Impact of slice-specific z-shimming on T2*-weighted EPI for functional MRI of the human spinal cord at 7 Tesla

Abstract

Motivation: Slice-specific z-shimming reduces signal losses in T2*-weighted EPI of the human spinal cord at 3T. Goal(s): To investigate its impact for acquisitions at 7T performed with thinner slices and shorter echo times that are less susceptible to signal losses. Approach: EPI images (16 slices, 0.8×0.8×3.0 mm3) with 31 different z-shim settings compensating linear field inhomogeneities within ±0.3 mT m-1 were acquired. For each slice, the image with the maximum signal in the spinal cord was determined and compared to the image without z-shim. Results: Averaged across 20 healthy volunteers, slice-specific z-shimming significantly improves overall EPI signal intensity and reduces signal variations across slices. Impact: Z-shimming can improve the signal intensity and homogeneity of T2*-weighted EPI of the human cervical spinal cord at 7T and could thus help to improve the performance of spinal cord fMRI.