Robust time-shifted spoke pulse design in the presence of large B0 variations with simultaneous reduction of through-plane dephasing, B1+ effects, and the specific absorption rate using parallel transmission.

ABSTRACT:

Purpose

To design parallel transmission spokes pulses with time-shifted profiles for joint mitigation of intensity variations due to B1+ effects, signal loss due to through-plane dephasing, and the specific absorption rate (SAR) at 7T.

Methods

We derived a slice-averaged small tip angle (SA-STA) approximation of the magnetization signal at echo time that depends on the B1+ transmit profiles, the through-slice B0 gradient and the amplitude and time-shifts of the spoke waveforms. We minimize a magnitude least-squares objective based on this signal equation using a fast interior-point approach with analytical expressions of the Jacobian and Hessian.

Results

Our algorithm runs in less than three minutes for the design of two-spoke pulses subject to hundreds of local SAR c

SUBMITTER: Guerin B 

PROVIDER: S-EPMC4824674 | biostudies-literature | 2016 Aug

REPOSITORIES: biostudies-literature