Predistorted B1 Shimming: A New Concept Based on Mutual Enhancement between Static B1 Shim & 1D Spoke RF Pulse Design. Application for Cardiac Imaging at 7 Tesla.

Sebastian Schmitter¹, Xiaoping Wu¹, Lance DelaBarre¹, Kamil Ugurbil¹, Pierre-Francois Van de Moortele¹

B1 shimming achieves high transmit B1 (B1+) efficiency with satisfactory B1+ homogeneity in small targets at 7T, however in large targets, e.g. heart, uniform |B1+| with static B1 shim results in low efficiency. Taking advantage of typical |B1+| profiles observed with transceiver arrays in the heart at 7T, we propose a new concept where, instead of aiming at homogeneous |B1+| profile, B1 shim is applied to achieve a predefined spatially distorted |B1+| pattern which, in turn, allows for efficient use of 1D spoke RF pulse design to provide homogeneous excitation in the heart while preserving high B1+ efficiency.