Practical Non-selective Refocusing Pulses for 7 T MRI

Introduction Imaging sequences reliant upon non-selective refocusing (e.g., 3D TSE, 3D GraSE, and 3D SE-EPI) widely employ either block/sinc refocusing pulses susceptible to field inhomogeneities or adiabatic pulses that demand high SAR. The aim of this work was to evaluate a sample of short, low-SAR, non-selective refocusing pulses by comparing signals acquired with a 3D SE-EPI sequence at 7 T. In reference to a 180° block pulse, all pulses result in overall signal gains with some pulses increasing signal by more than a factor of 2 in localized areas. SAR increases for all pulses are less than 2-fold with respect to the block pulse. This work thus demonstrates what signal improvements are possible under the condition that scan duration be minimally impacted and therefore aids high-field researchers and clinicians in choosing suitable refocusing pulses for practical 3D spin-echo imaging.