Removal of Magnetic Field Inhomogeneity Artifacts

A technique for reducing B₀ field inhomogeneity and magnetic susceptibility artifacts in gradient-recalled-echo (GRE) images is presented. The artifacts are mainly produced by intravoxel phase dispersion due to local gradients in the slice direction and can be very large at high field strengths. This 3D technique uses incremental phase encoding in the slice refocusing gradient to sample k-space over the full range of spatial frequencies of the excitation profile. A third Fourier transform of the resultant 2D set of images, generates an image set in which the artifacts produced by the low-order field gradients are separated from the high-order field gradients responsible for T₂* contrast. Application to high field brain imaging at 3.0 T for human and at 9.4 T for young rats illustrate the significant improvement in quality of the T₂*-weighted contrast images.