Correction of off resonance-related distortion in echo-planar imaging using EPI-based field maps

We present, here, a simple method for measurement and correction of off‐resonance related geometric distortion in echo‐planar imaging (EP1). This method uses high signal‐to‐noise ratio (SNR) EPI‐based field maps, rapidly acquired using a series of gradient recalled images collected across a range of TE values. This field map is distorted in the same manner as the EPI images to be unwarped, providing a direct look‐up table for the correct location of each pixel of data. This method adds very little scan time and is robust and easy to implement.