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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