An inverse problem approach to the correction of distortion in EPI images

Magnetic resonance imaging using the echo planar imaging (EPI) technique is particularly sensitive to main (B-o) field inhomogeneities. The primary ef fect is geometrical distortion in the phase encoding direction. In this pap er, we present a method based on the conjugate gradient algorithm to correc t for this geometrical distortion, by solving the EPI imaging equation. Two versions are presented: one that attempts to solve the full four-dimension al (4-D) imaging equation, and one that independently solves for each profi le along the blip encoding direction. Results are presented for both phanto m and in vivo brain EPI images and compared with other proposed correction methods.