SAR & Safety

                  1441.     Evaluation of Maximum Local SAR for Parallel Transmission (PTx) Pulses Based on Pre-Calculated Field Data Using a Selected Subset of "Virtual Observation Points"

Matthias Gebhardt¹, Dirk Diehl², Elfar Adalsteinsson³, Lawrence L. Wald⁴, Gabriele Eichfelder⁵

¹Siemens Healthcare, Erlangen, Germany; ²Siemens Corporate Technology, Erlangen, Germany; ³Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, MA, United States; ⁴Martinos Center for Biomedical Imaging, Harvard University, Charlestown, MA, United States; ⁵Applied Mathematics II, University of Erlangen-Nuremberg, Erlangen, Germany

This work addresses the complexity problem inherent in local SAR estimation for parallel transmission (pTx)  and shows that a relatively small subset of carefully selected “virtual observation points” is adequate for prediction and control of maximum local SAR in pTx. We tested the proposed algorithm to detect local SAR maxima by comparison with an exhaustive search over local SAR distribution in numerical simulations of adult male and female subjects for  an 8 channel whole body transmit array. The proposed method of model compression for local SAR successfully captured regions of local SAR maxima, but with dramatically reduced computation cost.

                  1442.     Safety of 17O and 23Na MR Imaging of the Human Brain at 9.4 Tesla

Ian C. Atkinson¹, Rachel Sonstegaard¹, Lilian Bityou², Neil H. Pliskin², Keith R. Thulborn¹

¹Center for MR Research, University of Illinois- Chicago, Chicago, IL, United States; ²Psychiatry, University of Illinois- Chicago, Chicago, IL, United States

Current FDA guidelines classify MR devices operating at 8 Tesla or lower as insignificant risk.   Vital sign and cognitive performance data supporting the safety of performing non-proton MR imaging of the human brain at 9.4 Tesla are presented.  These data add to the growing body of results that suggest ultra-high field MR imaging can be safely performed up to 9.4 Tesla.

                  1443.     Experimental Setup with a Whole-Body Resonator for Investigating Thresholds of Tissue Damage in Swine Model Exposed at 123 MHz – First Measurement Results

Gerhard Brinker¹, Christian Grosse-Siestrup², Chie Hee Cho², Katja Reiter², Katherina Habekost², Peter Wust², Razvan Lazar¹, Franz Hebrank¹, Eckart Stetter¹, Jacek Nadobny²

¹Siemens Healthcare, Erlangen, Germany; ²Campus Virchow Klinikum, Charité, Berlin, Germany

The SAR limits issued by IEC 60601-2-33 are to some extent unbalanced comparing the whole body SAR limit with the local SAR limit. In order to examine thresholds of tissue damage a measurement setup consisting by the Tx path components of a clinical 3T MR scanner is established. Initial results of RF exposure on dead swine (6.5 W/kg, 30 minutes) are presented. Temperature increments are measured at the hot spot locations both invasively in tissue as well as superficially using infrared camera. The experimental results correspond very well with results of simulation using realistic 3D-voxel model of a swine

                  1444.     Influence of a Receive-Array Coil on Specific Absorption Rate at 3T: Simulations and Experiments with Basic Geometries

Sukhoon Oh¹, Yeun Chul Ryu¹, Zhangwei Wang², Fraser Robb², Christopher M. Collins¹

¹PSU College of Medicine, Hershey, PA, United States; ²GE Healthcare, Aurora, OH, United States

Influence of a receive array and failure of its detuning circuit on specific absorption rate (SAR) is investigated with simulations and experiments at 3T. A simple array of two copper loops was placed around an agar-gel phantom. A gap in the circuit was placed and removed to simulate perfect and defective detuning conditions, respectively. In simulations, addition of the ¡°decoupled¡± array resulted in only a 3% higher average SAR than with no array present, whereas with the ¡°defective¡± circuit, an increase of 41% was observed. Trends in the SAR distributions between the different cases are similar in experiment and calculation.

                  1445.     Effects of Simplifying Rf Coil 3-D EM Simulation Models on Power Balance and SAR

Mikhail Kozlov¹, Robert Turner

¹Neurophysics, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Sachsen, Germany

We have investigated the effect on power balance and SAR of simplifying rf coil 3-D EM simulation models, using co-simulation of the RF circuit and 3-D EM fields. We find that sufficiently accurate SAR and power balance estimation cannot be achieved for actual coils using simplified coil models and any renormalization approach. Simulations must converge by mesh refinement not only for B1+ values, but also for radiated and load absorbed powers, and must include simulation of the scanner gradient shield. The effect on SAR of distance to absorbing boundaries and gradient shield depends strongly on RF coil design. Thus coils and their environment need to be specified as accurately as possible, much better than current common practice.  If simulation fails to give the correct power balance it is pointless to calculate SAR.  In their current implementations, the Ansoft HFSS frequency domain solver provides much more reliable data, and much faster, than the CST time domain solver.

                  1446.     Patch Antenna in Comparison to and in Combination with a Volume Coil for Excitation at 7T: Whole-Brain B1 Shimming and Consequent SAR

Chien-ping Kao¹, Zhipeng Cao¹, Sukhoon Oh¹, Yeun Chul Ryu¹, Christopher M. Collins¹

¹PSU College of Medicine, Hershey, PA, United States

Here we compare the homogeneity in whole-brain excitation that can be achieved with two adjustable transmit channels used to drive a patch antenna and to drive a body array with elements combined as to form two orthogonal mode 1 field patterns. Optimal whole-brain homogeneity achievable with B1 shimming and the resulting SAR is examined for the two approaches separately and combined. Combining the patch and the body array results in appreciable better achievable whole-brain homogeneity with significantly lower average and maximum local SAR than possible with either the patch antenna or body coil alone.

                  1447.     Comprehensive Numerical Study of 7T Transmit-Only, Receive-Only Array Coils

Mikhail Kozlov¹, Robert Turner¹

¹Neurophysics, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Sachsen, Germany

We present a reliable and fast workflow for comprehensive joint numerical study of 7T transmit-only, receive-only RF coils as complete devices. The flexibility of the workflow allows inclusion of almost all the RF and DC components used for tune/de-tune/match/decoupling. The S-parameter data and B1+ and B1- profiles obtained for a family of loop-based 8-channel TX-only, 8-channel RX-only coils allow estimation of the required impedance of de-tuning circuits.

                  1448.     Fast SAR Estimation Via a Hybrid Approach

Shumin Wang¹, Jeff H. Duyn¹

¹LFMI/NINDS/NIH, Bethesda, Center Dr. , United States

Estimation of local specific absorption rate (SAR) is a major challenge in high-field (>3.0 Tesla) multi-channel transmission systems. Conventional Finite-Difference Time-Domain (FDTD) method is often found inefficient to give subject-specific results. Recent studies sped up the process by applying Ampere’s law to obtain electrical field distributions via measured transverse B1 fields. The drawback is that only the longitudinal electrical fields can be calculated, which may yield large discrepancy. We present a fast numerical approach by calculating all three components of magnetic field by an integral-equation method and obtain the electric fields by Ampere’s law subsequently. Combined with fast subject modeling, this method may provide a viable approach for subject-specific SAR estimations.

                  1449.     Parallelized Algorithm for the Computation of N-Gram Specific Absorption Rate (SAR) on a Graphics Processor

Lohith Kini¹, Matthias Gebhardt², Khaldoun Makhoul³, Lawrence L. Wald^3,4, Elfar Adalsteinsson^1,4

¹EECS, Massachusetts Institute of Technology, Cambridge, MA, United States; ²Siemens Medical Solutions, Erlangen, Germany; ³MGH, Harvard Medical School, A. A. Martinos Center for Biomedical Imaging, Charlestown, MA, United States; ⁴Harvard-MIT Division of Health Sciences and Technology, MIT, Cambridge, MA, United States

Specific Absorption Rate (SAR) is a major concern in parallel transmission. Calculating the average N-gram SAR arising at each spatial location is a computationally intractable problem. We propose and demonstrate improvements to a recent algorithm, the fast region-growth algorithm, and exploit its parallelizable computation structure by implementing it on a commercial graphics card. This algorithm is up to 4-7 times faster in runtime regardless of model resolution and number of RF pulse time samples while maintaining accuracy with the fast region-growth algorithm.

                  1450.     Fast GPU FDTD Calculations: Towards Online SAR and B1+ Assessment and Control

Davi Correia¹, Astrid van Lier², Martijn de Greef¹, Henny Petra Kok¹, Johannes Crezee¹, Cornelis Antonius Theodorus van den Berg²

¹Academic Medical Center, Amsterdam, Noord Holland, Netherlands; ²University Medical Center, Utrecht, Netherlands

We present a novel implementation of the FDTD method on a graphics card and how the possibility of simulating SAR during an MRI procedure. It is now possible to simulate the electromagnetics fields distribution in minutes or even in seconds, depending on the resolution.

                  1451.     Local SAR in High Pass Birdcage and TEM Body Coils for Human Body Models at 3T

Desmond Teck Beng Yeo¹, Zhangwei Wang², Wolfgang Loew³, Mika Vogel³, Ileana Hancu¹

¹GE Global Research, Niskayuna, NY, United States; ²GE Healthcare Coils, Aurora, OH, United States; ³GE Global Research, Munich, Germany

The high pass birdcage body coil is commonly used in MRI for homogeneous excitation while the transverse electromagnetic volume coil is increasing used in high-field parallel transmit systems. In this work, the numerically computed normalized local SAR of four human body models, placed at three clinically relevant landmark positions, were compared for a 16-rung high-pass birdcage coil and a TEM body coil at 3T. Results show that while high local SAR may be predicted under certain conditions, any comparative generalizations of local SAR between these coils are untenable unless validated with a diverse set of human models at key landmark positions.

                  1452.     Evaluation of E-Field Distributions in Parallel Transmit Systems by Time-Domain Optical Electric-Field Sensors

Frank Seifert¹, Tomasz Dawid Lindel¹, Peter Ullmann²

¹Physikalisch-Technische Bundesanstalt (PTB), Abbestr. 2-12, D-10587 Berlin, Germany; ²Bruker BioSpin MRI GmbH, Ettlingen, Germany

Ensuring RF safety is crucial for parallel transmit MRI. During parallel transmission the E-field distributions inside and outside the body exhibit a complex time evolution which cannot be covered by calorimetric SAR measurements. We introduce an optical electric field sensor (OEFS) to map non-stationary E-fields during parallel transmit MRI. We tested a customized OEFS system for certain static phase settings of a 4-channel transmit array. Our measurements confirmed a pathologic single hot-spot SAR-distribution as expected from FDTD simulations. In conclusion, the featured OEFS is an appropriate tool to identify possible safety issues of parallel transmit technologies.

                  1453.     Flip Angle and SAR Maps Induced by a Head Displacement in Parallel Transmission and with Cartesian Feedback

Nicolas Boulant¹, Martijn Cloos¹, Alexis Amadon¹, Guillaume Ferrand², Michel Luong², Christopher Wiggins¹, Denis Le Bihan¹, David Ian Hoult³

¹NeuroSpin, CEA, Gif sur Yvette, France; ²Irfu, CEA, Gif sur Yvette, France; ³Institute for Biodiagnostics, National Research Council, Winnipeg, MB, Canada

Despite the considerable variations one can observe in peak local SAR among all possible driving configurations of a Tx-array, the question of how robust both SAR and flip angle distributions are with respect to small perturbations remains. A head displacement for instance not only changes the solutions of Maxwell’s equations but also the tuning of the coils. Now Cartesian feedback has been proposed as a solution to the latter problem. We therefore present the results of simulations showing the effects of small rotations of the head upon the flip angle and SAR with and without Cartesian feedback being applied.

                  1454.     Real Time RF Power Prediction of  Parallel Transmission RF Pulse Design at 7T

Cem Murat Deniz^1,2, Leeor Alon^1,2, Ryan Brown¹, Hans-Peter Fautz³, Daniel K. Sodickson¹, Yudong Zhu¹

¹Center for Biomedical Imaging, Department of Radiology, NYU School of Medicine, New York, NY, United States; ²Sackler Institute of Graduate Biomedical Sciences, NYU School of Medicine, New York, NY, United States; ³Siemens Medical Solutions, Erlangen, Germany

Prediction of parallel transmission RF pulse power deposition into a patient is one of the principal challenges at ultra-high field magnetic strength.  We introduced real time calibration system to predict the net power consequences of the parallel transmission RF pulse design before employing designed RF pulses into scanner. High accuracy was achieved in the  power deposition estimation of designed RF pulses with respect to actual net power measurements.

                  1455.     Development of an Anatomical Accurate Porcine Head Model to Study Radiofrequency Heating Due to MRI

Devashish Shrivastava¹, J Thomas Vaughan

¹CMRR, Radiology, University of Minnesota, Minneapolis, MN, United States

An anatomically accurate porcine head model was developed. The model was developed to help validate the temperature predictions of bioheat equations against direct in vivo fluoroptic measurements and predict non-uniform brain RF heating in swine and humans wearing/not-wearing implantable, conductive medical devices for a variety of field strengths, coil configurations, and head loading positions. The head model was developed by obtaining high resolution images of a porcine head using a Siemens 3T Trio (1.02 mm X 1.02 mm X 1.00 mm, Sequence type: T1MPRAGE) and manually segmenting the brain, cerebral spinal fluid, bone, cartilage, muscle, and air-cavity using MIMICS.

                  1456.     An MRI Simulator for Effects of Realistic Field Distributions and Pulse Sequences, Including SAR and Noise Correlation for Array Coils

Zhipeng Cao¹, Christopher T. Sica¹, Sukhoon Oh¹, John McGarrity¹, Timothy Horan¹, Bu Sik Park¹, Christopher M. Collins¹

¹PSU College of Medicine, Hershey, PA, United States

We present a Bloch-based MRI simulator that considers desired sample, field distributions (B0, B1, E1, Gx, Gy, Gz) and pulse sequence for determining effects of field distributions on images (including noise correlation) and SAR. The software is provided with a few basic libraries for simulation of head and body in 8-element transceiver arrays at 3T and 7T and a GUI for designing and executing some simple pulse sequences, but structure of input files is intentionally simple so users can generate their own sample, field distributions, and sequence files. Many fundamental capabilities are demonstrated.

                  1457.     MRI Acoustic Noise Can Harm Research and Companion Animals

Amanda M. Lauer¹, Abdelmonem M. El-Sharkawy², Dara L. Kraitchman², William A. Edelstein²

¹Otolaryngology-HNS, Johns Hopkins School of Medicine, Baltimore, MD, United States; ²Radiology/MRI Division, Johns Hopkins School of Medicine, Baltimore, MD, United States

Vertebrate animal MRI is an important part of medical research, and veterinary MRI imaging of companion animals is increasing. Human subjects are generally provided with hearing protection against the loud, potentially damaging acoustic noise produced by MRI scanners; this is generally not done for animal MRI subjects. Hearing damage can interfere with research functions for research animals or quality of life for companion animals. We compare typical MRI noise levels to animal hearing thresholds and conclude that MRI exposes many animals to levels of noise and duration that would exceed NIOSH limits for human exposure.

                  1458.     Subjective Acceptance of Ultra-High-Field MR Imaging at 7T in 573 Volunteers

Christina Heilmaier^1,2, Jens M. Theysohn^1,2, Stefan Maderwald^1,2, Oliver Kraff^1,2, Lale Umutlu^1,2, Mark E. Ladd^1,2, Susanne C. Ladd^1,2

¹Department of Diagnostic and Interventional Radiology and Neuroradiology, University Hospital Essen, Essen, NRW, Germany; ²Erwin L. Hahn-Institute for Magnetic Resonance Imaging, Essen, NRW, Germany

Subjective acceptance of ultra-high-field MRI has not been evaluated in larger study groups yet. For this purpose, 573 volunteers underwent a 7T examination and were afterwards asked about sensations and side effects. Analysis revealed an overall high subjective acceptance of 7T examinations with mainly non-specific factors such as unpleasant room temperature, little contact to the staff or noise being criticized. Compared to 1.5T volunteers described considerably more often nausea or a metallic taste on 7T; however, the average degree of these effects was very low. Volunteers lying ”head first” expressed more complaints than those lying “feet first”.

                  1459.     Dynamic Slew Rate Pulse (DSRP) for PNS Alleviation

Yongchuan Lai¹

¹GE healthcare, Beijing, China

In this study, a new gradient pulse, Dynamic Slew Rate Pulse (DSRP), is designed to reduce peripheral nerve stimulation (PNS). Compared with traditional trapezoid pulse, DSRP¡¯s pulse width is much smaller when dB/dt limitation is dominant.

                  1460.     Exposure Measurements on MR-Workers at the Stray Field of 1.5T, 3T, and 7T MR Systems

Jens Groebner¹, Reiner Umathum², Michael Bock², Wolfhard Semmler², Jaane Rauschenberg²

¹Medical Physics in Radiology , German Cancer Research Center, Heidelberg, Germany; ²Medical Physics in Radiology, German Cancer Research Center, Heidelberg, Germany

Due to the insufficient experimental data on static magnetic field exposure and new ICNIRP limitations an exposure measurement instrument was developed. With the new probe actual B₀ and time varying magnetic fields due to movement in the stray field can be detected simultaneously. Therefore, personal exposure of 10 healthcare workers and MR physicists during normal operating procedures could be determined. Peak exposure limits are exceeded during all procedures.

                  1461.     Physical Simulation Study of Active Noise Control Up to 5 KHz

Rudd W. Bernie¹, Li Mingfeng¹, Teik C. Lim¹, Jing-Huei Lee²

¹Mechanical Engineering, University of Cincinnati; ²Biomedical Engineering, University of Cincinnati, Cincinnati, OH, United States

We demonstrate that active noise control (ANC) is feasible to treat MRI noises at frequencies greater than 2 KHz. Several MRI scan noise and gradient signals were recorded and replayed in a sound quality chamber to simulate the MRI environment. A dummy “wore” headphones containing piezoceramic speakers with condenser microphones installed inside and outside the earpiece to measure the environmental sound in the immediate patient vicinity. During the simulation study, the sound pressure level (SPL) was measured, both with and without the ANC. Results presented show the ANC system attained significant SPL reduction at all frequencies up to 5 kHz.

                  1462.     Dental MRI: Compatibility of Dental Materials

Olga Tymofiyeva¹, Sven Vaegler¹, Kurt Rottner², Julian Boldt², Peter Christian Proff³, Ernst-Juergen Richter², Peter Michael Jakob¹

¹Dept. of Experimental Physics 5, University of Wuerzburg, Wuerzburg, Bavaria, Germany; ²Dept. of Prosthodontics, Dental School, University of Wuerzburg, Wuerzburg, Germany; ³Dept. of Orthodontics, Dental School, University of Regensburg, Regensburg, Germany

Recently, new approaches for application of MRI in various branches of dentistry have been proposed. Dental materials present in the subject’s mouth pose a major concern for dental applications of MRI. Partly contradictory results have been reported regarding the severity of image artifacts caused by different dental materials, usually without consideration of dental applications of MRI. This paper provides classification of standard dental materials from the standpoint of dental MRI, and can serve as a guideline in future dental MRI research.

                  1463.     De-Fibrillation in an MRI Environment

Gene Payne^1,2, Sathya Vijayakumar^1,2, Eugene Kholmovski^1,2, Jayne Davis³, Josh Blauer, ^2,4, Chris Gloschat, ^2,4, Kimberly Lilbok⁵, Rob MacLeod, ^3,4, Dennis Parker^1,2, Nassir F. Marrouche⁵

¹UCAIR, Department of Radiology, University of Utah, Salt Lake City, UT, United States; ²CARMA Center, University of Utah, Salt Lake City, UT, United States; ³CVRTI, University of Utah, Salt Lake City, UT, United States; ⁴Dept. of Biomedical Engineering, University of Utah, Salt Lake City, UT, United States; ⁵Dept. of Cardiology, University of Utah, Salt Lake City, UT, United States

While imaging subjects in an MRI scanner, it may sometimes be necessary to de-fibrillate in order to restore sinus rhythm or resuscitate. Normal de-fibrillator equipment is incompatible with the scanner's magnetic field. Presented is a procedure for de-fibrillating inside the MRI environment. With this procedure, the defibrillator unit was located outside the MRI environment, with select non-ferrous equipment inside and on the subject. This procedure was employed on four separate occasions with an animal subject on the scanner table, and was found to be successful. No problems or safety concerns were observed.

                  1464.     A Simple Cost-Efficient Magneto Alert Sensor (MALSE) Against Static Magnetic Fields

Tobias Frauenrath¹, Wolfgang Renz², Thoralf Niendorf^1,3

¹Berlin Ultrahigh Field Facility, Max-Delbrueck Center for Molecular Medicine, Berlin, Germany; ²Siemens Medical Solutions, Erlangen, Germany; ³Experimental and Clinical Research Center (ECRC), Charité Campus Buch, Humboldt-University, Berlin, Germany

While MR is a diagnostic imaging tool which saves lives, magnetic forces of fringe magnetic field components of MR systems on ferromagnetic components can impose a severe occupational health and safety hazard. With the advent of ultrahigh field MR Systems – including passively shielded magnet versions – this risk - commonly known as missile effect /1/ - is pronounced. Numerous accidents have been reported ranging from mechanical damage to patient death. These casualties are probably most widely known through television documentaries and printed media but still present the tip of the iceberg of safety violations (/2/ /3/ /4/). Various policies have been implemented around the world to safeguard healthcare workers, volunteers and patients with the ultimate goal of avoiding unforeseen disasters and injuries.

Transmit Array Control

                  1465.     Tuning the Output Impedance of RF Power Amplifiers with Frequency-Offset Cartesian Feedback

Marta Gaia Zanchi¹, Pascal Stang¹, John Mark Pauly¹, Greig Cameron Scott¹

¹Electrical Engineering, Stanford University, Stanford, CA, United States

We present a method and system based on Frequency Offset Cartesian feedback (FOCF) to electronically manipulate the output impedance of the RF power amplifiers for MRI transmitter arrays. In comparison to other methods, the output impedance synthesized by FOCF can have any value within a large area of the Smith chart, is stable over the power range, and does not hamper the amplifier efficiency. Through simulations and measurements, we demonstrate the ability to predictably manipulate the output impedance of a power amplifier near 64 MHz from very low to very high values.

                  1466.     On Stability and Performance of Frequency-Offset Cartesian Feedback for RF Power Amplifiers of MRI Transmitter Arrays

Marta Gaia Zanchi¹, Pascal Stang¹, John Mark Pauly¹, Greig Cameron Scott¹

¹Electrical Engineering, Stanford University, Stanford, CA, United States

Frequency Offset Cartesian feedback (FOCF) has been proposed to deal with the challenges associated with control of the RF transmission fields in arrays of coils. Critical milestones in the development of a FOCF system are to guarantee that stability exist—and can be found automatically—up to the full rated power of the RF amplifier, and to measure the increased performance of the amplifier for several control variables. In this work, we present the hardware and simulation methods developed to characterize and study stability and performance of our system, as well as the results of these milestone tests.

                  1467.     Investigation Non-Magnetic Amplifiers Applied in an MRI System

Xing Yang¹, Xu Chu², Tingting Song², Thomas K Foo³, Desmond Teck Beng Yeo³

¹GE Global Research Center , Shanghai, China; ²GE Global Research Center, Shanghai, China; ³GE Global Research Center, Niskayuna, NY, United States

Power loss saving and cost reduction can be achieved by placing the RF amplifiers near the magnet directly. This will requires that the amplifiers are compatible within a high magnetic field environment. In this study, a 1 kW (peak power) non-magnetic amplifier module was designed and constructed. The impact of the B0 field on the non-magnetic amplifier and the effect of non-magnetic amplifier on the performance of the system were investigated. The experimental results indicated that, at 3T, the magnetic field had no notable impact on the MOSFET behavior. Similarly, the non-magnetic amplifier had no appreciable impact on image quality.

                  1468.     An Automated Cartesian Feedback Transceiver for Use in High Magnetic Fields

David Ian Hoult¹, Glen Kolansky¹, Derek Foreman¹, John Rendell¹, Mikhail Barklon¹, Karl Edler¹, Lawrence Ryner¹, Denis Le Bihan²

¹Institute for Biodiagnostics, National Research Council Canada, Winnipeg, Manitoba, Canada; ²Commissariat à l'énergie atomique, NeuroSpin, Gif-sur-Yvette, France

Magnetic resonance has been performed at 123.2 MHz with an automated Cartesian feedback instrument immersed in ~ 2 T field. No change of electronic characteristics was observed upon field immersion. With a probe having a loaded Q-factor of 20, 40 dB current blocking with a 500 W RF power amplifier was obtained over a bandwidth of 20 kHz. A rectangular high power RF pulse exhibited no visible droop or phase change, while a ramp pulse exhibited no visible non-linearity or phase change.  In signal reception over 160 kHz, current blocking of 40 dB was observed, a performance previously unattainable.

B1 Mitigation Methods

                  1469.     Point-Spread-Functions for RF Imaging with TRASE: Implications for Phase Gradient Coil Design and Flip Angle Calibration

Jonathan C. Sharp¹, Donghui Yin², Boguslaw Tomanek¹, Scott B. King²

¹Institute for Biodiagnostics (West), National Research Council of Canada, Calgary, AB, Canada; ²Institute for Biodiagnostics, National Research Council of Canada, Winnipeg, MB, Canada

Imaging without B0-gradients by the ‘TRASE’ method is based on echo trains with refocusing pulses produced by RF phase gradient fields. K-space evolution occurs between successive echoes. The use of phase gradients means that pulse phases vary spatially. Also |B1| inhomogeneity, causing flip-angle errors, is always present. Both effects combine to result in each location in the sample experiencing a different pulse sequence, which results in a position-dependent point-spread-function (PSF).  We examine how the relationships between sequence design, coil design and flip angle calibration can be used to maximize the sample volume offering a good PSF.

                  1470.     Slice-Selective B₁ Phase Shimming at 9.4 Tesla

Jens Hoffmann¹, Juliane Budde¹, Gunamony Shajan¹, Rolf Pohmann¹

¹High Field Magnetic Resonance Center, Max Planck Institute for Biological Cybernetics, Tuebingen, Baden-Wuerttemberg, Germany

In this work, we demonstrate B₁ phase shimming in situ at 9.4 Tesla: A rapid calibration pre-scan provides B₁⁺ magnitude and phase maps that are used to predict the total field across the subject dependent on a phase configuration of choice. In addition, a GUI provides the option to select a region within a slice where the field is quickly and reliably optimized by a simulated annealing algorithm based on a suitable optimization criterion. The accuracy of this method is demonstrated in a saline phantom and used for B₁ shimming in the human brain.

                  1471.     A Geostatistical Approach to Denoise and Interpolate Experimental Complex-Valued B₁  Maps

Guillaume Ferrand¹, Michel Luong¹, Pierre Chauvet², Martijn Anton Cloos³, Alexis Amadon³

¹IRFU/SACM, CEA Centre de Saclay, Gif sur Yvette, France; ²Centre de Géosciences, Mines ParisTech, Fontainebleau, France; ³DSV/I2BM/NeuroSpin/LMRN, CEA Centre de Saclay, Gif sur Yvette, France

The knowledge of the complex-valued B1 map generated by each channel of a phased-array RF coil has become essential for high field MRI systems operating above 7 T, a cornerstone for static or dynamic shimming techniques, whose aim is to provide a uniform excitation over any ROI. The maps must be measured experimentally for each RF coil and each subject under examination using an MRI sequence; the more accurate and space resolved the maps, the higher the shimming quality. Unfortunately, high quality maps are time consuming and usually lead to a stronger SAR exposure for the subject. We propose in this abstract a new method based on geostatistical considerations to post-process noisy and poor space resolved B1 maps.

                  1472.     Investigation of Slice Excitation Using Transmit Arrays and Non-Selective RF Pulses

Mary Preston McDougall^1,2, Steven M. Wright, ¹², Ke Feng², Edwin Eigenbrodt², Chieh Wei Chang¹, Neal Hollingsworth², John Bosshard²

¹Biomedical Engineering, Texas A&M University, College Station, TX, United States; ²Electrical and Computer Engineering, Texas A&M University, College Station, TX, United States

Curved slice excitation has been used for imaging the spine and neck, cortical surface of the brain, and other applications.  RF pulses for generating curved slices are typically 2D or 3D pulses, and can be very time consuming.  This paper presents an approach which may be useful in certain applications, in which an array coil, conformed to the surface of interest, generates the slices using simple non-selective pulses.   Slice depth is controlled by pulse duration or power.   Examples are shown using a straightforward “forced current” approach using a single transmitter and a more general approach using a 64 channel transmitter.

                  1473.     Statistical Analysis of in Vivo B1 Maps at 7T

Douglas Kelley^1,2

¹Applied Science Laboratory, GE Healthcare, San Francisco, CA, United States; ²Radiology and Biomedical Imaging, University of California, San Francisco, San Francisco, CA, United States

The design of practical B1 compensation schemes requires knowledge of the statistical properties of the B1 distribution found in vivo. An analysis of B1 maps in the brain of 10 human subjects is presented, identifying several common features and highlighting the non-Gaussian nature of the distribution.

                  1474.     A Complementary Images Shimming Method to Mitigate B₁ Inhomogeneity for High Field MRI

Guillaume Ferrand¹, Michel Luong¹, Martijn Anton Cloos², Alexis Amadon²

¹IRFU/SACM, CEA Centre de Saclay, Gif sur Yvette, France; ²DSV/I2BM/NeuroSpin/LMRN, CEA Centre de Saclay, Gif sur Yvette, France

The B1 inhomogeneity is well known to be a source of artifact in high field MRI, and requires the use of multiple-channel parallel transmit coil to reduce the artifact by making either the B1 distribution (static shimming) or the flip angle distribution (dynamic shimming) as uniform as possible. We present here an intermediate and versatile approach to mitigate B1 inhomogeneity based on the principle of complementary images averaging (CIA) while maximizing the signal to noise ratio (S/N).

                  1475.     3D T2-Weighted Turbo Spin-Echo Body Imaging at 3T Using a Multi-Channel Parallel RF Transmission Technology: Initial Experience

Gwenael Henri Herigault¹, Gert H. van Yperen¹

¹BU-MRI, Philips Healthcare, Best, Netherlands

3D turbo spin echo (TSE) sequences with variable flip angles (VFA) have shown their potential for 3T body imaging. However, they come with an increased sensitivity to B1 inhomogeneity. Multi-channel parallel RF Transmission (MTX) has demonstrated that it is possible to improve B1 homogeneity and flip angle accuracy inside the body at high field.  This paper reports our initial experience using a 3D TSE-VFA sequence in combination with a MTX technology for abdomen and male pelvis 3T imaging. Significant signal and contrast uniformity improvements are reported using MTX as compared to the conventional 3T single RF channel technology.

Simulations: B1 Uniformity

                  1476.     Rapid B1 Field Calculation Using Integral Equations for RF Shimming

Hyoungsuk Yoo^1,2, Anand Gopinath¹, Thomas Vaughan^1,2

¹Department of Electrical and Computer Engineering, University of Minnesota, Minneapolis, MN, United States; ²Department of Radiology, Center for Magnetic Resonance Research, Minneapolis, MN, United States

In the method of moments, triangular patches and the Rao-Wilton-Glisson (RWG) basis functions to arbitrary shaped homogeneous lossy dielectric objects are used. The single TEM coil is modeled for 9.4T (400MHz) system, then electromagnetic scattering problem by human phantom model is solved based on the method of moments technique solution of the combined field integral equations.

                  1477.     GPU Accelerated FDTD Solver and Its Application in B1-Shimming

Jieru Chi¹, Feng Liu², Ewald Weber², Yu Li², Riyu Wei², Wenlong Xu³, Adnan Trakic², Hua Wang², Stuart Crozier²

¹Qingdao University, Qingdao, China; ²The School of Information Technology and Electrical Engineering, The University of Queensland, Brisbane, St.Lucia, Queensland, Australia; ³Dept. of Biomedical Engineering, China Jiliang university, Hangzhou, China

This study extends our recent works on CPU-base FDTD simulations into a Graphics Processing Unit (GPU)-based parallel-computing framework, producing substantially boosted computing efficiency at only PC-level cost. The new computational strategy enables intensive computing feasible for solving forward-inverse EM problems in modern MRI, as illustrated in the high-field B1-shimming investigation presented herein. Moreover, the new rotating RF excitation technique proposed here can compensate for B1 inhomogeneities while simultaneously controlling SAR and as such may have a number of applications in high-field MRI.

                  1478.     Optimum Coupling of Travelling Waves in a 9.4T Whole-Body Scanner

Frank Geschewski¹, Jörg Felder¹, N. Jon Shah^1,2

¹Institute of Neuroscience and Medicine 4, Forschungszentrum Jülich GmbH, Juelich, NRW, Germany; ²Faculty of Medicine, Department of Neurology, RWTH Aachen University, Aachen, Germany

We investigated optimum coupling of a newly designed patch antenna into the RF screen of a 9.4T whole body MR system.

                  1479.     RF Wave and Energy Propagation in High Field MRI

Christopher M. Collins¹, Chienping Kao¹, Andrew G. Webb²

¹PSU College of Medicine, Hershey, PA, United States; ²Leiden University Medical Center, Leiden, Netherlands

As shown in both animations of B1 field magnitude through time and Poynting vector analysis, travelling waves have significantly shorter length and slower speed in human tissues than in the surrounding air, and thus experience significant refraction at the surface of the body, resulting in a direction of travel within the body that is fairly independent of the original source. Nevertheless, how these waves interfere within the body to create B1 and E1 field patterns relevant to MRI depends very much on the position, geometry, and orientation of the source(s).

                  1480.     Contribution of the Inherent Traveling Wave in 7T to Large FOV Imaging

Bei Zhang¹, Daniel K. Sodickson¹, Qi Duan¹, Graham Wiggins¹

¹CBI, Department of Radiology, New York University, NEW YORK, NY, United States

As the traveling wave has become a hot topic in high field MR as a promising method for large FOV imaging since ISMRM 2008, a lot of applications of traveling wave in imaging have been discussed. Since the conductive interface in 7T allows the propagation of TE11 mode, all excitations can create a TE11 mode in the interface. Therefore, it needs to understand the traveling wave contribution even in the conventional transmission and reception methods. In this work, we do full-wave electrodynamic simulations with a body model to explore the contribution of the conductive surface to the large FOV imaging with a conventional excitation method. From the simulation results, it can be seen that the traveling wave created in the conductive interface extends the FOV and boosts the SNR. It is also found that: in order to effectively excite the working mode, the position of the excitation should be that the current distribution in the excitation and the H field pattern comply with the right-hand law.

                  1481.     A Horn Antenna Improves the Transmit Field Homogeneity in the Human Brain Using the Travelling Wave Technique

Bobo Hu¹, Sedig Farhat², Paul Glover²

¹Sir Peter Mansfield Magnetic Resonance Centre , University of Nottingham, Nottingham, United Kingdom; ²Sir Peter Mansfield Magnetic Resonance Centre, University of Nottingham, Nottingham, United Kingdom

The RF field inhomogeneity in the human brain imaging utilizing the travelling wave technique is a fundamental obstacle of its clinical implementation. This work proposes a horn antenna type of structure to improve the coupling of the travelling wave to the head and also enhance the field homogeneity, especially at the upper cerebrum area. Both the simulated B1 field map and Poynting vector plot shows the field homogeneity has been improved and more power flows into the head. The hot-spots at top of the cerebrum and forehead area are greatly reduced. A comparison of its performances against patch antenna and patch antenna with a match load were studied by using the numerical simulation (xFDTD, Remcom. Inc, PA).

                  1482.     Using Dielectrics and RF Shielding to Increase B₁⁺ Efficiency and Homogeneity

Jinfeng Tian¹, Carl J. Snyder¹, J. Thomas Vaughan¹

¹University of Minnesota, Minneapolis, MN, United States

Using finite difference time domain simulations, the effect of different relative permittivity of the dielectric located between the body and volume array at 7T is examined.  Additionally, RF shielding within the volume array is studied to predict B1 transmit patterns in the body.  These are combined to improve B1 efficiency and homogeneity at 7T.

                  1483.     Comparison on the Traveling Wave Excitation and the Conventional Excitation

Bei Zhang¹, Daniel K. Sodickson¹, Riccardo Lattanzi¹, Qi Duan¹, Ryan Brown¹, Bernd Stoeckel², Graham Wiggins¹

¹CBI, Department of Radiology, New York University, NEW YORK, NY, United States; ²Siemens Healthcare

This abstract uses the finite difference time domain (FDTD) method to simulate a stepped-diameter traveling wave system and TEM resonator system loaded with the same body model, and compare the simulation results of these two systems in terms of B1 mapping, SAR distribution and system efficiency. The result shows that the traveling wave system and conventional TEM body coil in 7T are simulated to compare in terms of B1 mapping, SAR distribution and system efficiency. Both systems show strong B1+ inhomogeneities in the torso, though these could in principle be mitigated with a parallel multi-port TEM excitation. The combination of strong attenuation of the traveling wave and high SAR in tissues near the patch antenna make the TWS less suitable for whole body imaging than a local standing wave transmitter such as the TEM.

                  1484.     B1+ Uniformity in Birdcage Body Coils Versus the Alignment and Shape of the RF Shield

Arslan Amjad¹, Eddy B. Boskamp¹

¹GE Healthcare, Waukesha, WI, United States

In order to make an image without shading, it is critical for the body coil to produce homogeneous B1+ field inside the imaging volume. Any variation in the shape or the alignment of either the body coil or the RF shield can deteriorate B1+ homogeneity and hence image quality. In this work the impact on B1+ field homogeneity using numerical simulations is studied under various non-ideal conditions.

                  1485.     A Simulational Study on the Homogeneity of Dual-Tuned Birdcage Coils

William M. Potter^1,2, Luning Wang^1,2, Kevin McCully³, Qun Zhao^1,2

¹Physics and Astronomy, University of Georgia, Athens, GA, United States; ²Bioimaging Research Center, University of Georgia, Athens, GA, United States; ³Kinesiology, University of Georgia, Athens, GA, United States

31P magnetic resonance spectroscopy signal sensitivity is low due concentrations of the nucleus and magnetic field inhomogeneity from currently available commercial surface coils. Dual-tuned (1H/31P) birdcage coils are advantageous in that they create a very homogeneous B1 field inside the coil. The practicality of building a dual-tuned coil, however, can be troublesome due to many factors such as coil structure (e.g., # of legs/rings, dimensions) and biological objects to be imaged. In this abstract, the homogeneity comparisons for the 8-leg, 16-leg, and the 24-leg, 4-ring low-pass birdcage coils are presented with the presence of simulated human head and thigh modules.

                  1486.     B1 Shimming Performance Versus Channel/Mode Count

Paul R. Harvey¹, Cecilia Possanzini¹, Jan Simons¹

¹Philips Healthcare, Best, Netherlands

This study reports on simulations of abdominal B1 shimming performance, using a multi-element volume body coil, as a function of transmit channel/mode count and available RF power. Results indicate that increasing channel/mode count provides limited improvement in uniformity at the cost of higher power.

Receive Arrays & Coils

                  1487.     Selection and Verification of a Throughput-Optimized Receive Array for Multiple-Mouse DCE-MRI

Marc Stephen Ramirez¹, James Andrew Bankson¹

¹Department of Imaging Physics, The University of Texas M. D. Anderson Cancer Center, Houston, TX, United States

A variety of receive array coil configurations were simulated to determine acceptable parallel imaging reduction factors for use in accelerated multiple-mouse MRI.  Based on these results, timing of accelerated multi-mouse DCE-MRI protocols were predicted and compared with timing of a single-mouse, single-coil DCE-MRI protocol to estimate improvements in throughput.  The coil configuration that yielded the highest multi-mouse throughput improvement was determined.  A phased-array coil based on the optimal configuration was designed, fabricated, and used for phantom imaging to verify that the predicted reduction factor per animal maintained image quality suitable for routine small-animal imaging studies.

                  1488.     Multiple-Animal MR Imaging Performed Using a 3-Tesla Whole-Body Scanner: A Feasibility Study Using a 16-Channel Array Coil

Akira Nabetani¹, Masayuki Yamaguchi², Akira Hirayama^1,2, Minoru Mitsuda^2,3, Ryutaro Nakagami^2,3, Atsushi Nozaki¹, Mamoru Niitsu³, Hirofumi Fujii^2,4

¹GE Healthcare Japan, Ltd., Hino, Tokyo, Japan; ²Functional Imaging Division, National Cancer Center Hospital East, Kashiwa, Chiba, Japan; ³Graduate School of Human Health Sciences, Tokyo Metropolitan University, Arakawa, Tokyo, Japan; ⁴Institute for Bioinformatics Research and Development Japan Science and Technology Agency, Chiyoda, Tokyo, Japan

We constructed and tested a new multiple-animal magnetic resonance imaging (MRI) device that uses a 3-Tesla (3-T) whole-body scanner. An array coil comprising 16 small circular coils was connected to 16 preamplifiers and receivers of the scanner. This device can be used to perform simultaneous whole-body scanning of 4 rats or 16 mice. This approach facilitates progress in preclinical MRI and may be helpful in pharmaceutical drug-development studies in which various doses of multiple compounds are assessed in a large number of animals.

                  1489.     An 8-Channel Coil Array for Small Animal 13C MR Imaging

Jian-Xiong WANG¹, Nan Tian², Fraser J. Robb³, Albert P. Chen⁴, Lanette Friesen-Waldner⁵, Brian K. Rutt⁶, Charles A. McKenzie⁵

¹Applied Science Laboratory, GE HEALTHCARE, London, ON, Canada; ²Department of Radiology, University of California at San Fransisco, San Fransisco, CA, United States; ³GE HEALTHCARE, Aurora, OH, United States; ⁴GE HEALTHCARE, Toronto, ON, Canada; ⁵The Department of Medical Biophysics, The University of Western Ontario, London, ON, Canada; ⁶Department of Radiology, Stanford University, Stanford, CA, United States

Synopsis: This work presented an 8-channel 13C receive coil array/preamp system with associated detunable transmit coil system for a clinic MRI scanner without additional hardware or modification to the scanner. Both MRI and CSI were obtained with this coil system. This offers parallel imaging possibility for metabolic imaging utilizing short lifetime hyperpolarized [1-13C]-pyruvate of the hyperpolarized 13C spins in solution.

                  1490.     A 21 Channel Transceiver Array for Non-Human Primate Applications at 7 Tesla.

Gregor Adriany¹, Noam Harel¹, Essa Yacoub¹, Steen Moeller¹, Geoff Ghose¹, Kamil Ugurbil¹

¹Center for Magnetic Resonance Research, University of Minnesota Medical School, Minneapolis, MN, United States

A combination of a 16 channel transceiver stripline array with a close fitting 5 channel receive loop array for non human primates applications is presented. The coils are arranged to allow simultaneous reception with all 21 elements and combine the benefits of close fitting receive only arrays with multi-channel transmit arrays. For a reduction factor of 3 the average g-factor for the combination of 16+5 receiver channels improved to 1.62 compared to 2.66 for the 5 channel coil.

                  1491.     A 32 Channel Receive-Only 3T Array Optimized for Brain and Cervical Spine Imaging

Azma Mareyam¹, Julien Cohen-Adad¹, James N. Blau¹, Jonathan R. Polimeni¹, Boris Keil¹, Lawrence L. Wald^1,2

¹A. A. Martinos Center for Biomedical Imaging, Dept. of Radiology, Masschussetts General Hospital, Charlestown, MA, United States; ²Division of Health Sciences and Technology, Harvard-MIT, Cambridge, MA, United States

Imaging of the cervical spinal cord along with the brain is crucial for the study of such pathologies as multiple sclerosis. Progress, however, is impeded by distortion and susceptibility artifacts, due to the cord's small size and to adjacent B0 inhomogeneities. We designed and built a new, highly-parallel 32 channel coil array to provide sufficient resolution, SNR and acceleration for imaging the brain, brainstem, and cervical vertebrae. Characterization of the coil showed SNR and acceleration improvement over existing Siemens head, neck and spine coils in this region.

                  1492.     Modular Coil Array for Highly Accelerated 2D Parallel Acquisition

Clifton R. Haider¹, Thomas C. Hulshizer¹, Casey P. Johnson¹, Petrice M. Mostardi¹, Phillip J. Rossman¹, Stephen J. Riederer¹

¹Radiology, Mayo Clinic, Rochester, MN, United States

The purpose of this work is to demonstrate the design and use of modular coil arrays that allow highly accelerated (R=8) 2D SENSE to be exploited in providing high diagnostic image quality for 3D contrast-enhanced MR angiograms in multiple vascular territories across a broad range of patient sizes. Volunteer and patient studies were conducted in the calves, feet, hands, brain, thighs, and abdomen. Results demonstrate high diagnostic image quality.

                  1493.     Design Optimization of a 32-Channel Head Coil at 7T

Boris Keil¹, Christina Triantafyllou^1,2, Michael Hamm³, Lawrence L. Wald^1,4

¹A.A. Martinos Center for Biomedical Imaging, Department of Radiology, MGH, Harvard Medical School, Charlestown, MA, United States; ²A.A. Martinos Imaging Center, Mc Govern Institute for Brain Research, MIT, Cambridge, MA, United States; ³Siemens Healthcare, Charlestown, MA, United States; ⁴Harvard-MIT Division of Health Sciences and Technology, MIT, Cambridge, MA, United States

The development of high-field coils with an increasing number of elements places increasingly constraints on the arrangement of the components, including preamplifier, cables and cable traps. For maximum spatial efficiency and reduced losses, most of the components needed to be placed adjacent to the corresponding coil loop. Reduced interaction with the transmit coil requires a sparse configuration of conductors, well isolated through cable traps. In this study a new generation of a 32-channel coil at 7T was constructed, tested, and compared to a previous 32-channel design. Substantial changes have been implemented to achieve better SNR, increased stability, lower transmit power.

                  1494.     Feasibility of Constructing Receive-Only Arrays for Human Imaging at 11.7T and 14T

Azma Mareyam¹, Jonathan R. Polimeni¹, James N. Blau¹, Lawrence L. Wald^1,2

¹A. A. Martinos Center for Biomedical Imaging, Dept. of Radiology, Masschussetts General Hospital, Charlestown, MA, United States; ²Division of Health Sciences and Technology, Harvard-MIT, Cambridge, MA, United States

Arrays of surface coils employing lumped capacitance are in widespread use at 7T, but become problematic at extremely high fields as stray capacitances and losses from discrete components increase. We constructed coils for 11.7T and 14.1T (500 and 600 MHz) using a double-sided microwave circuit board material milled into overlapping sections. Arrays of these distributed-capacitance coils were characterized, outperforming equivalent lumped-capacitance arrays at loaded to unloaded Q ratios.

                  1495.     A Numerically Optimised Receive-Only Coil Array at 3 T

Andreas Peter¹, Stefan Schonhardt¹, Jan G. Korvink^1,2

¹University of Freiburg - IMTEK, Freiburg, Germany; ²Freiburg Institute of Advanced Studies (FRIAS), Freiburg, Germany

In this contribution, we present the optimisation of a 2D coil array in order to decouple all adjacent and next neighbouring coils simultaneously. We have extended the geometric overlapping approach to non-adjacent elements by shape-optimisation of the coil elements. A combination of Matlab and FastHenry was used to optimise an array of seven elements at 3 T. From the optimised design, we produced a set of PCBs of the single hexagonal elements on a flexible polyimide substrate. All adjacent elements showed an isolation of > 25 dB, the next neighbouring elements even > 30 dB.

                  1496.     A User-Configurable 96 Channel Head Array for Use in a 32 Channel 3T System

Thimo Grotz¹, Boris Keil², Azma Mareyam², Simon Sigalovsky², Benjamin Zahneisen¹, Maxim Zaitsev¹, Jürgen Hennig¹, Lawrence L. Wald²

¹Dept. of Diagnostic Radiology, Medical Physics, University Hospital Freiburg, Freiburg, Germany; ²Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, MA, United States

Surface coils with a high numbers of receive elements are an important tool for many applications. Commercial scanners usually don’t support such high numbers of receive elements and non-standard hardware upgrades are needed to use such arrays. We present a 3T scanner compatible 96 channel head array coil which allows the selection of an arbitrary subset of 32 receiver channels from the 96 channels available, which makes it possible to benefit from the use of small receive elements on a standard MRI system.

                  1497.     Magnetic Resonance Imaging of Newborns and Premature Infants at 1.5T and 3T with an 8-Channel Phased Array Head Coil

Jörn Ewald¹, Florian M. Meise¹, Stefan Fischer², Torsten Hertz¹, Torsten Lönneker-Lammers³, Laura Maria Schreiber²

¹LMT Medical Systems GmbH, Luebeck, Germany; ²Section of Medical Physics, Department of Diagnostical and Interventional Radiology, Mainz University Medical School, Mainz, Germany; ³LMT Lammers Medical Technology GmbH, Luebeck, Germany

For a detailed understanding of diseases and developmental processes during the first year of live without harming the patient by using ionizing radiation, MRI of the neonatal brain is mandatory. So far this could be achieved by using an MR-safe. Because reduction of scan time (minimizing movement artifacts and specific absorption rate) is needed, phased array coils to apply parallel imaging techniques have to be developed. Since comparable field strength studies, for analyzing influences of image contrasts, may be performed, an 8-channel phased array head coil implemented in an MR-safe incubator was designed for 1.5T and 3T in this study.

                  1498.     An 8+4-Channel Phased Array for Magnetic Resonance Imaging of Newborns and Premature Infants at 3T in an MR-Safe Incubator

Florian M. Meise¹, Jörn Ewald¹, Stefan Fischer², Torsten Hertz¹, Torsten Lönneker-Lammers³, Laura Maria Schreiber²

¹LMT Medical Systems GmbH, Luebeck, Germany; ²Section of Medical Physics, Department of Diagnostical and Interventional Radiology, Mainz University Medical School, Mainz, Germany; ³LMT Lammers Medical Technology GmbH, Luebeck, Germany

MRI of newborns got growing attention over the past few years as it provides precise diagnostics without the use of ionizing radiation. Premature infants and newborns need optimum environmental conditions during the measurement procedure, (temperature and humidity). Since there is an MR-safe incubator available, imaging of the brain and thorax under optimum conditions is possible. Especially at high fields, SAR limits and movement artifacts from the patient can be challenging. Both issues can be dealt with by applying parallel imaging techniques. To Also to improve SNR with multi-element arrays, an 8+4-channel phased array implemented in an MR-safe incubator was designed.

                  1499.     A 4-Element Receive Array with Integrated Preamplifiers for Mouse Brain Imaging in a 14T Vertical Bore Scanner

Stephen Dodd¹, Herman Douglas Morris², Joseph Murphy-Boesch¹, Hellmut Merkle¹, Alan Koretsky¹

¹Laboratory of Functional and Molecular Imaging, NINDS, National Institutes of Health, Bethesda, MD, United States; ²Mouse Imaging Facility, National Institutes of Health, Bethesda, MD, United States

In order to take advantage of the sensitivity that high fields offer we have developed and describe here a 4-element receive-only array design for parallel imaging of the mouse brain at 14 T.  To achieve the necessary decoupling between array elements we designed and built small, low noise and low input impedance preamplifiers which can fit in the limited diameter of the vertical bore magnet.

Double Tuned RF Coils

                  1500.     A Nested Dual Frequency Birdcage/Stripline Coil for Sodium/Proton Brain Imaging at 7T

Graham C. Wiggins¹, Ryan Brown¹, Lazar Fleysher¹, Bei Zhang¹, Bernd Stoeckel², Matilde Inglese^1,3, Daniel K. Sodickson¹

¹Radiology, Center for Biomedical Imaging, NYU School of Medicine, New York, NY, United States; ²Siemens Medical Solutions USA Inc., New York, NY, United States; ³Neurology , NYU Medical Center, New York, NY, United States

The design of a novel dual frequency coil for 7T sodium/proton brain imaging is discussed. The nested coil utilized a high-pass birdcage for sodium detection and an eight-channel stripline array for proton detection. This design showed minimal interaction between the sodium and proton coils, allowing independent tuning at both frequencies. The proton striplines partially shielded the sodium birdcage, resulting in only an 8% SNR loss compared to that of the isolated birdcage, while transmit efficiency was reduced by 20%. The proton stripline coil provided adequate sensitivity for anatomical imaging and B0 shimming.

                  1501.     Double Tuned 31P/1H Elliptical Transceiver Phased Array for the Human Brain Studies at 7 T

Nikolai I. Avdievich¹, Jullie W. Pan¹, Hoby P. Hetherington¹

¹Neurosurgery, Yale University, New Haven, CT, United States

The improved SNR at 7T provides significant advantages for both 1H and X nuclei (31P, 13C etc). At 7T, transceiver phased arrays improve B1 homogeneity, transmit efficiency, and peripheral SNR compare to volume coils. Therefore, double tuned transceiver arrays may provide substantial advantages over conventional double tuned volume head coils. However, they are substantially more complicated than single tuned arrays since all coils must be decoupled at both frequencies. We have developed a 16-element (8 elements per frequency) 31P/1H 7T transceiver phased head array. The double tuned transceiver array improved both B1 homogeneity and efficiency in comparison to the TEM.

                  1502.     Single-Input Double-Tuned Birdcage Coil with Identical B1 Field Profile for 1H and 19F Imaging

Lingzhi Hu¹, Frank D. Hockett¹, Junjie Chen¹, Gregory M. Lanza¹, Samuel A. Wickline¹

¹Washington University School of Medicine, St. Louis, MO, United States

Based on coupled-resonator model, we have designed a single-input double-tuned birdcage working at both 1H and 19F frequencies on 4.7T MRI scanner. The good matching property and homogeneity of B1 field have been testified by S11 and S21 measurement and in vivo demonstration.  To achieve the highest sensitivity, we have also integrated an active decoupled surface coil with the double-tuned birdcage and increased the local SNR by over 10 folds. As the standard birdcage structure is preserved, the sensitivity profile of this new double-tuned birdcage is inherently identical at 1H and 19F resonant frequencies.

                  1503.     High SNR Dual Tuned Sodium/Proton Knee Coil

Ronald D. Watkins¹, Ernesto Staroswiecki^1,2, Neal Bangerter³, Brian Hargreaves¹, Garry Gold¹

¹Radiology, Stanford University, Stanford, CA, United States; ²Electrical Engineering, Stanford University, Stanford, CA, United States; ³Electrical and Computer Engineering, Brigham Young University, Provo, UT, United States

Preliminary results from a dual tuned 23Na sodium 1H proton knee coil are presented. A multiple ring birdcage design has been employed providing high sensitivity and uniformity to both nuclei without the need for frequency traps. Both coil sections are circularly polarized quadrature coils with direct drive cable connections. Cables are routed to a common potential node avoiding the need for baluns and avoiding parasitic cable loops. Registered images are presented for both sodium and proton acquisitions, avoiding the need to change the RF coil during the study

                  1504.     Design and Construction of a Heteronuclear 1H and 31P Double Tuned Coil for Breast Imaging and Spectroscopy

Sergei Obruchkov¹, Kenneth Bradshaw², Michael D. Noseworthy³

¹Medical Physics and Applied Radiation Sciences, McMaster University, Hamilton, ON, Canada; ²Sentinelle Medical, Toronto, ON, Canada; ³Electrical and Computer Engineering, McMaster University, Hamilton, ON, Canada

Dual tuned surface coil (31P and 1H) was designed and build to have high performance parameters for both channels. The coil was build to integrate into a Sentinelle Vanguard table for 3T Signa GE system. The ability to transmit on both channels simultaneously makes it possible to perform decoupling using the same coil.  1H imaging and 31P spectroscopy was demonstrated on the above coil.

                  1505.     Performance Comparison of a Hybrid Dual-Tuned ²³Na/¹H Birdcage to a Single-Tuned ²³Na Birdcage with Identical Geometry

Brock Peterson¹, Ron Watkins², Glen Morrell³, Steven Allen⁴, Danny Park¹, Josh Kaggie⁵, Garry E. Gold², Neal K. Bangerter¹

¹Department of Electrical & Computer Engineering, Brigham Young University, Provo, UT, United States; ²Department of Radiology, Stanford University, Stanford, CA, United States; ³Department of Radiology, University of Utah, Salt Lake City, UT, United States; ⁴Department of Physics, Brigham Young University, Provo, UT, United States; ⁵Department of Physics, University of Utah, Salt Lake City, UT, United States

Recent improvements in MRI sequences and hardware have renewed interest in sodium MRI.  Dual-tuned coils are highly desirable to allow inclusion of a sodium exam during a standard proton scan without moving the patient, and to allow accurate registration of sodium and proton images.  Unfortunately, many dual-tuned coil configurations come with a significant penalty in SNR performance.  In this work, we evaluate the sodium SNR performance penalty and B1 homogeneity associated with a hybrid low-pass sodium, high-pass hydrogen dual-resonant birdcage design.  We show that the addition of the high-pass hydrogen structure has a negligible effect on both sodium SNR performance and B1 homogeneity.

                  1506.     A Double-Tuned ¹H/²³Na Two Element Phased Array System for in Vivo ²³Na Magnetic Resonance Microscopy at 7 T

Friedrich Wetterling¹, Ute Molkenthin², Sven Junge², Andrew John Fagan³

¹School of Physics, Trinity College Dublin, Dublin, Ireland; ²Bruker BioSpin GmbH, Ettlingen, Germany; ³Centre for Advanced Medical Imaging, St. James’s Hospital, Dublin, Ireland

The aim of this study was to develop a ²³Na two-element phased array as part of a double-tuned ²³Na/¹H resonator system to maximize the ²³Na SNR and acquire ²³Na-Magnetic Resonance Microscopy (²³Na-MRM) images together with high resolution anatomical ¹H MRM images without the need to change the coil system during the experiment.  The coil element decoupling was optimized by using two-winding detector elements - a novel approach to improve detector element decoupling in noise-matched phased array designs.  An SNR improvement of 25 % in favour of the phased array coil was measured at a depth of 12 mm compared to a transceiver surface coil, which most likely derived from the better detector element decoupling.

Novel Coils & Techniques

                  1507.     Time Division Multiplexed - Sensitivity Encoding (TDM-SENSE) with a Mechanically Rotating RF Coil

Adnan Trakic¹, Hua Wang¹, Ewald Weber¹, Bing Keong Li¹, Michael Poole¹, Feng Liu¹, Stuart Crozier¹

¹The School of Information Technology and Electrical Engineering, The University of Queensland, Brisbane, QLD, Australia

While mechanically rotating a RF coil about an object being imaged brings a number of hardware advantages as was shown in recent studies, the approach violates the time-invariant definition of the Fourier Transform. This work presents Time Division Multiplexed - Sensitivity Encoding (TDM-SENSE) as a new alias-free image reconstruction and scan time acceleration scheme dedicated to the rotating RF coil (RRFC). In this initial study, two-fold scan time reduction was achieved by increasing the signal sampling rate and the angular frequency of coil rotation.

                  1508.     Optimization of Multi-Turn Litz Wire Radiofrequency Coils for Hyperpolarized Noble Gas Imaging of Rodent Lungs at 73.5mT

William Dominguez-Viqueira^1,2, Marc Carias², Giles E. Santyr^2,3

¹Imaging Laboratories, Robarts Research Institute, London, Ontario, Canada; ²Department of Medical Biophysics, University of Western Ontario, London, Ontario, Canada; ³Department of Medical Imaging, University of Western Ontario, London, Ontario, Canada

SNR at low magnetic field strength can be improved by reducing RF coil noise using Litz wire coils. In this work the number of turns was optimized for Litz wire coils for low field hyperpolarized noble gas imaging of rat lungs. The comparison was conducted at 0.866 MHz and 2.385 MHz corresponding to Larmor frequencies of ¹²⁹Xe and ³He at 73.5 mT. The quality factors and the signal to noise ratio (SNR) for each coil at each frequency were measured. Results demonstrate the advantages of multiturn Litz wire coils obtaining up to 300% improvement compared to copper coils.

                  1509.     The Intrinsic Magnetic Field Symmetries of the Spiral Birdcage Coil

Christopher P. Bidinosti¹, Chen-Yi Liu¹, Scott B. King²

¹Physics, University of Winnipeg, Winnipeg, Manitoba, Canada; ²Institute for Biodiagnostics, National Research Council of Canada, Winnipeg, Manitoba, Canada

Spiral birdcage coils have been used for transmit array spatial encoding (TRASE) as well as for partially correcting central image brightening. A Fourier transform method usually employed for designing wire-wound shim, gradient and low frequency RF coils is used here to analyze the magnetic field symmetries of the spiral birdcage coil.  Results show that twisting leads to a strong, intrinsic radial dependence in all magnetic field components. This knowledge will guide the optimization of coils used for TRASE, and may also lead to a more direct correction scheme for the problem of central brightening that occurs in high field MRI.

                  1510.     Inductive Coupled Local TX Coil Design

Weidong Wang¹, Xue Lian Lu², Jun You², Weijun Zhang², Haining Wang², Helmut Greim³, Markus Vester³, Jianmin Wang²

¹Siemens Mindit Magnetic Resonance Ltd , Shen Zhen, Guang Dong, China; ²Siemens Mindit Magnetic Resonance Ltd, Shen Zhen, Guang Dong, China; ³Siemens Medical Solutions Magnetic Resonance, Erlangen, Germany

A Transmit/Receive coil provides several advantages compared to receive only coils. On the other hand the local TX/RX option is not always available due to cost considerations. In this paper we present a novel method to implement a local TX/RX function with an inductive coupled TX local coil.  

                  1511.     Improving B1+ Uniformity at 3T Using Optimized Spiral Birdcage Phase Gradient RF Coils

Scott B. King¹, Chen-Yi Liu², Vyacheslav Volotovskyy¹, Christopher P. Bidinosti², Krzysztof Jasinski³, Mike J. Smith¹, Jonathan C. Sharp⁴, Boguslaw Tomanek⁴

¹Institute for Biodiagnostics, National Research Council of Canada, Winnipeg, Manitoba, Canada; ²Department of Physics, University of Winnipeg, Winnipeg, Manitoba, Canada; ³Department of Magnetic Resonance Imaging, Polish Academy of Sciences, H. Niewodniczanski Institute of Nuclear Physics, Krakow, Poland; ⁴Institute for Biodiagnostics (West), National Research Council of Canada, Calgary, Alberta, Canada

Due to RF wave behavior and sample interaction at high B0 fields, B1+ shimming aiming at uniform excitation is important for improved SNR and image uniformity, while avoiding complicated 2D spatially selective RF methods.  Using a single transmit channel at 3T we have demonstrated that an asymmetric variable pitch spiral birdcage with one end domed can be an effective method of B1+ shimming, enabling a more uniform B1+ field distribution.  New RF-only MRI methods could benefit from such uniform B1+ phase gradients. Furthermore, these optimized current distributions may provide insight into building blocks for Tx-array element designs.

                  1512.     An Inductively-Coupled Coil Designed for Clinical Use with a Limb-Positioning Platform

Marc Rea¹, Haytham Elhawary², Zion Tsz Ho Tse², Donald McRobbie¹, Michael Lampérth³, Ian Young⁴

¹Radiological Sciences Unit, Imperial College London, London, UK, United Kingdom; ²Brigham Womens Hospital, Boston, United States; ³Mechanical Engineering, Imperial College London; ⁴Electrical Engineering, Imperial College London, London, United Kingdom

An RF receive coil was developed for use with a limb-positioning platform. The coil uses two elements placed at a fixed distance on either side of the limb and normalises signal levels through rotations of the limb. The coil uses inductive coupling and a single receiver channel. Initial results with a phantom and a volunteer show the coil has good uniformity compared with a standard flex coil.

                  1513.     A Twin-Head Coil for Studying Two Brain Interaction with FMRI

Ray F. Lee¹, Weiming Dai¹, Gary Drozd¹, James Coan², John Mugler, III³

¹Neuroscience Institute, Princeton University, Princeton, NJ, United States; ²Psychology, University of Virginia, Chalottesville, VA, United States; ³Radiology, University of Virginia, Chalottesville, VA, United States

One of the major functions of the human brain is to mediate interactions with other people. Until recently, studying brain social interactions has not been possible due to the lack of measurable methods to observe two interacting minds simultaneously.  We have developed a novel twin-head MRI coil that can scan two subjects’ brains simultaneously while the subjects are socially interacting in one MRI scanner. Meanwhile, an even-odd mode scheme for decoupling two quadrature coils (not surface coils) is validated.

                  1514.     Efficiency of Single-Loop and Quadrature Surface RF Coils in the Human Brain at 9.4 Tesla

Dinesh K. Deelchand¹, Gregor Adriany¹, Can Akgun¹, Kamil Ugurbil¹, Pierre-Gilles Henry¹, Pierre-Francois Van de Moortele¹

¹Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN, United States

Single-loop and quadrature surface RF coils are often used for NMR spectroscopy since higher signal-to-noise ratio can be achieved in comparison to single channel volume coils. This study shows that single-loop coils are inefficient for human brain spectroscopy studies at 9.4 Tesla because the areas of high values in transmit and receive B₁ fields do not overlap in space. On the other hand, quadrature surface coils can still be used as long as the phase between the two coil elements is optimized for a given region-of-interest in order to increase the B₁ transmit efficiency.

                  1515.     Enhanced RF Excitation Homogeneity by Combining TEM and Counter Rotating Current Surface Coil Array: Numerical Simulations and Experiments at 4.0 T

Sukhoon Oh¹, Nikolai I. Avdievich², Hoby P. Hetherington², Christopher M. Collins¹

¹PSU College of Medicine, Hershey, PA, United States; ²Neurosurgery, Yale University, New Haven, CT, United States

Here we present simulated and experimental results combining an array of counter rotating current (CRC) surface coils and a TEM volume coil in transmission. The combination provides better homogeneity than the TEM alone for excitation, and simulated results are in good agreement with experiment for combining a 4-element array with the TEM. Further simulation shows a much improved result for increasing the number of CRC coils in the array to 8.

                  1516.     Numerical and Experimental Analysis and Demonstration of a Wire Medium Collimator for MRI

Xavier Radu¹, Alexander Raaijmakers², Astrid L. van Lier², christophe Craeye³, Cornelis A. van den Berg²

¹Laboratoire de Télécommunications et Télédétection, Université catholique de Louvain , Louvain, Belgium; ²Dept. of Radiotherapy, Imaging Division, Utrecht, Netherlands; ³Laboratoire de Télécommunications et Télédétection, Université catholique de Louvain, Louvain, Belgium

In this study we propose to use a metamaterial wire medium for the collimation and transfer of RF transmit and receive field from the source region to a distant location. The use of a such parallel wire medium in MRI opens several prospects:  (i) the possibility to design more reliable endoscopic sensors; (ii)  the possibility to create a flexible transmit configuration to excite particular regions with good homogeneity. Hereafter, the properties of wire media are investigated both numerically and experimentally. We show experimentally at 3 and 7T  that the collimation and transfer can be very efficient.

                  1517.     New Approaches of Rf Coil and Gamma Ray Radiation Shielding Assembly for Spect/Mri System

SeungHoon Ha¹, Mark Jason Hamamura¹, Werner W. Roeck¹, Lutfi Tugan Muftuler¹, Orhan Nalcioglu¹

¹University of California Irvine, Irvine, CA, United States

Several studies have reported on the design considerations of an MR compatible nuclear detector for combined SPECT/MRI.  In this study, we proposed a new RF coil and ¥ã-ray radiation shields assembly to retain the tremendous potential of SPECT/MRI to provide high sensitivity and specificity while minimizing the interference between the MRI and SPECT systems. The results demonstrated the new assembly is superoir to configuration of a conventioncal RF coil and ¥ã-ray radiation shield.

                  1518.     Understanding Parallel Transmit Array Efficiency

Yudong Zhu¹, Cem Deniz¹, Leeor Alon¹, Hans-Peter Fautz², Daniel Sodickson¹

¹New York University School of Medicine, New York, United States; ²Siemens, Erlangen, Germany

The efficiency of a conventional transmit coil is commonly evaluated based on amplitude of the created B1 field or spin flip angle given a certain input power. However it is not yet clear how the efficiency of a transmit array could be evaluated. This may be attributed to the shear number of possible weighting configurations (induced statically by B1 shimming coefficients or dynamically by parallel RF pulses) in driving individual Tx channels or ports. We hereby present an efficiency metric that is an extension of the conventional efficiency metric, and is as practical to quantify as is the conventional metric.

                  1519.     B1 Shimming with a Standard 2 Channel Headcoil at 7T: Possibilities & Limitations

Hans Hoogduin¹, Astrid van Lier, Hugo Kroeze, Dennis Klomp, Peter Luijten, Cat van den Berg

¹University Medical Center Utrecht, Utrecht, Netherlands

The possibility of B1 shimming with a standard 2 channel headcoil at 7T is investigated. Both simulations and in vivo results are presented. The results show that whole brain uniformity in B1+ is not possible with two channels. However, considerable improvements can be made as illustrated by a 3D magnetization prepared FLAIR acquisition.

Decoupling, Feeding & Tuning

                  1520.     Balanced Microstrip Feeds

Arthur W. Magill^1,2, Benoit Schaller¹, Rolf Gruetter^1,3

¹LIFMET, Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland; ²Radiology, University of Lausanne, Lausanne, Switzerland; ³Radiology, University of Geneva, Geneva, Switzerland

Two novel balanced feed designs for microstrip array elements are introduced. Balanced capacitive matching is the symmetric version of classic single ended feeding, connected across both strip ends. Balanced geometric matching uses the fact that a resonant microstrip is purely resistive at all points along its length, connecting directly at the match points. Feeds are modeled using odd-mode analysis and design equations presented. Balanced feeds are then compared to classic single-ended feeding using simulation (FDTD) and bench measurements at 300MHz. Balanced feeding was found to offer greater stability under variable loading conditions and reduced electric field production.

                  1521.     A Composite Decoupling Method for RF Transceiver Array Coils in MRI

Yunsuo Duan¹, Bradley S. Peterson¹, Feng Liu², Alayar Kangarlu³

¹MRI Research, Department of Psychiatry, NYSPI & Columbia University, New York, NY 10032, United States; ²MRI Research, Department of Psychiatry,, NYSPI & Columbia University, New York, NY 10032, United States; ³MRI Research, Department of Psychiatry, NYSPI & Columbia University,, New York, NY 10032, United States

We present a composite scheme for minimizing the mutual inductance of transceiver array coils with more than two channels, which combines a novel shielding-based decoupling design with simplified capacitive decoupling method. The significant advantage of this composite strategy is that the adjustment of decoupling parameters for each coil element barely affects other elements.  This characteristic of the new strategy greatly minimizes the coupling mechanism between different elements which is inherent to coil arrays and thereby simplifying the complex decoupling of transceiver array coils.

                  1522.     Transmit Coil Decoupling of 8-Channel Coil Arrays with Ultra-Low Output Impedance RF Power Amplifiers

Desmond Teck Beng Yeo¹, Eric Fiveland¹, Randy Giaquinto¹, Tingting Song², Xing Yang², Keith Park¹, Adam B. Kerr³, Xu Chu², Ileana Hancu¹

¹GE Global Research, Niskayuna, NY, United States; ²GE Global Research, Shanghai, China; ³Department of Electrical Engineering, Stanford University, Stanford, CA, United States

Inter-element inductive coupling presents an important challenge in parallel transmit coil arrays. An ultra-low output impedance RF amplifier (RFPA) was previously introduced to address this issue. In this work, the improvements in transmit decoupling between the ultra-low output impedance RFPAs and conventional RFPAs under different loading conditions were investigated with two types of coil arrays. Bench tests and imaging studies performed on a 3T MR scanner with 8-channel transmit and receive flat array and cylindrical coils showed improved inter-element transmit decoupling, and, strong correlation between image-based B1+ decoupling measures and inter-element scattering parameters (S21).

                  1523.     Using Piezoelectric Actuators for Remote Tuning of Transmit Coils

Carl J. Snyder¹, Lance DelaBarre¹, Jinfeng Tian¹, Can Akgun¹, J. Thomas Vaughan¹

¹University of Minnesota, Minneapolis, MN, United States

This study examines the use of piezoelectric actuators in concert with variable capacitors to allow remote tuning of transmit elements.  Tuning can be performed on a subject while in the magnet and can be periodically monitored throughout the study.

Gradient Coil Design

                  1524.     Minimax Current Density Coil Design

Michael Stephen Poole¹, Pierre Weiss², Hector Sanchez Lopez¹, Michael Ng³, Stuart Crozier¹

¹School of Information Technology and Electrical Engineering, University of Queensland, Brisbane, QLD, Australia; ²Institut de Mathematiques, Universite Paul Sabatier Toulouse 3, Toulouse, France; ³Department of Mathematics, Hong Kong Baptist University, Kowloon Tong, Hong Kong

Gradient and shim coils designed with minimum power or stored energy can possess regions of high current density. The maximum current density is included in the coil design process in this study to produce minimax current coils. These coils exhibit maximally spread wire patterns, reduced peak temperature and maximum efficiency for a given coil surface. An increase in inductance/resistance is observed for coils with considerably reduced maximum current density.

                  1525.     Computer Assisted MR Imaging Simulation for Guidance of Gradient Coil Development During Design Phase

Silke Maria Lechner^1,2, Mika W. Vogel¹, Bruce C. Amm³, Timothy J. Hollis⁴, Hans-Joachim Bungartz²

¹GE Global Research Europe, Garching, Germany; ²Technische Universität München, Garching, Germany; ³GE Global Research, Niskayuna, NY, United States; ⁴GE Medical Systems, Oxford, United Kingdom

In magnetic resonance (MR), fast and high-resolution imaging require strong and fast switching gradients. The design of this new gradient coil generation is challenging in terms of field non-linearity and induced field distortions resulting in image artifacts. This work introduces a simulation environment that extends and integrates existing simulation tools by including gradient designs within predictive image quality assessment software. To demonstrate the capabilities of this new environment, a three-axis uniplanar flat gradient set is modeled. Realistic model simplifications as well as magnetostatic evaluations and first application simulations are presented here to increase computational speed and to verify the model.

                  1526.     Wrapped Edge Gradient Coil for Mri-Pet Animal Imaging

Viktor Vegh¹, Quang M. Tieng²

¹Centre for Advanced Imaging, University of Queensland, Brisbane, Queensland, Australia; ²Centre for Magnetic Resonance, University of Queensland, Brisbane, Queensland, Australia

There is an increasing need to design and build systems that are capable of acquiring different modality medical images. This work describes a method of simulation of gradient coils which are appropriate for use in PET-MRI scanners. The proposed gradient coil with a gap in the middle has windings wrapped into the transverse plane at the edges for improved gradient fields. The design is developed for animal scanners with an inner bore size of 40cm. The gradient coil winding pattern, magnetic field produced and error in the gradient magnetic field are provided to establish quality of design.

                  1527.     Characterisation of a PatLoc Gradient Coil

Anna Masako Welz¹, Daniel Gallichan¹, Christian Cocosco¹, Rajesh Kumar², Feng Jia², Jeff Snyder¹, Andrew Dewdney³, Jan Korvink^2,4, Jürgen Hennig¹, Maxim Zaitsev¹

¹Dept. of Diagnostic Radiology, Medical Physics, University Hospital Freiburg, Freiburg, Baden-Württemberg, Germany; ²Dept. of Microsystems Engineering – IMTEK, University of Freiburg, Freiburg, Germany; ³Siemens Healthcare, Erlangen, Germany; ⁴4Freiburg Institute of Advanced Studies (FRIAS), University Freiburg, Freiburg, Germany

The proposed and self-build PatLoc gradient coil needs special characterisation to support and improve the quality of the images acquired with this gradient coil. Focusing on image acquisition, frequency shifts arising from eddy currents and concomitant fields were assessed and evaluated. Frequency drifts of around 0.1HZ from eddy currents and up to 300Hz from concomitant fields were observed. With encoding fields of around 3*105 Hz, both effects are negligible for most imaging applications.

                  1528.     Fast Optimization Method for General Surface Gradient Coil Design

Feng Jia¹, Zhenyu Liu², Jan G. Korvink^1,3

¹Department of Microsystems Engineering (IMTEK), University of Freiburg, Freiburg, Germany; ²Changchun Institute of Optics, Fine Mechanics and Physics (CIOMP), Chinese Academy of Sciences,, Changchun, China; ³Freiburg Institute of Advanced Studies (FRIAS), University of Freiburg, Freiburg, Germany

In this paper, we present an efficient numerical iterative optimization method for designing linear gradient coil on a current-carrying surface. Using the scalar stream function as design variable, the value of the magnetic field inside a computational domain is calculated using the least square finite element method. The first-order sensitivity is calculated using the adjoint equation method. The detailed numerical optimization skills are discussed in order to obtain a fast and effective optimization procedure. Numerical examples demonstrate that this method can be used to design a gradient coil on any surface.

                  1529.     Mechanically Adjustable Shielded Insert Gradient for Experimental Evaluation of Construction Tolerances

Dustin Wesley Haw¹, Brain Dalrymple¹, Frank Van Sas¹, Timothy James Scholl¹, Blaine Alexander Chronik¹

¹Department of Physics and Astronomy, University of Western Ontario, London, Ontario, Canada

Virtually all applications in MR require the rapid switching of gradient fields within the scanner, and many emerging applications take advantage of rapidly switched shim coils; eddy-currents generated in the system are therefore a constant challenge.  The construction tolerances required for these shielded systems are not well known.  Our goal is to examine the eddy-currents generated by driving a special shielded insert gradient coil of our own design.  We present initial results with this test system for the impedance of the shielded gradient insert as a function of shield positioning error, both inside and outside an idealized scanner bore.

                  1530.     Optimization of Insert Gradient Coils for Highly Localized Diffusion-Weighting

Rebecca E. Feldman¹, William Handler², Blaine A. Chronik²

¹Medical Biophysics, University of Western Ontario, London, Ontario, Canada; ²Physics and Astronomy, University of Western Ontario, London, Ontario, Canada

Localized gradients can deliver high gradient strengths and slew rates due to both increased gradient efficiency and elevated nerve stimulation thresholds. Gradients in diffusion-weighted imaging play two distinct roles. A gradient with a large linear range is required for imaging. However, for the diffusion weighting the gradient is only required to be strong. This abstract details the optimization for a diffusion-only gradient intended to be used as a fourth axis in addition to the three standard whole-body imaging gradients. Non-cylindrical and planar designs are considered. Using non-traditional designs, and a relaxed linearity constraint, exceptionally strong gradients can be designed.

Shims & Field Correction

                  1531.     Transient Eddy Current Simulation of a Uni-Planar Gradient Set

Silke Maria Lechner^1,2, Timothy J. Hollis³, Hans-Joachim Bungartz², Bruce C. Amm⁴, Guido Kudielka¹, Mika W. Vogel¹

¹GE Global Research Europe, Garching, Germany; ²Technische Universität München, Garching, Germany; ³GE Medical Systems, Oxford, United Kingdom; ⁴GE Global Research, Niskayuna, NY, United States

The use of computer assisted magnetic resonance imaging simulation strongly supports the design of new gradient hardware as it allows the prediction of gradient non-linearity or other distortion sources on image quality. This work utilizes finite element method simulations of a uni-planar gradient set to analyze and visualize the created transient eddy currents. Therefore, typical eddy current origins, such as thermal shield and cryostat, but also the included cooling tubes of the planar gradient set are investigated. Eddy current amplitudes and timing constants are presented for aluminum, stainless steel and copper, where interestingly, the eddy currents induced in copper cooling tubes are as strong as the induced currents in the warm bore.

                  1532.     Design and Implementation of a Real Time Multi-Coil Amplifier System

Terry W. Nixon¹, Christoph Juchem¹, Scott McIntyre¹, Douglas Lawrence Rothman¹, Robin A. de Graaf¹

¹MR Research Center, Yale University, New Haven, CT, United States

A custom Multi Coil Amplifier System (MCAS) was designed and built to drive an array of small electrical coils which are independent of the scanner’s shim and gradient coils. The system was designed to have up to 96, independent +/- 1A constant current channels. A controller was developed to interface between a host computer and the constant current amplifiers. The controller has independent memory for each channel and was interfaced to the spectrometer’s pulse programmer to allow rapid amplitude changes enabling both static and dynamic applications.

                  1533.     Reduced Susceptibility Artifacts in Diffusion Weighted Brain Imaging Using Specialized RF and Gradient Hardware

Joshua Kaggie^1,2, Seong-Eun Kim², Dennis L. Parker², K Craig Goodrich², Rock Hadley²

¹Physics, University of Utah, Salt Lake City, UT, United States; ²Utah Center for Advanced Imaging Research, University of Utah, Salt Lake City, UT, United States

Diffusion Weighted Imaging (DWI) susceptibility artifacts are reduced by combining an in-house gradient coil with the system gradient coil to form a composite gradient (CG) system with increased slew rates and gradient field strength.  A shielded endcap birdcage coil was developed for the CG system. A human brain was imaged using a 2D ss-EPI sequence.  The resulting phase encoding bandwidth was 6.25 Hz with the system gradients and 12.2 Hz with the CG, resulting in smaller susceptibility artifacts in human brain images acquired with the composite system.

                  1534.     Magnetic Field Modeling with a Set of Electrical Coils

Christoph Juchem¹, Terrence W. Nixon¹, Scott McIntyre¹, Douglas L. Rothman¹, Robin A. de Graaf¹

¹MR Research Center, Yale University, New Haven, CT, United States

The theoretical and experimental generation of linear magnetic field gradients as well as more complex magnetic field distributions (e.g. X2-Y2, Z2, Z2X) with a set of 24 circular, localized coils is presented. Gradients as being generated with the multi-coil approach allowed radial imaging of a mouse head. The multi-coil approach allows a flexible trade-off between accuracy and strength of the generated fields. Furthermore, the parameters are readily optimized for the specific object and volume-of-interest under investigation.

                  1535.     Multi-Coil Shimming of the Mouse Brain at 9.4 Tesla

Christoph Juchem¹, Peter B. Brown¹, Terrence W. Nixon¹, Scott McIntyre¹, Douglas L. Rothman¹, Robin A. de Graaf¹

¹MR Research Center, Yale University, New Haven, CT, United States

The first experimental realization of the multi-coil concept allowed improved shimming of the mouse brain at 9.4 Tesla. The field shapes that can be generated with a set of circular, electrical coils are shown to be much better suited to compensate for the multitude of strong, localized and complex magnetic field distortions apparent in the mouse brain than the conventional, low order spherical harmonic functions used so far.

                  1536.     A Method for Characterizing the Magnetic Field Response of a Gradient System

Signe Johanna Vannesjö¹, Maximilian Häberlin¹, Lars Kasper¹, Christoph Barmet¹, Klaas Paul Pruessmann¹

¹Institute for Biomedical Engineering, ETH and University Zürich, Zürich, Switzerland

MRI relies on dynamic linear gradients for signal encoding, but the realization of given gradient time-courses is usually imperfect due to physical limitations. To characterize the magnetic field response to gradient-channel inputs the system is here treated as a linear time-invariant system that can be fully described by its impulse response functions. The field response was measured up to 3rd order in space with a dynamic field camera, consisting of 16 NMR probes. The measured impulse response functions allowed for accurate prediction of actual k-space trajectories and also showed predictable higher-order effects.

                  1537.     Magnetic Field Gradient Waveform Monitor (MFGM)

Hui Han¹, Bruce J. Balcom

¹UNB, Fredericton, N.B, Canada

Numerous methods have been developed to measure MRI gradient waveforms and k-space trajectories for correcting the remaining hardware imperfections. The most widely used method to characterize eddy currents behavior is a slice selection method by Duyn. The most promising new strategy appears to be magnetic field monitoring (MFM) with RF microprobes.

The new concept, pure phase encode magnetic field gradient monitor (MFGM), was recently proposed by us to solve four critical problems related to the above two methods

                  1538.     Frequency-Division Multiplexing for Concurrent Imaging and Field Monitoring

Matteo Pavan¹, Signe Johanna Vannesjö¹, Christoph Barmet¹, David Brunner¹, Klaas Paul Pruessmann¹

¹ETH Zurich, Zurich, Switzerland

Frequency Division Multiplexing has been used from engineers since a long time to carry different signals in the same transmission line. The method consists to add signals with non-overlapping frequencies content to each other. Each signal can be fully recovered with passband filtering. In this work we use this technique to acquire in the same spectrometer channel both image information and magnetic-field-monitoring information. The image can be eventually reconstructed taking into account the actual measured magnetic field dynamic. Magnetic field monitoring is performed measuring the phase information in four fluorine probe; with this method additional channels are not need.

                  1539.     Fabrication of an MRI Superconducting Magnet with an Off-Center Homogeneous Field Zone for Imaging

Masaki Sekino¹, Akihisa Miyazoe¹, Hiroyuki Ohsaki¹, Tatsuhiro Hisatsune¹, Osamu Ozaki², Tsukasa Kiyoshi³, Hitoshi Wada³

¹The University of Tokyo, Kashiwa, Japan; ²Kobe Steel Ltd., Kobe, Japan; ³National Institute for Materials Science, Tsukuba, Japan

MRI requires a highly homogenous magnetic field zone which usually appears at the center of the MRI magnet coil. If this homogeneous zone is allowed to occur at an off-center position along the coil axis, the patient has a wide field of vision to carry out drawing or other interesting tasks for fMRI. In order to examine this idea, we fabricated a model magnet consisting of seven NbTi coils and generating a vertical magnetic field of 0.77 T; coil outer diameter is 307 mm, coil length 191 mm, designed field homogeneity 5 ppm @ 35mm DSV, and the location of homogeneous field zone 29.4 mm off-centered along the vertical coil axis.

                  1540.     Software Compensation of Eddy Current Fields in Higher Order Dynamic Shimming

Saikat Sengupta^1,2, Brian E. Welch, ^1,3, Adam Anderson^1,4, John Gore^1,4, Malcolm J. Avison^1,4

¹Vanderbilt University Institute of Imaging Science, Nashville, TN, United States; ²Biomedical Engineering, Vanderbilt University, Nashville, TN, United States; ³Philips Healthcare,, Cleveland, OH, United States; ⁴Radiology and Radiological Sciences, Vanderbilt University, Nashville, TN, United States

We present a novel method of eddy current compensation for higher order shim induced eddy currents in a multislice Dynamic Shimming (DS) experiment, without the use of extra hardware. This method is based on an assumption of reaching an eddy field steady state during a fast field echo (FFE) acquisition. Using calibration scans, we characterize eddy field interactions between any two shims in terms of correction factor vectors that remain invariant with sample and shim values, for a given time between shim switches. These factors are then used to prospectively compensate for expected eddy fields in any FFE DS experiment.

                  1541.     A Novel Localized Passive Shim Technique for Optimizing Magnetic Field of the Human Orbitofrontal Cortex at High Field

Mohan Jayatilake¹, Judd Storrs², Jing-Huei Lee²

¹Department of Physics and Center for Imaging Research, University of Cincinnati, Cincinnati, OH, United States; ²Department of Biomedical Engineering and Center for Imaging Research, 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. Simulated and experimental studies showed that the correction for magnetic field at orbitofrontal cortex (OFC) area required shims with third and higher orders, which are not practically implemented. We propose a novel localized passive shim technique with the use of combined diamagnetic and para/ferromagnetic material to improve the field homogeneity within subjects’ brains, particularly in the OFC.

                  1542.     A Single-Channel Planar Shim Coil for a Permanent Magnet

Ryosuke Shigeki¹, Katsumi Kose¹

¹Institute of Applied Physics, University of Tsukuba, Tsukuba, Ibaraki, Japan

A single-channel planar shim coil for a permanent magnet was developed using the target field approach. The winding pattern for the shim coil was calculated for a 1.0 T permanent magnet using the magnetic field inhomogeneity measured with a 3D lattice phantom. The designed shim coil improved the magnetic field homogeneity by about 5 times, which demonstrated the usefulness of our approach.

                  1543.     Slice Shimming Method for Reduction of Susceptibility Artifacts with PatLoc System

Hsuan-Chung Niu¹, Hsiao-Wen Chung², Teng-Yi Huang³, Fa-Hsuan Lin^4,5

¹Graduate Institute of Biomedical Electronic and Bioinformatics, National Taiwan University, Taipei, Taiwan; ²Department of Electrical Engineering, National Taiwan University, Taipei, Taiwan; ³Department of Electrical Engineering, National Taiwan University of Science and Technology, Taipei, Taiwan; ⁴Institute of Biomedical Engineering, National Taiwan University, Taipei, Taiwan; ⁵A. A. Martinos Center, Massachusetts General Hospital, Charlestown, MA, United States

In this work, we attempt to apply the PatLoc system to achieve a better shimming and improved the field homogeneity. Specifically, we used the surface gradient coils in the 8-channel PatLoc system as the shim coils to reduce the distortion of brain echo-planar imaging.

                  1544.     An Algorithm for Designing Passive Shim Sets Compensating for Anatomically Specific B0 Inhomogeneities

Zhipeng Cao¹, Rahul Dewal¹, Christopher T. Sica¹, Chien-ping Kao¹, Christopher M. Collins¹, Qing X. Yang¹

¹PSU College of Medicine, Hershey, PA, United States

A novel synergetic shimming strategy is proposed for compensation of high order local B0 inhomogeneities in the human brain. This approach utilizes passive shimming to compensate for high order local field inhomogeneities and active shimming to compensate for the linear components. Computer simulation results demonstrate the effectiveness of the proposed method in reduction of local field inhomogeneities in the human head, suggesting a valuable shimming method for high field MRI in human and animal studies.

Systems: Other

                  1545.     High Resolution Imaging Using a High-Field Yokeless Permanent Magnet

Katsumi Kose¹, Tomoyuki Haishi²

¹Institute of Applied Physics, University of Tsukuba, Tsukuba, Ibaraki, Japan; ²MRTechnology Inc., Tsukuba, Ibaraki, Japan

Temperature drift of the magnetic field of a thermally insulated yokeless permanent magnet (field strength = 1.04 T) was measured for about 68 hours. The temperature coefficient of the magnetic field was about -950 ppm/deg. The largest Larmor frequency change was about 50 Hz/min. The performance of the thermal insulation was evaluated with high resolution imaging (20~40 micron square) of several samples. The results have suggested that careful choice of the NMR lock interval and the pixel bandwidth will solve the temperature drift problem of the high field yokeless magnet.

                  1546.     Feedback Control System for Safe and Accurate Control of a Fully MRI-Compatible Hydraulic Treadmill

Mihaela Jekic¹, Eric L. Foster², John Arnold³, Jacob Bender¹, Subha V. Raman⁴, Orlando P. Simonetti⁵

¹Biomedical Engineering, The Ohio State University, Columbus, OH, United States; ²Davis Heart and Lung Research Institute, The Ohio State University, Columbus, OH, United States; ³Agricultural Technical Institute, The Ohio State University, Columbus, OH, United States; ⁴Internal Medicine, The Ohio State University, Columbus, OH, United States; ⁵Internal Medicine and Radiology, The Ohio State University, Columbus, OH, United States

We developed a feedback control system for a fully MRI-compatible water hydraulic treadmill, and tested its performance up to the speed of 5.5 miles/hr and the incline of 11.3º, corresponding to stage 6 of the standard Bruce treadmill protocol widely used in cardiac stress testing. Feedback is obtained using fiber optic sensors while the control is performed outside the MRI room using LabVIEW. In addition, we implemented several safety features to ensure the treadmill speed and elevation will remain within specified safety limits. The treadmill was found to perform accurately and safely immediately adjacent to the MRI table.

                  1547.     Magnetic Field Exposure Tests on a Siemens Inveon Small Animal PET System: A Feasibility Study for Multimodality PET and Field-Cyled MRI

Geron Andre Bindseil¹, William B. Handler¹, Timothy J. Scholl¹, Blaine A. Chronik¹

¹Department of Physics and Astronomy, University of Western Ontario, London, Ontario, Canada

One approach to PET/MRI is to use field-cycled (FCMRI) with a conventional PMT-based PET system. Combining PET with FCMRI would enable the use of commercially available, highly optimized PET systems with little physical modification. For this approach to be feasible, the PET detectors must experience no permanent changes in gain or efficiency after exposure to magnetic fields. The authors present results from a preliminary feasibility study testing the performance of a commercial small-animal PET system after exposure to magnetic fields. No significant permanent changes were observed in PET imaging performance.

                  1548.     Bo Coil Designs for in Vivo Delta Relaxation Enhanced MR in Humans

Chad Tyler Harris¹, Jamu K. Alford¹, William B. Handler¹, Timothy J. Scholl¹, Blaine Alexander Chronik¹

¹Department of Physics and Astronomy, University of Western Ontario, London, Ontario, Canada

Delta relaxation enhanced magnetic resonance (dreMR) is an emerging technology that utilizes an insert electromagnet to modify the main magnetic field as a function of time in an otherwise conventional MR scanner. In this study, we investigate the design and performance of insertable electromagnets suitable for performing localized dreMR imaging in human subjects. The two particular anatomical areas of interest are the head/neck, and the prostate; however, this approach may be extended to a variety of other application areas.

                  1549.     Low Power and High Field Strength B0 Coil: A Vision of Portable MR

Wen-Yang Chiang¹, Kelvin Wong¹, Stephen TC Wong¹

¹Center for Bioengineering and Bioinformatics, The Methodist Hospital Research Institute and Department of Radiology, The Methodist Hospital, Houston, TX, United States

In order to address the need of the MR coil with both high field strength and low power usage, a miniaturized B0 coil is presented. Finite element simulation showed that higher magnetic field strength was generated by a coil with sharp tip than that by a coil with blunt end. A cost effective way was introduced to fabricate this sharp tip coil. Focused magnetic field generated by the coil with a sharp tip was directly measured by a tunneling effect magnetic field sensor. This study will help in addressing the need of portable MR systems.

                  1550.     MR Compatible Sensor for Measuring Respiratory Motion Based on Acceleration.

Laure Rousselet^1,2, Marina Filipovic^1,2, Zhor Ramdan-Cherif^1,2, Valérie Laurent, ^2,3, Cédric Pasquier⁴, Jacques Felblinger^1,2

¹IADI, Nancy-Université, Nancy, France; ²U947, Inserm, Nancy, France; ³CHU de Nancy, Nancy, France; ⁴CIC801, INSERM, Nancy, France

MR acquisitions have to be synchronized with respiration to avoid motion artifacts. Pneumatic belts are the most current tool for this purpose. However, these belts suffer from signal drifts, leaks in pneumatic system and give only an average displacement. We present a MR compatible sensor which aims at measuring the acceleration of a localized region. Accelerometer is well correlated to image-based displacement measures and gives similar results to respiratory belts. The sensor presents practical advantages: it is small, easy to position on the patient, less cumbersome than respiratory bellows and allows for local displacement estimation.

                  1551.     An Optimized Insert Coil for High-Performance Delta Relaxation Enhanced MR Imaging of the Mouse

Jamu K. Alford¹, Timothy J. Scholl¹, William B. Handler¹, Blaine A. Chronik¹

¹Physics and Astronomy, The University of Western Ontario, London, ON, Canada

Delta relaxation enhanced magnetic resonance (dreMR) is an emerging method for field-cycled MR imaging, which utilizes a removable electromagnetic coil to modify the strength of the main magnetic field during an MRI pulse sequence.  This abstract describes major improvements made in a new, high-performance, second-generation dreMR system for mouse and small animal imaging. Comparisons are made between this second-generation dreMR coil and the prototype dreMR coil used in early dreMR studies.

                  1552.     A Safe and Artefact Free Device for Monitoring Galvanic Skin Conductance During FMRI

Peter Erhard¹, Dieter Leibfritz¹

¹Dept. of Chemistry, University of Bremen, Bremen, Germany

We developed a device for measuring galvanic skin response (GSR) during functional magnetic resonance imaging (fMRI). The goal was to prevent the volunteer from the risk of electric stimulation due to gradient induced currents into the leads of the device. This was achieved by inserting photo electronic switches into the leads close to the electrodes. These switches are turned off during gradient switching. As GSR data is only acquired during quiet periods, no additional filtering was implemented. First tests show efficient protection from electric stimulation. However the GSR signal is still contaminated by physiological noise and minor gradient cross talk.

                  1553.     MR Compatible Spirometer

Laure Rousselet¹, Marina Filipovic¹, Slavisa Jovanovic^1,2, Gilles Bosser³, Cédric Pasquier⁴, Jacques Felblinger¹

¹IADI, Nancy-Université, Nancy, France; ²U947, Inserm, Nancy, France; ³Physical Medicine and Rehabilitation, University Hospital of Nancy, Nancy, France; ⁴CIC801, INSERM, Nancy, France

MR compatible spirometer is needed for (i) monitoring of anaesthetized patient and (ii) sequence synchronization and/or image reconstruction to avoid motion artifacts. We present an MR compatible spirometer which aims at measuring patient’s air flow and lung volume in order to extract motion information. The proposed sensor could be connected to the respirator in order to monitor patients during MRI examination.  Spirometer is well correlated to internal displacement extracted from the images series, although a time delay appears due to the external position of the sensor.