Electronic Posters : Engineering
Click on to view the abstract pdf and click on to view the video presentation.
Safety: Implants & Devices

Monday May 9th
Exhibition Hall  14:00 - 16:00 Computer 66

14:00 3763.   RF Safety Assessment of a Generic Deep Brain Stimulator during 1.5T MRI Exposure 
Eugenia Cabot1, Tom Lloyd2, Andreas Christ1, Gregg Stenzel2, Wolfgang Kainz3, Steve Wedan2, and Niels Kuster1,4
1IT'IS Foundation, Zurich, Switzerland, 2Imricor Medical Systems, United States, 3FDA, Rockville, United States, 4Swiss Federal Institute of Technology (ETHZ), Zurich, Switzerland

A methodology for RF safety assessment of implants based on a 4 tier approach was evaluated for 1.5T scanners using a generic model of a deep brain stimulator. A combination of numerical (FDTD simulations) and experimental techniques was used. The different tiers were followed to assess the energy deposition and the temperature increase at the tip of the implant in a human head model. Each consecutive tier yields a less conservative result, but requires greater computational effort to demonstrate safety. Results showed that Tier 4 is technically feasible but too computationally demanding. An enhanced Tier 3 is then suggested.

14:30 3764.   Radio-Frequency Heating at Deep Brain Stimulation Lead Electrodes due to Imaging with Head Coils in 3 T and 7T 
Devashish Shrivastava1, Jingeng Tian1, Aviva Abosch1, and John T Vaughan1
1University of Minnesota, Minneapolis, MN, United States

Radio-frequency (RF) heating was measured using fluoroptic probes at the deep brain stimulation (DBS) lead electrodes and 5 mm away from the distal lead tip due to head imaging with a transcieve head coil in 3 tesla (T) and 7T at the whole head average SAR of 3 W/kg. The effect of the loop orientation of the extra-cranial portion of the lead on the RF heating was studied. Clinically harmful RF heating may be produced in both fields with head coils. The RF heating was a function of the extra-cranial lead placement and head coil.

15:00 3765.   Measurements of RF Heating During 3.0T MRI of a Pig Implanted with DBS 
Krzysztof R Gorny1, Stephan J Goerss2, Michael F Presti3, Sun Chul Hwang4, Dong-Pyo Jang4, Inyong Kim4, Kendall H Lee5, and Matt A Bernstein1
1Radiology, Mayo Clinic, Rochester, MN, United States, 2Neurosurgery, Mayo Clinic, Rochester, MN, United States, 3Neurology, Mayo Clinic, Rochester, MN, United States,4Neurologic Surgery, Mayo Clinic, Rochester, MN, United States, 5Neurologic Surgery, Mayo Clinic, Rochester, MN

We use fluoroptic thermometry to measure local heating near DBS electrodes implanted in pig's brain during 3.0T MRI. For IR SPGR and resting state fMRI sequences temperature changes of less then 0.3° were observed. These data could be valuable in assessment of safety during 3.0T MRI of patients with implanted DBS systems.

15:30 3766.   Fast T1-Thermometry of the RF Induced Heating of Conductive Wires 
Daniel Gensler1, Florian Fidler1, Marcus Warmuth2, Theresa Reiter2, Peter Nordbeck2, Oliver Ritter2, Mark E Ladd3, Harald H Quick4, Peter M Jakob1, and Wolfgang R Bauer2
1Forschungszentrum Magnet-Resonanz-Bavaria e.V., Wuerzburg, Bavaria, Germany, 2Medizinische Klinik und Poliklinik I, Universitätsklinikum Würzburg, Wuerzburg, Bavaria, Germany, 3Erwin L. Hahn Institut für Magnetresonanz, Universität Duisburg-Essen, 4Institut für Medizinische Physik, Friedrich-Alexander-Universität Erlangen-Nürnberg

The number of MRI examinations in patients with medical implants is highly increasing, raising several safety issues. Major intention of the current work is to develop a fast T1-based method, which allows controlled heating of an implant while simultaneously quantifying the spatial temperature distribution during MRI. For this purpose an inversion recovery sequence was implemented where the heating is caused by additional RF pulses. The presented T1-based thermometry method allows spatial and temporal quantification of dynamic RF-induced heating near a conducting medical implant. Hence it is possible to precisely analyze the spatial temperature distribution of an implant using a single measurement even in inhomogeneous surroundings.

Tuesday May 10th
  13:30 - 15:30 Computer 66

13:30 3767.   An MR Thermometry-GBHTM ‘Hybrid’ Model to Determine Radiofrequency Heating near Implanted Leads in High Field Imaging 
Devashish Shrivastava1, Ute Goerke1, Shalom Michaeli1, Jingeng Tian1, Aviva Abosch1, and John T Vaughan1
1University of Minnesota, Minneapolis, MN, United States

A proton resonance frequency (PRF) shift based MR thermometry method and the newly developed generic bioheat transfer model (GBHTM) were used together as an ‘hybrid’ model to determine radiofrequency (RF) heating near a deep brain stimulation (DBS) lead electrodes in 3T. The PRF shift method was used to image temperatures outside the susceptibility artifact region of the DBS lead after an SAR intensive spin echo sequence. The imaged temperatures were used as inputs to the GBHTM to determine RF heating in the artifact region near the lead. The ‘hybrid’ model predicted accurate peak temperatures at the DBS electrodes.

14:00 3768.   Resonant Traps as a Safety Measure: Influence of Inaccurate Tuning 
Falk Uhlemann1, Peter Mazurkewitz1, and Oliver Lips1
1Philips Research Laboratories, Hamburg, Germany

Guidewires or cabling inside catheters can cause severe heating during MRI. The associated common mode currents can be reduced by resonant traps. We investigate if safety issues can arise from inaccurately tuned traps (due to e.g. tolerances, movement, surrounding tissue). Tip heating of wires inside the MR is analyzed depending on their length and trap tuning. Results show that the effect of inaccurate tuning or inadvertent detuning has to be considered, since the safety can easily be deteriorated. Slight detuning can result in configurations where the trap even increases the tip heating of the wire.

14:30 3769.   Influence of Electrical Connections on Catheter Heating 
Oliver Lips1, Bernd David1, Sascha Krueger1, Kai-Michael Luedeke1, and Steffen Weiss1
1Philips Research Laboratories, Hamburg, Germany

The dependence of catheter heating on the electrical connections is investigated. RF simulations and corresponding measurements analyze the effect of different impedances at various positions along the connections. Additionally, tip heating for several, realistic active tracking set-ups is measured employing catheters equipped with standard cables as well as transformer-cables. Using standard wires resonant heating was observed in several connecting conditions. Transformer cables do not show a relevant tip heating in any configuration. Thus, it is advisable to prevent RF heating inside the catheter in order to avoid any negative influence from the electrical connections.

15:00 3770.   Assessment of RF induced heating of coronary stents in 7T MRI 
Davide Santoro1, Julia Marie Vogt2, Wolfgang Renz3, Johanna Gellermann4, Frank Seifert5, Valeriy Tkachenko4, Jeannette Schulz-Menger4, and Thoralf Niendorf1,4
1Berlin Ultra-High Field Facility (BUFF), Max Delbrück Center for Molecular Medicine (MDC), Berlin, Germany, 2Department of Physics, Humboldt University Berlin, Berlin, Germany, 3Siemens Healthcare, Erlangen, Germany, 4Experimental and Clinical Research Center (ECRC), Charité Campus Berlin Buch, 5Physikalisch-Technische Bundesanstalt (PTB)

The advantage of ultrahigh field MRI holds the promise to enhance, spatial and/or temporal resolution in MRI. Such improvements would benefit an ever growing set of indications for cardiovascular MR. However, intracoronary stents used for treatment of coronary artery disease are currently considered to be contra-indications for CMR at 7.0 T. The presence of a metallic implants in combination with RF wave lengths and RF power deposition used at 7.0 T may 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 coronary stents in agarose phantoms using electromagnetic field simulations, fiber optic temperature measurements and MR thermometry at 7.0 T.

Wednesday May 11th
  13:30 - 15:30 Computer 66

13:30 3771.   Detection and Countermeasures for RF Unsafe Conditions for MR-conditional Devices 
Ingmar Graesslin1, Steffen Weiss1, Emna Hassani1, Kai Nehrke1, Peter Vernickel1, and Sascha Krueger1
1Philips Research Laboratories, Hamburg, Germany

Aging population causes an increasing demand for MR-examinations in patients wearing implants, which usually is a contra-indication for an MR examination. Previous work proposed to cancel planned scans if a reverse-polarization pre-scan detected a device or as soon as unsafe situations were detected by pick-up-coils. This work has the objective to detect unsafe RF coupling events to a device during an MR measurement and to change the scan-parameters of the parallel TX-system rather than terminating the scan. The aim is to re-establish a safe situation while trying to maintain image quality. The proposed approach was evaluated in phantom as well as volunteer studies.

14:00 3772.   Reduction of RF Heating of Metallic Devices by Using a Two-Channel Transmit Array System : Application to Arbitrary Lead Geometries 
Yigitcan Eryaman1, Burak Akin1, Cagdas Oto2, Oktay Algin3, and Ergin Atalar1
1National Magnetic Resonance Research Center (UMRAM), Bilkent University, Ankara, Turkey, 2Veterinary Medicine,Department of Anatomy, Ankara University, Ankara, Turkey, 3Department of Radiology, Ataturk Training and Research Hospital, Ankara, Turkey

In this work, it is shown that the RF heating at the tip of metallic leads can be reduced by using a two-channel transmit array system. A zero electric field plane is steered inside the body by controlling the currents at two ports of the birdcage coil. As the field is steered, the RF current artifact near the lead tip is monitored and the excitation pattern which minimizes the current artifact is found. Phantom and animal experiments are performed with copper wires and DBS leads in order to demonstrate the reduction in tip temperature.

14:30 3773.   Comparison of RF Heating in Cables equipped with different Types of Current Limitations 
Steffen Weiss1, Bernd David1, Oliver Lips1, Jan Hendrik Wuelbern1, and Sascha Krueger1
1Philips Research Laboratories, Hamburg, Germany

Various methods have been used to limit MR-induced RF currents and associated RF heating in wired interventional devices, including resistors, resonant RF chokes, transformers, and mechanical switches as current-limiting elements. Here, RF heating for six such transmission lines was evaluated at the tip and along the full length of the line using fiber-optic probes and an infrared camera simultaneously. While all methods effectively suppressed tip heating, heating at the current limiting elements was largest for resonant chokes and lowest for transformers and switches. The IR imaging method is suitable to quickly and globally identify sources of ohmic heating.

15:00 3774.   MR Safety Assessment of Potential RF Heating from Cranial Fixation Plates at 7 Tesla 
Oliver Kraff1,2, Karsten H Wrede1,3, Stephan Orzada1,2, Philipp Dammann1,3, Mark E Ladd1,2, and Andreas K Bitz1,2
1Erwin L. Hahn Institute for MRI, University Duisburg-Essen, Essen, Germany, 2Department of Diagnostic and Interventional Radiology and Neuroradiology, University Hospital Essen, Essen, Germany, 3Clinic for Neurosurgery, University Hospital Essen, Essen, Germany

Examination of patients with implants has become relevant at research facilities with ultra-high field strength systems. In this study we focus on miniplate implants used for refixation of the bone flap after craniotomy. Since typical temperature measurements performed with fiber-optic probes to assess potential heating yield only point-wise information, a much more detailed assessment of MRI-related heating due to interactions of the RF field with the implants was performed. The test protocol included full wave simulations on different numerical models as well as external measurements of the H and E field and SAR distribution using a 7T head coil.

Thursday May 12th
  13:30 - 15:30 Computer 66

13:30 3775.   A novel phantom design to reduce thermal losses during radio frequency (RF) induced heating testing according to ASTM F2182-09 standard 
Christian Koch1,2, Gregor Schaefers1, and Waldemar Zylka2
1MR:comp GmbH, MR Safety Testing Laboratory, Buschgrundstraße 33, 45894 Gelsenkirchen, North Rhine-Westphalia, Germany, 2Deptartment of Physical Engineering, Medical Physics Laboratory, University of Applied Sciences Gelsenkirchen, Neidenburger Str. 43, 45877 Gelsenkirchen, North Rhine-Westphalia, Germany
A new phantom design is proposed to improve the accuracy of calorimetrically determined whole phantom specific absorption rate (SAR) for RF heating measurements. Emphasis has been laid on reducing the thermal error caused by heat capacity of the phantom’s material. To assess this calorimetrical accuracy, numerical calculations of temperature distribution and averaged temperature rise have been carried out for two different phantom models. It is demonstrated that the thermal inaccuracy due to phantom body material can be reduced significantly, i.e. below the resolution of the temperature measurement device.

14:00 3776.   MR thermometry using a paramagnetic lanthanide complex for evaluation of RF safety 
Shalmali Dharmadhikari1,2, and Navin Bansal1,2
1Purdue University, West Lafayette, Indiana, United States, 2Indiana Univeristy, Indianapolis, Indiana, United States

Determination of RF-induced heating during MRI is important for safety evaluation of RF-devices, pulse sequences and implants. Calorimetric assessment of specific absorption rate (SAR) requires accurate measurement of small temperature changes produced during MRI. MR thermometry with TmDOTP5- enables temperate measurement with high temperature and spatial resolution. Since the temperature changes during MRI occur due to heat deposition as well as dissipation, a model considering the effect of heat loss, for computation of SAR has been proposed. Application and development of MR thermometry technique with TmDOTP5- to image SAR has been successfully demonstrated.

14:30 3777.   TEM cell for calibration of an electro-optic E-field sensor in a clinical scanner 
Frank Seifert1, Tobias Klepsch1, Tomasz David Lindel1, Werner Hoffmann1, and Bernd Ittermann1
1Physikalisch-Technische Bundesanstalt, Braunschweig und Berlin, Germany

EM field simulations of RF coils and coil arrays are basic tools for predicting SAR in the human body. Besides B1(+) measurements, complementary E-field measurements using MR compatible E-field sensors are inevitable for an experimental validation of such simulations using the MR scanner itself. However, the significance of such measurements is limited by the quality of the sensor’s calibration. We present a MR compatible transverse electromagnetic cell (TEM cell) used as calibrating device for a time-domain electro-optic E-field sensor via B1(+) measurements. Since in a TEM cell the E-Field is exactly related to the B1(+) field by E = 376.73 Ohm*2*B1(+)/µ0 the calibration procedure is based on MR techniques only.

15:00 3778.   Optical Dipole Probes for Quantitative Electric Field Measurements up to 7T 
Jens Groebner1, Reiner Umathum1, Stefan Hoffmann1, Moritz Cornelius Berger1, Michael Bock1, Florian Martin Meise1, Wolfhard Semmler1, and Jaane Rauschenberg1
1Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany

Up to now, E-field probes have been presented for relative SAR estimation. In this work, an optical dipole-controller system was developed, to measure absolute E-field values. The dipole probe was calibrated in a custom built Crawford TEM cell to assure the accuracy of the measured E-field values. The new probe can determine E-fields between 65 and 643.5 V/m, which could be demonstrated of a known 7 T head coil.

Electronic Posters : Engineering
Click on to view the abstract pdf and click on to view the video presentation.
Gradient & Shim Coil Design

Monday May 9th
Exhibition Hall  14:00 - 16:00 Computer 67

14:00 3779.   A Finite-Difference based Method for the Design of Gradient Coils in MRI 
Ling Xia1, Minhua Zhu1, Guofa Shou1, Feng Liu2, and Stuart Crozier2
1Department of Biomedical Engineering, Zhejiang University, Hangzhou, China, People's Republic of, 2School of Information Technology & Electrical Engineering, University of Queensland, Brisbane, Australia

This paper presents a finite difference (FD) based method for the design of gradient coils in MRI. The design method firstly uses the FD approximation to describe the current density of the coil space and then employs the stream function method to extract the coil pattern. During the numerical implementation, a linear equation has been constructed and solved using a regularization scheme. This abstract briefly describes the algorithm details through X-gradient coil design examples. The proposed gradient coil design scheme can be integrated into a finite-difference based EM framework, which can handle multi-physics including RF and gradient fields presented in the MR engineering.

14:30 3780.   A novel coil design method for manufacturable configurations at optimal performance 
Feng Jia1, Zhenyu Liu2, and Jan G Korvink1,3
1Freiburg Institute of Advanced Studies (FRIAS), University of Freiburg, Freiburg, Germany, 2Changchun Institute of Optics, Fine Mechanics and Physics (CIOMP), Chinese Academy of Sciences, Changchun, China, People's Republic of, 3Department of Microsystems Engineering (IMTEK), University of Freiburg, Freiburg, Germany

Based on an alternative differentiable objective function which is related with the maximum of current density, an iterative optimization method is proposed to design a biplanar micro-coil in this abstract. The main goal of this method is to increase the minimal distance between adjacent conductors of the coil. The planar surface can be discretized using a high-order triangular mesh. The magnetic field is calculated using the Biot-Savart law where the surface current density is expressed using a stream function and the surface integration is implemented using surface numerical integration based on the shape functions of the finite element.

15:00 3781.   Behaviour of Gradient Coils Designed With Varying Degrees of Minimised Maximum Current Density 
Michael Stephen Poole1, Peter While2, Hector Sanchez Lopez1, Larry Forbes2, and Stuart Crozier1
1ITEE, University of Queensland, Brisbane, QLD, Australia, 2Mathematics, University of Tasmania, Hobart, Tasmania, Australia

A new method to design gradient and shim coils was recently presented that spreads out close wires. This has the effect of being able to increase the coils efficiency when limited by minimum wire size. Also, it can be used to reduce the peak temperature in a coil. Here we investigate the behaviour of such coils on the interval between standard minimum power and the new minimax current density coils. Performance properties and heating experiments and simulations were performed and the results analysed.

15:30 3782.   Suppressing local hot spots in RF coils and shields due to gradient eddy currents 
Zhen Yao1, Aaron Shojinaga1, Yong Wu1, Timothy Eagan2, Shmaryu Shvartsman2, Thomas Chmielewski2, and Robert Brown1
1Department of Physics, Case Western Reserve University, Cleveland, OH, United States, 2ViewRay Inc., Oakwood Village, OH, United States

A design goal for MRI is to limit the eddy currents generated on the RF coils and shields due to the gradient coils and in particular to suppress the associated eddy current heating. It is important, for example, to avoid hot spots in the proximity of the patient as well as in the vicinity of soldering joints. We simulate the generation of eddy current and corresponding heat distributions resulting from gradient magnetic flux, and make successful comparisons to experimental measurements. Specific patterns of cuts for reducing troublesome heating locations are studied.

Tuesday May 10th
  13:30 - 15:30 Computer 67

13:30 3783.   Magnetic Particle Imaging: Linear Gradient Array for Imaging with a Traveling Wave 
Peter Klauer1,2, Martin Andreas Rückert1,2, Patrick Vogel1,2, Walter H. Kullmann1, Peter M. Jakob2,3, and Volker Christian Behr2
1Electrical Engineering, University of Applied Sciences Würzburg-Schweinfurt, Schweinfurt, Germany, 2Department of Experimental Physics 5 (Biophysics), University of Würzburg, Würzburg, Germany, 3Research Center for Magnetic Resonance Bavaria e.V (MRB), University of Würzburg, Würzburg, Germany

This work presents a new gradient design for magnetic particle imaging that will allow performing dynamic imaging in a linear sampling scheme rather than a Lissajous trajectory by generating a traveling wave. Aside from the simplified trajectory, this approach provides the possibility of increasing the field of view arbitrarily in one dimension without increasing the sampling time.

14:00 3784.   A Hybrid Field-harmonics Approach for Passive Shimming Design in MRI 
Feng Liu1, Jianfeng Zhu2, Ran Zhang3, Ling Xia2, and Stuart Crozier1
1School of Information Technology and Electrical Engineering, University of Queensland, Brisbane, Queensland, Australia, 2Department of Biomedical Engineering, Zhejiang University, Hangzhou, Zhejiang, China, People's Republic of, 3School of Electrical Engineering, Shandong University, Jinan, Shandong, China, People's Republic of

This paper presents a new passive shimming (PS) design scheme for the correction of static magnetic field inhomogeneities in MRI systems. The PS procedure usually employs field-based (a) or harmonics-based (b) methods to find an optimum iron piece configuration to improve the field uniformity in the imaging region. For the PS technique (a), the peak-to-peak field inhomogeneity is minimized and the harmonic components are inherently unconstrained; in the technique (b), selected unwanted harmonics are minimized and the overall field uniformity is consequently reduced. The approach (a) usually provides good field homogeneity but lacks flexibility in managing all terms of spherical harmonic field expansion; the approach (b) is capable of controlling targeted low-order harmonic terms but can have difficulty in producing optimal overall field homogeneity and in controlling high-order harmonics. The proposed algorithm attempts to combine the strengths of these two methods for a better PS solution. During the PS implementation, an explicit expression of the system matrix with both field and harmonics sensitivities is generated, and then an optimization procedure is performed for the determination of shim piece thicknesses and locations. An experimental study showed that the hybrid method provided good quality, flexible solutions for controlling individual harmonics impurities and also overall field uniformity.

14:30 3785.   Construction and optimization of local 3rd order passive shim system for human brain imaging at 4T MRI 
Mohan Lal Jayatilake1,2, Judd Storrs1,3, Jeff Osterhage1, and Jing-Huei Lee1,4
1Center for Imaging Research, University of Cincinnati, Cincinnati, OH, United States, 2Department of Physics, University of Cincinnati, Cincinnati, OH, United States,3Department of Psychiatry and Behavioural Neuroscience, University of Cincinnati, Cincinnati, OH, United States, 4School of Energy, Environmental, Biological, and Medical Engineering, University of Cincinnati, Cincinnati, OH, United States

Magnetic susceptibility variation can lead to B0 field inhomogeneity and cause artifacts including signal dropout and image distortions. We introduce a method that the addition of the third order passive shim system along with the first and second active shimming significantly improves the homogeneity of the static magnetic field within the human brain.

15:00 3786.   Optimization of computational speed for BE method of coil design 
Chad Tyler Harris1, William B Handler1, and Blaine A Chronik1
1Physics and Astronomy, University of Western Ontario, London, Ontario, Canada

The Boundary Element (BE) method is proving to be an extremely powerful and versatile tool in the electromagnetic design of gradient, shim, and shielding coils. We have been strongly motivated by its many strengths to optimize the computational implementation of the math since its first use. We have found that a significant decrease in computation time is achievable relatively easily. In this study, we describe the most important steps in the optimization of this algorithm, and show that it is able to produce detailed wire patterns in a matter of seconds.

Wednesday May 11th
  13:30 - 15:30 Computer 67

13:30 3787.   Synergistic active and passive shimming to optimize B0 field homogeneity in micro MR imaging 
Rahul Dewal1, Zhipeng Cao1, Christopher Sica2, Christopher Collins2, and Qing Yang1,2
1Bioengineering, The Pennsylvania State University, Hershey, PA, United States, 2Radiology, The Pennsylvania State University, Hershey, PA, United States

Passive shimming can be used to correct for the static B0 field inhomogeneities caused by air-tissue boundaries in the sinus cavities and ear canals. By placing pieces of shim material with high susceptibility values into the magnet at precise locations, the magnetic field can be perturbed such that higher-order inhomogeneities are corrected. This method uses a numerical optimization algorithm in conjunction with a Fourier transform-based fast magnetic field calculation method to determine the optimal configuration of shim materials for an agar gel phantom. Optimized active shims are calculated alongside passive shim optimization to form a synergistic shimming approach.

14:00 3788.   Fast Eddy Current Simulation in Thick Split Cylinders of Finite Length Induced by Coils of Arbitrary Geometry 
Hector Sanchez-Lopez1, Michael Poole1, Limei Liu1, and Stuart Crozier1
1School of Information Technology & electrical Engineering, The University of Queensland, Brisbane, QLD, Australia

In this paper we presented a new and fast eddy current simulation method. The approach is valid for currents induced in thick and split cylinders of finite length induced by coils of arbitrary geometry. The method divides thick conducting axially split/continues cylinders into thin layers (thinner than the skin depth) and expresses the current density on each as a normalized Fourier series. The coupling between each mode with every other is modeled with an inductive network method calculated in Fourier space. In this way, the eddy currents induced in realistic cryostat surfaces by coils of arbitrary geometry can be simulated.

14:30 3789.   Reducing Short Term Gradient Heating by Usage of Adapted Encoding Schemes 
Paul Freitag1
1Bruker BioSpin MRI GmbH, Ettlingen, Germany

Classic Cartesian phase encoding schemes cause high short temporal power dissipation in the gradient system in the K-space edges. Optimizing the phase encoding scheme allows to achieve an approximately constant averaged power dissipation. Applying this to fast 3D imaging sequences, a smaller field of view or shorter repetition times can be selected without damaging the gradient system. The proposed optimization algorithm can easily be integrated into routine sequences allowing performance gains of up to 20% regarding minimum repetition time.

15:00 3790.   Design of Gradient and Shim Coils for a Head-Only, Vertical, HTS MRI System 
Michael Stephen Poole1, Hector Sanchez Lopez1, Stuart Crozier1, Iwao Nakajima2, and Shin-ichi Urayama3
1ITEE, University of Queensland, Brisbane, QLD, Australia, 2Takashima Seisakusho Co., Ltd., Tokyo, Japan, 3Human Brain Research Center, Kyoto University Graduate School of Medicine, Kyoto, Japan

Gradient and shim coils were designed for a high-temperature superconductor magnet system. Particular attention was paid to minimisation of the eddy currents generated in the cryostat of the experimental magnet. The constrained space and requirement for wide wire spacing in the design dictated the use of minimax current density technique which more than doubled the efficiency of the transverse gradient coils.

Thursday May 12th
  13:30 - 15:30 Computer 67

13:30 3791.   Simple minimum energy method for calculating shielding coils on arbitrary geometries 
Dustin W Haw1, Chad T Harris1, William Bradfield Handler1, and Blaine A Chronik1
1Physics and Astronomy, University of Western Ontario, London, Ontario, Canada

A simple method for calculating shielding coils on arbitrary geometries is presented. This new method not a time-consuming iterative method. It is a direct calculation of an energy minimizing total current density.

14:00 3792.   A design method for asymmetric gradient coils with reduced hot spot temperatures 
Peter T. While1, Larry K. Forbes1, and Stuart Crozier2
1School of Mathematics and Physics, University of Tasmania, Hobart, TAS, Australia, 2ITEE, University of Queensland, Brisbane, QLD, Australia

Gradient heating and coil hot spots can result in system failure or image distortion. A previously reported method is extended to the design of asymmetric gradient coils with improved temperature distributions and reduced hot spot temperatures. The method combines an optimisation constraint derived from a spatial temperature distribution model with a relaxed fixed point iteration routine. In comparison to minimum power coils, the new coil windings are more spread out with lower maximum temperatures, at little or no cost to coil performance. For the design of coils with different thermal material properties, considerably different winding pattern solutions are obtained.

14:30 3793.   Bi-planar shim coil designed by Stream Function method improves B0 homogeneity along Z-axis 
Daiki Tamada1, Yasuhiko Terada1, and Katsumi Kose1
1Institute of applied physics, University of Tsukuba, Tsukuba, Ibaraki, Japan

A new method using stream function was proposed to correct inhomogeneity of the magnetic field with single-channel shim coils. The inhomogeneity achieved by the stream function method was comparable to that achieved by the target field method. Moreover, the inhomogeneity along z-axis was also corrected, which could not be done by the target field method. The method presented here provides large three dimensional homogeneity without multi-channel shim coils, which leads to the enlargement of available space for samples.

15:00 3794.   Design of compact planar GC for high field open MRI using the computational tool DUCAS 
Mitsushi Abe1, Yukinobu Imamura1, and Hiroyuki Takeuchi2
1Energy and Environmental Syustems Lab., Hitachi, Ltd., Hitachi, Ibaraki, Japan, 2Hitachi Medical Corp., Kashiwa, Chiba, Japan

Design of a compact planar GC for high field open MRI using the computational tool DUCAS was done. The DUCAS can treat arbitral sheet currents and was applied on the GC design. The designed GC is a ASGC. It has umbrella shaped shield coil and plane main coil with direct connection between them. These two characteristics made the GC size compact and the leakage field weak. Then we conclude this ASGC can be used as planar ASGC for high-field open MRI.

Electronic Posters : Engineering
Click on to view the abstract pdf and click on to view the video presentation.
MR+: Multimodality Systems & Methods

Monday May 9th
Exhibition Hall  14:00 - 16:00 Computer 68

14:00 3795.   On the Effects of Magnetic Fields up to 9.4T on PET Image Resolution and Quality Measured with an MR-BrainPET 
Nadim Jon Shah1,2, Hidehiro Iida3, Christoph Weirich1, Lutz Tellmann1, Joachim Kaffanke1, Liliana Caldeira4, Elena Rota Kops1, Stefan Spellerberg5, and Hans Herzog1
1Institute of Neuroscience and Medicine - 4, Research Centre Jülich, Jülich, Germany, 2Department of Neurology, Faculty of Medicine, JARA, RWTH Aachen University, Aachen, Germany, 3Department of Investigative Radiology, National Cardiovascular Center Research Institute, Osaka, 4Instituto de Biofísica e Engenharia Biomédica, Faculdade de Ciências da Universidade de Lisboa, Lisboa, Spain, 5Institute of Neuroscience and Medicine - 5, Research Centre Jülich, Jülich, Germany

In a hybrid MR-PET system, the magnetic field is expected to reduce the positron range in the x-y plane. The positron range of 18F and 120I was investigated from zero up to 9.4T in a 9.4T human whole-body scanner equipped with a BrainPET insert. The positron range (and thus resolution) of 18F is not affected much by the magnetic field. For the more energetic emitter, I120, there is a significant improvement in resolution at 9.4T.

14:30 3796.   Systematic Investigation and Correction of MR Influences on Simultaneous PET Measurements 
Christoph Weirich1, Daniel Brenner1, Lutz Tellmann1, Hans Herzog1, and Nadim Jon Shah1,2
1Institute of Neurosciene and Medicine - 4, Forschungszentrum Juelich, Juelich, Germany, 2Department of Neurology, Faculty of Medicine, JARA, RWTH Aachen University, Aachen, Germany

The combination of MRI (Magnetic Resonance Imaging) and PET (Positron Emission Tomography) offers the prospect of improved diagnostics, therapeutic monitoring and preclinical research. Recent studies showed an influence of MR measurements on simultaneous PET acquisitions resulting in drop of the measured count rate. This study aims at a systematic investigation and first steps towards a correction of this phenomenon. The overall measured PET count rate is sensitive to the action of MR gradients with each gradient direction exhibiting a different sensitivity.

15:00 3797.   Hybrid MR-PET - Simultaneous FET-PET and Chemical Shift Imaging 
N. Jon Shah1,2, Irene Neuner1,2, Joachim B. Kaffanke1, Christian Filss1, Gabriele Stoffels1, Hans Herzog1, and Karl-Josef Langen1
1Institute of Neuroscience and Medicine 4, Forschungszentrum Juelich, Juelich, Germany, 2Department of Neurology, Faculty of Medicine, JARA, RWTH Aachen University, 52074 Aachen, Germany
PET imaging is well established for the diagnosis of brain tumours. It is a valuable tool in the differential diagnosis of pathologies detected by MRI. Its metabolic specificity delivers valuable information about the malignancy and the extent of tumour tissue. Metabolic information from PET can be cross-validated and/or extended by MR spectroscopy. In heterogeneous brain tumours the ratio of Myo-Inositol to NAA in different parts may help to distinguish between brain tumour, oedema and scar tissue.

15:30 3798.   Reproducibility of MRI-DUTE-based attenuation correction maps in brain tumor patients 
Grace Sooyeon Kim1, Daniel Burje Chonde1, Thomas Benner1, Michael Hamm2, Alma Gregory Sorensen1, and Ciprian Catana1
1A.A. Martinos Center for Biomedical Imaging, Charlestown, MA, United States, 2Siemens Healthcare, Charlestown, MA, United States

Bone/air segmentation is a significant challenge in developing the MRI-based attenuation correction (AC) method. We determined good reproducibility of a dual-echo ultra-short echo time (DUTE) sequence-based AC method used in ten brain tumor patients over four time points (relative SD between 2.17 to 13.40%). We found that the DUTE-based method yielded a 85.30% average agreement with respect to the silver-standard segmented CT-based µ map. The greatest challenges with this method involve segmentation of the full thickness of the skull and distinguishing air from tissue in difficult sinus regions. Further development of the DUTE-based AC method is under way.

Tuesday May 10th
  13:30 - 15:30 Computer 68

13:30 3799.   PET-MR-US in drug delivery 
Yu Liu1, Brett Z Fite1, Charles F Caskey1, Chun-Yen Lai1, Dustin E Kruse1, Jai Woong Seo1, Benoit Larrat2, Erik Dumont3, and Katherine W Ferrara1
1Biomedical Engineering, UC Davis, Davis, CA, United States, 2Laboratoire Ondes et Acoustique, ESPCI, Paris, France, 3Image Guided Therapy, Pessac, France

Synopsis: There is intense research in the area of ultrasound-enhanced drug delivery, including enhanced accumulation of particles resulting from tumor insonation with a temperature elevation of ~5ºC. High field MRI (7T) has advantages in monitoring such treatments in that the region of treatment and temperature can be controlled; since T2* scales with field strength, temperature estimation is efficient and sensitive at high field. We have integrated a real-time high-field MR-guided focused ultrasound system (Image Guided Therapy, France) in studies of mild hyperthermia and apply this technology to improve local drug delivery by coupling PET, MRI and ultrasound (US).

14:00 3800.   Simultaneous PET/MRI: Evaluation of electromagnetic interactions and in vivo imaging in 9.4 T MRI 
Sri-Harsha Maramraju1,2, S-David Smith2, Sean Stoll2, Daniela Schulz2, Sergio Rescia2, Sachin Junnarkar2, Martin Purschke2, Bosky Ravindranath1,2, Paul Vaska1,2, Craig Woody2, and David Schlyer1,2
1SUNY Stony Brook University, Stony Brook, New York, United States, 2Brookhaven National Laboratory, Upton, New York, United States

The electromagnetic interactions between the PET and MRI systems were evaluated by assessing the MR image quality and evaluating the PET performance. Results from the MRS and EPI data show no signs of interference on the MR images during PET acquisition and the PET data were quantitative. Studies were carried out using radiolabeled iron oxide nanoparticles in mice to study the dynamics and biodistribution of nanoparticles in vivo. These studies help to understand the toxicological effects and biological fate of these nanoparticles in vivo.

14:30 3801.   RF coil design for simultaneous PET/MR 
Peter Herrick1, Richard Ansorge1, Rob Hawkes2, Steve Sawiak2, Joe Stevick1, and Adrian Carpenter2
1Cavendish Laboratory, University of Cambridge, Cambridge, Cambridgeshire, United Kingdom, 2Wolfson Brain Imaging Centre, Addenbrooke's Hospital, University of Cambridge, Cambridge, Cambridgeshire, United Kingdom

An engineering challenge of simultaneous PET/MR is to minimize and quantify the effect of RF coil hardware on PET signal intensity. This RF hardware is usually invisible in MRI, thus proposed segmentation methods for MR-based attenuation correction are not suitable. We have used Monte Carlo simulations of gamma-ray interactions to demonstrate the impact of structural components and coil positions on PET images. This shows that the adverse effects of using conventional RF coils can be dramatic, resulting in 25% loss of PET signal intensity and 0.5mm loss in spatial resolution. Quantitative measurements of uptake values are crucial for PET diagnosis.

15:00 3802.   Rapid Re-shimming for Rotated Views in MR-SPECT Imaging 
Mark Jason Hamamura1, Seunghoon Ha1, Werner W Roeck1, and Orhan Nalcioglu1,2
1Tu & Yuen Center for Functional Onco-Imaging, University of California, Irvine, CA, United States, 2Department of Cogno-Mechatronics Engineering, Pusan National University, Pusan, Republic of Korea

In a combined MRI and SPECT system (MR-SPECT), metallic components of the SPECT hardware distort the B0 field for MR imaging. Rotation of the SPECT hardware for tomographic imaging thus alters the B0 field and requires re-shimming. To perform rapid re-shimming, pre-determined field maps were utilized to calculate the optimum currents to apply to the shim channels. These calculations do not require any additional MRI acquisitions, allowing for re-shimming immediately after any rotation.

Wednesday May 11th
  13:30 - 15:30 Computer 68

13:30 3803.   Towards reliable calibrated transducers for MR-guided focused ultrasound 
Tobias Klepsch1, Julian Haller1, Klaus-Vitold Jenderka1, Werner Hoffmann1, Bernd Ittermann1, and Frank Seifert1
1Physikalisch-Technische Bundesanstalt, Braunschweig und Berlin, Germany

High Intensity Focused Ultrasound (HIFU) guided by MR thermometry is a promising tumor therapy in organs such as liver, uterus and prostate. Although the technique is already clinical routine the calibrated measurement of high intensity ultrasound fields still needs closer examination. We present an approach towards finding a traceable calibration for MR guided focused ultrasound (MRgFUS) using a reference heating element. Furthermore we examined the focal zone of a commercial MR compatible transducer with MR thermometry at 3 tesla. This was done either for a fixed position or during translational movement of the transducer.

14:00 3804.   Characterization of a MRI-RF Hyperthermia Dual-Function Coil Element Design 
Xing Yang1, Jing Wu2, Xu Chu1, Thomas K Foo3, and Desmond Teck Beng Yeo3
1Power Conversion Circuits Lab, GE Global Research, Shanghai, China, People's Republic of, 2Electrical and Computer Engineering, Northeastern University, Boston, MA, United States, 3Imaging Technologies, GE Global Research, Niskayuna, NY, United States

During an RF hyperthermia procedure, careful monitoring of tissue temperature is required in the tumor and healthy tissue. The ability to perform targeted heating and monitor temperature with the same multi-channel coil allows for faster acquisition via parallel imaging, and potentially higher SNR due to the smaller elements placed closer to the body. In this study, a MRI-RF hyperthermia dual-function coil element design is proposed, and its working principle is presented along with numerically computed characterization data of the trade-offs involved when the key design parameters are varied. These parameters include antenna dimension, adjacent coil overlap area, inter-element coupling, and antenna phase shifts.

Seunghoon Ha1, Mark Jason Hamamura1, Werner W. Roeck1, and Orhan Nalcioglu1
1University of California Irvine, Irvine, California, United States

Synopsis: Many studies have indicated that preoperative MRI is useful in local staging for surgical planning, especially for patients with lobular cancer. However, the low specificity of MRI, despite its high sensitivity, may lead to many unnecessary biopsies or over-treatment. Scintimammography (SMM) can be a tool to supplement MRI for improving the diagnostic specificity in breast cancer imaging. In this study, a unilateral breast array coil and CZT detector module specialized for MR-SMM is introduced. The variation of RF coil performance due to assembly with a CZT detector module is discussed with results from simulation and experiment.

15:00 3806.   Simultaneous, Dynamic SPECT-MRI Demonstrated in Three Small-Animal Prototypes 
James W Hugg1, Benjamin M W. Tsui2, Orhan Nalcioglu3, Dirk Meier4, Mark J. Hamamura3, Douglas J. Wagenaar1, and Bradley E. Patt1
1Gamma Medica, Northridge, CA, United States, 2Johns Hopkins University, Baltimore, MD, United States, 3University of California, Irvine, CA, United States, 4Gamma Medica, Oslo, Norway

We have built and tested three SPECT prototypes that can be inserted into small-animal or whole-body MRI systems for simultaneous, dynamic imaging of mice and rats. We have measured and characterized the Hall Effect due to the Lorentz force in the MR-compatible CZT gamma photon detectors. Otherwise, the MR and SPECT systems do not significantly affect each other. We have demonstrated simultaneous, dynamic SPECT-MR imaging in mice. We are developing MR attenuation and scatter corrections and MR priors for quantitative SPECT reconstruction. Imaging a SPECT agent can provide a molecular imaging contrast for MR images at pico- to nano-molar sensitivities.

Thursday May 12th
  13:30 - 15:30 Computer 68

13:30 3807.   Radiation induced RF coil degradation in hybrid MRI-accelerator systems 
Sjoerd Crijns1, Bas Raaymakers1, Jan Kok1, Kimmy Smit1, Jan Van Ooijen2, and Jan Lagendijk1
1Radiotherapy, UMC Utrecht, Utrecht, Netherlands, 2Philips Medical Systems, Best, Netherlands

The radiation damage to an RF receiver coil as a function of accumulated dose in a hybrid MRI-accelerator is characterized. We conclude that damage per treated patient is small and that any problems with standard receiver coils are not to be expected.

Seunghoon Ha1, Mark Jason Hamamura1, Werner W. Roeck1, and Orhan Nalcioglu1
1University of California Irvine, Irvine, California, United States

In medical imaging, single-photon emission computed tomography (SPECT) can provide specific functional information while magnetic resonance imaging (MRI) can provide high-spatial resolution anatomical information as well as complementary functional information. However, some of the major problems facing MRSPECT systems include the degradation of the signal to noise ratio (SNR) and distortion of the MR image. In this study, we present a new RF coil design to retain the tremendous potential of MRSPECT to provide high sensitivity and specificity while minimizing the interference between the MRI and SPECT systems. This new RF coil, described in the study for small animal imaging, could be used with multiple ã-ray radiation shields to prevent MR image distortion and degradation of the SNR. Experimental results demonstrating the advantages of the new assembly are presented.

14:30 3809.   Real-time target displacement prediction using Dynamic MRI for radiotherapy 
Nilesh N Mistry1, Jiachen Zhuo2, Kathleen Malinowski1,3, Rao Gullapalli2, and Warren D D'Souza1
1Radiation Oncology, University of Maryland School of Medicine, Baltimore, MD, United States, 2Radiology, University of Maryland School of Medicine, Baltimore, MD, United States, 3Fischell Department of Bioengineering, University of Maryland, A. James Clark School of Engineering, College Park, MD, United States

Advanced radiation therapy delivery techniques have the potential to deliver the required doses to the tumor while minimizing the dose to healthy normal tissue. However, these advancements require highly conformal dose delivery and without effective motion management techniques such therapies can be sub-optimal. In this work we explore the feasibility of using cine-MRI images acquired in conjunction with the real-time external surrogates to assist in the development of a robust model for real-time tumor displacement prediction.

15:00 3810.   Ultra-low-field MRI system for hybrid MEG-MRI 
Panu Tapani Vesanen1, Juha Hassel2, Jari S Penttilä3, Jaakko Oskari Nieminen1, Juhani Dabek1, Koos Zevenhoven1, Juho Luomahaara2, Sarianna Alanko1, Nadia Catallo4, Fa-Hsuan Lin5, Juha Simola6, Antti Ahonen6, and Risto J Ilmoniemi1
1Dept. of Biomedical Engineering and Computational Science, Aalto University, Espoo, Finland, 2VTT Technical Research Centre of Finland, Espoo, Finland, 3Aivon Oy, Espoo, Finland, 4Dept. of Health Sciences, University of L’Aquila, Italy, 5Institute of Biomedical Engineering, National Taiwan University, Taiwan, 6Elekta Oy, Helsinki, Finland

In ultra-low-field MRI (ULF MRI), spins precess in microtesla magnetic fields, and the signal is measured by superconducting quantum interference devices (SQUIDs). Low fields offer several advantages compared to conventional MRI such as narrow line-widths, enhanced T1 contrast, imaging of objects in the presence of metal, and a possibility for simultaneous magnetoencephalography (MEG) measurement. In this work, we describe the current state of our multichannel ULF-MRI system. We present phantom images and discuss technical solutions for coil design in a magnetically shielded environment.

Electronic Posters : Engineering
Click on to view the abstract pdf and click on to view the video presentation.
Coils & Arrays for UHF MRI

Monday May 9th
Exhibition Hall  14:00 - 16:00 Computer 69

14:00 3811.   Remote Tuning and Matching an 8-Channel Transceive Array at 7T 
Carl Snyder1, Christopher Rogers2, Lance DelaBarre1, Mattew Robson2, and J. Thomas Vaughan1
1University of Minnesota, Minneapolis, MN, United States, 2Oxford University, Oxford, Oxfordshire, United Kingdom

Here an 8-channel transceive array was remotely tuned and matched using piezoelectric actuators; this process, can be automated by monitoring and reducing the standing wave ratio on the transmission line leading to the coil.

14:30 3812.   An Improved Constellation Coil 
Arslan Amjad1
1GE Healthcare, Waukesha, WI, United States

Parallel transmit multi-port volume coils are becoming important due to increased field strengths in order to improve B1+ homogeneity and to minimize Specific Absorption Rate (SAR). Y. Zhu introduced a design for a parallel transmit volume coil, “constellation coil” that does not require tuning and is scalable to various field strengths. In this work, we have introduced a modified constellation coil that improves the B1+ homogeneity of Zhu’s design, and makes the B1+ profile similar to the birdcage structure.

15:00 3813.   A Full-Wavelength Dipole RF Coil Element for 7 T MRI with Maximized Longitudinal FOV and Two-Peak SAR Distribution 
Andreas Rennings1, A. Litinsky1, P. Schneider1, S. Orzada2, and S. Otto3
1General and Theoretical Electrical Engineering (ATE), Faculty of Engineering, University of Duisburg-Essen, 47048 Duisburg, Germany, 2Erwin L. Hahn Institute for Magnetic Resonance Imaging, University of Duisburg-Essen, 45141 Essen, Germany, 3High-Frequency Engineering (HFT), Faculty of Engineering, University of Duisburg-Essen, 47048 Duisburg, Germany
A novel RF coil element for 7 T is proposed. It is based on a recently published symmetrically fed dipole element with meander termination for better decoupling. The novel full-wavelength dipole offers two distinct improvements – an RF field of view that is maximized due to the longer extent and a lowered peak SAR-10g due to a more appropriate two-peak electric field distribution.

15:30 3814.   Novel 24 Element Multi-Transmit Volume Coil for High Field MRI 
Can Akgun1, Hyoungsuk Yoo2, Lance DelaBarre1, Carl J Snyder1, Gregor Adriany1, Pierre-Francois Van de Moortele1, Anand Gopinath3, Kamil Ugurbil1, and John Thomas Vaughan1
1Center for Magnetic Resonance Imaging, University of MInnesota, Minneapolis, MN, United States, 2Department of Biomedical Engineering, School of Electrical Engineering, University of Ulsan, Ulsan, Korea, Republic of, 3Department of Electrical and Computer Engineering, University of Minnesota, Minneapolis, MN, United States

At vert high field strengths multi-element RF transmit coils have been shown to benefit applications such as RF shimming and parallel transmission. In this work we present a 24 element TEM volume coil strategy that is as RF efficient as a traditional TEM volume coil. Simulation studies are performed at 7 T.

Tuesday May 10th
  13:30 - 15:30 Computer 69

13:30 3815.   Stepped Impedance Resonators for High Field MRI 
Can Akgun1, Lance DelaBarre1, Hyoungsuk Yoo2, Carl J Snyder1, Anand Gopinath3, Kamil Ugurbil1, and John Thomas Vaughan1
1Center for Magnetic Resonance Imaging, University of MInnesota, Minneapolis, MN, United States, 2Department of Biomedical Engineering, School of Electrical Engineering, University of Ulsan, Ulsan, Korea, Republic of, 3Department of Electrical and Computer Engineering, University of Minnesota, Minneapolis, MN, United States

Since its inception in high field MRI volume coils, there have been very few modifications of the traditional microstrip transmission line for optimal performance. In this study, two different microstrip designs with varying impedance lines referred to as stepped impedance resonators (SIRs) are presented. A 3-section SIR can be designed to produce a peak B1+ in the center, while a 7-section SIR can be designed to limit SAR effects when compared to the traditional microstrip resonator. Imaging and simulation results for 8 element volume coils with these designs are obtained at 7T for the human head.

14:00 3816.   Clinical neuroimaging using high dielectric materials at 7T 
Wouter M Teeuwisse1, Nadine B Smith1, and Andrew G Webb1
1Radiology, Leiden University Medical Center, Leiden, Netherlands

High dielectric materials based on calcium titanate suspensions in deuterated media can significantly improve clinically relevant scans at 7 Tesla with essentially zero background signal. Increases in the transmit field of up to 100% are measured in the cerebellum and temporal lobes. T1-weighted, FLAIR and especially T2-weighted scans show increased signal-to-noise and tissue contrast with thin dielectric pads surrounding the head.

14:30 3817.   Abdominal Imaging at 7T with a 32-channel Body Array Coil - Initial Results 
Jochen Leupold1, Florian Meise2, Matt Finnerty3, Tsinghua Zheng3, Jürgen Hennig1, and Michael Bock2
1Dept. of Radiology, Medical Physics, University Medical Center, Freiburg, Germany, 2Abt. Medizinische Physik in der Radiologie, Deutsches Krebsforschungszentrum, Heidelberg, Germany, 3Quality Electrodynamics (QED), Mayfield Village, OH, United States

Application of ultrahighfield-MR (UHF-MR) at 7T on humans is currently mainly limited to the brain due to the expected strong inhomogeneity of the B1-field in the body and abdomen. We present first results of a 7T transmit/receive body coil array, which has been designed as an array of multiple small coil elements with the goal to minimize coil induced B1-inhomogeneities.

15:00 3818.   30 channel unilateral breast coil for ultra high resolution MRI at 7T 
Ingmar Jacob Voogt1, Bart L van de Bank1, Peter R Luijten1, Dennis W Klomp1, Michel Italiaander1, and Rudy Roon1
1Radiology, UMC Utrecht, Utrecht, Utrecht, Netherlands

The specificity in dynamic contrast enhanced MRI in breast cancer may be increased by enabling the simultaneous detection of high morphological details. Therefore the high sensitivity of 7T is used to obtain sufficient SNR in the high spatial resolution that needs to be obtained within the time frame of contrast enhancement time curves. Therefore a 30 channel dedicated unilateral breast coil was designed for 7T that enables high acceleration while maintaining SNR.

Wednesday May 11th
  13:30 - 15:30 Computer 69

13:30 3819.   A 7-Tesla High Density Tx/Rx Mammography Coil 
Tsinghua Zheng1, Xiaoyu Yang1, Matthew Finnerty1, Jeremiah Heilman1, Joseph Herczak1, Hiroyuki Fujita1,2, Graham Wiggins3, Ryan Brown3, and Bernd Stoeckel4
1Quality Electrodynamics, LLC, Mayfield Village, Ohio, United States, 2Physics, Case Western Reserve University, Cleveland, Ohio, United States, 3Radiology, NYU Langone Medical Center, New York, New York, United States, 46Siemens Medical Solutions USA, Inc, Malvern, Pennsylvania, United States

We have constructed a7T transmit-and-16-channel receive array breast coil for Siemens Magnetom 7T scanner. Comparison of in vivo volunteer images with a commercially available 4 channel breast array coil at 3T showed significant advantage of the 7T breast array coil with its ultra high spatial resolution, which is critical to the early breast cancer detection.

14:00 3820.   A Prototype Head Coil for 11.7T using the Inductive Birdcage Geometry 
Joseph Murphy-Boesch1, Stephen Dodd1, Peter van Gelderen1, Alan Koretsky1, and Josef H. Duyn1
1LFMI/NINDS, National Institutes of Health, Bethesda, MD, United States

A shielded inductive resonator configured as a backward-wave transmission structure has been designed for use as a transmit/receive head coil at 11.7 Tesla. Transmission line analysis and a four-element distributed impedance model have been used to optimize the design for high-frequency. A prototype coil constructed with these methods displays a homogeneous mode in excess of 500 MHz. The coil frequencies are in good agreement with the model, and an axial field plot of the unloaded coil shows good field uniformity at mid-elevation.

14:30 3821.   A Flexible Microstrip Transceiver Coil for Imaging Flexed Human Knee Joints at 7 Tesla 
Karupppasamy Subburaj1, Yong Pang1, Serena Scott1, Bagrat Amirbekian1, Richard B Souza1,2, Sharmila Majumdar1, and Xiaoliang Zhang1
1Department of Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, California, United States, 2Department of Physical Therapy and Rehabilitation Science, University of California San Francisco, San Francisco, California

Traditional cylindrical knee coils designs present difficulties when imaging flexed knee joints in kinematic studies. We present a novel flexible TR coil based on microstrip transmission lines for in-vivo MR imaging of flexed human knee joints at 7T. This single channel coil was designed to have wing shaped symmetrical loops on a partially foldable teflon substrate to take advantage of 2nd harmonic resonance and a large coverage volume. The coil has a good Q factor ratio and the resonant frequency can be tuned to a broad range in order to adapt to various knee sizes.

15:00 3822.   Radio-Frequency Heating in Swine with an 8 Channel, 7 T (296 MHz) Head Coil 
Devashish Shrivastava1, Jeramy Kulesa1, Jinfeng Tian1, Gregor Adriany1, Lance DelaBarre1, and J T Vaughan1
1CMRR, University of Minnesota, Minneapolis, MN, United States

Radio-frequency (RF) heating was fluoroptically measured in the scalp; 5 mm, 10 mm, 15 mm, 20 mm, and 25 mm in the brain; and rectum in three anesthetized swine due to a continuous wave power deposition with a 7T head coil at the average whole head SAR of 2.94 W/kg. The RF heating was simulated using the new, theoretical generic bioheat transfer model (GBHTM) and the empirical Pennes’ bioheat transfer equation (BHTE). The average temperature change in the brain was 2.1 0C after 3 hours of the power deposition. The GBHTM simulated RF heating more accurately than the Pennes’ BHTE.

Thursday May 12th
  13:30 - 15:30 Computer 69

13:30 3823.   A Loop Coil Design Based on the Broadside-Coupled Split Ring Resonator at 7T 
Marcos Alonso Lopez Terrones1, Gunthard Lykowsky2, Jose Miguel Algarín1, Manuel J. Freire1, Maria Castillo Velazquez-Ahumada1, Peter M. Jakob2,3, and Ricardo Marques1
1Electronics and Electromagnetism, University of Seville, Seville, Andalucia, Spain, 2Research Center Magnetice Resonance Bavaria, Würzburg, Bavaria, Germany,3Experimental Physics 5, University of Würzburg, Würzburg, Bavaria, Germany

In the design of coils, it is required a uniform current distribution in the loop to generate a homogeneous magnetic field. In the broad-side coupled split ring resonator (BC-SRR) design, the sum of the currents flowing in the two rings is constant so that the field produced is homogeneous. A BC-SRR and two conventional loops were simulated and built at 7T. In the design of loops with distributed capacitance, it is not necessary to split the ring in several gaps. The total current flowing in the two loops of the BC-SRR design is constant independently of the number of gaps

14:00 3824.   A radiofrequency coil configuration for imaging the human vertebral column at 7 Tesla 
Maartje E Vossen1, Wouter M Teeuwisse1, Monique Reijnierse1, Nadine B Smith1, Chris M Collins2, and Andrew G Webb1
1Radiology, Leiden University Medical Center, Leiden, Netherlands, 2Radiology, Hershey Medical College

A quadrature transmit, eight-channel receive array RF coil configuration was designed for the acquisition of images of the entire human spinal column at 7 Tesla. RF transmission through the anterior part of the body was shown using electromagnetic simulations to be more efficient in terms of B1+ to SAR ratio than through the posterior side. Using this coil geometry, high resolution images from healthy volunteers could be acquired in clinically acceptable imaging times.

14:30 3825.   A 15-Channel receive array and 16 channel detunable transmit coil for human brain imaging at 9.4T 
G Shajan1, Jens Hoffmann1, and Rolf Pohmann1
1Magnetic Resonance Center, Max Planck Institute for Biological Cybernetics, Tuebingen, Baden Wuttenberg, Germany

Even more than at 7 T, constructive and destructive interferences cause strong inhomogeneities of the B1 field produced by a volume coil, causing shading over large parts of the image. In this study at 9.4T, we present initial results from a 16-channel actively detunable transmit array combined with a 15 element receive only array. In addition to the high sensitivity offered by the receive array, transmit field inhomogeneities can be significantly reduced by RF shimming methods for whole brain coverage at 9.4T.

15:00 3826.   Electrically auto-tuned RF coil design 
Sung-Min Sohn1, Anand Gopinath1, and J. Thomas Vaughan1,2
1Electrical and Computer Engineering, University of Minnesota, Minneapolis, Minnesota, United States, 2Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, United States

RF coil based on microstip transmission lines, the TEM coil, has been widely used for high-field MRI and has narrow bandwidth due to its high quality factor (Q). Although high Signal-to-Noise Ratio (SNR) of MR coils is obtained from this property it has a critical drawback, human body (loading) effect that causes the resonance frequency and Q of RF coil to change when different human bodies are loaded. This work proposes an adaptive impedance matching technique to avoid mismatch of the RF loaded coils at the Larmor frequency and alternative manual tuning that needs a several minutes and remains a major obstacle to the use of TEM coils in ultra-high-fields MRI systems.