We investigate the performance of parallel transmission arrays with 8, 16, 24, and 32 channels and varying loop sizes (18 coils total) for brain imaging at 7T. We compare RF-shimming performance of the arrays using the L-curve method showing optimal tradeoffs between excitation uniformity (slice), local-SAR, global-SAR and peak-power. For the numbers of channels simulated here, the coils with larger loops achieved a better local-SAR vs. excitation uniformity than those with smaller loops (this was true for axial/sagittal slice orientations). At constant local-SAR constraint, the 24-channel arrays showed the best performance in improving the excitation uniformity in the coronal/axial slices.
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