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Abstract #4158

Random RF Shimming may conceal possible local SAR hotspots for asymmetric parallel transmit coils

Emre Kopanoglu1, Mohamed Tachrount1, Ettore Flavio Meliado2,3, Dennis Klomp2,3, John Evans1, and Richard G. Wise1

1CUBRIC, School of Psychology, Cardiff University, Cardiff, United Kingdom, 2MR Coils B.V., Zaltbommel, Netherlands, 3Department of Radiology, University Medical Center Utrecht, Utrecht, Netherlands

While general-purpose pTx coils mostly have identical elements arranged symmetrically, coils built for a specific application may be asymmetrical. This asymmetry may lead to a high variation in local SAR distributions of individual coil-elements. For an arterial spin labelling pTx coil, we show that using 2,000,000 unconstrained random excitations to characterize the maximum local-SAR underestimates the local-SAR by 7%. We also show that for the investigated ASL coil, the neck elements, which could be exclusively used for labelling, yield 33% less SAR than the head-imaging coils. Therefore, 50% higher power limits can be used for labelling part of an ASL sequence than the imaging part.

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