Mapping of magnetic field inhomogeneity and removal of its artifact from MR images

Inhomogeneity of static magnetic field, induced by object susceptibility, is unavoidable in magnetic resonance imaging (MRI). This inhomogeneity generates distortions in both image geometry and its intensity. Based on node magnetic voltage values, a fast Finite Difference Method (FDM) is developed for susceptibility-induced mapping of magnetic. field inhomogeneity and applied to simulated MRI data. Its accuracy and speed of convergence are evaluated by comparing the method to Finite Elements Method (FEM), which had been validated experimentally. Effects of inhomogeneity on Spin Echo (SE) MRI are simulated using the proposed field calculation method. Also; a pixel based (direct) method as well as a grid based (indirect) method for removing the effects are developed. The fast execution of the algorithm stems from the multi-resolution nature of the proposed method. The main advantage of the proposed method is that it does not need any data except for the image itself. Efficiency of both correction methods in distortion removal is investigated.