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 hampared by the significant artifacts produced by B-0 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 T-2*-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-0 inhomogeneity field gradients in the sample are separated and removed from the high-order microscopic field gradients responsible for T-2* 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 T-2*-weighted contrast images.