New approach for correcting distortions in echo planar imaging.

A new method is described that can correct the distortions due to multiple off-resonance effects in echo planar imaging, including those caused by B(0) field inhomogeneities, eddy currents, and gradient waveform imperfections. The proposed method uses a phase encoded acquisition and is as effective as the method of Chen and Wyricz (Chen and Wyricz, Magn Reson Med 1999;41:1206-1213) in correcting for distortions. Unlike Chen and Wyricz's approach, this new method works directly in distorted space and requires fewer scans. It also avoids the difficulties of phase unwrapping inherent in field mapping methods. Results using this new method with phantoms and human head scans at 3.0 T demonstrate the efficacy of the method in correcting distortions in both spin echo echo planar imaging (EPI) and gradient echo EPI.