Slice-selective, large flip-angle parallel transmission pulses for brain imaging at 7 Tesla

Motivation: 'Spoke' pTx pulses utilizing SINC sub-pulses are popular for flip-angle (FA) uniformization at 7T [1,2] but can yield distorted slice profiles at large flip-angles and are sensitive to off-resonance effects [3]. Goal(s): We optimize gradient and RF pTx waveforms with explicit in-slice and out-of-slice ripple control to achieve uniform brain excitations at 7T and undistorted slice profiles. Approach: We optimize the Caley-Klein $β$ profile of slice-selective pTx pulses using low-resolution in-slice sampling of the B0 and pTx B1+ field maps, high-resolution sampling in slice direction. Results: Fully optimized pulses (FO) achieve ~10% FA NRMSE in-slice with ~1% ripple amplitude out-of-slice. Impact: We propose fully optimized slice-selective 7T brain pTx RF and gradient pulses with uniform flip-angle distribution in-slice (~10% NRMSE), negligible out-of-slice excitations and little in-slice phase variations.