Abstract

It is well known that spatial variations of the main magnetic field can cause large geometric distortions along the phase-encode direction of echo planar images (EPI) [1]. In fMRI, these distortions in the EPI data can lead to local shifts of 6-9mm [5] in inferior slices and signal pile-up [6]. Approaches to correcting distortions caused by field inhomogeneities include field mapping [5, 3] and non-linear registration with an undistorted reference image (usually a T1- or T2- weighted) [4, 1]. We previously developed a method for correcting distortion in the EPI images used in diffusion weighted imaging