Stephan Orzada¹, Andreas K. Bitz², Oliver Kraff¹, Mark Oehmigen^1,3, Marcel Gratz^1,3, Sören Johst¹, Maximilian N. Völker¹, Stefan H. G. Rietsch^1,3, Martina Flöser², Thomas Fiedler², Samaneh Shooshtary⁴, Klaus Solbach⁴, Harald H. Quick^1,3, and Mark E. Ladd^1,2
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.

Gang Chen^1,2,3, Riccardo Lattanzi^1,2, Daniel Sodickson^1,2, and Graham Wiggins^1,2
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.

Nikolai I Avdievich¹, Ioannis Giapitzakis¹, Andreas Pfrommer¹, and Anke Henning^1,2
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.

Eddy B Boskamp¹, Saikat Saha¹, Ricardo Becerra¹, and Michael Edwards^1
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.

Karthik Lakshmanan^1,2, Ryan Brown^1,2, and Graham C Wiggins^1,2
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.

Oliver Weinberger^1,2, Lukas Winter¹, Matthias A Dieringer¹, Antje Els¹, Celal Oezerdem¹, Antonino Cassara³, Harald Pfeiffer³, and Thoralf Niendorf^1,2
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 FA_SSFP of a standard high resolution 2D SSFP protocol or to shorten the used repetition time TR_SSFP by 54%.

Ingmar Voogt¹, Dennis W.J. Klomp¹, Hans Hoogduin¹, Peter R. Luijten¹, Cornelis A.T. van den Berg¹, and Alexander J.E. Raaijmakers^1
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.

Stefan HG Rietsch^1,2, Stephan Orzada¹, and Harald H Quick^1,2
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.

Andreas Pfrommer¹ and Anke Henning^1,2
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.

Pierre Balthazar Lechene¹, Joe Corea¹, Anita Flynn¹, Michael Lustig¹, and Ana Arias^1
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.