A Four Parameter Fitting Method to Quantify Fully the Sources of Phase Contrast in Gradient Echo MRI

Sam Wharton¹, Richard Bowtell¹

Until recently, the excellent contrast seen in gradient echo based phase images was thought to be entirely due to differences in the isotropic magnetic susceptibility of tissues. Recently, however, three additional contrast mechanisms have been proposed. These are: (i) exchange processes; (ii) field perturbations due to oriented NMR-invisible microstructures; (iii) anisotropy of the magnetic susceptibility. Here, we present a method for fitting and separating the contributions of each of the four proposed contrast mechanisms using MRI phase data acquired with the sample at multiple orientations to the main magnetic field, B0, in combination with diffusion tensor imaging data.