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

Abstract

Development of high magnetic field MRI techniques is hampered by the significant artifacts produced by B₀ 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 Jr‐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 B₀ 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.