Inhomogeneity correction using an estimated linear field map.

A fast and robust method for correcting magnetic resonance image distortion due to field inhomogeneity is proposed and applied to spiral k-space scanning. The method consists of acquiring a local field map, finding the best fit to a linear map, and using it to deblur the image distortions due to local frequency variations. The linear field map is determined using a maximum likelihood estimator with weights proportional to the pixel intensity. The method requires little additional computation and is robust in low signal regions and near abrupt field changes. Additionally, it can be used in combination with other deblurring methods. The application of this method is illustrated in conjunction with a multislice, T2-weighted, breath-held spiral scan of the liver.