Joint Annual Meeting ISMRM-ESMRMB 2014 10-16 May 2014 Milan, Italy


MR ENGINEERING (13:30-15:30)

4795-4818 RF Coils, Waveguides & Dielectrics
4819-4842 MR Engineering
4843-4865 Magnets, Gradients & Shimming

RF Coils, Waveguides & Dielectrics

Thursday 15 May 2014
Exhibition Hall  13:30 - 14:30

  Computer #  
4795.   1 High Resolution Double Resonant 1H/19F RF Coil for Small Rodent MRI and MRS at 3T
Helmar Waiczies1, Jan Rieger1, Andreas Graessl2, Andreas Pohlmann2, Matthias A. Dieringer2,3, and Thoralf Niendorf2
1MRI.TOOLS GmbH, Berlin, Germany, 2Berlin Ultrahigh Field Facility (B.U.F.F.), Max Delbrück Center for Molecular Medicine, Berlin, Germany, 33Working Group on Cardiovascular Magnetic Resonance, Experimental and Clinical Research Center (ECRC), Berlin, Germany

A dual-tuned 1H/19F birdcage coil with high B1+homogeneity for animal research at a clinical 3T-System has been constructed. The simulated B1+ fields and the measured B1+ maps were found to be in good agreement, including anatomical coverage, B1+ distribution and B1+ efficiency. The acquired ex vivo images showed superb sensitivity for 19F MRI as well as high spatial resolution for 1H MRI. This work demonstrates the feasibility of a double tuned birdcage coil tailored for 1H/19F MR in small rodents using a clinical 3T MR system. The proposed RF coil provides high homogeneity and sensitivity for very low concentrations of 19F. This progress may serve to enhance the capabilities of 19F MR based cell tracking in small rodents and benefits translational research en route to 19F MR in large animals or even humans.

4796.   2 Radiation Damping in a Detuned Probe by the Bloch-Kirchhoff Equations
James Tropp1
1Engineering, GE Healthcare Technologies, Fremont, CA, United States

We have calculated the rates of radiation damping as a function of probe detuning, by numerical solution of the Bloch-Kirchhoff equations.

4797.   3 An Active Decoupled HTS Film Coil for 1.5T MRI
Lian Xue1, Zungang Liu1, Changwu Hu1, Kuan Zhang1, Erzhen Gao1, QY Ma1, Nikolaus M Szeverenyi2, Rebecca Theilmann2, and William Bradley2
1Time Medical Systems, Inc., San Diego, CA, United States, 2Radiology, Univ. of California, San Diego, San Diego, CA, United States

A clinically useful 10 cm diameter high temperature superconductor (HTS) surface coil was designed, constructed, and tested for wrist imaging performance on a 1.5 Tesla scanner. The cryostat was constructed of fiberglass and had a liquid nitrogen hold time of 5 hrs and a vacuum hold time of 4 weeks. Comparison of this coil’s performance with a commercial 10 cm room temperature copper coil demonstrated a greater than 2 fold improvement in SNR. This receive coil has an active detuning circuit that can be used in future array coils designs.

4798.   4 Helix antennas: approaching the target from a different angle
Alexander J.E. Raaijmakers1, Abe van der Werf2, Hugo Kroeze1, Peter R. Luijten1, Cornelis A.T. van den Berg3, and Dennis W.J. Klomp1
1Radiology, UMC Utrecht, Utrecht, Utrecht, Netherlands, 2Machnet B.V., Roden, Netherlands, 3Radiotherapy, UMC Utrecht, Utrecht, Netherlands

Helix antennas are a commonly used type of antenna in communication technology. They emit a circularly polarized wave with high directivity. For MRI, the helix antenna has the unique property to transmit or receive along the longitudinal axis of the scanner. This unique property enables the coverage of regions that are otherwise hard to address, particularly at higher field strengths. For example, the helix antenna can be used to recover B1 at the apex of the head. For prostate imaging, the helix antenna can be used to increase sensitivity by placing the coil between the legs, along the longitudinal axis.

4799.   5 Electro-optic RF magnetic resonance signal based on a Ti:LiNbO3 waveguide
Reina Ayde1, Anne-Laure Perrier1, Jean Dahdah2, Raphael Sablong1, Lionel Duvillaret2, Gwenael Gaborit2,3, and Olivier Beuf1
1University of Lyon 1, CREATIS - CNRS UMR 5220 – INSERM U1044, Villeurbanne, Rhone-Alpes, France, 2Kapteos, Rhone-Alpes, France, 3University of Savoie, IMEP-LAHC UMR 5130, Rhone-Alpes, France

The use of metallic coaxial cables in Magnetic Resonance Imaging could induce local high Specific Absorption Rate (SAR). Optical fiber link could be a promising alternative to coaxial cables for MRI to ensure patient safety. Here, the conversion of the Radio-Frequency magnetic field into an electric signal by electro-optic effect was demonstrated and characterized. A waveguide crystal is used together with an endoluminal coil to demonstrate the ability of such transducer to perform a deported characterization of Radio-Frequency magnetic field at 3T. The results show a good agreement with theoretical values and a minimum magnetic detectable field of pT order.

4800.   6 Box Shaped Monopole Antenna for RF Excitation at 9.4T MRI
Irena Zivkovic1 and Klaus Scheffler1,2
1High Field MRI, Max Planck Institute for Biological Cybernetics, Tuebingen, Germany, 2Center for Integrative Neuroscience, Universuty of Tuebingen, Tuebingen, Germany

It is a big challenge to produce as homogeneous as possible B1+ field with single channel antenna in traveling wave configuration. For that purpose, we proposed a new and very simple antenna concept. Antenna is entirely made of copper and without any lumped elements. By small changes in geometry different RF excitation patterns can be produced. We presented design that produced as homogeneous as possible B1+ field in sagittal, coronal and transversal planes. The second proposed design produced B1+field pattern in lower brain and neck region.

4801.   7 A clinically useful HTS knee coil for 0.35 T MRI
Zungang Liu1, Changwu Hu1, Erzhen Gao1, Ronald Tse1, QY Ma1, Nikolaus M Szeverenyi2, and William G Bradley2
1Time Medical Systems, Inc., Shanghai, China, 2Radiology, Univ. of California, San Diego, CA, United States

A preliminary HTS volume knee coil was designed to improve the image quality of a low field MRI system. The coil is cooled by liquid nitrogen with a very low nitrogen boil-off rate. Knee images were obtained and compared to a commercial copper coil.

4802.   8 A field probe transceiver system with controllable RF coupling and decoupling
Ying-Hua Chu1, Yi-Cheng Hsu1, Shang-Yueh Tsai2, and Fa-Hsuan Lin1,3
1Institute of Biomedical Engineering, National Taiwan University, Taipei, Taiwan, 2Institute of Applied Physics, National Chengchi University, Taipei, Taiwan,3Department of Biomedical Engineering and Computational Science, Aalto University, Espoo, Finland

We propose a new approach to improve the isolation of NMR signals originating from the field probe and from the imaging object without using an independent transceiver. We use an RF coil (Tx loop) to pick up the RF energy during RF transmission to the field probe inside an RF shield. During RF reception, the Tx loop is detuned such that the NMR signal from the imaging object will not be picked up by the Tx loop and the field probe can remain isolated inside the RF shielding. This design is empirically demonstrated by an one-channel prototype system.

4803.   9 Design of a 24-Mesh Inductive Birdcage for Imaging of the Head at 500 MHz
Joseph Murphy-Boesch1, Qi Duan1, Steve Dodd1, Natalia Gudino1, Shumin Wang2, and Jeff Duyn1
1National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, United States, 2Department of Electrical and Computer Engineering, Auburn University, Auburn, AL, United States

An inductive birdcage resonator with 24 meshes has been assembled for imaging of the head in the confined space of an 11.7T head-only MRI system. To reduce radiative losses and de-tuning by the head, the resonator was suspended within its cylindrical shield with no direct RF connections. Four-port connection to the coil was effected using inductive couplers with balanced drive to further reduce E-fields. Bench sensitivity and field uniformity are similar to a 7T coil. Power testing using a custom phantom yielded differential temperature increases that can be used to validate EM simulations.

4804.   10 Modular and Versatile Multi-Row Transmit Array based on a Novel Decoupled Coil Element Design
Riccardo Stara1, Simone A. Winkler2, Ronald D Watkins2, Alessandra Retico3, Michela Tosetti4, and Brian K Rutt2
1Dipartimento di Fisica, Università di Pisa, Pisa, Italy, 2Department of Radiology, Stanford University, Stanford, CA, United States, 3Istituto Nazionale di Fisica Nucleare, Pisa, Italy, 4IRCCS Stella Maris, Pisa, Italy

B1+ shimming and parallel transmission can benefit from an increased number of transmit channels and from 3D segmentation. However, one of the remaining challenges in RF coil designs for parallel transmission is the decoupling between coil elements. We present a novel transmission line element used in a modular two-row 16-channel transmit array design. The proposed element employs cylindrical shielding to provide intrinsic geometric decoupling, without any additional hardware. The proposed 16-channel array can be configured for 8-channel single-row and 16-channel two-row mode using two Butler matrices. Numerical simulations and preliminary experiments show improved decoupling performance and B1+/E performance.

4805.   11 A 16-Channel Transceiver Array for 7 Tesla Equine Joint MRI
Hai Lu1, Ziyuan Fu2, and Shumin Wang2
1Auburn University, Auburn, Alabama, United States, 2Auburn University, Alabama, United States

Multi-channel transceiver arrays are highly desired for 7 Tesla MRI due to the lack of volume transmitters. We developed a 16-channel transceiver array for equine joint MRI at 7T by splitting the single-channel power input equally into 16 coil elements. The design and implementation details are discussed. Actual imaging results further demonstrate the feasibility of the design.

4806.   12 A flexible transceiver array of monolithic transmission line resonators
Roberta Kriegl1,2, Jean-Christophe Ginefri1, Marie Poirier-Quinot1, Luc Darrasse1, Ewald Moser2,3, and Elmar Laistler2,3
1Laboratoire d'Imagerie par Résonance Magnétique Médicale et Multi-Modalités (IR4M), Université Paris Sud, Orsay, Essonne, France, 2Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Vienna, Austria, 3MR Center of Excellence, Medical University of Vienna, Vienna, Vienna, Austria

A novel transceiver array composed of monolithic transmission line resonators, fabricated on flexible substrate, for MRI at 7 T is presented. Individual array elements are mutually decoupled via overlapping annexes; inductive matching and fine-tuning using pick-up loops in over-coupled mode was implemented. The decoupling and parallel imaging performance of the array was assessed in bench and MRI experiments in terms of transmission S-parameters, noise correlation values and GRAPPA g-factors, comparing planar and bent array configuration. It is shown that the developed array may be form-fitted to non-planar samples without degrading its performance.

4807.   13 High Resolution Rodent Cochlea Imaging on a 3T Clinical Magnet
Joshua D Kaggie1,2, K Craig Goodrich1, Seong-Eun Kim1, Michael J Beck1, Dennis L Parker1,2, Robb Merrill1, Travis A Abele3, Richard Wiggins3, and J Rock Hadley1
1Utah Center for Advanced Imaging Research, Radiology, University of Utah, Salt Lake City, UT, United States, 2Physics, University of Utah, Salt Lake City, UT, United States, 3Neuroradiology, University of Utah, Salt Lake City, UT, United States

This work developed a small animal system that could acquire good in vivo 100μm isotropic resolution images of a guinea pig cochlea on a 3T clinical MR system. The system used improved gradients, RF coils, and animal holder/monitoring equipment when compared to a standard clinical magnet. FLASH imaging was used to assess the quality of the system. Gadolinium increased the SNR and contrast of the cochlea during FLASH imaging. The small animal system obtained good 100μm isotropic resolution images of the cochlear chambers in a scan time of only 33 minutes.

4808.   14 Optimization of 7 T YBCO Coils for in-vivo and ex-vivo MRI of Small Animals; Assessment of Achievable SNR Gain -permission withheld
Jarek Wosik1,2, Kurt H. Bockhorst3, Krzysztof Nesteruk4, Dhivya Ketharnath1, Tan I-Chih5, and Ponnada A Narayana3
1Electrical and Computer Engineering, University of Houston, Houston, Texas, United States, 2Texas Center for Superconductivity, University of Houston, Houston, Texas, United States, 3Health Science Center, University of Texas, Houston, Texas, United States, 4Polish Academy of Sciences, Institute of Physics, Warsaw, Poland, Poland, 5Center for Molecular Imaging, University of Texas, Houston, Texas, United States

We report on assessment of achievable SNR gain due to reduction of thermal noise by cooling receiver coil made out of copper or superconducting materials. High field MRI 300 MHz receiver probe with tuning/matching and decoupling circuitry was used. The coil was fabricated by patterning double-sided thin superconducting YBCO film on 0.4 mm thick sapphire substrate and comprises of two split rings rotated 180 deg. versus each other. Our main interest in this work is in identification all losses limiting SNR, such as rf losses from coil, body, cryostat and tuning/maching/decoupling circuitry and in discussion on the probe performance optimization.

4809.   15 An interleaved opposing monopole transmit-receive array for 7T brain imaging
Gang Chen1, Martijn Cloos1, and Graham Wiggins1
1The Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, NY, United States

At high field, electric dipole antennas are seeing increasing use. When placed close to a relatively high dielectric material such as the body the self-resonant length shortens somewhat, but for 7T head imaging this still comes out to an inconvenient length of 40 cm or more. We describe here a modified monopole antenna where the ground plane is replaced by a strip of conductor. These are arranged in an 8 element array which allows alternating monopoles to be driven from opposing ends of the array, which extends excitation into inferior brain regions while also providing diverse B1 profiles along Z.

4810.   16 31P Birdcage insert for an 8-channel, multi-transmit, 1H coil at 7T
Bart L. van de Bank1, Stephan Orzada2, Miriam W. Lagemaat1, Andreas K. Bitz2,3, and Tom W.J. Scheenen1,2
1Radiology, Radboud University Medical Center, Nijmegen, Netherlands, 2Erwin L. Hahn Institute, University Duisburg-Essen, Essen, Germany, 3Medical Physics in radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany

A dedicated 31P birdcage coil was designed, validated and constructed as an insert for an 8 channel, multi-transmit, octagonal shaped, 1H coil to enable homogeneous excitation and acquisition of 31P compounds combined with 1H multi-transmit capabilities to asses metabolic processes in-vivo at 7T.

4811.   17 Image quality improvement via phase correction for travelling wave MRI at 3T
Fabian Vazquez1, Oscar Marrufo2, Sergio E Solis1, and Alfredo O Rodriguez3
1Dep Phys, FC UNAM, Mexico, DF, Mexico, 2Dep Neuroimage, INNN-MVS, DF, Mexico, Mexico, 3Dep Elec Ing, UAM Iztapalapa, Mexico, DF, Mexico

Travelling wave magnetic resonance imaging (twMRI) offers an approach to acquire larger fields-of-view images at 7T or greater. Images have two main problems: inhomogeneous acquisition due to the physical restriction in coaxial waveguide at 7T, and added noise in parallel-plate waveguide (PPWG) at 3T. We measured the signal phase added by a PPWG in twMR images at 3T, using a transmission circular coil and other one for reception tuned at 128 MHz. Phantom images were acquired with the PPWG in clinical scanner at 3T. The phase shift information was used to improve the image quality and results compared.

4812.   18 Improved surface coil performance at any depth in a lossy sphere with a dielectric disc
Wei Luo1,2, Yang Qing1, and Christopher M. Collins3
1Radiology, Pennsylvania State University, Hershey, PA, United States, 2Engineering Science & Mechanics, Pennsylvania State University, University Park, PA, United States, 3Radiology, New York University, New York, NY, United States

A simple hybrid coil-HPM design using a simple loop coil and a high-permittivity material (HPM) disc was optimized at 3T using PSO/FDTD method including the consideration on HPM location, geometry, material properties, MRI coil location, and coil geometry for the first time. The coil efficiency of the optimized hybrid design was better than the one produced by the optimized single loop coil at any depth in a lossy sphere, particularly by an average increase of 87% and 22% at the center and superficial regions, respectively. The performance of this simple hybrid design encourages us to expect more improvement with a more sophisticated design.

4813.   19 Improving central transmit efficiency and homogeneity using interleaved shielded dielectric discs and coil elements in a 4-element transmit/receive array at 7 T
Manushka V. Vaidya1,2, Christopher M. Collins1,2, Ryan Brown1, Daniel K. Sodickson1,2, and Riccardo Lattanzi1,2
1Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, NY, United States, 2Sackler Institute of Graduate Biomedical Sciences, New York University School of Medicine, New York, NY, United States

We performed simulations and experiments to evaluate the benefits of placing shielded dielectric discs between adjacent coil elements in a 4-element transmit/receive array surrounding a uniform cylindrical dielectric phantom at 7 T. Our results showed that array performance is improved in the presence of suitably-configured dielectric discs. In particular, the B1 homogeneity improved by ~27% and the transmit efficiency and SNR at the center improved by ~5%. The proposed array design performs better than, and is based on different physical principles than, conductive shields placed above or completely surrounding the coil elements.

4814.   20 Signal-to-Noise Ratio gain at 3T using a thin layer of high-permittivity material inside enclosing receive arrays
Riccardo Lattanzi1,2, Manushka V Vaidya1,2, Giuseppe Carluccio1, Daniel K Sodickson1,2, and Christopher M Collins1,2
1The Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, NY, United States, 2The Sackler Institute of Graduate Biomedical Sciences, New York University School of Medicine, New York, NY, United States

Cushions of high-permittivity material (HPM) placed between radiofrequency (RF) coils and the object can enhance transmit and receive performance. We investigated in simulation the signal-to-noise ratio (SNR) gain when covering the inside of a receive array uniformly surrounding a dielectric sphere with a continuous 1 cm layer of HPM (εr = 500). The SNR gain was positive for every voxel when the array had at least 32 coils (average ~ 10%, maximum ~ 30%). Our results suggest that using a thin encircling layer of HPM could be a practical method to improve performance of receive head arrays at 3T.

4815.   21 Appearant B1+ Asymmetry in Symmetric Objects at High Fields
Wyger Brink1 and Andrew Webb1
1Radiology, Leiden University Medical Center, Leiden, Zuid-Holland, Netherlands

This work investigates, in particular, the origin of the distinct left-right asymmetry in the B1+ field typically observed in the head at 7 T.

4816.   22 Characterization of a Dielectric Phantom for High-Field MRI Applications
Qi Duan1, Jeff H. Duyn1, Natalia Gudino1, Jacco A. de Zwart1, Peter van Gelderen1, Daniel K. Sodickson2,3, and Ryan Brown2,3
1AMRI, LFMI, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland, United States, 2The Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, United States, 3NYU WIRELESS, Polytechnic Institute of New York University, New York, United States

In order to predict wavelength effects on MRI performance and tissue heating at high field, a generic recipe for an inexpensive and nontoxic phantom with biologically-relevant dielectric properties was developed. The recipe includes deionized water, NaCl, sucrose, and benzoic acid. 117 samples were prepared with a range of NaCl and sucrose concentrations, and their dielectric properties were measured and fitted to a three-dimensional polynomial. Nonlinear relationships between sucrose and NaCl concentrations and measured dielectric properties were observed, and strong interactions were found between individual component concentrations in determining dielectric properties.

4817.   23 An Electromagnetic-Simulation based Investigation of the Dielectric Padding Approach for Head Imaging at 7 T
Andreas Rennings1, Keran Wang1, Le Chen1, Friedrich Wetterling2, and Daniel Erni1
1General and Theoretical Electrical Engineering (ATE), University of Duisburg-Essen, Duisburg, NRW, Germany, 2Faculty of Engineering, Trinity College, Dublin University, Dublin, Ireland

We present a simple model and used it for electromagnetic simulations to get physical inside to the dielectric padding approach. Furthermore we determined the best suited values for the pad permittivity and the cross-sectional-planes with best and worst coefficient-of-variation (CoV) for the |B1+| profile.

4818.   24 Effects of high-permittivity materials on absolute RF coil performance as a function of B0 and object size
Riccardo Lattanzi1,2, Manushka V Vaidya1,2, Giuseppe Carluccio1, Daniel K Sodickson1,2, and Christopher M Collins1,2
1The Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, NY, United States, 2The Sackler Institute of Graduate Biomedical Sciences, New York University School of Medicine, New York, NY, United States

Previous work has shown that transmit efficiency and signal-to-noise ratio (SNR) can be improved by placing pads of high-permittivity material (HPM) between the radiofrequency coil and the sample. We employed dyadic Green’s functions for multi-layered spherical geometries to calculate the ultimate intrinsic SNR and the SNR of a 32-element loop array surrounding uniform spheres with different radii. Ultimate performance limits did not change, but could be approached more closely by the finite array with HPM added between the coil and the object. For a head-sized sphere, the SNR advantage was larger at 1.5T and 3T compared to higher B0 values.


MR Engineering

Thursday 15 May 2014
Exhibition Hall  13:30 - 14:30

  Computer #  
25 Implementation of low-cost, instructional tabletop MRI scanners
Clarissa Z Cooley1,2, Jason P Stockmann3,4, Cris LaPierre2,4, Thomas Witzel2, Feng Jia5, Maxim Zaitsev5, Pascal Stang6,7, Greig Scott7, Yang Wenhui8, Wang Zheng8, and Lawrence L Wald2,9
1Electrical Engineering, Massachusetts Institute of Technology, Cambridge, MA, United States, 2Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, MA, United States, 3Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, Massachusetts, United States, 4Department of Physics, Harvard University, Cambridge, MA, United States, 5Department of Radiology – Medical Physics, University Medical Centre Freiburg, Freiburg, Baden-Württemberg, Germany, 6Procyon Engineering, San Jose, CA, United States, 7Electrical Engineering, Stanford University, Stanford, CA, United States, 8Department of Electromagnetic Detection and Imaging Technology, Institute of Electrical Engineering, Chinese Academy of Sciences, Beijing, China, 9Harvard Medical School, Boston, MA, United States

A low-cost, open-interface classroom MRI scanner is demonstrated. The scanner was used in an undergraduate lab course to interactively teach the concepts of free induction decay, flip angle measurement, B0 shimming, gradient echo, spin echo, 1D projection, and 2D as well as 3D MR imaging. An open library of GUIs, pulse sequences, and reconstruction codes is being developed in MATLAB to help build a user base.

4820.   26 New cardiac and breathing monitoring tool in MRI.
André Guillou1,2, Gregory Petitmangin2, Roger Abächerli3, Laurent Bonnemains1, and Jacques Felblinger1
1Inserm U947 (IADI), Nancy, Lorraine, France, 2Schiller, Wissembourg, Alsace, France, 3Schiller, Baar, Zoug, Switzerland

As the ECG in MRI is disturbed by MR gradient swithings, hall sensors are used as input for gradient artifact reduction tools (as adaptive filtering), to provide clean ECG trace. Placed in the MR bore, this sensor was found to give additional information about respiration and heart pulse. We explored the possibility to use these data for patient monitoring during cardiac MRI.

27 Design of multi-channel switching system for matrix coils
Huijun Yu1, Frank Huethe2, Sebastian Littin1, Feng Jia1, Jürgen Hennig1, and Maxim Zaitsev1
1Dept. of Radiology, Medical Physics, University Medical Center Freiburg, Freiburg, Germany, 2Dept. of Clinical Neurology and Neurophysiology, University of Freiburg, Germany

We present a hardware design of multi-channel switches for a dedicated matrix gradient coil. The switching system is used to control the combination of the matrix coil elements. The system consists of a controller and a number of analog switches. The analog switches are designed to be placed in the immediate vicinity of the matrix coil elements inside the magnet bore. A timer circuit in combination with a current source charges the bootstrap capacitor periodically and generates the power supply for the floating driver output circuit. The realized setup for switching high currents switched correctly following the coil setting code. Due to its modular design, the number of channels can be customized in future systems by choosing the appropriate number of analog switches.

4822.   28 Toward 10.5T MRI
J. Thomas Vaughan1, Lance DelaBarre1, Jinfeng Tian1, Sungmin Sohn1, Devashshish Shrivastava1, Gregor Adriany1, and Kamil Ugurbil1
1CMRR - Dept. of Radiology, University of Minnesota, Minneapolis, MN, United States

To safely and successfully image the whole human at 10.5T, new RF methods and technologies must be developed. This abstract outlines and shows results for the first steps toward 10.5T MRI.

4823.   29 Magnetic Carrier for Hyperpolarized 13C Sample Transfer from DNP Polarizer to MR Scanner
Hong Shang1, Timothy Skloss2, Cornelius vonMorze1, Lucas Carvajal1, Mark Van Criekinge1, Peder E.Z. Larson1, Ralph Hurd3, and Daniel B. Vigneron1
1Radiology and Biomedical Imaging, UCSF, San Francisco, California, United States, 2GE Healthcare, Wisconsin, United States, 3GE Healthcare, California, United States

A specialized magnetic carrier was constructed to supply a suitable magnetic field(> 50 G) to preserve the polarization during hyperpolarized sample transfer, especially for hyperpolarized C-13 urea. It improved the SNR measured in the MR scanner by 2 fold for C-13 urea in our experimental tests.

4824.   30 Eulerian Video Magnification for Heart Pulse Measurements in MRI Scanners
Nicolai Spicher1,2, Christopher Brumann1, Markus Kukuk1, Mark E. Ladd2,3, and Stefan Maderwald2
1University of Applied Sciences and Arts Dortmund, Dortmund, Germany, 2Erwin L. Hahn Institute for Magnetic Resonance Imaging, University Duisburg-Essen, Essen, Germany, 3Division of Medical Physics in Radiology, German Cancer Research Center Heidelberg, Germany

The Eulerian Video Magnification approach is used in this work for color amplification of video data to offer an alternative to the conventional contact-based hardware for peripheral pulse triggering or monitoring units in MR scanners; the triggering is obtained by contactless video analysis. Two different test scenarios, one inside the scanner room of a 7T scanner and one inside the scanner bore during MR measurements at 3T, are shown. The results of the algorithm bear good resemblance with the measured pulse oximeter logs. The validation of real-time feasibility remains to be done.

4825.   31 A platform independent infrastructure for real-time MRS/MRI data streaming, processing and storage
Brian J. Soher1
1Radiology, Duke University Medical Center, Durham, NC, United States

The dynamic flow of MR data from scanners to external computers during data acquisition is complicated by the hierarchical study/series organization of data acquisition and processing and by the variety of hardware, software and network infrastructures inherent to MR platforms. These and other issues slow application prototyping. We introduce a platform/OS independent software package, called RTView, that simplifies dynamic data transfer through the use of the Python programming language and standard network communication protocols known as XML-RPC. We demonstrate the use of the RTView platform for streaming real-time multinuclear 31P MR spectroscopy data off a 3T Siemens Trio.

4826.   32 advanced heart tissue phantom as a reference for MRI sequence evaluation
Michael Werner Eder1 and Volker Rasche2
1University Hospital Ulm, Ulm, BW, Germany, 2University Hospital Ulm, BW, Germany

For evaluating dynamic cardiac MR imaging sequences a advanced heart simulator has been built. The phantom uses a polyvinyl alcohol (PVA) based tissue model and is able to simulate heart beat and breathing motion. The device is specially designed to fit into a clinical environment. No modifications of the MRI system are required that could cause the loss of approval. As the phantom feeds trigger signals directly over the physiology board all evaluated sequences can be transferred directly to clinical examination without the need of sequence reprogramming. Its design allows the use of cardiac anterior and posterior dedicated receiver coils.

4827.   33 Virtual Phantom MRI: a novel quantitation method. Temporal stability and spatial linearity validation.
Giulio Gambarota1,2, Pierre-Antoine Eliat3, Johanne Bezy-Wendling1,2, and Hervé Saint-Jalmes1,2
1Université de Rennes 1, LTSI, Rennes, F-35000, France, 2INSERM, UMR 1099, Rennes, F-35000, France, 3PRISM - Biosit CNRS UMS 3480, INSERM UMS 018, Rennes, F-35000, France

The field of MRI is rapidly moving towards more quantitative approaches. In this context, virtual phantoms that would provide a reference signal could be useful for quantification purposes in MRI. The aim of the present study was i) to implement a dedicated experimental set-up to generate MR images of virtual phantoms ii) to test its temporal stability and signal linearity. This approach is here referred to as Virtual Phantom (ViP) MRI. MR images of virtual phantoms were generated using a stand-alone, independent unit. Thus, ViP MRI can be performed on MR scanners from different vendors.

4828.   34 Touch NMR: An NMR data processing application for mobile device
Qiyue Li1, Zhiwei Chen1, Zhiping Yan2, and Zhong Chen1
1Department of Electronic Science, Xiamen University, Xiamen, Fujian, China, 2Chenggong Hospital Affiliated to Xiamen University, Xiamen, Fujian, China

Mobile devices are playing a more and more important role in daily life. However, there was no useful application on mobile devices to help NMR researchers handle their data. To meet the needs, a free iPad application, Touch NMR, designed for basic NMR data processing is introduced. The software system can process FID data of Agilent, Bruker and JEOL formats. It can accomplish basic NMR data operations: FFT, manual/automatic phase correction, automatic baseline correction, referencing, peak picking, integration and so on. Besides 1D data, DEPT spectra edit, T1/T2 fitting, and 2D spectrum with projections in the two dimensions can also be accomplished in Touch NMR. In addition, the application takes full advantage of multi-touch technology and gives users a better experience.

4829.   35 Hybrid inverse/FDTD computational electromagnetic methodology and its potential application in MR RF field design
Sherman Xuegang Xin1,2 and Christopher Michael Collins1
1Bernard and Irene Schwartz Center for Biomedical Imaging, New York University School of Medicine, New York, NY, United States, 2Biomedical Engineering, Southern Medical University, Guangzhou, Guangdong, China

The inverse method in computational electromagnetic calculation has its particular advantage, that is, the source electromagnetic field can be specially designed from the targeted field, which can be designed exactly. However, it is difficult to directly use inverse method for the human body in the high-field MR environment, where the complicated coil-tissue interaction must be considered. A new methodology, i.e. hybrid inverse/FDTD method, which has not been reported previously to the best of the authors’ knowledge, was proposed here for goal-oriented RF source field design loaded with human body at high-field MRI.

4830.   36 Automation system based on piezoelectric motor for tuning and matching miniature monolithic NMR coils
Zhoujian Li1, Georges Willoquet1, Marie Poirier-Quinot1, Luc Darrasse1, and Jean-christophe Ginefri1
1Imagerie par Résonance Magnétique Médicale et Multi-Modalités (IR4M), UMR8081 CNRS, Univ. Paris Sud, Orsay, France

An automation system based on a piezoelectric motor that offers high resolution displacement is developed to automatically tune and match miniature monolithic coils used in MR microscopy. Tuning is done by approaching a dielectric slice to shift down the resonant frequency and matching is achieved by inductive coupling to a pick-up loop. The piezo-motor is driven by a dedicated board, which communicates with control software for automation. The resolution achieved by the developed system allows automatic matching and tuning with respect to specified matching level and target frequency with configurable tolerance.

4831.   37 Integral Equations Based Modeling Approach to Dielectric Shimming
Wyger Brink1 and Andrew Webb1
1Radiology, Leiden University Medical Center, Leiden, Zuid-Holland, Netherlands

This work presents a numerical approach using an integral equations method to model the effect of a dielectric shim in the RF field. By including body loading effects explicitely into the Green's function, the problem complexity is reduced to the interactions within the dielectric shim.

4832.   38 Evaluation of electric fields induced in the patient during body rotations in the static magnetic field of a MRI-LINAC system
Adnan Trakic1, Limei Liu1, Hector Sanchez Lopez1, Luca Zilberti2, Feng Liu1, Ewald Weber1, and Stuart Crozier1
1The School of Information Technology and Electrical Engineering, The University of Queensland, Brisbane, QLD, Australia, 2Divisione Elettromagnetismo, Istituto Nazionale di Ricerca Metrologica, Torino, Italy

This novel study evaluates the induced electric field and current densities due to the rotation of the patient in a static magnetic field produced by the split superconducting magnet of a realistic MRI-Linear Particle Accelerator (LINAC) system. It was found that rotating the patient in the radial orientation relative to the magnet gap with periods larger than about 15.3 seconds would not exceed the ICNIRP exposure limits. This new research provides useful insights into the safe use of the MRI-LINAC technology and optimal orientations of the patient during image-guided treatment.

4833.   39 A quiet, fast, high-resolution desktop MRI capable of imaging solids
Aleksandar Nacev1, Edward Anashkin1, Juan Pablo Rigla Perez2, Jose Maria Benlloch Baviera2, Mario Urdaneta1, Azeem Sarwar1, Pavel Stepanov1, Irving Weinberg1, and Stanley Thomas Fricke3
1Weinberg Medical Physics, Bethesda, MD, United States, 2Institute for Instrumentation in Molecular Imaging (I3M), Valencia, Spain, 3Children's National Medical Center, Washington, DC, United States

An inexpensive MRI device that can image solid structures with short T2 times was developed by adding gradient coils, pulse sequences, and a GUI to a 0.34T commercial spectrometer. Gradient coils were created by hand winding or additive manufacturing. The 3D-printed coils produced a homogenous gradient and minimized acoustic noise. The GUI was created so that custom pulse sequences could be programmed, data gathered, and images reconstructed. Custom pulse sequences were encoded in C including: gradient echo pulse sequence; spin echo pulse sequences; and three dimensional volume acquisitions. Images were obtained under one second with 50 micron resolution.

4834.   40 Metamaterial cell for B1+ field manipulation at 9.4T MRI
Irena Zivkovic1 and Klaus Scheffler1,2
1High Field MRI, Max Planck Institute for Biological Cybernetics, Tuebingen, Germany, 2Center for Integrative Neuroscience, University of Tuebingen, Tuebingen, Germany

Many techniques have been developed to improve magnitude and homogeneity of B1+ field at high field MRI. In order to manipulate B1+ field, we have designed one cell metamaterial (MM) plate. When proposed material was placed between RF transmit coil and phantom, B1+ magnitude and homogeneity significantly improved. Measured results show over 100% increase of B1+ magnitude in specific area in the case when box monopole antenna was used as a transmitter. When small loop antenna was used as a transmitter, there was zero B1+ field without MM plate and significant B1+ when MM plate was inserted.

4835.   41 Rotating sample acquisition in ultra-low-field MRI
Yi-Cheng Hsu1, Koos C. J. Zevenhoven2, Ying-Hua Chu1, Juhani Dabek2, Risto J. Ilmoniemi2, and Fa-Hsuan Lin1,2
1National Taiwan University, Taipei, Taiwan, 2Department of Biomedical Engineering and Computa of Biomedical Engineering and Computational Science, Aalto University, Finland

We propose the rotating sample acquisition (RSA) to achieve efficient ultra-low-field MRI (ULF-MRI). Specifically, the sample rotates in the instrument and we measure ULF-MRI signals without any phase encoding. The concomitant field artifacts can be minimized because only frequency encoding is used. Using empirical data, we demonstrate that RSA is more efficient than conventional Fourier encoding when only three SQUID sensors are used. The RSA method holds promise for a portable imaging system using no phase encoding gradients and few NMR signal detectors.

4836.   42 MPI meets MRI: A first MPI/MRI hybrid scanner
Patrick Vogel1,2, Steffen Lother1,2, Martin A. Rückert1, Walter H. Kullmann3, Peter M. Jakob1,2, Florian Fidler2, and Volker C. Behr1
1Experimental Physics 5 (Biophysics), University of Würzburg, Würzburg, Bayern, Germany, 2Research Center for Magnetic Resonance Bavaria e.V., MRB, Würzburg, Bayern, Germany, 3Institute of Medical Engineering, University of Applied Sciences Würzburg-Schweinfurt, Schweinfurt, Bayern, Germany

This abstract describes the first setup of a bimodal Magnetic-Particle-Imaging/Magnetic-Resonance-Imaging tomograph and shows the first results.

4837.   43 Evaluation of a Ultra High Dielectric Constant (uHDC) Package for Enhanced Cervical Spine Imaging
Christopher Sica1, Sebastian Rupprecht1, Wei Luo2, Jeff Vesek3, Raffi Sahul4, Seongtae Kwon4, Michael Lanagan2, Dan Nguyen3, and Qing Yang1
1Radiology, Penn State College of Medicine, Hershey, Pennsylvania, United States, 2Engineering Science and Mechanics, Penn State University, Pennsylvania, United States, 3Radiology, Hershey Medical Center, Hershey, Pennsylvania, United States, 4TRS Technologies, State College, Pennsylvania, United States

Previously, we explored the use of dielectric pads containing water and barium titanate beads to enhance imaging of the cervical spine. One drawback to that approach was the volume of dielectric required for enhancement. In this work, we quantify the performance of a ultra high dielectric constant (uHDC) package containing monolithic blocks of relative permittivity ~800. This package is reduced in volume relative to our previous configuration. SNR gains of 20 – 40% were observed on discs C1 – C4. Gains of about 10% were found on C5, and a slight loss on C6. Average reduction of system power was 64.18%.

4838.   44 Automatic selection of anterior floating coil array based on lipid layer signal analysis
Bing Wu1, Qingyu Dai1, Xuelian Lu1, and Jiabin Yao1
1GE healthcare, Beijing, Beijing Municipality, China

A rapid and robust method for determining the location of floating anterior coil array is proposed, hence allowing automatic selection of the proper coil element in real time scan. In vivo experiments have been proposed for verification. This method may be combined with standard system scout scan and adds little or no additional scan time.

4839.   45 Catheter-mounted expandable loop (CAMEL) balloon RF coil for high-resolution intracardiac MR imaging
Nelly A. Volland1,2, J. Rock Hadley1,2, Eugene G. Kholmovski1,2, Nassir F. Marrouche2, and Dennis L. Parker1,2
1Utah Center for Advanced Imaging Research, University of Utah, Salt Lake City, Utah, United States, 2Comprehensive Arrhythmia Research & Management Center, University of Utah, Salt Lake City, Utah, United States

Purpose: A catheter-mounted expandable loop (CAMEL) balloon RF coil for cardiac applications was developed and evaluated. Methods: The coil inductive flexible loop was sandwiched between two balloons to protect the coil from fluids. The inner balloon was inflated with saline to expand the coil and reduce the susceptibility mismatch between the inner balloon volume and phantom solution. Results and conclusion: A balloon CAMEL coil prototype was successfully constructed. MR images were acquired at 3T in a saline phantom. The SNR with in the coil sensitive volume was over 20 times the SNR of the external coils currently commercially available.

4840.   46 Faster imaging for MEG-MRI
Angelo Galante1, Allegra Conti2, Cinzia De Luca2, Vittorio Pizzella3, Gian Luca Romani3, Raffaele Sinibaldi2, Marcello Alecci4, Piero Sebastiani5, Antonello Sotgiu5, and Stefania Della Penna3
1MESVA, Department of Life, Health & Environmental Sciences, L'Aquila University, L'Aquila, AQ, Italy, 2Department of Neuroscience and Imaging, University of Chieti, CH, Italy, 3Institute of Advanced Biomedical Technologies, University of Chieti, CH, Italy, 4MESVA, Department of Life, Health & Environmental Sciences, L'Aquila University, AQ, Italy, 5ITA S.r.l., AQ, Italy

Results from a new hybrid MEG-MRI system, working at 8.9mT without prepolariztion pulses, are presented. When scaled to a full size system, suitable for human imaging, they give indications that this approach allows faster imaging and better spatial resolution if compared to other existing devices based on SQUID parallel imaging in the kHz range and prepolarization pulses.

4841.   47 A novel MR-guided radiotherapy system: simulation and experimental validation
Teo Stanescu1,2, Jason Marle3, Tony Tadic1, Jeff Winter4, Michael Sweitzer3, and David Jaffray1,2
1Radiation Physics, Princess Margaret Cancer Centre, University Health Network, Toronto, Ontario, Canada, 2Radiation Oncology, University of Toronto, Toronto, Ontario, Canada, 3Varian Medical Systems, Palo Alto, CA, United States, 4IMRIS, Minnetonka, MN, United States

Numerical simulations and experiments were performed to quantify the magnetic field decoupling between sub-components (i.e. linear accelerator gantry, patient couch assembly and 1.5T MR) for an MR-guided linac system.

4842.   48 Role of Birdcage Volume Resonators for High-Resolution Wrist Imaging at High and Ultra-High Fields
Yusuf A Bhagat1, Po-Hsiang Lai1, Xu Zhu1, Insoo Kim1, and Zhouyue Pi1
1Emerging Technology Lab, Samsung R&D Institute America, Richardson, Texas, United States

This educational review draws attention to birdcage volume resonators as a simple alternative to phased-array receive coils for high-resolution microstructural imaging of the human wrist. The value of quadrature volume coils for transmit-receive (Tx-Rx) applications is better realized at ultra-high fields (greater than or equal to7T) due to lack of body Tx coils. Here, by virtue of examples, we discuss the design of birdcage resonators for wrist imaging at 3T and 7T. Further, we highlight their utility for specific absorption rate-compliance, patient setup for improved tolerance and a rapid spin-echo based technique for high-quality imaging of trabecular (spongy) bone microstructure.


Magnets, Gradients & Shimming

Thursday 15 May 2014
Exhibition Hall  14:30 - 15:30

  Computer #  
4843.   25 The effect of anchoring of MR scanners to prevent earthquake hazards – an analysis of the damages to the 602 MR scanners in Great East Japan Earthquake
Sachiko Yamaguchi-Sekino1, Yoshio Machida2, Toshio Tsuchihashi3, Haruo Isoda4, Takeshi Noguchi5, and Toshiharu Nakai6
1National Insitiute of Occupational Safety and Health, Japan, Kawasaki, Kanagawa, Japan, 2Tohoku University, Graduate School of Medicine, Miyagi, Japan,3Department of Radiology, Nippon Medical School Hospital, Tokyo, Japan, 4Nagoya University, Graduate School of Medicine, Aichi, Japan, 5National Institute for Material Science, Ibaraki, Japan, 6NeuroImaging & Informatics, National Center for Geriatrics and Gerontology, Aichi, Japan

In order to evaluate the potential risk to MR scanners and consider patient safety under large earthquakes, we have performed a survey study to investigate damages in MR scanners caused by Great East Japan Earthquake. It was confirmed that the extent of damage was significantly different between seismic scale (SS) 5 and SS over 6. Logistic regression analysis suggested that anchoring for MR facilities reduced the occurrence of quake-induced damages in MR scanners. And significant decrease in machine damages was observed in the group of base isolation structure for medical facilities compared with earthquake-proof structures.

4844.   26 A whole body conduction cooled MRI magnet design for ultra-high field strength of 7T
Michael Martens1, Tanvir Baig1, Zhen Yao1, Charles Poole1, Robert Deissler1, Robert Brown1, David Doll2, and Michael Tomsic2
1Department of Physics, Case Western Reserve University, Cleveland, Ohio, United States, 2Hyper Tech Research Inc., Columbus, Ohio, United States

A 7T conduction-cooled MRI whole-body magnet design using Nb3Sn superconductor is found for a current density of 179.95 A/mm2, a maximum peak field on a bundle of 11.59T, and operating at 8K. The high current density on wire allowed by the larger peak field helps to reduce the superconductor volume in comparison with high field NbTi magnet designs. Although the present manufacturing cost of Nb3Sn is higher than NbTi, the wire volume reduction and the 99% decrease in liquid helium usage may make Nb3Sn conduction cooled magnets a viable alternative for ultra-high field magnet systems.

4845.   27 Sequencial Abnormal Events in High-Temperature Superconducting MRI Magnet
Shin-ichi Urayama1, Yasuyuki Terao2, Osamu Ozaki2, Hitoshi Kitaguchi3, Shinya Kawashima2, Takashi Hase2, Ken-ichi Sato4, and Hidenao Fukuyama1
1Human Brain Research Center, Kyoto University, Kyoto, Kyoto, Japan, 2Kobe Steel, Ltd., Kobe, Japan, 3National Institute for Materials Science, Ibaraki, Japan, 4Sumitomo Electric Industries, Ltd., Osaka, Japan

Because of recent deficit of liquid helium, helium-free MRI magnets with high temperature superconducting (HTS) materials have been expected as one of the solutions. We have developed a 3T HTS-MRI system for human brain research with Bi-2223 tapes and showed its feasibilities at 1.5T. However, in spite that we succeeded energizing to 3T three times, sequencial abnormal events were happened for longer than ten minutes during the ramp-down at the third trial to 3T. Here, we show these unique events specific to HTS magnets.

4846.   28 Experimental Investigations on Gradient Coil Induced Magnet Heating in MRI System
Longzhi Jiang1, Yihe Hua2, Liya Ma3, Sung Moon1, Jun Li2, Kishore Mogatadakala1, and Tim Havens1
1Global MRI, GE Healthcare, Florence, SC, United States, 2GE Global Research, Shanghai, China, 3GE Healthcare, Beijing, China

The dynamic coupling between gradient coil and magnet has generated image quality issues at low frequencies and limited operational duty cycle at medium and high frequencies due to induced magnet Joule heating. With the combined demand for high patient through-put and high performance gradient coils in high field MRI systems, numerous researchers have attempted to develop both improved simulation capability and experimental apparatus to understand the Joule heating induced helium boil-off. However, to the authors’ best knowledge, the effects of dynamic coupling induced Joule heating is not yet fully understood. In this study, a novel experimental apparatus was devised to understand gradient coil induced magnet heating under different gradient coil mounting conditions. The apparatus included a whole body magnet with hermetically sealed cooling system having very limited helium volume and a gradient coil with minimum interaction. This paper demonstrates consistent correlation between the full mechanical-electro-magnetic coupling model and the experimental results. Furthermore, 100% operational duty cycle has been achieved for clinical protocols.

4847.   29 Integrated Image Reconstruction and Gradient Nonlinearity Correction
Joshua D. Trzasko1, Shengzhen Tao1, Yunhong Shu1, Armando Manduca1, and Matt A. Bernstein1
1Mayo Clinic, Rochester, MN, United States

The gradient fields used for spatial encoding in clinical MRI are never truly linear over the imaging FOV. As standard MRI signal models presume gradient linearity, reconstructed images exhibit geometric distortion unless gradient deviations are properly accounted for. Geometric distortion is typically corrected via image-domain interpolation. Although this approach is straightforward, it does not account for the effects of finite sampling, undersampling, or noise, and may degrade spatial resolution. In this work, we propose a correction strategy that accounts for gradient nonlinearity during – rather than after – k-space to image reconstruction, and lessens the tradeoff between geometric accuracy and spatial resolution.

4848.   30 Accurate Measurement of MRI Gradient Characteristics
Gerald B Matson1,2 and Hui Liu1
1Center for Imaging of Neurodegenerative Diseases, Department of Veterans Affairs, San Francisco, California, United States, 2Pharmaceutical Chemistry, University of California, San Francisco, San Francisco, California, United States

The imperfect fidelity of MRI gradient systems results in altered k-space trajectories, which can result in image degradation. Under the assumption that the gradient system is linear and time invariant, accurate measurement of the MRI gradient impulse response function (GIRF) can be used to predict the actual output gradient waveform as opposed to the requested waveform. In this study we demonstrate a simple sample and coil arrangement can be used to obtain GIRFs of high precision that can accurately predict gradient output waveforms. This capability could potentially be used to predict actual k-space trajectories for improved fidelity of image reconstruction.

4849.   31 Integrated RF/Shim Coil Array for Parallel Reception and Localized B0 Shimming in the Human Brain at 3T
Trong-Kha Truong1, Dean Darnell1, and Allen W Song1
1Brain Imaging and Analysis Center, Duke University, Durham, NC, United States

Multi-coil shimming with localized shim coils can effectively shim high-order B0 inhomogeneities, but requires an additional shim coil array outside or inside the RF coil, which compromises the shimming performance and/or SNR. To address these limitations, we recently proposed a new concept that enables parallel RF excitation/reception and B0/B1 shimming with a single coil array, thus maximizing both the SNR and shimming performance, and demonstrated its feasibility in phantom experiments. Here, we further validate it in vivo by demonstrating its ability to perform parallel reception and localized B0 shimming in the human brain at 3T, specifically for distortion correction in DTI.

4850.   32 Which is the impact of the coil track width and frequency over a split gradient coil performance?
Fangfang Tang1, Hector Sanchez Lopez1, Fabio Freschi2, Feng Liu1, Yu Li1, and Stuart Crozier1
1School of Information Technology and Electrical Engineering, The University of Queensland, Brisbane, Queensland, Australia, 2Politecnico di Torino Corso Duca Degli Abruzzi, Department of Energy, Torino, Italy

In order to study the influence on gradient coils of different track widths and frequencies, 30 split and shielded, whole-body x-gradient coils were designed. The track width was set from 1mm to 30mm with an increment of 1mm. The 30 designed split x-gradient coils were analyzed to study the interaction between the coils and the metallic surroundings, which took into account the skin and proximity effects. This study provides very valuable information which will guide coil engineers to choose the optimal wire track on regards the MRI coil applications.

4851.   33 Design, Construction and Initial Evaluation of a Folded Insertable Head Gradient Coil
Trevor Paul Wade1,2, Andrew Alejski1, Janos Bartha1, Dina Tsarapkina1, R. Scott Hinks3, Graeme C. McKinnon3, Brian K. Rutt4, and Charles A. McKenzie2
1Robarts Research Institute, The University of Western Ontario, London, Ontario, Canada, 2Medical Biophysics, The University of Western Ontario, London, Ontario, Canada, 3GE Healthcare, Waukesha, WI, United States, 4Radiology, Stanford University, Stanford, CA, United States

A symmetric, folded gradient, was designed for human brain imaging, with a target gradient strength of 80 mT/m and slew rate of 2900 mT/m/s. This design should limit forces and torques leading to a quieter coil with better eddy-current performance. The ultra-short design allows for human brain imaging without the need for shoulder cut-outs. The insertable coil was built using litz wire for transverse axes and hollow copper for Z to facilitate cooling. It was successfully interfaced with a clinical scanner and its electrical and imaging performance was characterised.

4852.   34 A Traveling-Wave Approach to Acoustic Noise Reduction in MR Gradient Coils
Simone Angela Winkler1, Andrew Alejski2, Trevor Wade2, Charles McKenzie2, and Brian K Rutt1
1Dept of Radiology, Stanford University, Stanford, California, United States, 2Robarts Research Institute, The University of Western Ontario, London, Ontario, Canada

We present a new wave-based framework for understanding acoustic noise in MR gradient coils, and propose two new concepts for acoustic noise reduction. Results of this wave-based coupled structural-acoustic modeling, as well as experimental measurements, demonstrate that the addition of an impedance matching “horn” and an absorbing end cap both act to decrease acoustic noise inside the gradient coil. Simulation results show mean sound pressure level reductions of 2 dB for horn and end cap, and 3 dB for both used in combination. Experimental results show mean SPL reductions of 4 dB for horn and 9 dB for end cap.

4853.   35 Fast Shimming strategy using intermediate space conversion
Hongpyo Lee1, Sung-Min Gho1, Eunhae Joe1, Joonsung Lee2,3, and Dong-Hyun Kim1
1Electrical and Electronic Engineering, Yonsei University, Sin-chon dong, Seoul, Korea, 2Nanomedical Research Center, Yonsei University, Sin-chon dong, Seoul, Korea, 3SIRIC, Yonsei University, Sin-chon dong, Seoul, Korea

In this abstract, we introduce an in vivo volumetric shim strategy which can be performed in a very short time using an intermediate space conversion idea. Linear shimming and high-order shimming approaches are presented.

4854.   36 Balancing a 500 mm central gap split gradient coil for a hybrid MRI-linac scanner.
Hector Sanchez-Lopez1, Fangfang Tang1, and Stuart Crozier1
1School of Information Technology & electrical Engineering, The University of Queensland, Brisbane, QLD, Australia

This study aims to present a robust guideline to design a 500 mm transversal and 620 mm axial gap split x-gradient coil to be installed in a hybrid Linac-MRI scanner. The target torque (force) was varied from 0 to 15 Nm (15N) while the changes on slew rate, achieved net torque (force), peak current density, average power loss in the coil and cryostat and stored magnetic energy were observed. We found a nearly zero torque (force) coil capable to produce more than 200 T/m/s, and 33 µT/mA.

4855.   37 A Robust guideline to design a split gradient coil for a hybrid Linac-MRI scanner
Hector Sanchez-Lopez1, Fangfang Tang1, and Stuart Crozier1
1School of Information Technology & electrical Engineering, The University of Queensland, Brisbane, QLD, Australia

This study aims to present a robust guideline to design a 500 mm transversal and 620 mm axial gap split x-gradient coil to be installed in a hybrid Linac-MRI scanner. The methodology is divided in two parts: selection of the optimal shielding strategy (this work) and torque/force balancing. Four shielding approaches are studied in order to determine the most suitable for torque balancing and high coil performance. We found that coils designed using the minimizations of the magnetic energy in the whole system are the most suitable for torque/force balancing, optimal pre-emphasis, high slew rate and lower power loss.

4856.   38 Designing biplanar gradient coils with minimum power dissipation for NMR microscopy
Peter T. While1, Markus V. Meissner1, and Jan G. Korvink1,2
1Department of Microsystems Engineering (IMTEK), Laboratory for Simulation, University of Freiburg, Freiburg im Breisgau, Baden-Württemberg, Germany,2Freiburg Institute for Advanced Studies (FRIAS), University of Freiburg, Freiburg im Breisgau, Baden-Württemberg, Germany

High-resolution NMR microscopy demands strong gradient fields. Power dissipation in micro-gradient coils is a primary concern and must be controlled carefully to avoid over-heating the system or the sample and to maximize the duty cycle. In this work, a recently reported method for designing minimum power gradient coils that accounts for the subsequent means of fabrication is applied to the design of a 3-axis biplanar micro-gradient system. A survey of results is presented, comparing coils designed for x-, y- and z-gradients, using both the standard and the new approach, and contrasting the merits of building using tracks or wires.

4858.   40 Temperature simulations for the inverse boundary element gradient coil design method
Michael Stephen Poole1, Clemente Cobos Sanchez2, and N Jon Shah1,3
1INM-4, Forschungszentrum Jülich, Jülich, Germany, 2Ingeniería en Automática, Electrónica, Arquitectura y Redes de Computadores, Universidad de Cádiz, Cadiz, Spain, 3Department of Neurology, RWTH Aachen, Aachen, Germany

In this work we describe a method by which the temperature of gradient coils, designed with arbitrary geometry using the inverse boundary element method, can be simulated. The method requires tuning of the thermal parameters of the coil and its support. This simulation method should aid the coil design process by allowing the thermal performance of multiple coil designs to be estimated without construction.

4859.   41 Realization of a synergistic passive and active shimming system to optimize B0 field homogeneity in micro MR imaging
Rahul Dewal1, Zhipeng Cao2, Sebastian Rupprecht3, and Qing X. Yang1,3
1Bioengineering, Penn State College of Medicine, Hershey, PA, United States, 2Institute of Imaging Science, Vanderbilt University, Nashville, TN, United States, 3Radiology, Penn State College of Medicine, Hershey, PA, United States

The B0 field inhomogeneity artifacts near the air-tissue interfaces in animal and human brains at high field are difficult to remove with standard active shim coils as the associated gradients are high-order and highly localized. Several passive and localized active shimming methods have been proposed to deal with this problem but have high calibration or hardware requirements. Here, a synergistic shimming system that simultaneously optimizes the linear active shim coil settings and passive shim element configuration is demonstrated via application to an in vivo mouse brain. This synergistic shimming approach is expected to be extensible to high-field human MRI systems.

4860.   42 Toward Gradient Systems with Really Identical Gradient Coils
Gerrit Schultz1, Feng Jia1, and Maxim Zaitsev1
1Dept. of Radiology - Medical Physics, University Medical Center Freiburg, Freiburg, Germany

Cylindrical gradient coils are typically designed on three different layers having different radii. As a consequence, the x- and y- gradients or, in case a magic angle gradient system is constructed, all three gradient coils may be designed to be similar, but they are not identical. Identical designs are desirable to further reduce the differences of the coil properties such as switching speed or maximum gradient strength. MR acquisitions would potentially profit from such an approach, and, with identical designs, also the optimization and fabrication of gradient systems may be facilitated. In this abstract, gradient system designs are proposed that consist of such identical gradient coils.

4861.   43 Experimental validation of modal gradient coil design methodologies
Elliot Charles Smith1, Hector Sanchez Lopez1, Michael Poole2, and Stuart Crozier1
1ITEE, The University of Queensland, Brisbane, Queensland, Australia, 2Institute of Neuroscience and Medicine, Jülich, Jülich, Germany

In this work we validated the feasibility of design and analysis of a coil which excites only certain eigenmodes in a surrounding structure. The work validated previous theoretical results.

4862.   44 Fast Method for Parametric System Identification of Gradient Systems
Yu-Chun Chang1,2, Martin Eschelbach1, Nikolai Avdievitch1, Klaus Scheffler1, and Anke Henning1,3
1Max Planck Institute of Biological Cybernetics, Tuebingen, Baden-Wuerttemburg, Germany, 2Graduate School of Neural & Behavioural Sciences, University of Tuebingen, Tuebingen, Baden-Wuerttemburg, Germany, 3Institute for Biomedical Engineering, University and ETH Zurich, Switzerland

A method for characterising a gradient system is introduced. This is a parametric method and thus the system has an analytic form. It is fast and requires only one measurement in each gradient direction and can thus be completed in minutes. It can also be extended to characterise the shim system. Monitoring the B0 field is done using a 16 channel field camera. The predicted model is compared to measured data.

4863.   45 Measurement and Correction of Gradient Nonlinearity by Spherical Harmonic Fitting using the ADNI Phantom
Shengzhen Tao1, Joshua D. Trzasko1, Jeffrey L. Gunter1, Seung-Kyun Lee2, Ek T. Tan2, Yunhong Shu1, Kaely B. Thostenson1, and Matt A. Bernstein1
1Mayo Clinic, Rochester, MN, United States, 2GE Global Research, Niskayuna, NY, United States

Standard strategies to correct image distortion due to gradient non-linearity are based on a parameterization of the gradient field. The correction coefficients are predetermined and the same set of coefficients is applied to all systems in the field. In this work, we develop a simple method to measure and fit the gradient correction on a per-system basis using the Alzheimer’s Disease Neuroimaging Initiative phantom. A 3D spherical harmonic approximation of the distortion is determined and used for correction. The proposed method does not require detailed knowledge of gradient system and can be used in a variety of settings.

4864.   46 Phantom Results with a Matrix Shim Coil
Derek A. Seeber1, Kevin Koch2, and Dirk Beque3
1GE Healthcare, Florence, SC, United States, 2Applied Science Lab, Milwaukee, WI, United States, 3GE Reseach, Munich, Germany

A 27 cm diameter phantom was placed inside a 3T system consisting of a gradient coil with a 24 channel matrix shim array in a 6x4 array and was used to shim the phantom. The phantom studies demonstrate a 3 times reduction in frequency spread as compared with gradient only shimming across the entire phantom. Slice by slice shimming is shown to further reduce the frequency spread by an additional factor of 2 over a global shim. The low induced gradient voltages in the shim coils and fast switching times demonstrate a potential for dynamic shimming in the future.

4865.   47 Automatic Gradient Delay Correction Using Center-Acquisition-at-Partial-Ramp Imaging (CAPRI)
Anna-Katinka Bracher1, Erich Hell2, Johannes Ulrici2, and Volker Rasche1
1Internal Medicine II, University Hospital of Ulm, Ulm, BW, Germany, 2Sirona Dental Systems, HE, Germany

Center-Out imaging sequences like UTE are very sensitive to trajectory imprecision in waveform and to k-space shift due to system delays. In this article an automatic delay correction method is introduced to determinate the delays by direct measurement of the echo peak shift. Therefore a conventional UTE imaging sequence is combined with an additional pre-phasing gradient to shift k-space center along the rising slope of the readout gradient. Furthermore the signal acquisition is started in front of k-space origin to acquire a partial echo for echo peak detection.