Image distortion correction for MRI in low field permanent magnet systems with strong B0 inhomogeneity and gradient field nonlinearities

Abstract

Objective: To correct for image distortions produced by standard Fourier reconstruction techniques on low field permanent magnet MRI systems with strong B inhomogeneity and gradient field nonlinearities. Materials and methods: Conventional image distortion correction algorithms require accurate Δ B maps which are not possible to acquire directly when the B inhomogeneities also produce significant image distortions. Here we use a readout gradient time-shift in a TSE sequence to encode the B field inhomogeneities in the k-space signals. Using a non-shifted and a shifted acquisition as input, Δ B maps and images were reconstructed in an iterative manner. In each iteration, Δ B maps were reconst..