Son Chu¹, Vincent Gras², Paul McElhinney¹, Nicolas Boulant², and Shajan Gunamony^1
1Imaging Centre of Excellence, University of Glasgow, Glasgow, United Kingdom, ²University of Paris-Saclay, CEA, CNRS, BAOBAB, NeuroSpin, Gif sur Yvette, France

The promise of supra-linear boost in signal-to-noise-ratio is driving the development of MRI at extremely high static field strengths, such as 10.5T and beyond. The shorter wavelengths in tissues at high Larmor frequency causes destructive interference of the electromagnetic field, resulting in image inhomogeneity and increased local specific absorption rate (SAR). An efficient transmit array is vital in this regime to optimally use the available RF power, achieve efficient excitation and operate within SAR constraints. This work presents the design and optimization of an 8-channel transmit array for MRI at 11.7T and its performance evaluation using RF pulse design simulations.

Michel Luong¹, Guillaume Ferrand¹, Edouard Chazel², Paul-François Gapais^2,3, Vincent Gras², Nicolas Boulant², and Alexis Amadon^2
1CEA, IRFU, Université Paris-Saclay, Gif sur Yvette, France, ²Université Paris-Saclay, CEA, CNRS, BAOBAB, NeuroSpin, Gif sur Yvette, France, ³Multiwave Imaging SAS, Marseille, France

A geometrically decoupled 16Tx-32Rx RF coil has been designed for the Iseult 11.7T project. It has 16 transceive resonators and 16 receive-only loops. This peculiar architecture satisfied three major concerns: compactness-made compatibility with a local B0 shim insert, easy tuning and performance prediction. Simulations show high flip angle homogeneity in the whole brain (NRMSE<6%) with k_T-points, accounting for all constraints (pulse length, SAR, power budget). Predicted global SNR in phantom with SoS reconstruction is 2.47±0.2 times higher as compared to 7T (with the commercial 8Tx-32Rx Nova coil) or equivalently, the SNR scales as B0 to the power of 1.74±0.16.

Myung Kyun Woo^1,2, Lance DelaBarre¹, Matt Waks¹, Russell Lagore¹, Steve Jungst¹, Andrea Grant¹, Kamil Ugurbil¹, and Gregor Adriany^1
1Center for Magnetic Resonance Research, Minneapolis, MN, United States, ²Department of Electrical and Computer Engineering, Seoul National University, Seoul, Korea, Republic of

For whole brain human head imaging at 10.5 Tesla, we interlaced a 16-channel sleeve antenna transceiver with a 16-channel asymmetric dipole antenna receiver for a combined, close fitting 16-channel transmit/32 -channel receiver array. Integration of high dielectric constant material (HDC) significantly improved receiver performance in the upper brain. Simulation results indicate excellent B1 efficiency and coverage of the combined array for the whole brain imaging at 447 MHz. To further improve array performance, we developed new on-coil transmit/receive (T/R) switches capable of preamplifier decoupling. We are now in the process of building this novel closefitting 32-channel array.

Alexander Bratch^1,2, Jerahmie Radder², Alireza Sadeghi-Tarakameh², Gregor Adriany², Kamil Ugurbil², and Brian Rutt^1
1Department of Radiology, Stanford University, Stanford, CA, United States, ²Center for Magnetic Resonance Research (CMRR), Department of Radiology, University of Minnesota, Minneapolis, MN, United States

In this work, we demonstrate a new double bent dipole geometry for use as a hybrid RF/B0 shimming element for 10.5T imaging, featuring two B0 shimming channels per RF channel. Initial simulations compare this element to standard dipoles and loops. Bench assessments and simulations further demonstrate excellent inter-element decoupling, and initial steps toward a 32-channel Tx/64-channel B0 array show promising results.

Nikolai I. Avdievich¹, Anton V Nikulin^1,2, Loreen Ruhm ¹, Arthur W Magill ³, Anke Henning⁴, and Klaus Scheffler^1,2
1High-Field MR Center, Max Planck Institute for Biological Cybernetics, Tübingen, Germany, ²Biomedical Magnetic Resonance, University of Tübingen, Tübingen, Germany, ³Medical Physics in Radiology, German Cancer Research Center, Heidelberg, Germany, ⁴Advanced Imaging Research Center, University of Texas Southwestern Medical Center, Dallas, TX, United States

The advancement of clinical applications of 7T MRI depends heavily on the development of new RF coil designs. Recent works based on Ultimate Intrinsic SNR theory demonstrated that an optimal central SNR at 7T requires combining surface loops with dipole antennas. In this work, we developed and evaluated two novel 32-element 7T human head loop/dipole array designs. Both coils demonstrated superior Tx-efficiency, longitudinal coverage, and SNR in comparison to widely used commercial array coil. While the transceiver (TxRx)-dipole/receive(Rx)-loop array demonstrated best SNR, the TxRx-loop/Rx-dipole array showed the best Tx-efficiency.  In addition, double-row TxRx-loop/Rx-dipole array provides 3D RF shimming capability. 

Jiying Dai^1,2, Ettore Flavio Meliadò^1,2, Mark Gosselink¹, Catalina Arteaga², Alexander J. E. Raaijmakers^1,3, and Dennis W. J. Klomp^1
1UMC Utrecht, Utrecht, Netherlands, ²Tesla Dynamic Coils B.V., Zaltbommel, Netherlands, ³Technische Universiteit Eindhoven, Eindhoven, Netherlands

The 7T operating frequency of ¹H and ¹⁹F RF transceivers is in far field regime, while for remaining nuclei these are in near-field regime. Consequently, the optimal setup for far field is based on antennas, while for near field these are based on loop coils. Owing to their intrinsic field orthogonality, these setups can be merged with low RF coupling and thus low penalty in efficiency as we demonstrated for a quintuple tuned head coil. Here we show that the design is generalized and can in principle be used for any body part, as demonstrated in brain, breast and extremity. 

Jérémie Clément¹, Joseph V Hajnal^1,2, and Özlem Ipek^1
1Biomedical Engineering Department, School of Biomedical Engineering and Imaging Sciences, King's College London, London, United Kingdom, ²Centre for the Developing Brain, School of Biomedical Engineering and Imaging Sciences, King's College London, London, United Kingdom

7T MRI has potential for adding value in studies of infant brain and heart. In this study we introduce the first integrated high channel count receive array designed to enable both head and torso imaging of young infants at 7T. The array performance was evaluated in terms of noise correlation matrix, signal-to-noise ratio, and spatial coverage. The initial results are promising with the array providing a large coverage of the targeted regions in phantom. After further safety checking, the next step will be to conduct in-vivo studies, paving the way for future high performance infant examinations at 7T.