Gradient preemphasis calibration in diffusion-weighted echo-planar imaging

This article describes a method which enables fast and objective pulse-sequ ence-specific preemphasis calibration, using standard pulse sequences and s ystem hardware. The method is based on a k-space measurement technique, and has been applied to single-shot, diffusion-weighted, spin-echo, echo-plana r imaging (DW-SE-EPI), which is particularly sensitive to eddy-current-indu ced image distortions. The efficiency of the technique was demonstrated not only by the reduction of eddy-current fields to a negligible level using f ull preemphasis compensation, but also by the fact that adjustment of the s low time-base alone sufficed for the practical elimination of image distort ions in the DW-SE-EPI images and the subsequent diffusion tensor maps (in a phantom and a human brain). By seeking to eliminate directly the effect of eddy-current-induced phase shifts during the EPI data collection, the meth od is free of the complications and restrictions associated with other eddy -current correction techniques for DW-SE-EPI (such as acquisition of additi onal calibration scans, intense postprocessing, extensive pulse-sequence mo difications), making their use redundant. (C) 2000 Wiley-Liss, Inc.