Parallel transmit coil dimensions affect SAR sensitivity to motion at 7T

Synopsis: Subject motion in parallel-transmit (pTx) causes channels’ electric field interference patterns to change, influencing SAR distributions. This can cause safety limits to be exceeded when SAR-constrained pulses are designed for one position, with reports of local-SAR more than tripling due to motion in the literature. Here, we investigate the effect of pTx coil geometry by simulating 6 differently sized coil models and testing SAR sensitivity at 19 displaced positions. While our results agree with those previously reported for the similar-sized coil, we generally observe lower SAR motion-sensitivity in larger coil models, and much higher sensitivity for the smallest coils.