MRI geometric distorsion: A simple approach to correcting the effects of non-linear gradient fields

International audienceWe present a method to correct intensity variations and voxel shifts caused by non-linear gradient fields in Magnetic Resonance Images. The principal sources of distortion are briefly exposed, as well as the methods of correction currently in use. The implication of the gradient fields non-linearities on the signal equations are described in a detailed way for the case of 2D and 3D Fourier imagery. A model of these nonlinearities, derived from the geometry of the gradient coils, is proposed and then applied in post-processing to correct any images regardless of the acquisition sequence. Initial position errors, as large as 4 mm (i.e. 4 voxels of 1x1x1.4 mm3 ) before correction, are reduced to less than the voxel sizes after correction