tsukuba, Tsukuba, Ibaraki, Japan, 2MRTechnology, Inc., Tsukuba, Ibaraki, Japan

In this study, we proposed a novel single-channel shim coil design method using circular current elements to correct higher order inhomogeneities. We succeeded in decreasing PP value of the ĢB0 by 40%. In conclusion, the novel SCSC design method is simple and useful for shimming a ĢB0 including higher order terms.

2580.   Gradient Coil Induced Joule Heating in a MRI magnet
Yihe Hua1, Longzhi Jiang2, Graeme C Mckinnon3, Seung-Kyun Lee4, and Anbo Wu1
1GE Global Research, Shanghai, China, 2GE Healthcare, Florence, SC, United States, 3GE Healthcare, Waukesha, WI, 4GE Global Research, Niskayuna, NY, United States

In conductive cooling magnet, joule heating in 4K region is critical due to the cold head capability limitation. When a MRI scanner is operating, the current in gradient coil will induce EC in magnet metal structure, which will vibrate by the Lorentz force due to the main field. The motion will further generate motional EC. In this article Joule heating in cryostat, AC loss in superconductive wires and dielectric loss in coil epoxy are calculated for one 1.5T MRI magnet including full metal VV, TS and coil former with 2D harmonic analysis. The z-gradient coil is optimized towards heating minimization.

2581.   Fringe field effects on hyperpolarized 129Xe for a continuous flow SEOP setup
Martin Kunth1, Christopher Witte1, and Leif Schröder1
1Leibniz-Institut für Molekulare Pharmakologie (FMP), Berlin, Germany

We studied the influence of fringe field effects on hyperpolarized 129Xe for a spin exchange optical pumping polarizer system working in continuous flow mode when the magnetic optical pumping field of the polarizer is in direct proximity to the magnet of the spectrometer. The configuration of the pumping field was modified to three coils with a variable current of the center coil and a single shot 129Xe NMR spectrum was acquired every 2 seconds. Our data show that the 129Xe NMR signal can be optimized by modifying the net fringe field.

2582.   Design and Optimization of a Permanent Magnet for Small-sized MRI Based on Particle Swarm Optimization Algorithm
Yiyuan Cheng1, Ling Xia1, Wei He1, Feng Liu2, and Stuart Crozier2
1Department of Biomedical Engineering, Zhejiang University, Hangzhou, Zhejiang, China, 2The School of Information Technology and Electrical Engineering, The University of Queensland, Brisbane, Australia

The main magnet, an important part of an MRI system, is used to produce the static magnetic field in the imaging area. In a permanent MRI magnet, there is a widespread end effect that causes a non-uniform magnetic field distribution and affects the imaging quality. In this paper, we have designed an H-type permanent magnet for small-sized MRI applications; in particular, the novel design has been realized by adding a shimming ring outside the pole piece to improve the magnetic field uniformity. Particle swarm optimization (PSO) algorithm is used to solve the complex and nonlinear optimization problems. The simulation results show that the magnet optimized by the proposed method generates a homogeneous magnetic field that can be easily implemented in practice and at a low cost.

2583.   Passive Shimming of MRI Magnets with B0 >= 3T at Reduced Field
Yuri Lvovsky1, Zhenyu Zhang1, Timothy Hollis2, and Ye Bai2
1GE Healthcare, Florence, SC, United States, 2GE Healthcare, BeiJing, China

Method of passive shimming of MRI magnet is presented. To reduce forces and torque during shim tray insertion / removal, after the initial virgin map is taken at full field the magnet is partially ramped down where coarse iterations are performed using maps acquired at lower field. Test results proved successful shimming of the magnet.

2584.   Cryogen-Free 3T-MRI System for Human Brain Research using Bi-2223 High-Temperature Superconducting Tapes
Shin-ichi Urayama1, Osamu Ozaki2, Hitoshi Kitaguchi3, Kazuyuki Takeda4, Iwao Nakajima5, Naoki Ohnishi6, Michael Poole7, Ken-ichi Sato8, and Hidenao Fukuyama1
1HBRC, Kyoto University, Kyoto, Japan, 2Kobe Steel, Ltd., Kobe, Japan, 3National Institute for Materials Science, Tsukuba, Japan, 4Kyoto University, Kyoto, Japan,5Takashima Seisakusyo, Tokyo, Japan, 6Astrostage, Inc., Tokyo, Japan, 7University of Queensland, Queensland, Australia, 8Sumitomo Electric Industries, Ltd., Osaka, Japan

The demand for the exhaustible natural resource helium is increasing rapidly, with 20% of global production used as the cryogen in superconducting MRI magnets. High-temperature superconducting (HTS) materials show great potential for realizing helium-less magnets. This is the first report for a cryogen-free 3T-MRI scanner for human brain research using Bi-2223 tapes operating at a temperature of 20K.

2585.   Simulation of Magneto-mechanical Coupling in a 3T Head-only Magnet Design
Dominic M Graziani1, Seung-Kyun Lee1, Jean-Baptiste Mathieu1, Graeme C McKinnon2, Thomas K Foo1, and John F Schenck1
1GE Global Research, Niskayuna, NY, United States, 2Applied Science Lab, GE Healthcare, Waukesha, WI, United States

We present an investigation on the effects of magneto-mechanical coupling on the eddy current in a prototype 3T head only scanner design. Transverse and longitudinal actively shielded gradient coils were modeled in COMSOL along with an aluminum cylinder, fixed at both ends, representing a conducting surface of the magnet. Magneto-mechanical resonance was observed for both gradient designs at frequencies between 2-3.5 kHz. At resonance, the peak gradient strength changed by up to ~10% for the longitudinal gradient and ~1.5% for the transverse gradient.

2586.   Development of a low-field NMR unit using a crossed coil setup for calibration of a PASADENA polarizer
Robert Borowiak1, Elmar Fischer1, Sebastien Bär1, Jochen Leupold1, Frank Huethe2, Thomas Lange1, Jeff Snyder1, Jürgen Hennig1, Dominik von Elverfeldt1, and Jan-Bernd Hövener1
1Medical Physics, Dep. of Radiology, University Medical Center Freiburg, Freiburg, Baden-Württemberg, Germany, 2Neurozentrum, scientific workshop, University Medical Center Freiburg, Freiburg, Baden-Württemberg, Germany

Low-field NMR has received increasing attention in the recent years as several new approaches were published. As previous polarizers had no detection ability at B0 = 1.8 mT, we developed an apparatus specifically for the fields required by SABRE and PASADENA (B0 = 1 – 6 mT), suitable for RF calibration and the direct detection of NMR signal. PASADENA and SABRE are unique liquid-state hyperpolarization techniques which have achieved 13C NMR signal enhancement of several orders of magnitude.

2587.   An Open Source Low-Cost NMR System
Michael D Twieg1, Matthew J. Riffe2, Natalia Gudino2, and Mark A. Griswold1,3
1Department of Electrical Engineering and Computer Science, Case Western Reserve University, Cleveland, OH, United States, 2Department of Biomedical Engineering, Case Western Reserve University, Cleveland, OH, 3Deptartment of Radiology, Case Western Reserve University and University Hospitals of Cleveland, Cleveland, OH

We present a low cost NMR system aimed for use in simple NMR experiments. The system is based on an Arduino microcontroller platform and a MATLAB interface. Most of the RF chain is broadband, allowing it to be easily used with a wide range of frequencies and transmit/receive coils. The system is capable of several simple NMR experiments, allowing the measurement of T1, T2, ρ0, and self diffusion coefficient (D). The total cost of the system, neglecting a host computer and bench top power supplies, is less than $400. Documentation on the project is open source.
Traditional Poster Session - Engineering

Gradients, Shims & Field Monitoring
Click on to view the abstract pdf. Click on to view the poster (Not all posters are available for viewing.)
Monday 7 May 2012
Exhibition Hall  14:15 - 16:15

2588.   Design of High Performance Gradient Coil for 3T Head Specialty Scanner
Jean-Baptiste Mathieu1, Bruce C Amm1, Silke Lechner-Greite2, Seung-Kyun Lee1, Ek Tsoon Tan1, Thomas K-F Foo1, John F Schenck1, Matt A Bernstein3, and John Huston3
1Diagnostics and Biomedical Technologies, GE Global Research, Niskayuna, NY, United States, 2Diagnostics and Biomedical Technologies, GE Global Research Europe, Garching, Germany, 3Mayo Clinic, Rochester, MN, United States

We report on the design of a head-only shielded gradient prototype to be inserted in a specialty 3T head-only magnet for high-performance neuroimaging. The gradient is force- and torque- balanced, and employs asymmetric X and Y gradient and symmetric Z gradient design. This design delivers peak specifications of 88mT/m and 630T/m/s with a commercial gradient driver and a linearity of 16.9% over a 26 cm diameter spherical volume (DSV). The expected image distortion due to gradient nonlinearity was evaluated with simulated brain image with nonlinearity correction.

2589.   Conventional and Linked Gradient Coil Designs: a Comparative Study
Alice Borceto1, Andrea Viale2, Leonardo Bertora2, Richard Bowtell3, and Franco Bertora1
1Robotics Brain and Cognitive Science, Istituto Italiano di Tecnologia, Genova, GE, Italy, 2Paramed Medical System, Genova, Italy, 3University of Nottingham, Sir Peter Mansfield Magnetic Resonance Centre, Nottingham, United Kingdom

A comparative study of two different types of gradient coil design (conventional and 3D or "linked" designs) is presented. "Linked" coils generally have better performance characteristics than conventional designs, but they are more expensive to manufacture due to their complexity. The analysis is performed by assessment of inductive energy, resistive power dissipation and cost factors for different coil geometries for three coil configurations: (i) cylindrical, (ii) biplanar and (iii) split. If high performance is needed, "linked" gradient coils can be preferable. On the contrary, if lower performance is sufficient, conventional gradient coils provide better value for money.

2590.   Radial Multi-Coil Imaging
Christoph Juchem1, Terence W Nixon1, and Robin A de Graaf1
1Yale University School of Medicine, New Haven, CT, United States

Radial MR imaging is presented in which the linear gradient fields are generated by a matrix of individual, generic coils. The ability of this multi-coil concept for magnetic field modeling to flexibly trade accuracy for efficiency is applied to increase the available gradient strength and imaging bandwidth multi-fold. MC imaging bears the potential of providing an inexpensive alternative for specialized imaging applications for which maximum gradient strength and performance are not required.

2591.   Design and Implementation of High-Performance Non-Linear PatLoc Gradient Coil
Maxim Zaitsev1, William Punchard2, Andrew Dewdney3, Daniel Gallichan1, Jason Stockmann4, Chris A. Cocosco1, Sebastian Littin1, Anna Masako Welz1, Hans Weber1, Piotr Starewicz2, and Jürgen Hennig1
1University Medical Centre Freiburg, Freiburg, Germany, 2Resonance Research Inc., United States, 3Siemens Healthcare, Germany, 4Yale University, United States

To overcome present limitations on gradient performance and investigate unconventional encoding topologies a PatLoc (parallel imaging technique using localized gradients) concept was proposed recently. PatLoc relaxes requirements of gradient homogeneity and global uniqueness of spatial encoding in favour of local gradient strength. To date the proof-of-concept PatLoc imaging has been performed with prototype hardware with performance inferior to that of linear gradients. The purpose of this project was to design and implement a PatLoc head gradient insert capable of generating local gradients exceeding those of proprietary linear gradient inserts.

2592.   3D Gradient System for Two B0 Field Directions by Using Concomitant Fields in Earth Field MRI
Steffen Lother1,2, Uvo C. Hölscher1, Peter M. Jakob1,2, and Florian Fidler1
1Research Center Magnetic-Resonance-Bavaria (MRB), Wuerzburg, Bavaria, Germany, 2Department for Experimental Physics 5 (Biophysics), University of Wuerzburg, Wuerzburg, Bavaria, Germany

We built for our earth field MRI setup a gradient system that is capable of dealing with two B0 field directions. It is benefiting to have the opportunity to orientate the prepolarizing field parallel and perpendicular to the B0 field. We were able to show with the help of the concomitant fields the number of necessary coils can be reduced. We spare two coils in comparison to two independent gradient sets. These gradients can even be used for further B0 field directions and therefore this promise new applications and results in more compact setups.

2593.   High Resolution 3D TrueFISP images of Guinea Pig Inner Ear using the Composite Gradient Systems on a Clinical 3T MRI System
Seong-Eun Kim1, K Craig Goodrich1, Richard Wiggins1, Jason Mendes1, and Dennis L Parker1
1UCAIR Department of Radiology, University of Utah, Salt Lake City, Utah, United States

Our composite system has the distinct advantage that both of standard and insert gradient systems can be operated simultaneously and/or independently. With simultaneous acquisition, the gradient strength available from either system alone can be increased. The use of composite gradients will allow high resolution SSFP images without increasing TR or bandwidth, allowing for improved inner ear imaging. To test the utility of this composite gradient system we scanned the temporal bone of guinea pigs with the composite and body gradients only and compared image quality.

2594.   Performance Analysis of Multi-Coil Magnetic Field Modeling
Christoph Juchem1, and Robin A de Graaf1
1Yale University School of Medicine, New Haven, CT, United States

Magnetic field modeling based on individual generic coils has been shown recently to enable the accurate and flexible generation of a multitude of field shapes for MR. Here, the analysis of fundamental performance properties of the multi-coil (MC) concept is presented. The results are compared to dedicated wire patterns for the generation of magnetic field shapes that resemble spherical harmonic functions. Improved magnetic field homogeneity with MC shimming has been demonstrated previously. Along with the higher efficiency for the generation of shim fields as demonstrated in this work, MC shimming bears significant potential to replace conventional spherical harmonic shim systems.

2595.   Matrix Shimming for Whole Body Gradient coils
Derek A. Seeber1, Timothy Bergfeld1, Kevin Koch2, Richard Hackett1, David Lee1, and William Einziger1
1GE Healthcare, Florence, SC, United States, 2GE Healthcare, Waukesha, WI, United States

A matrix array shim coil system was designed to be included into a widebore gradient coil consisting of 28 channels in a 7 circumferential by 4 axial coil matrix array. The matrix shim coil is designed from multi-layer Kapton circuit boards and is integrated into a gradient coil between the inner and outer gradient coil. Simulations from brain images were analyzed and demonstrate improved performance over a traditional 3rd order harmonic shim set.

2596.   Improvement of DTI measurement using the Composite Gradient Systems on a Clinical 3T MRI System
Seong-Eun Kim1, K Craig Goodrich1, J Rock Hadley1, Richard Wiggins1, Eun-Kee Jeong1, and Dennis L Parker1
1UCAIR Department of Radiology, University of Utah, Salt Lake City, Utah, United States

Our composite system has the distinct advantage that both of standard and insert gradient systems can be operated simultaneously and/or independently. With simultaneous acquisition, the gradient strength available from either system alone can be increased. The composite gradient system can acquire better DTI measurements with less artifacts in human studies than can be obtained with insert or body gradient coils alone. It can also provide high resolution fMRI datasets with better imaging quality compared to data obtained using the standard gradient system.

2597.   Study of concomitant fields in multipolar PatLoc imaging
Anna Masako Welz1, Frederik Testud1, Jürgen Hennig1, Jan G. Korvink2,3, and Maxim Zaitsev1
1Department of Radiology, Medical Physics, University Medical Center Freiburg, Freiburg, Germany, 2Dept. of Microsystems Engineering, IMTEK, University Freiburg, Freiburg, Germany, 3Freiburg Institute of Advanced Studies (FRIAS), University Freiburg, Freiburg, Germany

FFor spatial encoding in magnetic resonance imaging only the Bz component of the magnetic vector is of interest. For linear gradients concomitant fields are well known and investigated. With new imaging techniques, such as PatLoc, using higher order harmonics the concomitant fields of these gradients are in focus. Concomitant fields calculated from the spherical harmonics potential are compared and evaluated against a simplified model since the effect of the concomitant fields on image distortion and PNS is important especially for human imaging.

2598.   Characterization of PatLoc Gradient with a Field Camera
Frederik Testud1, Daniel Gallichan1, Christoph Barmet2, Johanna Vannesjö2, Anna Masako Welz1, Christian A. Cocosco1, Klaas Prüssmann2, Jürgen Hennig1, and Maxim Zaitsev1
1Medical Physics, University Medical Center Freiburg, Freiburg, Germany, 2Institute for Biomedical Engineering, University and ETH Zurich, Zürich, Switzerland

A field camera consisting of 16 proton based field probes is used to characterize the Parallel Acquisition Technique with Localised gradients (PatLoc) gradient coil. Higher order magnetic field monitoring is performed with a 16 channel proton field camera. The recorded field dynamics are used to test the linearity of the PatLoc gradient coil performance in combination with standard linear gradients and to measure the gradient impulse response functions of the five channel gradient system.

2599.   Gradient Waveform Pre-Equalization using the Magnetic Field Gradient Waveform Monitor Method
Frederic G. Goora1,2, Hui Han2, Bruce G. Colpitts1, and Bruce J. Balcom2
1Department of Electrical and Computer Engineering, University of New Brunswick, Fredericton, New Brunswick, Canada, 2MRI Research Centre, Department of Physics, University of New Brunswick, Fredericton, New Brunswick, Canada

The accuracy of applied magnetic field gradients in magnetic resonance imaging directly impacts the corresponding image quality and measurements of molecular motion. These distortions result from the generation of eddy currents within the magnet structure and from distortion of the magnetic field gradient coil excitation current due to gradient current amplifier limitations (such bandwidth and stability) and the reactive gradient coil load which fundamentally limit the minimum excitation current rise and fall times which further distort the applied magnetic field gradient. We present a method that utilizes the magnetic field gradient waveform monitor method to measure the magnetic field gradient waveform and determine a pre-equalized gradient amplifier current excitation waveform such that an optimal approximation of the desired / ideal magnetic field gradient results.

2600.   Gradient waveform measurement using prephased gradient moments.
Peter Latta1, Marco L. H. Gruwel1, Vladimír Jellúš2, and Boguslaw Tomanek1
1Institute for Biodiagnostics, National Research Council of Canada, Winnipeg, Manitoba, Canada, 2MR Application Development, Siemens AG, Healthcare, Erlangen, Germany

One of the commonly used methods for k-space trajectory/gradient waveform characterization is based on utilizing the FID phase evolution sampled from a thin slice excited at a known distance. In many cases like breast or extremity imaging, there is no source of signal near the magnet’s isocenter. This introduces problems with rapid phase accrual. Additional complications arise from measuring high gradient amplitudes when modification of this approach is necessary to avoid problems with low signal amplitudes caused by spin dephasing. Here we propose alternative methods for gradient characterization based on the gradient moment mapping.

2601.   Validation strategies for NMR probes in field measurement applications
Saikat Sengupta1, John C. Gore1, and E. Brian Welch1
1Radiology and Radiological Sciences, Vanderbilt University, Nashville, TN, United States

Nuclear magnetic resonance probes can provide real time, location specific, measurements of signal phase and magnitude. Here, we propose and demonstrate three different approaches to test the performance of NMR probes in the scanner. The approaches are, (a) motion simulation (b) spectrometer frequency offsets and (c) higher order field perturbations using a real time shim-switching module. Real time probe data is shown to encode each of these different perturbations faithfully, thereby demonstrating strategies for testing the performance and characterization of the probes against known and calibrated inputs.

2602.   Real-time control of multiple coils for the generation of gradient and shim fields
Stefan Wintzheimer1, Toni Drießle1, Michael Ledwig1, Ralf Kartäusch1, Peter Michael Jakob2,3, and Florian Fidler1
1Research Center Magnetic-Resonance-Bavaria, Würzburg, Bavaria, Germany, 2Research Center Magnetic-Resonance-Bavaria, 3Experimental Physics 5, University of Würzburg

In this study a novel matrix gradient design is presented, which is capable of generating both linear gradient fields for imaging and at the same time high order shim fields. Using a home-built 50-ch gradient amplifier with a customized MR console allows real-time control of fieldprofiles while measuring MR signal. This system was used to create field profiles for shimming complex field distrortions as well as imaging of an sample object in a whole body magnet. Furthermore the new design is able to switch every field order very fast due to low inductivity of the coils.

2603.   Signal Considerations in Slicewise Dynamic B0 shimming.
Saikat Sengupta1, E. Brian Welch1, John C. Gore1, and Malcolm J. Avison1
1Radiology and Radiological Sciences, Vanderbilt University, Nashville, TN, United States

Dynamic Shimming improves Bo field homogeneity compared with global volume shimming. The most common approach for estimating slice-wise shim values involves removing the redundancy of functionally degenerate shim terms from an in-plane field regression and assuming a linear through plane inhomogeneity profile. This approach yields excellent inplane inhomogeneity compensation but compromises intravoxel signal recovery. Here, we present a slice-wise shim calculation method based on maximizing the voxel signal. Signal simulations and in vivo T2* measurements are presented which demonstrate improved signal recovery performance compared to both the degeneracy analysis and static global shimming approaches.

2604.   Echo Planar Imaging at 7T with 3rd Order Slice-Wise Dynamic Shim Update (DSU) and Full Eddy-Current Compensation (ECC)
Ariane Fillmer1, Signe Johanna Vannesjo1, Matteo Pavan1, Klaas Paul Pruessmann1, Peter Boesiger1, and Anke Henning1
1Institute for Biomedical Engineering, University and ETH Zurich, Zurich, ZH, Switzerland

The transition to ultra high field strengths yields advantages as increased SNR and higher BOLD contrast, but at the expense of decreased B1 and B0 homogeneity. This work presents the application of Dynamic Shim Updating (DSU) with full 3rd Order eddy-current compensation to Echo Planar Images, which are the basis for fMRI. Due to a highly accurate calibration of the pre-emphasis very fast switching of shim terms during the sequence is possible, without extending the scan time. The presented results exhibit a significant gain in image quality.

SEA imaging using a dual planar array and fourth gradient coil for phase compensation
John C. Bosshard1, Mary P. McDougall1,2, and Steven M. Wright1,2
1Electrical & Computer Engineering, Texas A&M University, College Station, TX, United States, 2Biomedical Engineering, Texas A&M University, College Station, TX, United States

Single Echo Acquisition (SEA) imaging is performed using a fourth gradient coil to provide opposite coil phase compensation for dual-planar or "sandwich" arrays having an array plane directly above and below a sample, allowing simultaneous imaging of dynamic or single-shot events at the top and bottom boundaries of a sample.

2606.   A passive copper shield for the split MRI system
Limei Liu1, Hector Sanchez Lopez1, Michael Poole1, Ewald Weber1, Feng Liu1, and Stuart Crozier1
1the University of Queensland, Brisbane, Queensland, Australia

the eddy currents generated by the switching gradient fields produce undesired joule heating, noise and image artefacts in the MRI system. It is found that these eddy current effects are worsened in the split MRI system which is designed for the hybrid PET-MRI technology to provide high resolution images for the target tissues. In this work, a passive copper shield was applied outside of the split gradient coils to reduce the eddy currents induced in the cryostat inner bore in order to protect the contained helium vessel. The results show that the passive copper shield can effectively reduce the power heating in the cryostat inner bore. However, it sacrifices the gradient linearity in the region of interest.

2607.   Evaluation of effects of permanent magnet circuits on gradient field linearity
Yasuhiko Terada1, Hirotaka Fujisaki1, and Katsumi Kose1
1Institute of Applied Physics, University of Tsukuba, Tsukuba, Ibaraki, Japan

We experimentally evaluated the effects of permanent magnetic circuits on gradient field linearity. The gradient field generated by a gradient coil set differed when it was inserted in different magnetic circuits. For a magnet with a wide gap compared with the coil gap, the field linearity was as large as the calculated one. For a magnet with a narrow gap close to the coil gap, the gradient field linearity significantly decreased. This is because of the mirror image currents flowing in the pole pieces. This indicates that the design of gradient coils requires consideration of the mirror current effect.

2608.   Towards Truly Quiet MRI: Animal Scale Gradient as a Test Platform for Acoustic Noise Reduction
AbdEl-Monem M El-Sharkawy1, and William A. Edelstein1
1Division of MR Research, Department of Radiology, Johns Hopkins University, Baltimore, MD, United States

MRI acoustic noise often exceeds 100 dB, causing patient anxiety and discomfort, and is an obstacle to interventional MRI procedures. Clinical MRI acoustic noise reduction is a long-standing unsolved engineering challenge made especially difficult because special equipment and large-scale engineering test facilities are needed for experiments. Our approach is to produce a Truly Quiet (< 70 dB) small-scale animal imager. Results serve as a test platform for acoustic noise reduction measures that can be implemented in clinical scanners. We have so far decreased noise in an animal scale system from 108 dB to 81 dB, a 27 dB reduction.
Traditional Poster Session - Engineering

Transmit Arrays
Click on to view the abstract pdf. Click on to view the poster (Not all posters are available for viewing.)
Monday 7 May 2012
Exhibition Hall  14:15 - 16:15

2609.   RF Coil Array for Accelerated Excitation in Three Dimensions
Jörg Felder1, Suk-Min Hong2, Avdo Celik1, Joshua Park2, Frank Geschewski1, Hong-Bae Jeong2, Etienne Besançon1, Myung-Kyun Woo2, Daniel Brenner1, Zang-Hee Cho2, and N. Jon Shah1,3
1Institute for Neuroscience and Medicine - 4, Forschungszentrum Jülich GmbH, Jülich, Germany, 2Neuroscience Research Institute, Gachon University, Incheon, Korea, 3Department of Neurology, Faculty of Medicine, JARA, RWTH Aachen University, Aachen, Germany

We present a coil array for neuroimaging at 9.4T which is capable of accelerated excitation and reception in all three directions. It employs sixteen receive elements while two coils are combined during transmission due to the limited number of independent transmitter channels. The array has been approved for application in a clinical trial and first in vivo experiments demonstrate its imaging capabilities.

2610.   Impact of number of Tx channels for RF shimming – an in vivo study
Alexander Childs1, Shaihan J Malik1, Declan P O'Regan1, and Joseph V Hajnal1
1Robert Steiner MRI Unit,Imaging Sciences Department, MRC Clinical Sciences Centre, Hammersmith Hospital, Imperial College London, London, United Kingdom

Multi-channel transmission allows individualised subject specific RF shimming to be used to mitigate B1+ inhomogeneity and improve image signal and contrast uniformity. Using a whole body 3T system with 8 transmit channels, we have performed a systematic study in vivo of RF shim performance in both the pelvis and thighs for coil configurations with 1, 2, 4 or 8 independent channels. As the number of channels was increased, B1+ homogeneity progressively and significantly increased, while total RF power requirements for the same homogeneity systematically decreased. T1w images also showed perceptible progressive improvement with number of channels used for shimming.

2611.   B1-control Receive Array Coil for Abdominal Imaging
Yukio Kaneko1, Yoshihisa Soutome1, Masayoshi Dohata1, Hideta Habara1, Hisaaki Ochi1, and Yoshitaka Bito1
1Central Research Laboratory, Hitachi Ltd., Kokubunji, Tokyo, Japan

B1 inhomogeneity increases as strength of magnetic field increases. Various methods to reduce the B1 inhomogeneity have been developed. However, B1 inhomogeneity still remains in some cases of abdominal imaging, and a more effective method is required. In this study, a B1-control loop is combined with a receive array coil by using PIN diodes for generating the B1-control loop during the RF transmit period. A 12-channel gB1-control receive array coilh was fabricated, and both its receive sensitivity and the effect of B1 homogenization were confirmed experimentally. The B1-control receive array coil can improve B1 inhomogeneity, while maintaining receive sensitivity.

2612.   Simulation Study of Parallel Transmit Arrays for 3T Body Imaging under Local and Global SAR Constraints
Bastien Guerin1, Matthias Gebhardt2, Peter Serano1, Elfar Adalsteinsson3,4, Michael Hamm2, Josef Pfeuffer2, Juergen Nistler2, and Lawrence L. Wald1,4
1Martinos Center for Biomedical Imaging, Dept. of Radiology, Massachusetts General Hospital, Charlestown, MA, United States, 2Siemens Healthcare, Erlangen, Germany, 3Dept of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, MA, United States, 4Harvard-MIT Division of Health Sciences Technology, Cambridge, MA, United States

Despite intense research in pTx hardware development there has been little theoretical work on the benefit of increasing the number of transmit channels. In this work we compare the performance of three pTx arrays with 4, 8 and 16 channels using an HFSS/ADS co-simulation and a pulse design algorithm constraining simultaneously global/local SAR and average/maximum forward power. We show that increasing the number of channels from 4 to 16 allows reduction of local SAR by as much as 90% for constant excitation error and reduction of excitation error by as much as 10% for constant local SAR (2 spokes excitations).

2613.   Comparison of 7+1ch tx arrays and Implementation for torso imaging at 3T - Four different coil geometries with phantom and human body
Yeun Chul Ryu1, Sukhoon Oh1, Christopher Sica1, Wei Luo2, Yong-Gwon Kim3, and Christopher M. Collins1,4
1Radiology, The Pennsylvania State University, Hershey, PA, United States, 2Engineering Science and Mechenics, The Pennsylvania State University, University Park, PA, United States, 3Radiological Science, Konyang University, Korea, 4Bioengineering, The Pennsylvania State University, Hershey, PA, United States

Here, we report a progress toward a case where 8 elements are placed in the space above the patient table as transmit coil and additional receive coil (or array) to get more intensive signal from the chest. The 8-channel tx body array was suggested. Through the simulations, we compared 4 different 7+1 tx array structures and showed the utilities of B1+ shimming in multi-channel tx body imaging at 3T. This structure and shimming over the body size phantom we propose provide an enhanced homogeneous B1 field in large ROI imaging. As the result of B1 shimming with 4 different tx array structure and with 2 different objects, the resultant B1 fields guarantee consistent homogeneity over a large ROI.

2614.   Improving the Sensitivity of Individually Shielded Elements of RF Transceiver Array Coils Using Dielectric Materials in MRI
Yunsuo Duan1, Bradley S Peterson1, Feng Liu1, and Alayar Kangarlu1
1MRI Research, Psychiatry, Columbia University/NYSPI, New York, NY, United States

Decoupling by individualy shielding coil elements provides desired isolations between the coil elements of transceiver array coils. However, it severely degrades the sensitivity of the coil element. We propose to improve the coil sensitivity by inserting dielectric media between the coil elements and the shields. The results shows that the sensitivity can be improved form 32% to 86% while maintaining the good isolation.

2615.   Mode Matrix Tranceiver Surface Coil
Taner Demir1, Esra Abaci Turk1,2, and Ergin Atalar1,2
1UMRAM, Bilkent University, Ankara, Turkey, 2Electrical and Electronics Engineering, Bilkent University, Ankara, Turkey

The concept of a mode matrix tranceiver surface coil for transmit array system is introduced. The coil performance is experimentally tested and the concept of mode matrix transmission is verified.

2616.   Methodology for UHF multichannel coil evaluation
Lance DelaBarre1, Pierre-Francois van de Moortele1, Carl Snyder1, Jinfeng Tian1, Steen Moeller1, and J. Thomas Vaughan1
1Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN, United States

Evaluating the performance and safety of high field RF coils with multiple elements is necessary to improve coil designs, but it is challenging due to the complexity of the coil itself. A methodology to evaluate coil performance is demonstrated using a 7T coil as an example.

2617.   B1+ and Coupling Variability of Transmit Head Coils and Arrays for Ultra-High Field MRI: Simulation Studies and Experiments
Narayanan Krishnamurthy1, Daniel Stough1, Tiejun Zhao2, Shailesh Raval1, Fernando Boada1, and Tamer S Ibrahim1
1University of Pittsburgh, Pittsburgh, Pennsylvania, United States, 2Siemens Medical Solutions

Variation of spin excitation in surface/TX array and volume head coils were evaluated in these UHF MRI experiments. Phantoms with varying conductive and dielectric loads were used to evaluate the robustness of the TX B1+ field of different MR coils.

2618.   An analytical method to optimize transmit efficiency for local excitation with a transmit array
Giuseppe Carluccio1,2, Christopher Michael Collins2, and Danilo Erricolo1
1Electrical and Computer Engineering, University of Illinois at Chicago, Chicago, Illinois, United States, 2Radiology, Pennsylvania State University, Hershey, Pennsylvania, United States

We present an analytically-based method for rapid optimization of the local RF magnetic (B1+) field intensity for a given RF power through a transmit array. With knowledge of the B1+ field distribution generated by each single coil of the array, both the phases and the amplitudes of each coil current are optimized to provide the maximum magnitude of the B1+ field in a specific location of the body, and the minimum power transmitted through the array and, consequently, reducing the whole body SAR.

2619.   Simultaneous tuning of multiple modes for an RF transmit array
Mikhail Kozlov1, and Robert Turner1
1Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Saxony, Germany

We implement a dual-domain optimization approach, which results in improved performance for 7 and 9.4 T head arrays in multi-mode operation, without limiting the use of static RF shimming and even pTX. For both 7 and 9.4T arrays, dual-domain optimization resulted in negligible Parray_refl (less than 3% of Ptransmit) for given modes and nearly optimal transmit performance in all modes.

2620.   Performance consequences of broken cylindrical symmetry for a 7T head RF transmit array
Mikhail Kozlov1, and Robert Turner1
1Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Saxony, Germany

We numerically simulated a transmit-only strip-line 8-channel 7T RF transmit coil array designed and built by Vaughan. A non-split tuning resonance Sxx can be obtained, despite relatively high (-6dB) adjacent element coupling, but excitation uniformity can be very poor when coupling is asymmetrical. By installing different values at specific capacitor positions it is possible to improve excitation uniformity, but reflected power Parray_refl remains high. For CP mode excitation, decoupling of array elements whilst simultaneously equalizing currents through the front and end capacitors significantly improves transmit performance without improving inhomogeneity. Equalizing element currents does not necessarily improve excitation homogeneity.

2621.   Analysis of Circumferential Shielding as a Method to Decouple Radio-Frequency Coils for High-Field MRI
Jean-Guy Belliveau1,2, Kyle Gilbert1, Mohamed Abou-Khousa1, and Ravi Menon1,2
1Robarts Research Institute, London, Ontario, Canada, 2Biomedical Engineering, University of Western Ontario, London, Ontario, Canada

We perform an engineering analysis on common performance metrics for circumferentially shielded radiofrequency coils for MRI. Various circumferentially shielded radiofrequency coils have previously been presented; however, an in-depth analysis of the effect of shielding on coil performance has not previously been undertaken. Our analysis demonstrates that (1) shielding helps with multiple element isolation; (2) the nature of the shielding geometry can potentially increase local SNR and decrease SAR; and (3) shielding has advantages for B1+ shimming techniques and parallel imaging.
Traditional Poster Session - Engineering

TX Coils (Non-Array)
Click on to view the abstract pdf. Click on to view the poster (Not all posters are available for viewing.)
Monday 7 May 2012
Exhibition Hall  14:15 - 16:15

2622.   Shared-conductor versus overlapped-loop quadrature surface coils: which performs better in human brain at 7T?
Arthur W. Magill1,2, Martin Meyerspeer1,3, and Rolf Gruetter1,4
1Laboratory of Functional and Metabolic Imaging, Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland, 2Department of Radiology, Univeristy of Lausanne, Lausanne, Switzerland, 3ZMPBMT, Medizinische Universitaet Wien, Vienna, Austria, 4Department of Radiology, University of Geneva, Geneva, Switzerland

The performance of two quadrature surface coil designs is compared at 7 Tesla in the human head. The first design is a traditional overlapped pair of loops; the second is a pair of loops with a common the central conductor.

2623.   A Twisted Loop Coil for High Field MRI
Wolfgang Loew1, Randy Giaquinto1, Scott Dunn1, Ronald Pratt1, Diana Lindquist1, and Charles Dumoulin1
1Imaging Research Center, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio, United States

A novel RF coil design for a 7T animal scanner was developed. The new approach uses a loop coil twisted around a cylindrical former. The RF homogeneity of this new design was compared to an identically-sized birdcage using B1 mapping, and found to be more uniform. SNR comparisons between the coils showed the expected sensitivity ratio between a linear and quadrature coil. The RF homogeneity and SNR characteristics of the new coil were evaluated in in-vivo mouse images acquired with the twisted loop design. The new coil has fewer parts and is easier to tune than a comparably-sized birdcage coil.

2624.   Quadrature Transmit Coil for Ultra High Field MRI
Zhiyong Zhai1, and Michael A. Morich1
1Philips Healthcare, Cleveland, Ohio, United States

At ultra high fields such as 7T, B1 field distribution is dominated by the tissue dielectric effects. A transmit coil with uniform B1 remains a challenge compared to 1.5T or 3T. Here we suggest a new type of volume transmit coil for 7T and above - a birdcage structure with discontinuous (or broken) rungs. Simulations show that such a coil structure, when tuned properly, can generate similar B1 to that of a birdcage volume coil. It provides a new and more flexible way of making volume transmit coil for ultra-high fields MRI.

2625.   An Asymmetric Insert Quadrature Birdcage Coil for Hyperpolarised 129Xe Lung MRI at 1.5 T
Xiaojun Xu1, Martin H Deppe1, Nicola De Zanche2, and Jim M. Wild1
1Academic Radiology, University of Sheffield, Sheffield, South Yorkshire, United Kingdom, 2Department of Medical Physics, Cross Cancer Institute and University of Alberta, Canada

A whole body asymmetric birdcage transmit receive coil is demonstrated for hyperpolarised 129Xe MR lung imaging. The objective was to develop an insert body transmit-receive birdcage RF coil for imaging of hyperpolarised 129Xe in the lungs at 17.7 MHz at 1.5 T. The design makes efficient use of the available bore space within a clinical MR system, has homogenous B1 field and is transparent to the 1H body coil making anatomical 1H imaging of the chest possible without moving the coil. In future work, the coil will be used as a transmit-only coil in conjunction with a custom receive array.

2626.   Investigation of fractal-shaped alternating impedance microstrip coil for 7 Tesla MRI
Xia Li1,2, JuCheng Zhang1, WenLong Xu1, XiaoFang Liu1,2, and BingQiao Xu1
1China Jiliang University, Hangzhou, Zhejiang, China, 2Zhejiang University, Hangzhou, Zhejiang, China

This work presents the electromagnetic properties of Koch fractal-shaped alternating impedance microstrip coil for ultra high field MRI. Based on the fractal theory, a first order Koch geometry microstrip coil was modeled and simulated. A conventional and two alternating impedance microstrip line coil was also simulated for comparison. Results indicate that, narrowing the width of high impedance sections will enhance magnetic field quantity but lead to less homogeneity. The Koch fractal-shaped alternating impedance microstrip coil shows less discontinuous of electric field at the joints of high-low impedance sections and lower electric field emission. The magnetic field peak of Koch fractal-shaped alternating impedance microstrip coil was found to be broadened, which gives a more uniform magnetic field distribution.

2627.   A Double Resonant Solenoid Coil for 35Cl/ 23Na Imaging of the Rat Brain at a Whole Body 7 Tesla MRI
Manuela Rösler1, Reiner Umathum1, Armin Nagel1, Yaron Gordon1, Peter Bachert1, Wolfhard Semmler1, and Florian Meise1
1Dept. of Medical Physics in Radiology, German Cancer Research Center, Heidelberg, Germany

Sodium and Chlorine ions are central in the physiology of living organisms. To detect them quasi-simultaneously in a rat brain would improve the understanding of (patho-) physiological processes. The aim of the study was to design and characterize double resonant coils for imaging 35Cl and 23Na in the rat brain. For all measurements a 7Tesla whole body MRI was used to simplify the translation of small animal experiments to human applications.

2628.   A High-pass Birdcage Coil for Small Animal Imaging at 600MHz/14.1T
Arthur W. Magill1,2, Hongxia Lei1,3, and Rolf Gruetter1,2
1Laboratory of Functional and Metabolic Imaging, Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland, 2Radiology, Univeristy of Lausanne, Lausanne, Switzerland, 3Radiology, University of Geneva, Geneva, Switzerland

A high-pass quadrature birdcage coil was simulated, built and tested for use at 600MHz (14.1T). The resulting coil produces a highly homogeneous B1 field over the the field-of-view, despite the short RF wavelength.

2629.   A Hybrid Design for Dual-tuned Quadrature 13C/1H Volume Coil at High Field
Xiaoliang Zhang1,2, Duan Xu1, Ye Li1, Ilwoo Park1, Yong Pang1, Peter Shin1, Kayvan Keshari1, David Wilson1, and Daniel B Vigneron1,2
1Department of Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, California, United States, 2UCSF/UC Berkeley Joint Graduate Group in Bioengineering, San Francisco and Berkeley, California, United States

In this work, we propose a hybrid technique for double-tuned volume coil design by combing microstrip coil design and conventional low pass birdcage design for high field in vivo MR applications. This aims to provide an efficient solution to diminishing technical challenges in designing such coils at high fields, such as the increased interaction between the two nuclear channels, enlarged separation of the two resonance frequencies, and issues caused by high operation frequency required by proton.

2630.   A 1H and 23Na Two Coil System Optimized for Imaging Mini-Pig Knee Cartilage at a Whole Body 7 Tesla MRI
Florian M Meise1, Armin M Nagel1, Tobias Gotterbarm2, Sebastian Hagmann2, Manuela Rösler1, Marc-Andre Weber3, Wolfhard Semmler1, and Reiner Umathum1
1Dept. of Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, BW, Germany, 2Dept. of Orthopaedic Surgery, University Hospital Heidelberg, Heidelberg, BW, Germany, 3Dept. of Diagnostic and Interventional Radiology, University Hospital Heidelberg, Heidelberg, BW, Germany

Investigation of integration and vitality of cartilage transplants as well as the underlying cartilage matrix are important to optimize therapeutic approaches for cartilage damage. The aim of this study was to design an SNR optimized coil system for co-registered 1H and 23Na imaging of mini-pig knee cartilage at a whole body 7 Tesla MRI scanner, without the common loss of sensitivity due to a double resonant coil design.

2631.   Double Resonant 1H/31P Coil Configuration for 31P MR Spectroscopy at a Whole Body 7 T MR Tomograph
Andreas Korzowski1, Reiner Umathum1, Peter Bachert1, and Florian Martin Meise1
1Dept. of Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, BW, Germany

The aim of this study was to find, implement, and test the optimum double-resonant configuration for two concentric surface coils at f0(31P) = 120.3 MHz and f0(1H) = 297.15 MHz at an experimental 7-T whole-body MR tomograph.

2632.   Helical microcoil system for high resolution magnetic resonance imaging
Oliver G. Gruschke1, Nicoleta Baxan2, Dominik von Elverfeldt2, Jürgen Hennig2, Vlad Badilita3, and Jan G. Korvink1,4
1Lab. of Simulation, University of Freiburg - IMTEK, Freiburg, Germany, 2Dept. of Radiology Medical Physics, University Medical Center, Freiburg, Germany, 3Lab. for Microactuators, University of Freiburg - IMTEK, Freiburg, Germany, 4Freiburg Institute for Advanced Studies – FRIAS, University of Freiburg, Freiburg, Germany

A solenoid wound wirebonded microcoil is integrated with a custom-built transmit and receive switch and low noise amplifiers. The system allows high resolution imaging in a short period of time with a high SNR.

Viktor Vegh1, Miriam Ariens1, Jeremy Ullmann1, Nyoman Kurniawan1, and David Reutens1
1Centre for Advanced Imaging, University of Queensland, Brisbane, Queensland, Australia

We developed five different 5mm radio frequency solenoid coils for ex vivo structural imaging of the zebrafish brain. We investigated the use of different conductors and coatings, and configuration of the radio frequency electronic circuit. We analysed the five coils based on signal-to-ratio maps. Using the best performing coil, we were able to obtain images of the adult zebrafish brain with six micron resolution. We compared our findings to an image obtained using the scanner proprietary 5mm radio frequency coil. A significant improvement in image detail was evident with the use of the new coil.

Miriam Ariens1, Jeremy Ullmann1, Nyoman Kurniawan1, Harriet Lo2, David Reutens1, and Viktor Vegh1
1Centre for Advanced Imaging, University of Queensland, Brisbane, Queensland, Australia, 2Institute of Molecular Bioscience, University of Queensland, Brisbane, Queensland, Australia

We investigated the use of dedicated radio frequency solenoid coils of diameter 1.4mm for the purpose of imaging zebrafish embryos 24 and 48 hours post fertilization. We compared seven different coil conductor materials with different coatings and evaluated coil performance based on the signal-to-ratio map we calculated. The best performing coil was chosen for the diffusion imaging of zebrafish embryos. We were able to achieve around 30 micron resolution and delineate the developing spine.

2635.   A Quadrature Volume Transmit Coil for Breast Imaging and Spectroscopy at 7 Tesla
Joseph V Rispoli1, Sergey Cheshkov2,3, Ivan Dimitrov2,4, Craig Malloy2,3, Steven M Wright1,5, and Mary Preston McDougall1,5
1Biomedical Engineering, Texas A&M University, College Station, Texas, United States, 2Advanced Imaging Research Center, University of Texas Southwestern Medical Center, Dallas, Texas, United States, 3Radiology, University of Texas Southwestern Medical Center, Dallas, Texas, United States, 4Philips Medical Systems, Cleveland, Ohio, United States, 5Electical and Computer Engineering, Texas A&M University, College Station, Texas, United States

A quadrature volume transmit coil for breast imaging and spectroscopy at 7 Tesla is discussed. The Helmholtz-saddle coil configuration utilizes "Forced Current Excitation" to ensure equal current at the feed point of each element in each array. Results demonstrate excellent B1 homogeneity and validate the design for use at 7T.
Traditional Poster Session - Engineering

Novel RF Technology
Click on to view the abstract pdf. Click on to view the poster (Not all posters are available for viewing.)
Monday 7 May 2012
Exhibition Hall  14:15 - 16:15

2636.   A Digital Cartesian Feedback Loop for the MRI Transmitter
Klaus M. Huber1, Wünsch Christian2, Seisenberger Claus3, Nisznansky Martin2, Demharter Nikolaus2, and Vester Markus2
1Siemens Corporate Technology, Erlangen, Germany, 2Siemens Healthcare, Erlangen, Germany, 3Siemens Corporate Technology, Munich, Germany

Functional MRI (fMRI) and Diffusion-weighted MRI (DWI/DTI) are two important MR applications which are known to be sensitive to random system instabilities. The RF power amplifier and the transmit path usually are major contributors to this non-perfect system behavior. We implemented a feedback loop in the digital part of the transmitter hardware which can be configured flexibly according to application-specific needs. The configuration is done by choosing the appropriate linear combination of the measured and digitized complex wave parameters as an actual value for the control loop. Results for both control of the forward power and control of the actual B1-field are presented.

2637.   Low-loss adjustable networks for automated matching of transmit coils
Giorgos Katsikatsos1, and Klaas Paul Pruessmann1
1Institute for Biomedical Engineering, ETHZ, Zurich, ZH, Switzerland

A low-loss, high power handling, custom-made capacitor is used a building unit for an automated L-matching-network controlled by an external computer. The capacitors are adjusted mechanically by piezoelectric motors. Each L-network is characterized completely by its S-matrix and those S-matrices are used in the analytical solution of the invert problem. The result is highly reproducible since it achieves matching for arbitrary loads.

2638.   An Envelope-Tracking Transmit Array Amplifier
Pascal P Stang1, John M Pauly1, and Greig C Scott1
1Electrical Engineering, Stanford University, Stanford, CA, United States

Modern MRI pulse sequences demand high-fidelity RF transmit reproduction at multi-kilowatt power levels. Typical MRI power amplifiers are Class-AB architectures which excel at predictable linear performance, yet become inefficient when used at less than their peak power. We present an envelope-tracking linear RF power amplifier system to explore the potential efficiency gain and performance impact of this method in the context of MRI transmit arrays. The efficiency improvement from envelope tracking varies with both pulse shape and amplitude, however for sync pulses, preliminary measurements show DC power consumption reduced by 20-35% compared to operation at full supply rail while delivering the same RF output.

2639.   Shielded Current Sensors for Monitoring Parallel Transmission
Karl Edler1, Marie-France Hang1, Alexis Amadon1, Nicolas Boulant1, Martijn A Cloos1, and Christopher J Wiggins1
1NeuroSpin/I2BM/DSV/CEA, Gif-sur-Yvette, France

Toroidal sensors were attached to the conductors of two decoupled transmit loops and were used to monitor the current during an RF-pulse. These non-resonant sensors were approximately matched to 50 Capital Greek Omega and were also shielded to minimize their coupling to other sources. During the transmit pulse the preamplifiers were replaced with attenuators so that the received signal would remain within the dynamic range of the receiver channels. The results were also compared with the forward power as measured by connecting the directional couplers on the rear of the RF power amplifiers to spare receiver channels.

2640.   Active Decoupling for Prostate MR Imaging and Spectroscopy with Extended Field of View at 7T
Catalina S. Arteaga de Castro1, Ozlem Ipek1, Mariska P. Luttje1, Marco van Vulpen1, Juus Noteboom1, Peter R. Luijten1, Uulke A. van der Heide2, and Dennis W.J. Klomp1
1University Medical Center Utrecht, Utrecht, Netherlands, 2Netherlands Cancer Institute, Amsterdam, Netherlands

Prostate imaging at higher magnetic fields like 7 Tesla is challenging. Even after B1 shimming the B1 strength at the prostate location remains low. Endorectal coils are used to increase the receive sensitivity at the prostate, but as transmitters they can substantially increase the B1. In contrast from receive only coils that need PIN diodes to be decoupled from the transmitters, the ERC remains tuned when combined with external coils. We use active decoupling as an alternative to PIN diode decoupling by transmitting with the ERC with an optimized amplitude and phase to counteract the coupling caused by the field of the external elements.

2641.   Design and Evaluation of a Dipole Antenna TX/RX element as a Building Block for Combined MR imaging and RF Hyperthermia at 7.0 T
Celal Özerdem1, Lukas Winter1, Werner Hoffmann2, Helmar Waiczies1, Reiner Seemann2, Davide Santoro1, Alexander Müller1, Abdullah Ok1, Tomasz Lindel2, Bernd Ittermann2, and Thoralf Niendorf1,3
1Berlin Ultrahigh Field Facility (B.U.F.F.), Max-Delbrueck-Center for Molecular Medicine, Berlin, Germany, 2Physikalisch Technische Bundesanstalt (PTB), Berlin, Germany, 3Experimental and Clinical Research Center (ECRC), Charité - University Medicine Campus Berlin Buch, Berlin, Germany

Combining RF hyperthermia and MR imaging is conceptually appealing to pursue spatially and temporally controlled and monitored RF heating. The benefits of this approach could be used as an adjunctive therapy for established cancer treatments including radiotherapy and chemotherapy , targeted drug delivery and targeted MR contrast agent delivery. This study evaluates the design of a bow tie dipole antenna building block both for MR imaging and RF heating at 7.0T.

2642.   A Millimeter Scale Implanted Coil with an Integrated Wireless Amplifier for Imaging of the Rodent Kidney
Chunqi Qian1, Stephen Dodd1, Der-Yow Chen1, Joe Murphy-Boesch1, and Alan Koretsky1
1LFMI/NINDS, National Institutes of Health, Bethesda, MD, United States

An implantable resonator with an integrated parametric amplifier has been constructed to provide enhanced localized sensitivity of internal organs in the rodent. The sample coil was one element of a non-linear double frequency resonator that mixed the MR signal with a pump frequency to produce an amplified output at the Larmor frequency. The resonator/wireless amplifier was 3mm x 3mm x 7mm in size, and it enabled high resolution images to be obtained to identify small vascular structures of a rat kidney in vivo.

2643.   A dipole antenna for pelvis imaging at 7T
Sedig S Farhat1, Daniel J Lee1, Carolyn Costigan1, Penny A Gowland1, and Paul M Glover1
1University of Nottingham, Nottingham, Nottinghamshire, United Kingdom

There are very few surface coils that work well at 7T. Up until now the majority of RF coils have been designed as near field antennas. The aim of this work was to design and build a transmit/receive dipole antenna for imaging the human pelvis. The dipole antenna shows the desired improvement in SNR and homogeneous coverage. Coverage goes much further into the pelvis than is shown in the image, indicating that the dipole antenna is better suited for imaging structures deeper into the body than loop or strip transmitting elements.

2644.   A Novel Highly Homogeneous Wireless Birdcage Resonator Coil
Haoqin Zhu1, Mehran Fallah-Rad1, Michael Lang1, Wayne Schellekens1, Kirk Champagne1, and Labros Petropoulos1
1R&D, IMRIS Inc, Winnipeg, MB, Canada

In this paper, a wireless HP birdcage coil was presented. The design of this coil can be extended to low pass, bandpass or dual frequency configurations. Simulated B1 field of the HP b-cage within the body coil showed an increase of more than 15dB in magnitude compared to B1 field of body coil only. SNR measurements on phantom showed comparable numbers between the wireless coil and the 12-channel OEM coil. Additionally, volunteer head images were of similar quality and uniformity between the two coils.
Traditional Poster Session - Engineering

Receive Arrays
Click on to view the abstract pdf. Click on to view the poster (Not all posters are available for viewing.)
Monday 7 May 2012
Exhibition Hall  14:15 - 16:15

2645.   A Compact 10-channel RF Array Coil for MR Imaging of Mice
Chieh-Wei Chang1, Wen-Yang Chiang1, Steven M Wright1,2, and Mary Preston McDougall1,2
1Biomedical Engineering, Texas A&M University, College Station, TX, United States, 2Electrical Engineering, Texas A&M University, College Station, TX, United States

Our 10-channel cardiovascular phased array and transmitting volume coil without active detune is presented. Parallel imaging techniques in MRI provide the capability to reduce scan time based on the partial or entire removal of phase-encoding steps, especially offering benefit to cardiovascular MRI of the murine model. Our 10-channel array, transmit coil, and a modular 16-channel low impedance preamplifier board that together constitute a compact parallel imaging of system. The integrated anesthesia chamber provides streamlined imaging capability. The dual plane pair element design [9] described 1) ensures that no coil-to-coil decoupling mechanism is needed other than the preamplifiers and 2) inherently decouples from a homogenous transmit field, eliminating the need for active decoupling and 3) reduces, and in this case, eliminates, the need for baluns and/or cable traps. The transmit coil design described ensures an extremely uniform sensitivity pattern, and the 16-channel preamplifier board described is compact and modularized for straightforward use with any array coil.

2646.   Parallel imaging capabilities of an 11-channel coil for MRgHIFU imaging.
Emilee Minalga1, Allison Payne1, Robb Merrill1, Nick Todd1, Sathya Vijayakumar1, Dennis L. Parker1, and J. Rock Hadley1
1Utah Center of Advanced Imaging Research, University of Utah, Salt Lake City, UT, United States

This work describes the parallel imaging capabilities of an 11-channel breast RF coil for magnetic resonance guided high intensity focused ultrasound. The coil was built to be compatible with a breast magnetic resonance guided high intensity focused ultrasound treatment cylinder and uses capacitive decoupling of adjacent loops. The coil is evaluated for SNR performance, temperature imaging performance, and parallel imaging capabilities. The coil was found to give better SNR over a single loop chest coil. This SNR increase translates to better anatomy imaging and temperature measurements and allows for the use of parallel imaging.

2647.   31-Channel 3T Cardiac Array Optimized for SNR and g-Factor
Scott B King1, Mike J Smith1, Jarod Matwiy1, Hung-Yu Lin1, and Boguslaw Tomanek2
1Institute for Biodiagnostics, National Research Council of Canada, Winnipeg, Manitoba, Canada, 2Institute for Biodiagnostics, National Research Council of Canada, Calgary, Alberta, Canada

Most array coils used for body imaging utilize regular shaped rectangular or circular surface coils evenly distributed to cover the entire torso. The cardiac region comprises a relatively small volume compared to the entire human torso, therefore, an optimized cardiac array coil should reflect this, to make the best use of a limited number of receivers. Here, a 31-channel cardiac array was designed and constructed for focused performance within the cardiac region, providing improved SNR in addition to better g-factor performance. Up to 200% SNR gains and more aggressive reduction factors were achieved relative a 12-channel OEM cardiac array.

2648.   A 16 Element Phased Array Surface Coil for Time-Resolved CE-MRA at SENSE Accelerations up to 12
Paul T. Weavers1, Chris C. Cline1, Casey P. Johnson1, Phillip J. Rossman1, Thomas C. Hulshizer1, and Stephen J. Riederer1
1MR Research Laboratory, Mayo Clinic, Rochester, Minnesota, United States

A 16 element receive coil specifically designed for the calves has been constructed. The design permits close proximity of the coil to the anatomy even as the leg narrows from knee to calf, and is flexible enough to fit around a wide range of patient sizes. G-factor maps made with the 16ch coil at R = 12 compare favorably to g-maps produced with a previous 8ch coil at R = 8. In-vivo CE-MRA results are demonstrated using an accelerated acquisition with R = 12 2D SENSE providing 1mm3 resolution, a 3.5 sec update time and a 12.4 sec temporal footprint.

2649.   A localized 16-channel linear planar array for 3T human brain imaging
Hsuan-Chung Niu1, Ying-Hua Chu1, Jo Lee1, Wei-Chao Chen2, Wen-Jui Kuo3, and Fa-Hsuan Lin1,4
1Institute of Biomedical Engineering, National Taiwan University, Taipei, Taiwan, 2SDI corporation, Changhua, Taiwan, 3Institute of Neuroscience, National Yang Ming University, Taipei, Taiwan, 4Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, MA, United States

To provide localized sensitivity and to adapt to spatiotemporal resolution enhancement by parallel MRI, we develop a 16-channel linear planar array for brain imaging at 3T. The size of the array is about 10 cm x 10 cm with 16 slim rectangular distributed over two sides of a circuit board. Isolation between channels brought by appropriate overlapping and pre-amplifier decoupling is demonstrated with minimal noise correlation. Preliminary experiment results demonstrate up to 4x acceleration of human temporal lobe structure imaging with 1 mm spatial resolution.

2650.   A 3.0T Flexible Transmit and 16 Channel Receive Array Shoulder Coil
Tsinghua Zheng1, Matthew Finnerty1, Xiaoyu Yang1, Paul Taylor1, and Hiroyuki Fujita1,2
1Quality Electrodynamics, LLC, Mayfield Village, Ohio, United States, 2Dept. of Physics, Case Western Reserve University, Cleveland, Ohio, United States

A flexible transmit and 16 channel receive shoulder array coil for 3.0 Tesla was constructed and tested. The coil uses one quadrature transmit coil for transmitting and an array of sixteen receive elements for receiving. Initial phantom and volunteer imaging demonstrated excellent image quality and uniformity, and the coil required significant less transmit power than receive only shoulder coils.

2651.   Open access 3-channel receive-only coil for interventional brain imaging.
Emilee Minalga1, Allison Payne1, Nick Todd1, Robb Merrill1, Dennis L. Parker1, and J. Rock Hadley1
1Utah Center of Advanced Imaging Research, University of Utah, Salt Lake City, UT, United States

This work describes the design of an open access 3-channel brain RF coil for interventional MR imaging. The coil was built to be compatible with a head stereotactic device and uses capacitive decoupling of adjacent loops. The coil is evaluated for SNR performance, temperature imaging performance, and a comparison of anatomy scans. The coil was found to give better SNR over both the body coil and a 12-channel commercial coil. This SNR increase translates to better anatomy imaging and temperature measurements.

2652.   An Eight-element Phased Array Coil for Carotid Artery Imaging at 3 Tesla
Yong-Qin Zhang1, Hua-Bin Zhu2, Ben-Sheng Qiu3, and Xin Liu3
1Paul C. Lauterbur Research Centre for Biomedical Imaging, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen, Guangdong Province, China, 2Suzhou Zhongzhi Medical Technology Co., Ltd., 3Paul C. Lauterbur Research Centre for Biomedical Imaging, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences

To improve the penetration depth, coverage and signal-to-noise ratio (SNR) of carotid coil in clinical applications and its suitability for different people, we designed a bilateral eight-channel receive-only phased array coil for use at 3T. The SNR map and g-factor map of the proposed coil is given in the results. And simultaneously preliminary comparison demonstrates that the SNR of the new design is much higher than commercially available 4-element carotid coils in most cases. The quantitative and qualitative performance comparison between two carotid coils will be done in further studies.

2653.   A Novel Phased Array Coil for Limb Imaging Incorporating 3D Coil Overlaps
Randy Giaquinto1, Wolfgang Loew1, Suraj Serai1, Jean Tkach1, Kathleen Emery1, and Charles Dumoulin1
1Imaging Research Center, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio, United States

Single channel flex coils or adult sized knee/wrist coils are currently used for imaging the pediatric elbow. This frequently results in uncomfortable patient positioning, patient motion, poor fat suppression and degraded images. Furthermore, the use of single loop or simple volume coils prevent the use of accelerated imaging based upon parallel imaging strategies. In this work, we present a novel eight-channel phased array coil built on a lightweight polycarbonate frame. This coil has improved SNR over flex coils used in our institution and overcomes the challenges of cross-coil coupling in a three-dimensional array construction.

2654.   Sensitivity Simulation of 16ch Spine/Torso Array Coil at 3T
Yoshihisa Soutome1, Masayoshi Dohata1, Hisaaki Ochi1, and Yoshitaka Bito1
1Central Research Laboratory, Hitachi Ltd., Kokubunji, Tokyo, Japan

To improve the workflow efficiency of scans by decreasing the frequency of coil exchange, we have designed a 16-channel spine/torso array coil, and investigated its sensitivity at 3T with a torso phantom using numerical simulations with method of moments. We also compared the sensitivity of the designed coil with that of the traditional spine and torso array coils, and evaluated the performance of a 32-ch torso array consisted of two designed coil. Simulation results suggest that the designed coil can be commonly used as a spine array coil and a posterior torso coil.

2655.   A Two-part 16-Channel Receive Phased Array for Imaging of Rabbit Heart and Aorta on a 3T Clinical MRI System
Stefan Fischer1, Mark Schuppert1, Maxim Terekhov1, Stefan Weber1, Andrei L. Kleschyov2, and Laura Maria Schreiber1
1Section of Medical Physics, Department of Diagnostic and Interventional Radiology, University Medical Center of the Johannes Gutenberg University, Mainz, Germany, 2II-Medical Department, University Medical Center of the Johannes Gutenberg University, Mainz, Germany

In this study a dedicated rabbit heart/aorta 16-channel receive array was developed to achieve high SNR in the relevant anatomical region. A split design with two 8-ch parts was chosen. To validate the array SNR and g-factor maps were evaluated. Compared with a 15-ch knee coil the SNR of the 16-ch rabbit array was 50% higher in the center of a 2 liter bottle phantom und 2.3-fold higher in the peripheral area. The two-part design allows minimizing array-to-object distance for rabbit MRI and also simultaneously imaging of two objects with eight channels each increasing the throughput.

2656.   A Monte Carlo simulation study on receiver gain variation of linear combined MRI coil array
Liang Liu1, Faiz Ikramulla1, Velibor Pikelja1, Jonathan Nass1, and Ashok Menon1
1Invivo, Philips Healthcare, Pewaukee, WI, United States

Combiners/splitters have been widely used in MRI phased array for channel reduction and mode selection. Unlike uncombined MRI coil array where signals are weighted differently by the associated noise level in image reconstruction, combined MRI channels use RF switch and combiner circuits to merge received signals directly and both the magnitude and phase of the signals require finely tuning prior combining. For coils with the combiner circuits built after the preamplifiers stage, the gain variations of these preamplifiers have significant impact on the performance of final combined signals. A Monte Carlo simulation was tested based on real preamplifier data to investigate this effect and aimed to help determine specifications for coil designers.

2657.   A New RD Coil Design for Prostate MRI
Seunghoon Ha1, Mark Jason Hamamura1, Werner W Woeck1, and Orhan Nalcioglu1,2
1Center for Functional Onco-Imaging, University of California Irvine, Irvine, California, United States, 2Department of Cogno-Mechatronics Engineering, Pusan National University, Pusan, Korea

Despite increasing the number of receiver coils and upgrading to higher magnetic fields, prostate MRI using the conventional torso-pelvic RF coil does not provided sufficient image quality to clearly visualize all features of interest due to the extended distance from the coil elements to the prostate region. The endorectal RF coil provides a higher SNR due to its close proximity to the prostate region, but involves invasive positioning and carefully patient monitoring to prevent excess RF power deposition. In this study, we propose a new non-invasive coil with a competitive SNR for prostate MRI and compare its performance against other commercial coils.

2658.   A carbon receive array of 8 elements, interoperable with proton scanning, for human temporal lobe
James Tropp1, Paul Calderon2, Lucas Carvajal3, Fraser Robb2, P. E. Z. Larson3, P. Shin3, D. B. Vigneron3, and S. J. Nelson3
1Global Applied Science Lab, GE Healthcare Technologies, Fremont, CA, United States, 2GE Healthcare Technologies, 3University of California San Francisco

We describe the design, construction, and test of an array receive coil intended for carbon imaging of human temporal lobe, in particular with hyperpolarized substrates. Preliminary images of an oil phantom are shown.

2659.   Phased array probehead for magnetic resonance
Oliver G. Gruschke1, Elmar Fischer2, Maxim Zaitsev2, Jürgen Hennig2, and Jan G. Korvink1,3
1Lab. of Simulation, University of Freiburg - IMTEK, Freiburg, Germany, 2Dept. of Radiology Medical Physics, University Medical Center, Freiburg, Germany,3Freiburg Institute for Advanced Studies – FRIAS, University of Freiburg, Freiburg, Germany

The integration of a Helmholtz coil with our previously published phased array of microcoils, allows creating a high-resolution probehead. Increasing the usability and creating the option for a future use in a MR scanner with a small bore diameter.

2660.   Multi-element wireless stacked phased array coil
Haoqin Zhu1, Grace Wang1, and Labros Petropoulos1
1R&D, IMRIS Inc, Winnipeg, MB, Canada

A novel wireless stacked decoupled phased array was presented. It was shown that this coil can greatly improve image quality in terms of SNR and penetration. SNR improvements of 35% were measured compared with a single element coil of similar size. Such coil design will allow to increase the number of elements on the phased array design without increasing the overall coil dimensions. The wireless technology will allow for user friendly lighter coils without sacrificing image quality. This design can be extended for standard phased array coils combined with preamplifier decoupling to further enhance the isolation between the adjacent elements.

2661.   An Implanted 8-channel array coil for high-resolution macaque MRI at 3T
Thomas Janssens1, Boris Keil2, Jennifer A. McNab2, Reza Farivar2, Annelies Gerits1,2, Jonathan R. Polimeni2, Lawrence L. Wald2,3, and Wim Vanduffel1,2
1Laboratory for Neuro- and Psychophysiology, K.U.Leuven, Leuven, Belgium, 2A.A Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Charlestown, Massachusetts, United States, 3Harvard-MIT Division of Health Sciences and Technology, Cambridge, Massachusetts, United States

Close proximity of a phased-array surface coil results in increased SNR and improved performance during accelerated imaging, two characteristics that are essential for high-resolution macaque MRI. Here, a receive-only 8-channel phased-array coil was developed and implanted on top of the skull of a monkey underneath the head fixation post. The data show a 5.4- and 3.6-fold increase in SNR in the brain periphery compared to, respectively, an external single and 4-channel coil. Even for very high resolutions, high SNR and image quality in anatomical, functional, and diffusion images was obtained, indicating the advantage of an implanted phased-array coil approach.

2662.   A 6-channel brain coil for MR guided high intensity ultrasound.
Emilee Minalga1, Robb Merrill1, Nick Todd1, Allison Payne1, Dennis L. Parker1, and J. Rock Hadley1
1Utah Center of Advanced Imaging Research, University of Utah, Salt Lake City, UT, United States

This work describes design and evaluation of a 6-channel brain RF coil for magnetic resonance guided high intensity focused ultrasound. The coil was built to be compatible with a head stereotactic device and a brain magnetic resonance guided high intensity focused ultrasound treatment system. The coil used capacitive decoupling of adjacent loops. The coil is evaluated for SNR performance, temperature imaging performance, and anatomy imaging. The coil was found to give better SNR over both the body coil and a 12-channel commercial head coil. This SNR increase translates to better anatomy imaging and temperature measurements.
Traditional Poster Session - Engineering

RF Safety
Click on to view the abstract pdf. Click on to view the poster (Not all posters are available for viewing.)
Monday 7 May 2012
Exhibition Hall  14:15 - 16:15

2663.   In silico electromagnetic simulation of a murine glioma model at 7T MRI conditions
Jose I Rey1, Eduardo G Moros2, Robert J Gillies1, and Gary V Martinez1
1Cancer Imaging, Moffitt Cancer Research Center, Tampa, FL, United States, 2Radiation Oncology, Moffitt Cancer Research Center, Tampa, FL, United States

In silico study of mouse glioma animal model under 7T MRI conditions. Includes analysis of electric field intensities (E), currents (J), and specific energy absorption (SAR) in normal, brain and tumor tissue. FDTD simulations show that glioma tumors have distinct dielectric properties that confer significant variations in electromagnetic response. This study is relevant to preclinical MR method scenarios leading to clinical translation.

Fast MR thermometry using phase referenced asymmetric spin-echo EPI for high field
Markus Nikola Streicher1, Andreas Schäfer1, Dimo Ivanov1, Laurentius Huber1, Bibek Dhital1, Enrico Reimer1, Dirk Müller1, Andre Pampel1, Robert Trampel1, and Robert Turner1
1Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany

The proton resonance frequency shift MR-thermometry method is inherently very sensitive to magnetic field perturbations in time. We show an improved referenced spin-echo EPI sequence which enables paired water and fat image acquisition in 100 ms, and allows correction for almost all causes of in-vivo field drift, such as breathing. Frequency-selectivity of the spin-echo sequence is achieved by using reversed gradient amplitudes for excitation and refocusing. With an appropriate choice of parameters, the technique provides not only fat and water separation, but immediate acquisition of the reference map at the same slice position and with maximum signal amplitude.

2665.   Improving SNR in small temperature change MR Thermometry to acquire SAR Maps of a pair of ASL Labelling Coils
Aaron Oliver-Taylor1, Chris Randell2, Roger J Ordidge3, and David L Thomas4
1Department of Medical Physics and Bioengineering, University College London, London, England, United Kingdom, 2PulseTeq Products Division, Renishaw PLC, United Kingdom, 3Centre for Neuroscience, University of Melbourne, Melbourne, Victoria, Australia, 4Institute of Neurology, University College London, London, England, United Kingdom

Presented is a method to acquire SAR maps of a pair of ASL labelling coils using proton resonance shift MR thermometry. Accurate SAR measurements can only be made from the linear initial temperature change when RF heating commences, however due to the low power of the ASL coils (1W) this temperature change is small and consequently suffers from low SNR. Regular EPI phase images were acquired over an extended period of RF heating, and the time series of each voxel fit to a suitable function to improve SNR. Resultant SAR maps are accurate and reproducible.

2666.   From 7T to 10.5T: B1+, SAR and Temperature Distribution for Head and Body MRI
Jinfeng Tian1, Devashish Shrivastava1, John Strupp1, Jay Zhang1, and Thomas Vaughan1
1U. of Minnesota, Minneapolis, MN, United States

Spurred by the success of 7T whole-body MRI, whole-body MRI systems of 9.4T or above were installed or will be installed to push the boundary. In this abstract, the RF performance of a 16-ch TEM array at 7T and 10.5T are compared with FDTD simulation. Results showed the head is a power sink absorbing the propagating EM waves at 7T and 10.5T torso MRI, thus creating high B1 and SAR in the head. The major RF artifacts, the high SAR and temperature rise in the head at 7T, are all seen and more sever at 10.5T.

2667.   Patient-specific SAR estimation for the 8-channel radiative antenna array at 7 T prostate MRI
Ozlem Ipek1, M de Greef2, A Raaijmakers1, P.R. Luijten3, J. J.W. Lagendijk1, and C.A.T. van den Berg1
1Radiotherapy, UMC Utrecht, Utrecht, Netherlands, 2Image Science Institute, UMC Utrecht, Utrecht, Netherlands, 3Radiology, UMC Utrecht, Utrecht, Netherlands

The patient-specific worst-case local SAR with 8 channel radiative antenna array is studied in 3 different patient models, by calculation of the largest eigenvalue of the Q-matrix for each voxel. The models that we used vary both in size and fat/muscle ratio. In this way,the probability of a generic model is investigated for worst-case local SAR estimation of an external surface array. A generic model is not found in 3 models due to huge variance in fat/muscle ratio.

2668.   Fast Subject-Specific SAR Calculation for Multi-Channel RF Transmission
Shumin Wang1
1Auburn University, Auburn, AL, United States

Safety assessment for multi-channel RF transmission systems requires the analysis of specific absorption rate (SAR) in a subject-specific manner. Since SAR depends on individual subject anatomy and on the multi-channel excitation scheme, traditional approaches that rely on generic subject models and worst-case scenario evaluations may result in excessive overestimations. With the advancement of computational electromagnetics techniques, fast full-wave simulations of actual subject models have been proposed. In this study, we demonstrate that high simulation accuracy can be achieved with these techniques in real time.

2669.   From Single Element Complex B1 Mapping to Local SAR Estimation using Multi-channel Transceiver Coil at 7T
Xiaotong Zhang1, Jiaen Liu1, and Bin He1
1Biomedical Engineering, University of Minnesota, Minneapolis, Minnesota, United States

Quantitative patient-specific local SAR estimation is highly desired in UHF MRI applications. In this work, using a 16-channel transceiver head coil at 7T, based on previously proposed method, we report our simulation study from single element complex B1 mapping to in-vivo local SAR estimation on a realistic geometry head model. Promising simulation results suggest its feasibility and reliability. Establishment of real-time EPT technique may have a significant impact on patient-specific SAR management in parallel transmission at UHF.

2670.   Radio-Frequency Heating in Swine due to a 3T (123.2 MHz) and 7T (296 MHz) Head Coil
Devashish Shrivastava1, Lynn Utecht1, Jinfeng Tian1, Timothy Hanson2, and JT Vaughan1
1University of Minnesota, Minneapolis, MN, United States, 2University of South Carolina

Radio-frequency (RF) heating was measured using fluoroptic probes in the scalp; 5 mm, 10 mm, 15 mm, 20 mm and 25 mm in the brain; and rectum in eight anesthetized swine due to a continuous wave power deposition from a 15 rung, 3T head coil and an 8 channel, 7T head coil (N=4 for each coil). The heating was simulated using the analytical generic bioheat transfer model (GBHTM) and the empirical ‘gold standard’ Pennes’ bioheat transfer equation (BHTE). The RF power induced temperature changes did not achieve plateau. The GBHTM simulated the heating more accurately than the Pennes’ BHTE.

2671.   Implications of posture changes on local SAR and B1+ homogeneity in RF shimming at 3T
Desmond Teck Beng Yeo1, Zhangwei Wang2, and Ileana Hancu1
1Diagnostics and Biomedical Technologies, GE Global Research, Niskayuna, NY, United States, 2GE Healthcare Coils, Aurora, OH, United States

Predicting local SAR risks in multi-channel transmit MR systems is a challenging task. One approach uses EM simulations to predict local SAR while optimizing the voltage feeds’ complex weights to obtain a uniform excitation profile. The weights are then applied to the coils’ voltage sources and the RF waveforms monitored to ensure they conform to the calculated weights. This approach provides some information about local SAR risks. Our work uses EM numerical computations and a posable HBM to investigate how B1+ homogeneity and local SAR may change when optimized weights are applied after a subject is repositioned following RF shimming optimization.

2672.   Effect of Body Type, Tissue Conductivity and Body Location within the RF Coil on Tangential Electrical Fields in 1.5T MRI
Shiloh Sison1, Xiaoyi Min2, Yan Liu3, Kevin Feng3, Ji Chen3, John Nyenhuis4, Gabriel Mouchawar2, and Jon Dietrich2
1St. Jude Medical, Sunnyvale, CA, United States, 2St. Jude Medical, 3University of Houston, 4Purdue University

The body type, conductivity and location within an RF coil partially determine the maximum tangential electric field along implantable cardiac rhythm device lead paths. The simulation conditions which have the possibility of generating the largest temperature rise at the electrodes of the lead are an obese male with tissue conductivity 80% of nominal and landmark Z ~0mm. Around this Z landmark the effect of 20mm to 50mm shifts in the X and Y direction are negligible. The IEC limit of 3.2 W/kg for head SAR may result in a whole body SAR of less than 2 W/kg for some landmarks.

2673.   Design and SAR Estimation of a Segmented Loop for Dual Coil CASL at 9.4 T
Jonas Bause1, G. Shajan1, Jens Hoffmann1, Klaus Scheffler1, and Rolf Pohmann1
1MR Center, Max-Planck Institute for biological Cybernetics, Tuebingen, Germany

Dual-Coil Continuous Arterial Spin Labeling (DC-CASL) can reduce magnetization transfer and increase SNR. Here a balanced detunable segmented loop coil for DC-CASL in humans at 9.4T was developed and FDTD simulations were performed to estimate the optimal phase shift as well as the local SAR. The simulations showed that sufficient labeling is possible without exceeding the IEC limits when the duty cycle is limited to 25 %. An additional safety margin of 37 % was included in the SAR calculations to account for deviations in the position of the coils.

2674.   Maximum SAR Estimation of a Multiple Channel Travelling Wave System based on Waveguide Theory
Jan Paška1, David O Brunner2, Juerg Froehlich1, and Klaas P Pruessmann2
1Laboratory for Electromagnetic Fields and Microwave Electronics, ETH Zurich, Zurich, Switzerland, 2Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland

Waveguide theory was used to analyze a travelling wave multiple channel setup. This allowed us to reduce the size of the numerical domain and increase the model resolution, allowing a more precise estimation of the EM fields. The SAR was calculated in the worst case, under the condition that 1W is dissipated in the human body. MR images based on the derived power limit were acquired, with the travelling wave multiple channel system in transceive mode.

2675.   Matrix and Model Order Reduction Approach for Rapid Safety Prediction and Supervision of Local and Global SAR in Parallel Transmit Coils
Esra Neufeld1, Maximilian Fütterer1, Matthias Gebhardt2, Michael Oberle1, and Niels Kuster1,3
1IT'IS Foundation for Research on Information Technologies in Society, Zurich, Switzerland, 2Imaging & Therapy Division, Siemens AG, Erlangen, Germany, 3Swiss Federal Institute of Technology (ETHZ), Zurich, Switzerland

Parallel transmit coils can lead to high local SAR thus posing a safety issue even when the total energy deposition is monitored. A method based on pre-computed matrices and model order reduction is presented to allow efficient safety prediction and online supervision, provided a mapping of the patient to a reference model can be established. The method has been applied to a detailed anatomical model with variable BMI. Rapid, conservative estimations with known overestimation can be provided for any set of steering parameters. The impact of position, posture and anatomy remains to be investigated.

2676.   Influence of Skin Tissue and Air Cavities on Local SAR Estimation in Parallel MR Excitation
Ara Yeramian1, Stefanie Buchenau1, Chris A. Cocosco1, Matthias Gebhardt2, Dirk Diehl3, Jürgen Hennig1, Jan Korvink4, and Maxim Zaitsev1
1Medical Physics, University Medical Center Freiburg, Freiburg, BW, Germany, 2Healthcare Sector, Siemens AG, Erlangen, Germany, 3Corporate Technology, Siemens AG, Erlangen, Germany, 4IMTEK, Freiburg, Germany

Whole-body Specific Absorption Rate (SAR) estimation and hot spot detection in parallel excitation is achieved through EM simulations of RF parallel excitation coils and virtual whole-body models. It has been proposed that whole-body models comprising fat, muscle, and lung tissues only (essential tissues) are sufficient for accurate SAR estimation. In addition to these essential tissues, due to their dielectric properties contrasts with their surroundings, we investigate the influence of skin tissue and air cavities in the head, pharynx, trachea, bronchi, and the intestines on local SAR in an 8-channenl pTx environment.
Traditional Poster Session - Engineering

RF: Other
Click on to view the abstract pdf. Click on to view the poster (Not all posters are available for viewing.)
Monday 7 May 2012
Exhibition Hall  14:15 - 16:15

2677.   Electromagnetic Field Evaluations Inside a Body-Tissue-Simulating Cylinder Phantom Excited by an Ideal First-Order Circularly Polarized Mode
Andreas Rennings1, Le Chen1, Friedrich Wetterling2, Mark E. Ladd3, and Daniel Erni1
1General and Theoretical Electrical Engineering (ATE), Faculty of Engineering, Univ. of Duisburg-Essen, Duisburg, Germany, 2Computer Assisted Clinical Medicine, Faculty of Medicine, Univ. of Heidelberg, Mannheim, Germany, 3Erwin L. Hahn Institute for Magnetic Resonance Imaging, Univ. of Duisburg-Essen, Essen, Germany

The RF field excitation homogeneity problem of MRI at high resonance frequencies is investigated on the basis of the simplest two-dimensional setup including a cylinder phantom with spatially constant but frequency-dependent material parameters and an impressed surface current distribution between the phantom’s surface and a surrounding perfect electric conductor (PEC) shield. This simple arrangement has been chosen intentionally in order to reduce the set of parameters to a minimum and therefore maximize the physical insight, which allows quite general and helpful statements about the B1+ pattern quality for the widely used first-order circularly polarized (CP) excitation mode. The coefficient of variation (CoV) of the B1+ distribution is most suited as a figure of merit for the homogeneity, since it normalizes the standard deviation to the mean value of the field pattern. Only two parameters of the arrangement have been varied – the excitation frequency ranging from 30°MHz up to 450°MHz and the diameter of the phantom ranging from a few centimeters up to 40 cm, which covers more or less every MR imaging scenario. A characteristic B1+ pattern will be introduced, which indicates the transition between a regime with the well-known central brightening and another one without.

2678.   Dgital Beam Forming in the MRI
Anand Gopinath1, Emad Ebbini1, Lance DelaBarre2, and Tommy Vaughan2
1Department of Electrical and Computer Engineering, University of Minnesota, Minneapolis, Minnesota, United States, 2Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, United States

In high field MRI systems, B0 of 7T and above, inhomogeneity in the RF B1+ field is mitigated by RF shimming in which multi-channel coil elements are excited with different magnitude and phases to obtain a uniform field in a region of interest (ROI). This process is termed analog beam –forming. The alternative is to digitize the receive signals and perform digital beam forming: to focus on a single ROI, or multiple closely spaced ROIs, perform element pattern correction to exclude mutual coupling effects, perform nulling in a specific region and other applications. This paper provides a discussion of digital beam forming.

2679.   RF signal incoupling into multi-layered dielectric media: the role of surface waves
Ozlem Ipek1, I.J Voogt2, P.R. Luijten2, J. J.W. Lagendijk1, and C.A.T van den Berg1
1Radiotherapy, UMC Utrecht, Utrecht, Netherlands, 2Radiology, UMC Utrecht, Utrecht, Netherlands

The role of the surface waves at ultra high field imaging is investigated for a loop coil and a dipole antenna. Loop coil represents a magnetic dipole, which is placed vertically and horizontally along B0 direction while the dipole antenna represents the electric dipole placed on a dielectric half-space. Surface waves measured in the water substrate which is placed on a EG gel phantom at 7 T MRI. They may lead to a larger lateral FOV of an RF coil then expected.

2680.   Development and Stability Testing of an MRI Compatible Isolated Tissue System
Simon Richardson1,2, Bernard Siow2, Andrew Batchelor3, Mark F. Lythgoe1, and Daniel D.C. Alexander2
1UCL Centre for Advanced Biomedical Imaging, Division of Medicine and Institute of Child Health, University College London, London, United Kingdom, 2Centre for Medical Image Computing, Dept of Computer Science, University College London, London, United Kingdom, 3Wolfson Inst for Biomedical Research, University College London, London, United Kingdom

We have developed an MRI compatible isolated tissue maintenance chamber and tested its performance in maintaining rat optic nerve functionally and structurally for 10 hours. Electrophysiology, electron microscopy and detailed diffusion MRI have been used to assess the tissue stability within this system. The chamber is versatile, controllable and reliable and can be used with any horizontal bore MRI system. This is the first temporal validation of tissue functional, structural and MR stability in an MRI compatible isolated tissue system.

2681.   On The Direct MRI of Histological Tissue Section: Expanding Standardized off-the-shelf Sample Mounting from Coverslips To Glass
Dung Minh Hoang1,2, Chao Zhang1, Evelyn Voura1,3, Latifa Fakri-Bouchet4, and Youssef Zaim Wadghiri1
1Radiology, NYU - School of Medicine, New York, New York, United States, 2Radiology, NYU - Medical Center, New York, New York, United States, 3Neurosurgery, NYU - School of Medicine, New York, New York, United States, 4University Lyon 1 - Claude Bernard, Lyon, France

A set of five histological coils were designed and tested to accommodate standard off-the-shelf mounting commonly used for tissue examination under a microscope with sizes enabling a wide range of tissue on either coveslips or glass slides. We compared the sensitivity of all the coil sizes designed in-house with a 7T system acquired during overnight scans (8-hours). Our results show that samples with sizes as small as 10x10mm and as thin as 5um thick can be imaged with excellent anatomical details

2682.   Consistent Phase Contrast Volumetric Imaging from a Set of 2D Slices
Andrzej Jesmanowicz1, and Robert W. Cox2
1Biophysics, Medical College of Wisconsin, Milwaukee, WI, United States, 2National Institute of Mental Health, National Institutes of Health, Bethesda, MD, United States

A new RF pulse synthesizer that is based on the Texas Instruments DAC5688 chip was used to create a consistent volumetric phase contrast imaging from the set of 2D slices. This DAC chip has a sufficient quality to create coherent transmit pulses and their reference waveforms for compensating the phase of different slices.
Traditional Poster Session - Engineering

Receive Efficiency & Noise Mitigation
Click on to view the abstract pdf. Click on to view the poster (Not all posters are available for viewing.)
Monday 7 May 2012
Exhibition Hall  14:15 - 16:15

2683.   Software-based optimization of coil geometries for decoupling a pair of loop and Fo8 elements: does separation between coil elements matter?
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

In this study we developed a software that uses FEM based RF electromagnetic field modeling to simulate the coils and a Least Squares approach to automatically calculate the optimal geometries of a pair of loop and Fo8 coil elements to minimize coupling. We also investigated how the relative dimensions change for maximum decoupling when the distance between those elements was increased.

2684.   Calibration of electromagnetic field simulations of MR coil arrays for accurate quantitative comparison with the measured image SNR
Christopher Stumpf1, Robert Rehner2, Sebastian Martius3, Markus Vester2, Rainer Engelbrecht1, and Lorenz-Peter Schmidt1
1Chair for Microwave Engineering, University of Erlangen-Nuremberg, Erlangen, Bavaria, Germany, 2Siemens Healthcare, Erlangen, Germany, 3Siemens Corporate Technology, Erlangen, Germany

A new method for comparing simulated electromagnetic field results of local receive antennas to measured SNR images is shown. Electromagnetic field simulation is a powerful tool for designing MR antennas. Simulation results cannot be compared directly to measured SNR images due to system properties like e.g. magnetization of the investigated sample or receiver bandwidth. The new calibration method allows a quantitative comparison of simulated field results to measured SNR images of an arbitrary antenna structure. In this work the theory of this method is given and results are shown with an example of a 4-element antenna array.

2685.   A high-power RF switch for arterial spin labelling with a separate tagging coil
Arthur W. Magill1,2, Hongxia Lei1,3, and Rolf Gruetter1,3
1Laboratory of Functional and Metabolic Imaging, Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland, 2Department of Radiology, Univeristy of Lausanne, Lausanne, Switzerland, 3Department of Radiology, University of Geneva, Geneva, Switzerland

A high-power RF switch is demonstrated, designed to switch an RF power amplifier between imaging and tagging coils in an arterial spin labelling setup. The improvement offered by resonating the diodes with a parallel inductor is shown.

2686.   298MHz Micro miniature 2KW Transmit Receive Switch for 7.0 Tesla TR Arrays
Ronald D. Watkins1, Robert H Caverly2, and William E. Doherty3
1Radiology, Stanford University, Stanford, California, United States, 2ECE Department, Villanova University, Villanova, Pa., 3RF Devices, Microsemi Corp, Lowell, Ma., United States

This work will present the time domain modeling, design, and packaging of a micro miniature 2KW Transmit Receive switch for 7 Tesla proton imaging. It will demonstrate significant advances in packaging and low magnetic susceptibility packaging, all with commercial readily available parts. These miniaturized switches are a critical subsystem circuit needed for high element count TR array at ultra high field and can be mounted directly to the coil and reside within the image field of view.

2687.   Multi-Slice N-fold Acceleration with Scalable Digital Transmit and Receive Systems
Andrzej Jesmanowicz1, and William J O’Reilly2
1Biophysics, Medical College of Wisconsin, Milwaukee, WI, United States, 2Tornado Medical Systems, Toronto, ON, Canada

A System is presented that demonstrates a fully digital transmit and receive system for multislice EPI acceleration. The transmit system is based on a TI DAC5688 chip, which provides superior tailored pulse generation with almost two orders of magnitude lower spurious inter-modulated frequencies. A 32 channel coil is used to measure the 4-slice separation of simultaneous axial slice excitation.

2688.   On the Optimum Source Impedance for MRI Phased Array Coils
Paul Joseph Cassidy1
1School of Engineering, Griffith University, Gold Coast, QLD, Australia

Analytical expressions are presented for MRI phased array preamplifiers in terms of blocking impedance, S21 decoupling, minimum noise factor and gain based on CMOS common-source inductively degenerated low noise amplifiers. These expressions support the idea of using a source impedance greater than 50 Ohms for enhanced decoupling and minimum noise factor at the expense of gain.

2689.   SNR Degradation in Receive Arrays Due to Preamplifier Noise Coupling and A Method for Mitigation
Graham Charles Wiggins1, Ryan Brown1, Bei Zhang1, Marcus Vester2, Stefan Popescu2, Robert Rehner2, and Daniel Sodickson1
1The Bernard and Irene Schwartz Center for Biomedical Imaging, NYU Medical Center, New York, NY, United States, 2Siemens Healthcare, Erlangen, Germany

Neighboring elements in a receive array can be decoupled by various means. However next nearest neighbors still exhibit substantial inductive coupling, which is usually mitigated through the use of preamplifier decoupling. It is commonly assumed that any remaining coupling effects can be removed by characterizing the coupling through measurement of the noise correlation matrix and application of optimum SNR reconstruction.

2690.   Mitigation of inductive coupling in array coils by wideband port matching
Markus Vester1, Stephan Biber2, Robert Rehner2, Graham Wiggins3, Ryan Brown3, and Daniel Sodickson3
1HIM MR PLM SD HW, Siemens Healthcare, Erlangen, Germany, 2HIM MR PLM HW, Siemens Healthcare, Erlangen, Germany, 3Radiology, NYU Medical Center, New York, United States

We suggest a method for mitigating the effects of coil coupling. It is based on a wideband matching technique which can be implemented by a simple circuit modification. The reduced effective reflection will result in less degradation of preamp noise figure in a receive array, and in lower power loss in the transmitter isolators in a parallel transmit system.

2691.   Broadband damping of cable modes
Ed B Boskamp1, Masahiro Fujimoto1, Arslan Amjad1, and Michael Edwards1
1GE Healthcare, Waukesha, WI, United States

Currents induced on coaxial cable shields are common in MRI due to the E fields present in the bore during the RF pulses. These cable modes can increase SAR. Cable modes can result from coupling between cable and any coil. They affect the tuning and isolation. The standard method to eliminate cable modes is a balun. We present a different method to damp the cable modes using conductive plastics. This method is broadband, and inexpensive.

2692.   Stand Alone Apparatus for Measuring Noise Correlation of Phased Array Coils Outside of Magnetic Field
Sergei Obruchkov1,2, and Kenneth Bradshaw2,3
1School of Chemical and Physical Sciences, Victoria University, Wellington, New Zealand, 2System Design Engineering, University of Waterloo, Waterloo, Ontario, Canada, 3Hologic (Sentinelle Devision), Toronto, Ontario, Canada

Presently, the performance of a coil is tested through both bench and scanner tests. Scanner tests tend to be expensive in time and in resources. Scanner tests also introduce variation in the results due to the difference in the scanners themselves. It is an objective of this paper to show that a coil’s actual performance can be determined not with an expensive MRI scan but with a newly designed bench tester.
Traditional Poster Session - Engineering

Travelling Wave & Dielectric Padding
Click on to view the abstract pdf. Click on to view the poster (Not all posters are available for viewing.)
Monday 7 May 2012
Exhibition Hall  14:15 - 16:15

2693.   Traveling Wave MRI in a Vertical Bore 21.1-T System
Alexey A Tonyushkin1,2, Jose Antonio Muniz3,4, Samuel Colles Grant3,4, and Andrew J M Kiruluta1,2
1Radiology, Massachusetts General Hospital, Boston, MA, United States, 2Physics, Harvard University, Cambridge, MA, United States, 3Center for Interdisciplinary Magnetic Resonance, National High Magnetic Field Laboratory, Tallahassee, FL, United States, 4Chemical & Biomedical Engineering, The Florida State University, Tallahassee, FL, United States

Originally implemented clinically at 7 T, traveling wave nuclear magnetic resonance is a far-field imaging technique that relies on successful mode propagation in a waveguide. However, for higher field magnets with smaller bores, hollow waveguides are below cut-off requirements for mode propagation. This work demonstrates the first traveling wave MRI experiments on a 21.1-T (900-MHz) vertical widebore magnet. Coupled with a simple transceive loop coil, the setup utilizes a high dielectric material within a cylindrical waveguide to achieve a traveling wave regime that allows the propagation of numerous modes (TEmn, TMmn and HEmn).

2694.   A Travelling Wave Antenna with Matched Waveguide for Head Imaging at 7 T: Simulation Results
Daniel James Lee1, and Paul M Glover1
1Physics and Astronomy, University of Nottingham, Nottingham, Nottinghamshire, United Kingdom

The travelling wave approach to MRI uses an antenna to propagate a TW through the bore of a 7T+ scanner. Using a waveguide to match the incident wave into the head a stronger B1+ can be generated. This has been simulated and assessed using SEMCAD X. This design is compatible with the use of local receive coils and local shim coils. This work indicates that this setup is capable of generating B1+ in the head with increased efficiency compared to normal TW methods. Multiple modes can be generated allowing for a multi-transmit approach to improve B1+ homogeneity across the brain.

2695.   Travelling-Wave Excitation for Primate MRI at 7T Whole Body MRI-System
Johannes Mallow1, Tim Herrmann2, Judith Mylius3, Joerg Stadler3, and Johannes Bernarding1
1Department of Biometry and Medical Informatics, OvG University Magdeburg, Magdeburg, Germany, 2Department of Biometry and Medical Informatics, OvG University Magdeburg, Magdeburg, Saxony-Anhalt, Germany, 3Leibniz-Institute for Neurobiology, Magdeburg, Germany

fMRI for primates at 7T whole body MRI is still a big challenge because no body-coil is provide and the necessary fixation unit does not fit into commercial volume coils. This study shows how the travelling-wave concept can be optimized to work as an efficient body-coil replacement. By simulating the RF-system including the complete 7T whole body scanner it was possible to consider all the important parameters of the experiment. Directional characteristics, distance to the object, and the excitation parameters of the constructed patch antenna were optimized A phased array coil was designed for primate fMRI of macaques.

2696.   Multimodal travelling wave MRI with two coaxial modules
Stefan Alt1, Reiner Umathum1, Wolfhard Semmler1, and Michael Bock1,2
1Dept. of Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany, 2Radiology - Medical Physics, University Hospital Freiburg, Freiburg, Germany

To provide a "body coil" for high-field MRI systems, FDTD simulation results of a novel travelling wave setup are shown, that used two coaxial modules. The setup is able to excite higher-order modes of wave propagation enclosed in a defined imaging area. While this creates diverse distributions of the transverse magnetic field for B1-shimming, the transmission efficiency remains inferior to resonant structures.

2697.   Optimization of dielectric substrate for a 7 T radiative antenna: role of surface waves
Ozlem Ipek1, J. J.W. Lagendijk1, and C.A.T. van den Berg1
1Radiotherapy, UMC Utrecht, Utrecht, Utrecht, Netherlands

The radiative antenna is optimized in terms of size and dielectric properties of the substrate. The role of surface waves is studied as a function of the thickness of the dielectric substrate and the relative electrical permittivity. As a result, optimal in-coupling of RF signal is strongly determined by the surface waves.

2698.   Imaging with dielectric waveguide approach for 3T MRI
Alexey A. Tonyushkin1,2, Norman B. Konyer3, Michael D. Noseworthy3,4, and Andrew J.M. Kiruluta1,2
1Radiology Dept., Massachusetts General Hospital, Harvard Medical School, Boston, MA, United States, 2Physics Dept., Harvard University, Cambridge, MA, United States, 3Imaging Research Centre, St. Joseph's Healthcare, Hamilton, Ontario, Canada, 4Electrical and Computer Engineering Dept., McMaster University, Hamilton, Ontario, Canada

Recent developments in ultra-high field MRI have allowed researchers to explore the traveling wave regime. While traveling wave MRI is uncommon due to engineering constraints, it holds promise in a future to solve various RF transmission issues. Unfortunately, the traveling wave approach is forbidden for clinical MR systems due to their much lower field, and therefore, hard-to-fulfill cut-off requirements. We demonstrate a possible solution for the traveling wave approach at relatively low field clinical 3T system using a high dielectric insert inside an unmodified MRI. We show simulations and experimental MR images, which were generated using our propagating mode approach.

2699.   MRI Signal Enhancement via High-Permittivity Material Pads
M D Ketterman1, Q X Yang2,3, A G Webb4, Z G Herse2, T Neuberger5, G Carluccio6, and M Lanagan1
1Materials Research Laboratory, The Pennsylvania State University, University Park, Pennsylvania, United States, 2Radiology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania, United States, 3Bioengineering, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania, United States, 4Radiology, Leiden University Medical Center, Leiden, Netherlands, 5High Field MRI Facility, The Pennsylvania State University College of Medicine, University Park, Pennsylvania, United States, 6Electromagnetics Laboratory, University of Illinois, Illinois, United States

High permittivity pads have recently been used to increase signal to noise in 3 and 7 tesla neuroimaging. A model, using multi-regional travelling-wave analysis within the near-field, has been constructed to account for the improved impedance matching local to the pads.

2700.   Improved material for passive RF shimming with high dielectric pads
Wei Luo1, Yeun Chul Ryu2, Sukhoon Oh2, Zachary Herse2, Ketterman David Matthew1, Qing X Yang2, Lanagan T Michael1, and Christopher M Collins2
1Department of Engineering Science and Mechanics, The Pennsylvania State University, University Park, PA, United States, 2Radiology, The Pennsylvania State University, Hershey, PA, United States

High dielectric materials (HDM) have been successfully used to improve the sensitivity and homogeneity of the RF magnetic field (B1+ and B1- field) in human MRI. Previously an HDM of a suspension made by calcium titanate (CaTiO3) powder in distilled or deuterated water was found advantageous for use in human brain MRI due to the strong effect of a minimal amount of this HDM. In this study, we developed and characterized a composite material using distilled water and sintered beads of BaTiO3. The bead/water composite showed a higher dielectric constant and lower conductivity compared to the BaTiO3 suspension, which should result in an even a higher effect per amount of material compared to the powder/water slurry.

2701.   High Dielectric Constant (HDC) Pad for High Field MRI: Reducing SAR and Enhancing SNR
Zhangwei Wang1, Mike Lanagan2, and Qing X Yang3
1Coils, GE Healthcare, Aurora, OH, United States, 2Electrical Engineering, The Pennsylvania State University, University Park, PA, United States, 3Radiology and Neurosurgery, The Pennsylvania State University, Hershey, PA, United States

Motivated by exciting experimental data demonstrated previously at 7T, this computer modeling study explored the potential utilization of high dielectric constant (HDC) material in between the targeted region of the sample and coil elements for ultra-high field human head imaging. The computation experiments show that placement of HDC pad introduced large changes in B1+ field and reduced average SAR, although local peak SAR increase a little

2702.   MRI Enhancement via high dielectric constant (εr = 510) pad at 3T: brain imaging
Qing Yang1,2, Chris Collins3, Michael Lanagan4, Zachary Herse3, Sebastian Rupprecht3, Wei Luo3, Yeun Chul Ryu3, Megha Patel3, and Jeff Vesek3
1The Penn State College of Medicine, Hershey, Pennsylvania, United States, 2Neurosurgery, The Penn State College of Medicine, Hershey, Pennsylvania, United States, 3The Penn State College of Medicine, 4The Penn State University

High dielectric constant (HDC) pads provide a simple, effective, low-cost method for improving the quality and safety of MRI in a number of applications at 3T. Our results indicate that when HDC-pads (filled with barium titanate (BaTiO3)and deuterium oxide (D2O) are placed bilaterally along the sides temporally of the head, axial T2 Turbo Spin Echo (TSE) scans of the brain show an increase in SNR (28-42%), reduced RF power (23.7%), and an enhanced clarity of the temporal lobes. This data suggests that not only do the scans provide clinicians with an enhanced view of the temporal lobes to further aid diagnoses, but the time required to scan is decreased along with the amount of RF power needed per scan.

2703.   Numerical analysis on effects of high dielectric material with 4-channel phase array
Wei Luo1, Giuseppe Carluccio2,3, Sukhoon Oh3, and Christopher M Collins3
1Department of Engineering Science and Mechanics, The Pennsylvania State University, University Park, PA, United States, 2Department of Electrical and Computer Engineering, University of Illinois at Chicago, Chicago, IL, United States, 3Radiology, The Pennsylvania State University, Hershey, PA, United States

The effects of high dielectric material (HDM) in human MRI have been studied intensively in recent years. Most of the effort has been made to understand the effect of HDM from the aspect of the transmit EM field. In this study, we took consider also the receive EM field in simulation of a 4-channel phase array. The transmit EM field analysis was done to validate the simulation, followed by the receive EM field analysis. The knowledge of the effect of HDM on the receive EM field will provide us a complete picture of the overall behavior of HDM in human MRI, providing better insight to HDM design and better performance of MRI.
Traditional Poster Session - Engineering

Safety & Devices
Click on to view the abstract pdf. Click on to view the poster (Not all posters are available for viewing.)
Monday 7 May 2012
Exhibition Hall  14:15 - 16:15

2704.   Analysis of radio frequency heating induced by a coronary stent at 7.0 T
Davide Santoro1, Alexander Müller1,2, Lukas Winter1, Wolfgang Renz1,3, Andreas Grässl1, Celal Özerdem1, Valeriy Tkachenko4, Jeanette Schulz-Menger4, and Thoralf Niendorf1,4
1Berlin Ultra-High Field Facility (BUFF), Max Delbrück Center for Molecular Medicine (MDC), Berlin, Germany, 2Department of physics, Humboldt-Universität zu Berlin, Berlin, Germany, 3Siemens Healthcare, Erlangen, Germany, 4Working Group on Cardiovascular Magnetic Resonance, Experimental and Clinical Research Center (ECRC), Medical University Berlin, Charité Campus Buch, Berlin, Germany

The advantage of ultrahigh field MRI holds the promise to enhance spatial and temporal resolution. Such improvements could be advantageous for several applications in cardiovascular MRI. However, intracoronary stents used for treatment of coronary artery disease are currently considered to be contra-indications for CMR at 7.0 T. The antenna effect induced by a metallic implant in combination with RF wave lengths could increase the RF power deposition at 7.0 T and induce local heating which might cause myocardial tissue damage, influence coagulation or endothelial function. For all these reasons it is essential to carefully assess RF induced heating in coronary stents commonly used in percutaneous coronary intervention. This work examines RF induced heating of a copper tube and a coronary stent in agarose phantoms using electromagnetic field simulations, fiber optic temperature measurements and MR thermometry at 7.0 T.

2705.   Influence from Static Magnetic Fields on Fiber-Optical Temperature Probes - Effects on Safety Measurements at 7T
Jens Groebner1, Moritz Cornelius Berger1, Wolfhard Semmler1, and Jaane Rauschenberg1
1Dept. of Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany

Fiber-optical temperature probes are commonly used in MR safety measurements on implants. In this work it could be shown that fiber-optical temperature measurements are B0-dependant and exhibit non-linear temperature dependence: A temperature drop of 2.6°C at 7T compared to the earth magnetic field and relative temperature differences of 0.30°C between 20°C and 60°C at 7T were observed.

2706.   Realistic MHD modeling based on MRI blood flow measurements.
Julien Oster1, Raul Llinares2, Zion Tse3, Ehud Schmidt3, and Gari Clifford1
1Department of Engineering Science, University of Oxford, Oxford, United Kingdom, 2Departamento de Comunicaciones, Universidad Politecnica de Valencia, Valencia, Spain, 3Department of Radiology, Brigham & Women’s Hospital, Harvard Medical School, Boston, MA, United States

Electrocardiogram (ECG) recordings, required during MRI for both triggering and monitoring, are distorted by the MagnetoHydroDynamic (MHD) voltage induced from the blood flow through the aorta. The MHD effect makes clinical ECG analysis difficult and reduces triggering quality in high field MRI. We propose a MHD model, based on MRI blood flow measurements. The MHD induced body potential was computed with an aorta model of 15 cylindrical sections inside a torso model. The model exhibited a good consistency compared to a real MHD signal. The proposed MHD model may allow assessment of new ECG/MHD separation and denoising techniques.

2707.   A Novel MRI-compatible Tactile Stimulator for Cortical Mapping of Foot Sole Pressure Stimuli with fMRI
Ying Hao1, Brad Manor1,2, Jing Liu3, Lewis Lipsitz2, Vera Novak2, Xiaoying Wang3, Jing Fang1,4, and Jue Zhang1,4
1Academy for Advanced Interdisciplinary Studies, Peking University, Beijing, Beijing, China, 2Department of Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, United States, 3Department of Radiology, Peking University First Hospital, Beijing, Beijing, China, 4Department of Engineering, Peking University, Beijing, Beijing, China

Foot sole somatosensory feedback is critical to the motor control of standing and walking. To enable study of cortical networks underlying foot sole somatosensation, their relationship to motor control, and mechanisms of neural adaptation that optimize behavior in the presence of sensory impairment, we developed a pneumatic tactile stimulator capable of producing straight-line oscillations with preset frequency, magnitude and surface area over which pressures are applied to the foot sole. Image tests (anatomical/functional/field map) of a phantom demonstrated that the device is compatible with 3T MRI. GRE-EPI images of seven healthy young adults using a typical block-design stimulation protocol revealed significant sensorymotor activation.

2708.   Acoustic noise control during auditory fMRI using a DSP system - first initial in vivo results
Daniel Güllmar1, Markus Hädrich1,2, and Jürgen R Reichenbach1
1Medical Physics Group / IDIR I, Jena University Hospital, Jena, Thuringia, Germany, 2University of Applied Sciences Jena, Jena, Thuringia, Germany

We implemented a template driven active noise cancellation algorithm on a DSP system in order to attenuate the acoustic noise which accompanies especially fmri acquisitions. Employing acoustic stimuli, we found that stopping filter adaptation during stimulus presentation yields to much better activation in terms of HRF amplitude in the auditory cortex, whereas without noise control at all, no activation was detected in the auditory cortex, although the stimuli were detected.

2709.   Evaluation of ISO/IEC JWG Tier 3 Approach for RF Heating in 1.5 MRI with Implantable Cardiac Rhythm Devices
Yan Liu1, Kevin Feng2, Ji Chen2, Xiaoyi Min3, Shiloh Sison3, Gabriel Mouchawar3, and Jon Dietrich3
1University of Houston, Houston, TX, United States, 2University of Houston, 3St. Jude Medical

The ISO/IEC Joint Working Group developed tiers to establish the worst case RF heating for active implantable devices. Tier 3 utilizes the maximum simulated tangential electric field (Etan) along lead paths. Tier 3 was evaluated in five human body models by comparing Etan and maximum of rms tangential electrical fields over lead paths (Erms). Tier 3 can overestimate the effective E by more than a factor of 2 (factor of 4 in heating). Knowing tier 1 and tier 2 are more stringent than tier 3 indicates that the ISO/IEC JWG tiers 1-3 are over conservative for implantable cardiac rhythm devices.

2710.   Using transmission line theory to analyze RF induced tissue heating at implant lead tips
Daniel Zemann1, and Karin Moertlbauer1
1Institute of Ion Physics and Applied Physics, University of Innsbruck, Innsbruck, Tirol, Austria

We present a method to analyze the RF induced tissue heating at the lead tip of medical implants. This is done by applying the theory of field-to-transmission line interaction to a single insulated wire embedded in a tissue-like medium. A comparison of calculations with FDTD simulations was done. With our approach it is possible to analyze the effect of characteristic transmission line impedance, wire bending and/or electric field configuration on the current distribution of conducting leads.

2711.   Sound Level Comparison between Insert, Whole Body, Composite Gradients
K Craig Goodrich1, Seong-Eun Kim1, Robb Merrill1, Yong Wang2, Richard Wiggins1, J Rock Hadley1, and Dennis L Parker1
1UCAIR, University of Utah, Salt Lake City, Ut, United States, 2Otolaryngology, University of Utah, Salt Lake City, Ut, United States

This work is a comparison of Sound Pressure Levels (SPL) using three gradient modes: 1) Head/neck insert operating alone, 2) Whole body gradients operating alone, and 3) Composite mode gradients where the gradient fields of the first 2 modes are superimposed. SPL of three pulse sequences (GRE, CISS and EPI) for the three gradient modes were measured. Then for GRE SPL as a function of receiver bandwidth, slew rate and field of view were explore. Then SPL for increased insert proportion of gradient field strength was measure up to maximum composite mode gradient strength. Attempts were made to attenuate SPL of the composite system.

2712.   MR testing of gradient-induced vibrations using an optical contact-free sensor within the switched gradient magnetic field of a 1.5 Tesla MR system.
Gregor Schaefers1, Michael Scholten2, Pascal Bartnik3, Amin Douiri3, and Wolfgang Görtz3
1MR Safety Testing Laboratory, MR:comp GmbH, Gelsenkirchen, NRW, Germany, 2MR:comp GmbH, Germany, 3MR:comp GmbH

A likely, but less investigated interaction of the switched gradient field with medical implants is vibration. Vibrations are caused by induced eddy-currents in electrically conductive structures of medical devices. Measurement of vibrations in an MR environment is a complex experiment. It seems that optical systems will be the best choice for minmizing interferences due to measurement. By placing an optical sensor in the magnet bore, near to different test objects it was feasible detecting gradient-induced vibrations quantitatively and contact-free.

2713.   Optimized methodology for worst-case determination of orthopedic implants for magnetic resonance safety testing
Bruno Camps-Raga1, Wolfgang Görtz1, Amin Douiri1, Michael Scholten1, Mark J. Pawlenka1, and Gregor Schaefers1
1MR:comp GmbH, MR Safety Testing Laboratory, Buschgrundstr. 33, 45894 Gelsenkirchen, Germany

A methodology for worst-case selection through computer simulation techniques to be used as an input to determine worst-case object and position in subsequent RF heating tests following ASTM2182-09 is described.

2714.   Simultaneous EEG-fMRI: evaluating the effect of the cabling configuration on the gradient artefact.
Muhammad E.H. Chowdhury1, Karen J Mullinger1, and Richard W Bowtell1
1SPMMRC, School of Physics and Astronomy, University of Nottingham, Nottingham, Nottinghamshire, United Kingdom

EEG data recorded during simultaneous fMRI are compromised by large gradient artefact (GA) voltages. The GA is usually corrected using average artefact correction, but any change in the GA during data acquisition significantly reduces the efficacy of correction. Here we characterise the GA contribution from the cabling between the EEG cap and amplifier for two cable configurations: a ribbon cable and a cable bundle. We demonstrate that the GA amplitude and its sensitivity to cable movement can be reduced by minimising cabling wire loop areas. Use of a cable bundle consisting of twisted wires is recommended for future EEG/fMRI studies.

2715.   Design of an fMRI-compatible analogue and digital joystick
Jonathan Howard1, and Rexford Newbould2
1Imanova Ltd, London, United Kingdom, 2Imanova Ltd, London, London, United Kingdom

A wide variety of neuroscience experiments require the use of an fMRI-compatible joystick. Several commercial models are available, generally using fibre-optic position and switch detection. However, these devices can be cost-prohibitive, especially for smaller fMRI studies without large funding levels. Further, fibre-optic devices often contain a limited number of fiber-optic sensor components, resulting in a dramatically reduced resolution of the analogue position signal. In this work, an inexpensive 2-DOF analogue and digital joystick for neuroscience studies in an MRI/fMRI environment is designed. This design can readily be replicated at low cost.
Traditional Poster Session - Engineering

Click on to view the abstract pdf. Click on to view the poster (Not all posters are available for viewing.)
Monday 7 May 2012
Exhibition Hall  14:15 - 16:15

2716.   Simultaneous Diffusion, Perfusion MRI and FET-PET
Ke Zhang1, Irene Neuner1,2, Christian Filss1, Karl-Josef Langen1, Hans Herzog1, and Nadim Joh Shah1,3
1Institute for Neuroscience and Medicine Medical Imaging Physics, Medical Imaging Physics (INM-4), Forschungszentrum Jülich, Jülich, Germany, 2Faculty of Medicine, Department of Psychiatry and Psychotherapy, JARA, RWTH Aachen University, Aachen, Germany, 3Faculty of Medicine, Department of Neurology, JARA, RWTH Aachen University, Aachen, Germany

PET with metabolic imaging is the clinical established technique for the diagnosis of cerebral gliomas. Diffusion MRI is the anatomical tool to demonstrate the plasticity of the brain. Perfusion MRI can precisely investigate the angiogenesis in the tumour and help classify and grade brain tumours. In this study, diffusion, perfusion MRI and FET-PET were simultaneously acquired using a hybrid 3T MR-PET scanner. Using the hybrid approach, data from two representative human brain tumour cases are presented. The results demonstrates that hybrid technique offers fast, complete and valuable information for diagnosis and neurosurgery of brain tumours.

2717.   Simultaneous PET/MR Hybrid Imaging: MR based continuous valued attenuation map generation and its effect on quantitative PET imaging
Krishnan Bharath Navalpakkam1, Harald Braun2, Susanne Zeigler2, Harald H Quick2, Joachim Hornegger1, and Torsten Kuwert3
1Pattern Recognition Lab, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany, 2Institute of Medical Physics, Erlangen, Germany, 3Clinic of Nuclear Medicine, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany

MR-based attenuation correction for PET images is till an open issue. An accurate attenuation correction is needed for PET quantification. In this work, we generate a continuous valued CT-like attenuation map from Ultrashort Echo Time and two-point DIXON VIBE sequences using ε-insensitive Support Vector Regression (ε-SVR). Further, we compare the PET quantification accuracy using attenuation maps from a segmented CT and predicted CT with respect to a patient CT as the gold standard. Results show that a continuous estimation of attenuation values outperforms a segmentation based attenuation map.

2718.   Identifying appropriate contrast MR images to construct a digital head phantom for functional near infrared spectroscopy
Hiroshi Kawaguchi1, Takayuki Obata1,2, Kazuki Kurihara3, Yosuke Takahashi3, Eiji Okada3, and Hiroshi Ito1
1Molecular Imaging Center, National Institute of Radiological Sciences, Chiba, Japan, 2Research Center for Charged Particle Therapy, National Institute of Radiological Sciences, Chiba, CHiba, Japan, 3Department of Electronics and Electrical Engineering, Keio University, Yokohama, Japan

Functional near-infrared spectroscopy (fNIRS) requires a realistic three-dimensional digital head phantom (based on the segmentation of anatomical head images) to improve the accuracy of image reconstruction and visualization of image data. We test several MR imaging protocols, i.e. T2-weighted (T2W), Fat saturated proton-density (FSPDW) and FIESTA image, for their suitability to extract the scalp, skull and CSF in the subarachnoid space to construct a digital head phantom for fNIRS. The combination of FIESTA and FSPDW produced more accurate results when segmenting the superficial tissues. Furthermore, the combined acquisition time of FIESTA and FSPDW is shorter than that of T2W.

2719.   Sequential integrated PET/CT-MR system: Comparison of image registration accuracy of PET/CT versus PET/MR
Felix Pierre Kuhn1, Florian Wiesinger2, Scott Wollenweber3, Andrei Samarin1, Gustav von Schulthess1, and Daniel Schmid1
1Radiology, University Hospital, Zurich, Switzerland, 2GE Global Research, Munich, Germany, 3GE Healthcare, Waukesha, United States

Multi-modality imaging combines morphological and functional information originating from different imaging platforms and is based on the critical assumption of accurate registration. In the presented work a tri-modality PET/CT+MR system is used to investigate the hardware registration performance between sequential PET and MR versus gold standard PET/CT.

2720.   MR-based FoV Extension in Whole-Body MR/PET Using Continuous Table Move
Jan Ole Blumhagen1,2, Ralf Ladebeck1, Matthias Fenchel1, Klaus Scheffler2,3, and Harald H. Quick4
1Magnetic Resonance, Siemens Healthcare, Erlangen, Bavaria, Germany, 2Division of Radiological Physics, University of Basel Hospital, Basel, Switzerland, 3MRC Department, Max Planck Institute for Biological Cybernetics, Tübingen, Germany, 4Institute of Medical Physics, Friedrich-Alexander-University Erlangen-Nürnberg, Erlangen, Germany

In whole-body MR/PET attenuation correction, an MR-based FoV extension is of emerging interest. However, gradient nonlinearities and B0 inhomogeneities often hamper an accurate spatial encoding at the edges of large FoVs. Recently, we proposed a method to axially extend the FoV by determining an optimal readout gradient field which locally compensates B0 inhomogeneities and gradient nonlinearities. In this work a combination of the mentioned axial FoV extension and Continuous Table Movement is presented. In experiments on volunteers a significant distortion reduction has been achieved at off-center positions of up to 300 mm off from the iso-center.

2721.   Effects of Simultaneous Operation on the Biograph mMR
Sebastian Fürst1, Isabel Dregely1, Stephan Nekolla1, Markus Schwaiger1, and Sibylle Ziegler1
1Department of Nuclear Medicine, Technische Universität München, Munich, Bavaria, Germany

The introduction and immediate success of combined positron emission tomography (PET) and computed tomography (CT) scanners in the clinical environment have significantly increased interest in other multimodal imaging systems and accelerated their development, with PET and MR being in the centre of the efforts. Previous studies already showed that the performance of the first integrated whole-body PET/MR machine, the Biograph mMR, compares well to the one of stand-alone PET and MR scanners. The aim of the present work was to investigate the effects of MR sequences on PET data acquisition with a focus on energy spectra and count rates.

2722.   Systematic Evaluation of Phantom Fluids for Simultaneous PET/MR Hybrid Imaging
Susanne Ziegler1, Harald Braun1, Philipp Ritt2,3, Jens U. Krause1, Carsten Hocke3, and Harald H. Quick1
1Institute of Medical Physics, University of Erlangen-Nuremberg, Erlangen, Germany, 2Pattern Recognition Lab, University of Erlangen-Nuremberg, Erlangen, Germany, 3Clinic for Nuclear Medicine, University Hospital Erlangen, Erlangen, Germany

With the recent advent of PET/MR hybrid systems the need for simultaneous PET and MR phantom measurements arises. However, phantom fluids that are used in MRI are not necessarily applicable in PET, and vice versa. In this study different fluids were systematically evaluated in regard to their usability for phantom measurements in simultaneous PET/MR hybrid imaging. Crucial were the criteria: homogeneity of RF excitation in MRI, miscibility with FDG for PET imaging and compatibility with the plexiglas material of the phantom. Our results show that triethylene glycol represents a viable fluid for simultaneous PET and MR phantom measurements.

2723.   MR-based FoV Extension of Human Attenuation Correction in Whole-Body MR/PET Hybrid Imaging
Jan Ole Blumhagen1,2, Ralf Ladebeck1, Matthias Fenchel1, Harald H. Quick3, and Klaus Scheffler2,4
1Magnetic Resonance, Siemens Healthcare, Erlangen, Bavaria, Germany, 2Division of Radiological Physics, University of Basel Hospital, Basel, Switzerland,3Institute of Medical Physics, Friedrich-Alexander-University Erlangen-Nürnberg, Erlangen, Germany, 4MRC Department, Max Planck Institute for Biological Cybernetics, Tübingen, Germany

In whole-body MR/PET, the human tissue attenuation correction (AC) of PET data can be based on the MR data. However, the MR FoV is limited due to B0inhomogeneities and gradient nonlinearities. Therefore, the human AC map may be truncated and thus the PET reconstruction may be biased. In this work we explored extending the MR-based AC map using a purely MR-based FoV extension. We applied this method to whole-body MR/PET examinations on patients and evaluated the impact on the PET reconstruction. The reported bias was reduced and the PET reconstruction was in good agreement with a PET/CT reference measurement.

2724.   Building a combined cyclotron and MRI facility: implications for interference
Mark BM Hofman1, Joost PA Kuijer1, Jan Willem de Ridder1, Lars R Perk2, and Rudolf M Verdaasdonk1
1Physics and Medical Technology, VU University Medical Center, Amsterdam, Netherlands, 2BV Cyclotron VU, Amsterdam, Netherlands

With the introduction of hybrid PET/MRI systems, it has become more likely that cyclotron and MRI systems will be located close to each other. This study considered the theoretical interference of a cyclotron facility on a MRI system. Measurements and simulation showed that the magnetic field of a cyclotron can be considered a magnetic dipole field. In a specific case of an 18 MeV cyclotron and a 3T superconducting whole body MR system a minimum distance of 11-21 m (depending on location and criteria applied) has to be considered to prevent interference.

2725.   New Insights into PET Count Rate Reduction during Simultaneous MR-PET Measurements
Daniel Brenner1, Christoph Weirich1, Jürgen Scheins1, Etienne Besancon1, Lutz Tellmann1, Hans Herzog1, and N. Jon Shah1,2
1Institute of Neuroscience and Medicine - 4, Forschungszentrum Jülich, Jülich, Germany, 2JARA - Faculty of Medicine, RWTH Aachen University, Aachen, Germany

Minor influences of MRI on the PET detectors during simultaneous MR-PET measurements with the 3T MR-BrainPET have been observed and shown to result in a drop of the measured count rate of up to three percent. This study analyses the distortions generated in the output signal of the PET detector by the time varying MR gradients. Pronounced effects are visible at start and beginning of the gradient ramps while an increased noise level was observed during the gradient flat top.