SAR Reduction by K-Space Adaptive RF Shimming

Hanno Homann¹, Kay Nehrke², Ingmar Graesslin², Olaf Dssel¹, Peter Brnert²

Parallel transmission allows compensating for RF transmit field inhomogeneities and simultaneous SAR reduction by RF shimming. This study demonstrates that the trade-off between these two objectives can be overcome by using several different, adapted RF pulses: When sampling the center of the k-space, a highly uniform but relatively SAR-intensive excitation is performed to achieve optimal contrast. In the outer k-space, the homogeneity requirement is relaxed to reduce the average SAR. The concept is discussed theoretically; proof-of-principle is given based on phantom and in vivo images.