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 i nhomogeneity caused by susceptibility changes between different anatom ical regions. This results in geometric and intensity distortions in t he image, especially near tissue/air and tissue/bone interfaces. A new approach is presented to reduce geometric and intensity distortions i n EPI. A phase-encoded multireference scan is used to estimate the amp litude and phase errors in the measured signals due to the field inhom ogeneity. The EPI data is corrected using both the amplitude and phase of the measured errors. This technique has been evaluated using EPI p ulse 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 st udies show that in the absence of object motion the new correction tec hnique can effectively reduce the geometric and intensity distortions.