Clarisa Zimmerman¹, Lawrence L Wald², Matthew S Rosen³, and James Blau^4
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.

Chad Tyler Harris¹, William B Handler¹, and Blaine A Chronik^1,2
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.

Eddy SM Lee¹, Ludovic de Rochefort², Gianni Ferrante³, and Brian K Rutt^1
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.

Daiki Tamada¹, Keisuke Maruyama¹, Katsumi Kose¹, and Takashi Nakamura^2
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.

Daiki Tamada¹, Katsumi Kose¹, and Tomoyuki Haishi^2
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.

Yihe Hua¹, Longzhi Jiang², Graeme C Mckinnon³, Seung-Kyun Lee⁴, and Anbo Wu^1
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.

Martin Kunth¹, Christopher Witte¹, and Leif Schröder^1
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.

Yiyuan Cheng¹, Ling Xia¹, Wei He¹, Feng Liu², and Stuart Crozier^2
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.

Yuri Lvovsky¹, Zhenyu Zhang¹, Timothy Hollis², and Ye Bai^2
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.

Shin-ichi Urayama¹, Osamu Ozaki², Hitoshi Kitaguchi³, Kazuyuki Takeda⁴, Iwao Nakajima⁵, Naoki Ohnishi⁶, Michael Poole⁷, Ken-ichi Sato⁸, and Hidenao Fukuyama^1
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.

Dominic M Graziani¹, Seung-Kyun Lee¹, Jean-Baptiste Mathieu¹, Graeme C McKinnon², Thomas K Foo¹, and John F Schenck^1
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.

Robert Borowiak¹, Elmar Fischer¹, Sebastien Bär¹, Jochen Leupold¹, Frank Huethe², Thomas Lange¹, Jeff Snyder¹, Jürgen Hennig¹, Dominik von Elverfeldt¹, and Jan-Bernd Hövener^1
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.

Michael D Twieg¹, Matthew J. Riffe², Natalia Gudino², and Mark A. Griswold^1,3
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.

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 Huston^3
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.

Alice Borceto¹, Andrea Viale², Leonardo Bertora², Richard Bowtell³, and Franco Bertora^1
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.

Christoph Juchem¹, Terence W Nixon¹, and Robin A de Graaf^1
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.

Maxim Zaitsev¹, William Punchard², Andrew Dewdney³, Daniel Gallichan¹, Jason Stockmann⁴, Chris A. Cocosco¹, Sebastian Littin¹, Anna Masako Welz¹, Hans Weber¹, Piotr Starewicz², and Jürgen Hennig^1
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.

Steffen Lother^1,2, Uvo C. Hölscher¹, Peter M. Jakob^1,2, and Florian Fidler^1
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.

Seong-Eun Kim¹, K Craig Goodrich¹, Richard Wiggins¹, Jason Mendes¹, and Dennis L Parker^1
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.

Christoph Juchem¹, and Robin A de Graaf^1
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.

Derek A. Seeber¹, Timothy Bergfeld¹, Kevin Koch², Richard Hackett¹, David Lee¹, and William Einziger^1
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.

Seong-Eun Kim¹, K Craig Goodrich¹, J Rock Hadley¹, Richard Wiggins¹, Eun-Kee Jeong¹, and Dennis L Parker^1
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.

Anna Masako Welz¹, Frederik Testud¹, Jürgen Hennig¹, Jan G. Korvink^2,3, and Maxim Zaitsev^1
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.

Frederik Testud¹, Daniel Gallichan¹, Christoph Barmet², Johanna Vannesjö², Anna Masako Welz¹, Christian A. Cocosco¹, Klaas Prüssmann², Jürgen Hennig¹, and Maxim Zaitsev^1
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.

Frederic G. Goora^1,2, Hui Han², Bruce G. Colpitts¹, and Bruce J. Balcom^2
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.

Peter Latta¹, Marco L. H. Gruwel¹, Vladimír Jellúš², and Boguslaw Tomanek^1
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.

Saikat Sengupta¹, John C. Gore¹, and E. Brian Welch^1
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.

Stefan Wintzheimer¹, Toni Drießle¹, Michael Ledwig¹, Ralf Kartäusch¹, Peter Michael Jakob^2,3, and Florian Fidler^1
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.

Saikat Sengupta¹, E. Brian Welch¹, John C. Gore¹, and Malcolm J. Avison^1
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.

Ariane Fillmer¹, Signe Johanna Vannesjo¹, Matteo Pavan¹, Klaas Paul Pruessmann¹, Peter Boesiger¹, and Anke Henning^1
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.

John C. Bosshard¹, Mary P. McDougall^1,2, and Steven M. Wright^1,2
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.

Limei Liu¹, Hector Sanchez Lopez¹, Michael Poole¹, Ewald Weber¹, Feng Liu¹, and Stuart Crozier^1
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.

Yasuhiko Terada¹, Hirotaka Fujisaki¹, and Katsumi Kose^1
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.

AbdEl-Monem M El-Sharkawy¹, and William A. Edelstein^1
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.

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 Shah^1,3
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.

Alexander Childs¹, Shaihan J Malik¹, Declan P O'Regan¹, and Joseph V Hajnal^1
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.

Yukio Kaneko¹, Yoshihisa Soutome¹, Masayoshi Dohata¹, Hideta Habara¹, Hisaaki Ochi¹, and Yoshitaka Bito^1
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.

Bastien Guerin¹, Matthias Gebhardt², Peter Serano¹, Elfar Adalsteinsson^3,4, Michael Hamm², Josef Pfeuffer², Juergen Nistler², and Lawrence L. Wald^1,4
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).

Yeun Chul Ryu¹, Sukhoon Oh¹, Christopher Sica¹, Wei Luo², Yong-Gwon Kim³, and Christopher M. Collins^1,4
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.

Yunsuo Duan¹, Bradley S Peterson¹, Feng Liu¹, and Alayar Kangarlu^1
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.

Taner Demir¹, Esra Abaci Turk^1,2, and Ergin Atalar^1,2
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.

Lance DelaBarre¹, Pierre-Francois van de Moortele¹, Carl Snyder¹, Jinfeng Tian¹, Steen Moeller¹, and J. Thomas Vaughan^1
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.

Narayanan Krishnamurthy¹, Daniel Stough¹, Tiejun Zhao², Shailesh Raval¹, Fernando Boada¹, and Tamer S Ibrahim^1
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.

Giuseppe Carluccio^1,2, Christopher Michael Collins², and Danilo Erricolo^1
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.

Mikhail Kozlov¹, and Robert Turner^1
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.

Mikhail Kozlov¹, and Robert Turner^1
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.

Jean-Guy Belliveau^1,2, Kyle Gilbert¹, Mohamed Abou-Khousa¹, and Ravi Menon^1,2
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.

Arthur W. Magill^1,2, Martin Meyerspeer^1,3, and Rolf Gruetter^1,4
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.

Wolfgang Loew¹, Randy Giaquinto¹, Scott Dunn¹, Ronald Pratt¹, Diana Lindquist¹, and Charles Dumoulin^1
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.

Zhiyong Zhai¹, and Michael A. Morich^1
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.

Xiaojun Xu¹, Martin H Deppe¹, Nicola De Zanche², and Jim M. Wild^1
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.

Xia Li^1,2, JuCheng Zhang¹, WenLong Xu¹, XiaoFang Liu^1,2, and BingQiao Xu^1
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.

Manuela Rösler¹, Reiner Umathum¹, Armin Nagel¹, Yaron Gordon¹, Peter Bachert¹, Wolfhard Semmler¹, and Florian Meise^1
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.

Arthur W. Magill^1,2, Hongxia Lei^1,3, and Rolf Gruetter^1,2
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.

Xiaoliang Zhang^1,2, Duan Xu¹, Ye Li¹, Ilwoo Park¹, Yong Pang¹, Peter Shin¹, Kayvan Keshari¹, David Wilson¹, and Daniel B Vigneron^1,2
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.

Florian M Meise¹, Armin M Nagel¹, Tobias Gotterbarm², Sebastian Hagmann², Manuela Rösler¹, Marc-Andre Weber³, Wolfhard Semmler¹, and Reiner Umathum^1
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.

Andreas Korzowski¹, Reiner Umathum¹, Peter Bachert¹, and Florian Martin Meise^1
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.

Oliver G. Gruschke¹, Nicoleta Baxan², Dominik von Elverfeldt², Jürgen Hennig², Vlad Badilita³, and Jan G. Korvink^1,4
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 Reutens^1
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 Vegh^1
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.

Joseph V Rispoli¹, Sergey Cheshkov^2,3, Ivan Dimitrov^2,4, Craig Malloy^2,3, Steven M Wright^1,5, and Mary Preston McDougall^1,5
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.

Klaus M. Huber¹, Wünsch Christian², Seisenberger Claus³, Nisznansky Martin², Demharter Nikolaus², and Vester Markus^2
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.

Giorgos Katsikatsos¹, and Klaas Paul Pruessmann^1
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.

Pascal P Stang¹, John M Pauly¹, and Greig C Scott^1
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.

Karl Edler¹, Marie-France Hang¹, Alexis Amadon¹, Nicolas Boulant¹, Martijn A Cloos¹, and Christopher J Wiggins^1
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  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.

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. Klomp^1
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.

Celal Özerdem¹, Lukas Winter¹, Werner Hoffmann², Helmar Waiczies¹, Reiner Seemann², Davide Santoro¹, Alexander Müller¹, Abdullah Ok¹, Tomasz Lindel², Bernd Ittermann², and Thoralf Niendorf^1,3
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.

Chunqi Qian¹, Stephen Dodd¹, Der-Yow Chen¹, Joe Murphy-Boesch¹, and Alan Koretsky^1
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.

Sedig S Farhat¹, Daniel J Lee¹, Carolyn Costigan¹, Penny A Gowland¹, and Paul M Glover^1
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.

Haoqin Zhu¹, Mehran Fallah-Rad¹, Michael Lang¹, Wayne Schellekens¹, Kirk Champagne¹, and Labros Petropoulos^1
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.

Chieh-Wei Chang¹, Wen-Yang Chiang¹, Steven M Wright^1,2, and Mary Preston McDougall^1,2
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.

Emilee Minalga¹, Allison Payne¹, Robb Merrill¹, Nick Todd¹, Sathya Vijayakumar¹, Dennis L. Parker¹, and J. Rock Hadley^1
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.

Scott B King¹, Mike J Smith¹, Jarod Matwiy¹, Hung-Yu Lin¹, and Boguslaw Tomanek^2
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.

Paul T. Weavers¹, Chris C. Cline¹, Casey P. Johnson¹, Phillip J. Rossman¹, Thomas C. Hulshizer¹, and Stephen J. Riederer^1
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.

Hsuan-Chung Niu¹, Ying-Hua Chu¹, Jo Lee¹, Wei-Chao Chen², Wen-Jui Kuo³, and Fa-Hsuan Lin^1,4
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.

Tsinghua Zheng¹, Matthew Finnerty¹, Xiaoyu Yang¹, Paul Taylor¹, and Hiroyuki Fujita^1,2
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.

Emilee Minalga¹, Allison Payne¹, Nick Todd¹, Robb Merrill¹, Dennis L. Parker¹, and J. Rock Hadley^1
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.

Yong-Qin Zhang¹, Hua-Bin Zhu², Ben-Sheng Qiu³, and Xin Liu^3
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.

Randy Giaquinto¹, Wolfgang Loew¹, Suraj Serai¹, Jean Tkach¹, Kathleen Emery¹, and Charles Dumoulin^1
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.

Yoshihisa Soutome¹, Masayoshi Dohata¹, Hisaaki Ochi¹, and Yoshitaka Bito^1
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.

Stefan Fischer¹, Mark Schuppert¹, Maxim Terekhov¹, Stefan Weber¹, Andrei L. Kleschyov², and Laura Maria Schreiber^1
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.

Liang Liu¹, Faiz Ikramulla¹, Velibor Pikelja¹, Jonathan Nass¹, and Ashok Menon^1
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.

Seunghoon Ha¹, Mark Jason Hamamura¹, Werner W Woeck¹, and Orhan Nalcioglu^1,2
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.

James Tropp¹, Paul Calderon², Lucas Carvajal³, Fraser Robb², P. E. Z. Larson³, P. Shin³, D. B. Vigneron³, and S. J. Nelson^3
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.

Oliver G. Gruschke¹, Elmar Fischer², Maxim Zaitsev², Jürgen Hennig², and Jan G. Korvink^1,3
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.

Haoqin Zhu¹, Grace Wang¹, and Labros Petropoulos^1
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.

Thomas Janssens¹, Boris Keil², Jennifer A. McNab², Reza Farivar², Annelies Gerits^1,2, Jonathan R. Polimeni², Lawrence L. Wald^2,3, and Wim Vanduffel^1,2
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.

Emilee Minalga¹, Robb Merrill¹, Nick Todd¹, Allison Payne¹, Dennis L. Parker¹, and J. Rock Hadley^1
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.

Jose I Rey¹, Eduardo G Moros², Robert J Gillies¹, and Gary V Martinez^1
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.

Markus Nikola Streicher¹, Andreas Schäfer¹, Dimo Ivanov¹, Laurentius Huber¹, Bibek Dhital¹, Enrico Reimer¹, Dirk Müller¹, Andre Pampel¹, Robert Trampel¹, and Robert Turner^1
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.

Aaron Oliver-Taylor¹, Chris Randell², Roger J Ordidge³, and David L Thomas^4
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.

Jinfeng Tian¹, Devashish Shrivastava¹, John Strupp¹, Jay Zhang¹, and Thomas Vaughan^1
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.

Ozlem Ipek¹, M de Greef², A Raaijmakers¹, P.R. Luijten³, J. J.W. Lagendijk¹, and C.A.T. van den Berg^1
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.

Shumin Wang^1
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.

Xiaotong Zhang¹, Jiaen Liu¹, and Bin He^1
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.

Devashish Shrivastava¹, Lynn Utecht¹, Jinfeng Tian¹, Timothy Hanson², and JT Vaughan^1
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.

Desmond Teck Beng Yeo¹, Zhangwei Wang², and Ileana Hancu^1
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.

Shiloh Sison¹, Xiaoyi Min², Yan Liu³, Kevin Feng³, Ji Chen³, John Nyenhuis⁴, Gabriel Mouchawar², and Jon Dietrich^2
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.

Jonas Bause¹, G. Shajan¹, Jens Hoffmann¹, Klaus Scheffler¹, and Rolf Pohmann^1
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.

Jan Paška¹, David O Brunner², Juerg Froehlich¹, and Klaas P Pruessmann^2
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.

Esra Neufeld¹, Maximilian Fütterer¹, Matthias Gebhardt², Michael Oberle¹, and Niels Kuster^1,3
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.

Ara Yeramian¹, Stefanie Buchenau¹, Chris A. Cocosco¹, Matthias Gebhardt², Dirk Diehl³, Jürgen Hennig¹, Jan Korvink⁴, and Maxim Zaitsev^1
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.

Andreas Rennings¹, Le Chen¹, Friedrich Wetterling², Mark E. Ladd³, and Daniel Erni^1
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.

Anand Gopinath¹, Emad Ebbini¹, Lance DelaBarre², and Tommy Vaughan^2
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.

Ozlem Ipek¹, I.J Voogt², P.R. Luijten², J. J.W. Lagendijk¹, and C.A.T van den Berg^1
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.

Simon Richardson^1,2, Bernard Siow², Andrew Batchelor³, Mark F. Lythgoe¹, and Daniel D.C. Alexander^2
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.

Dung Minh Hoang^1,2, Chao Zhang¹, Evelyn Voura^1,3, Latifa Fakri-Bouchet⁴, and Youssef Zaim Wadghiri^1
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

Andrzej Jesmanowicz¹, and Robert W. Cox^2
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.

Volkan Emre Arpinar¹, and L Tugan Muftuler^1,2
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.

Christopher Stumpf¹, Robert Rehner², Sebastian Martius³, Markus Vester², Rainer Engelbrecht¹, and Lorenz-Peter Schmidt^1
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.

Arthur W. Magill^1,2, Hongxia Lei^1,3, and Rolf Gruetter^1,3
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.

Ronald D. Watkins¹, Robert H Caverly², and William E. Doherty^3
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.

Andrzej Jesmanowicz¹, and William J O’Reilly^2
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.

Paul Joseph Cassidy^1
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.

Graham Charles Wiggins¹, Ryan Brown¹, Bei Zhang¹, Marcus Vester², Stefan Popescu², Robert Rehner², and Daniel Sodickson^1
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.

Markus Vester¹, Stephan Biber², Robert Rehner², Graham Wiggins³, Ryan Brown³, and Daniel Sodickson^3
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.

Ed B Boskamp¹, Masahiro Fujimoto¹, Arslan Amjad¹, and Michael Edwards^1
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.

Sergei Obruchkov^1,2, and Kenneth Bradshaw^2,3
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.

Alexey A Tonyushkin^1,2, Jose Antonio Muniz^3,4, Samuel Colles Grant^3,4, and Andrew J M Kiruluta^1,2
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).

Daniel James Lee¹, and Paul M Glover^1
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.

Johannes Mallow¹, Tim Herrmann², Judith Mylius³, Joerg Stadler³, and Johannes Bernarding^1
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.

Stefan Alt¹, Reiner Umathum¹, Wolfhard Semmler¹, and Michael Bock^1,2
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.

Ozlem Ipek¹, J. J.W. Lagendijk¹, and C.A.T. van den Berg^1
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.

Alexey A. Tonyushkin^1,2, Norman B. Konyer³, Michael D. Noseworthy^3,4, and Andrew J.M. Kiruluta^1,2
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.

M D Ketterman¹, Q X Yang^2,3, A G Webb⁴, Z G Herse², T Neuberger⁵, G Carluccio⁶, and M Lanagan^1
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.

Wei Luo¹, Yeun Chul Ryu², Sukhoon Oh², Zachary Herse², Ketterman David Matthew¹, Qing X Yang², Lanagan T Michael¹, and Christopher M Collins^2
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.

Zhangwei Wang¹, Mike Lanagan², and Qing X Yang^3
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

Qing Yang^1,2, Chris Collins³, Michael Lanagan⁴, Zachary Herse³, Sebastian Rupprecht³, Wei Luo³, Yeun Chul Ryu³, Megha Patel³, and Jeff Vesek^3
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.

Wei Luo¹, Giuseppe Carluccio^2,3, Sukhoon Oh³, and Christopher M Collins^3
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.

Davide Santoro¹, Alexander Müller^1,2, Lukas Winter¹, Wolfgang Renz^1,3, Andreas Grässl¹, Celal Özerdem¹, Valeriy Tkachenko⁴, Jeanette Schulz-Menger⁴, and Thoralf Niendorf^1,4
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.

Jens Groebner¹, Moritz Cornelius Berger¹, Wolfhard Semmler¹, and Jaane Rauschenberg^1
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.

Julien Oster¹, Raul Llinares², Zion Tse³, Ehud Schmidt³, and Gari Clifford^1
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.

Ying Hao¹, Brad Manor^1,2, Jing Liu³, Lewis Lipsitz², Vera Novak², Xiaoying Wang³, Jing Fang^1,4, and Jue Zhang^1,4
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.

Daniel Güllmar¹, Markus Hädrich^1,2, and Jürgen R Reichenbach^1
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.

Yan Liu¹, Kevin Feng², Ji Chen², Xiaoyi Min³, Shiloh Sison³, Gabriel Mouchawar³, and Jon Dietrich^3
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.

Daniel Zemann¹, and Karin Moertlbauer^1
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.

K Craig Goodrich¹, Seong-Eun Kim¹, Robb Merrill¹, Yong Wang², Richard Wiggins¹, J Rock Hadley¹, and Dennis L Parker^1
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.

Gregor Schaefers¹, Michael Scholten², Pascal Bartnik³, Amin Douiri³, and Wolfgang Görtz^3
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.

Bruno Camps-Raga¹, Wolfgang Görtz¹, Amin Douiri¹, Michael Scholten¹, Mark J. Pawlenka¹, and Gregor Schaefers^1
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.

Muhammad E.H. Chowdhury¹, Karen J Mullinger¹, and Richard W Bowtell^1
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.

Jonathan Howard¹, and Rexford Newbould^2
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.

Ke Zhang¹, Irene Neuner^1,2, Christian Filss¹, Karl-Josef Langen¹, Hans Herzog¹, and Nadim Joh Shah^1,3
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.

Krishnan Bharath Navalpakkam¹, Harald Braun², Susanne Zeigler², Harald H Quick², Joachim Hornegger¹, and Torsten Kuwert^3
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.

Hiroshi Kawaguchi¹, Takayuki Obata^1,2, Kazuki Kurihara³, Yosuke Takahashi³, Eiji Okada³, and Hiroshi Ito^1
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.

Felix Pierre Kuhn¹, Florian Wiesinger², Scott Wollenweber³, Andrei Samarin¹, Gustav von Schulthess¹, and Daniel Schmid^1
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.

Jan Ole Blumhagen^1,2, Ralf Ladebeck¹, Matthias Fenchel¹, Klaus Scheffler^2,3, and Harald H. Quick^4
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.

Sebastian Fürst¹, Isabel Dregely¹, Stephan Nekolla¹, Markus Schwaiger¹, and Sibylle Ziegler^1
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.

Susanne Ziegler¹, Harald Braun¹, Philipp Ritt^2,3, Jens U. Krause¹, Carsten Hocke³, and Harald H. Quick^1
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.

Jan Ole Blumhagen^1,2, Ralf Ladebeck¹, Matthias Fenchel¹, Harald H. Quick³, and Klaus Scheffler^2,4
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.

Mark BM Hofman¹, Joost PA Kuijer¹, Jan Willem de Ridder¹, Lars R Perk², and Rudolf M Verdaasdonk^1
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.

Daniel Brenner¹, Christoph Weirich¹, Jürgen Scheins¹, Etienne Besancon¹, Lutz Tellmann¹, Hans Herzog¹, and N. Jon Shah^1,2
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.