In vivo rapid magnetic field measurement and shimming using single scan differential phase mapping.

In vivo shimming is a powerful tool for alleviating subject-dependent magnetic field distortions in MRI, although the usually lengthy procedure has limited its use. A magnetic field measurement method called single scan differential phase mapping that can reduce the measurement time of conventional methods by more than half when used with multiple gradient-recalled echo imaging was developed. An automatic high-order shimming using the present method was implemented in a commercial MRI system. In vivo field inhomogeneity features and the shimming performances were investigated. The method was found to be useful for improving the quality of echo-planar images.