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Abstract #0544

Fully optimized time-shifted radio-frequency spoke pulses for simultaneous reduction of intra-voxel dephasing, flip-angle non-uniformity and the specific absorption rate at ultra-high field using parallel transmission

Bastien Guerin 1 , Jason Stockmann 1,2 , Mehran Baboli 3 , Andrew V Stenger 3 , and Lawrence L Wald 1,4

1 Department of Radiology, Massachusetts General Hospital, Charlestown, MA, United States, 2 Physics department, Harvard University, Cambridge, MA, United States, 3 John A. Burns School of Medicine, University of Honolulu, Honolulu, United States, 4 Division of Health Sciences Technology, Harvard-MIT, Cambridge, MA, United States

We propose a slice-selective parallel transmit (pTx) pulse design that simultaneously addresses the problems of B1+ inhomogeneity, through-plane dephasing and SAR at ultra-high field. The technique is based on a new small tip-angle equation including the effects of thick-slice averaging, time-shifting of the spoke sub-pulses and the presence of a background through-plane B0 gradient. We fully optimize the spoke amplitudes and time-shifts using a fast primal-dual optimization with analytical gradients and Hessian. We also show that time-shifting the spoke sub-pulse also helps reducing SAR. We demonstrate the method on a 3D-printed B1/B0 phantom and an 8-channel 7T pTx system.

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