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Abstract #4420

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

Bastien Guerin1,2, John Drago1,2,3, Juergen Herrler4, Lawrence Wald1,2, and Jason Stockmann1,2
1Massachusetts General Hospital, Charlestown, MA, United States, 2Harvard Medical School, Boston, MA, United States, 3EECS, Massachusetts Institute of Technology, Cambridge, MA, United States, 4Siemens Healthineers, Erlangen, Germany

Synopsis

Keywords: RF Pulse Design & Fields, RF Pulse Design & Fields

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 $$$\beta$$$ 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.

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Keywords