Removal of local field gradient artifacts in T₂*-weighted images at high fields by gradient-echo slice excitation profile imaging

Development of high magnetic field MRI techniques is hampered by the significant artifacts produced by B(o) field inhomogeneities in the excited slices. A technique, gradient-echo slice excitation profile imaging (GESEPI), is presented for recovering the signal lost caused by intravoxel phase dispersion in T₂*-weighted images. This technique superimposes an incremental gradient offset on 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 initial two-dimensional image set generates an image set in which the artifacts produced by the low-order B(o) inhomogeneity field gradients in the sample are separated and removed from the high-order microscopic field gradients responsible for T₂* contrast. Application to high field brain imaging, at 3.0 T for human and at 9.4 T for immature rat imaging demonstrates the significant improvement in quality of the T₂*- weighted contrast images.