ISMRM 24th Annual Meeting & Exhibition • 07-13 May 2016 • Singapore

Scientific Session: RF Coil Arrays

Monday, May 9, 2016
Summit 2
14:15 - 16:15
Moderators: Randy Duensing, Fraser Robb

A 32-channel integrated body coil for 7 Tesla whole-body imaging
Stephan Orzada1, Andreas K. Bitz2, Oliver Kraff1, Mark Oehmigen1,3, Marcel Gratz1,3, Sören Johst1, Maximilian N. Völker1, Stefan H. G. Rietsch1,3, Martina Flöser2, Thomas Fiedler2, Samaneh Shooshtary4, Klaus Solbach4, Harald H. Quick1,3, and Mark E. Ladd1,2
1Erwin L. Hahn Institute for MRI, Essen, Germany, 2Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany, 3High Field and Hybrid MR Imaging, University Hospital Essen, Essen, Germany, 4High Frequency Technology, University of Duisburg-Essen, Duisburg, Germany
Due to the severe problems with B1 inhomogeneity, volume resonators are not a good choice for body applications at ultra-high fields, and local multi-channel arrays are commonly used for transmission. In this work we present an integrated 32ch transmit/receive body array for 7 Tesla whole-body imaging. First in vivo images show a human volunteer imaged completely in 4 stations.

Approaching the Ultimate Intrinsic SNR with Dense Arrays of Electric Dipole Antennas
Gang Chen1,2,3, Riccardo Lattanzi1,2, Daniel Sodickson1,2, and Graham Wiggins1,2
1The Center for Advanced Imaging Innovation and Research (CAI2R), Department of Radiology, New York University School of Medicine, New York, NY, United States, 2The Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, NY, United States, 3The Sackler Institute of Graduate Biomedical Science, New York University School of Medicine, New York, NY, United States
Coil designs motivated by the ideal current patterns corresponding to the Ultimate Intrinsic SNR (UISNR) have been used to boost central SNR at 3T and 7T. For a cylindrical phantom and a current distribution defined on a concentric cylindrical surface, the ideal current pattern for optimal central SNR includes both divergence-free and curl-free components. While loops are exclusively divergence-free, recent work has shown that electric dipole antennae include both divergence-free and curl-free current components. Here we explore in simulation whether arrays with an increasing number of electric dipole antennas can approach UISNR in the center of a head-sized phantom at 7T, and investigate selected practical design considerations.

Optimization of the Transceiver Phased Array for Human Brain Imaging at 9.4 T: Loop Overlapping Rediscovered.
Nikolai I Avdievich1, Ioannis Giapitzakis1, Andreas Pfrommer1, and Anke Henning1,2
1High-field Magnetic Resonance, Max Planck Institute for Biological Cybernetics, Tübingen, Germany, 2Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland
Ultra-high field (UHF) (>7T) transmit (Tx) and transceiver surface loop phased arrays improve Tx-efficiency and homogeneity for human brain imaging. Overlapping the loops enhances Tx-efficiency and SNR by increasing the penetration depth. However, overlapping can compromise decoupling and SNR by generating a substantial mutual resistance. Therefore, UHF Tx-arrays are commonly constructed using gapped loops. Based on analytical optimization we constructed a 9.4T 8-loop head transceiver array. Both the magnetic and electric coupling were compensated at the same time by overlapping and excellent decoupling was obtained. Tx- and Rx-performance of the array was compared favorably to that of a gaped array.

Comparison of 3T whole body parallel transmit arrays based on measured data from full scale models
Eddy B Boskamp1, Saikat Saha1, Ricardo Becerra1, and Michael Edwards1
1Engineering, GE Healthcare, Waukesha, WI, United States
In this study we are comparing 16 channel TEM, 8 channel TEM and 8 loop array pTx body coils based on experimental data obtained from full scale whole body prototypes as opposed to only simulation. Besides SAR, efficiency and uniformity, there are additional criteria to include when selecting a body coil for parallel transmit. Examples are star intensity artifact, E fields that heat up cables and baluns, VSWR, and perturbation sensitivity, which may make it impossible to build a certain design given obtainable tolerances.

A 3D Loop-Loopole Receive  Array for Spine Imaging at 3.0 T.
Karthik Lakshmanan1,2, Ryan Brown1,2, and Graham C Wiggins1,2
1Center for Biomedical Imaging, Department of Radiology, NYU School of Medicine, Newyork, NY, United States, 2Center for Advanced Imaging Innovation and Research (CAI2R), NYU School of Medicine, Newyork, NY, United States
High channel count RF receive coil arrays have become commonplace due to the advent of parallel imaging techniques and due to technical advances in receive chain technology. Using these general purpose coil arrays SNR can be maximized over wide depths by covering the imaging region with an array of planar loops. This is usually achieved by reducing the coil dimensions while still maintaining sufficiently high unloaded-to-loaded Q ratio. In this work we aim to improve upon the SNR of a high element count array by adding concentric orthogonal "Loopole" elements. The asymmetric behavior of the loopoles combined with its orthogonal location provided SNR improvements both at shallow and deep regions in an imaging plane.

Detailing Local Multi-Channel RF Surface Coil versus Body RF Coil Transmission for Cardiac MRI at 3 Tesla: Which Configuration is Winning the Game?
Oliver Weinberger1,2, Lukas Winter1, Matthias A Dieringer1, Antje Els1, Celal Oezerdem1, Antonino Cassara3, Harald Pfeiffer3, and Thoralf Niendorf1,2
1Berlin Ultrahigh Field Facility (BUFF), Max Delbrueck Center for Molecular Medicine (MDC), Berlin, Germany, 2Experimental and Clinical Research Center (ECRC), Charité Medical Faculty, Berlin, Germany,3Physikalisch Technische Bundesanstalt (PTB), Berlin, Germany
In this work a local four-channel transmit/receive RF coil dedicated for cardiac MR at 3T is compared to a conventional built-in body RF coil in conjunction with a four-channel receive-only RF coil. SAR and B1+simulations of both configurations are shown. The invivo efficiency performance of both coils in respect to B1+/sqrt(SAR) is demonstrated in 12 healthy subjects. The efficiency surplus of the local RF coil was used to increase the applicable flip angle FASSFP of a standard high resolution 2D SSFP protocol or to shorten the used repetition time TRSSFP by 54%.

Design of a 8-channel transceive dipole array with up to 64 receive-only loop coils
Ingmar Voogt1, Dennis W.J. Klomp1, Hans Hoogduin1, Peter R. Luijten1, Cornelis A.T. van den Berg1, and Alexander J.E. Raaijmakers1
1UMC Utrecht, Utrecht, Netherlands
We have developed an array combination consisting of eight fractionated dipole antennas combined with 64 receive loops. Loops are combined in 16 linear groups of four. Eight are equipped with a transmit dipole antenna, eight are not. The coupling between all elements is below -15 dB. The transmit efficiency is not influenced by the presence of the receive loops. Phantom MRI measurements show strong enhancement of the SNR. Finally, preliminary human scans (T2w images) have been acquired.

Parallel Transmit (pTx) Capability of Various RF Transmit Elements and Arrays at 7T UHF MRI
Stefan HG Rietsch1,2, Stephan Orzada1, and Harald H Quick1,2
1Erwin L. Hahn Institute for MR Imaging, University of Duisburg-Essen, Essen, Germany, 2High Field and Hybrid MR Imaging, University Hospital Essen, Essen, Germany
First steps towards whole body imaging with remote arrays at 7T UHF MRI are currently undertaken. Parallel transmit (pTx) capabilities of transmit arrays can be evaluated by the number of degrees of freedom which characterize the shim capabilities. In this work, 16 different pTx arrays with different transmit elements and combinations of transmit elements are simulated to examine inter element coupling behavior, singular values to determine the degrees of freedom and shim capabilities. Combining dipoles and loops seems to be the most promising approach among the investigated pTx arrays.

About the Ultimate SNR for Cylindrical and Spherical RF Arrays in a Realistic Human Head Model
Andreas Pfrommer1 and Anke Henning1,2
1Max Planck Institute for Biological Cybernetics, Tuebingen, Germany, 2Institute for Biomedical Engineering, UZH and ETH Zurich, Zurich, Switzerland
In this work we investigated differences in the ultimate SNR in a realistic human head model for two configurations with the RF array elements distributed on either a cylindrical or a spherical holder. The basis set of solutions in our approach was created by vector cylindrical and spherical harmonics, which are known to form a complete set of eigenfunctions to Maxwell’s equations in free-space. Assuming both surfaces have the same radius, the spherical geometry yielded higher SNR in grey and white matter compared to the cylindrical one. Moreover it allowed higher acceleration factors with the same g-factors.

High-quality flexible printed MRI receive coils towards garment integration
Pierre Balthazar Lechene1, Joe Corea1, Anita Flynn1, Michael Lustig1, and Ana Arias1
1EECS, UC Berkeley, Berkeley, CA, United States
Close proximity of MRI receive coils to the patient can allow an increase of signal-to-noise ratio (SNR). Integrating the coils into garments that tightly conform to the body can provide such proximity. This work develops flexible printed MRI coils on a mesh with the potential to be integrated into garments. The dielectric used in the coil’s capacitors is optimized to provide SNR within 91% of conventional coils. Encapsulation enhances the coils mechanical robustness, allowing bending below 1mm of radius of curvature. It is shown that, by cutting and sewing, the coils can be tailored to intimately fit a brassiere cup.

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