1. A method for magnetic resonance imaging (MRI) comprising use of an MRI gantry and associated computers and hardware to: acquire MRI map prescan data from a predetermined imaged patient volume; decompose said acquired map prescan data to produce a transmit RF field inhomogeneity map and a receive RF field inhomogeneity map for said imaged patient volume based on a three-dimensional geometrical model of said inhomogeneity maps; and use at least one of said transmit RF field inhomogeneity map and said receive RF field inhomogeneity map to generate intensity-corrected target MRI diagnostic scan image data representing said imaged patient volume.