REMOVAL OF LOCAL-FIELD GRADIENT ARTIFACTS IN T-2-ASTERISK-WEIGHTED IMAGES AT HIGH FIELDS BY GRADIENT-ECHO SLICE EXCITATION PROFILE IMAGING

Development of high magnetic field MRI techniques is hampared by the s ignificant artifacts produced by B-0 field inhomogeneities in the exci ted slices. A technique, gradient-echo slice excitation profile imagin g (GESEPI), is presented for recovering the signal lost caused by intr avoxel phase dispersion in T-2-weighted images. This technique superi mposes an incremental gradient offset on the slice refocusing gradient to sample k-space over the full range of spatial frequencies of the e xcitation profile. A third Fourier transform of the initial two-dimens ional 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 demonstrate s the significant improvement in quality of the T-2-weighted contrast images.