Nonlinear phase correction of navigated multi‐coil diffusion images

Cardiac pulsatility causes a nonrigid motion of the brain. In multi‐shot diffusion imaging this leads to spatially varying phase changes that must be corrected. A conjugate gradient based reconstruction is presented that includes phase changes measured using two‐dimensional navigator echoes, coil sensitivity information, navigator‐determined weightings, and data from multiple coils and averages. A multi‐shot echo planar sequence was used to image brain regions where pulsatile motion is not uniform. Reduced susceptibility artifacts were observed compared to a clinical single‐shot sequence. In a higher slice, fiber directions derived from single‐shot data show distortions from anatomical scans by as much as 7 mm compared to less than 2 mm for our multi‐shot reconstructions. The reduced distortions imply that phase encoding can be applied in the shorter left–right direction, enabling time savings through the use of a rectangular field of view. Higher resolution diffusion imaging in the spine permits visualization of a nerve root. Magn Reson Med, 2006. © 2006 Wiley‐Liss, Inc.