Reduction of geometric and intensity distortions in echo-planar imaging using a multireference scan

Echo-planar imaging (EPI) is very sensitive to patient-induced field inhomogeneity caused by susceptibility changes between different anatomical regions. This results in geometric and intensity distortions in the image, especially near tissue/air and tissue/bone interfaces. A new approach is presented to reduce geometric and intensity distortions in EPI. A phase-encoded multireference scan is used to estimate the amplitude and phase errors in the measured signals due to the field inhomogeneity. The EPI data is corrected using both the amplitude and phase of the measured errors. This technique has been evaluated using EPI pulse sequences implemented with conventional gradients and implemented with imaging systems that have special resonating gradients and fast analog to digital converters. The results in both phantom and human studies show that in the absence of object motion the new correction technique can effectively reduce the geometric and intensity distortions.