Atlas-based automated positioning of outer volume suppression slices in short-TE 3D MR spectroscopic imaging of the human brain

Abstract

Spatial suppression of peripheral lipid-containing regions in volumetric MR spectroscopic imaging (MRSI) of the human brain requires placing large numbers of outer volume suppression (OVS) slices, which is time consuming, prone to operator error and may introduce subject-dependent variability in volume coverage. We developed a novel, computationally efficient atlas-based approach for automated positioning of up to 16 OVS slices and the MRSI slab. Standardized positions in MNI atlas space were established offline using a recently developed iterative optimization procedure. During the scanning session, positions in subject space were computed using affine transformation of standardized positions in MNI space. This atlas-based approach was characterized offline using MPRAGE data collected in 11 subjects. The method was further validated in 14 subjects on a clinical 3T scanner using 3D short TE (15-20ms) Proton-Echo-Planar-Spectroscopic-Imaging (PEPSI) in upper cerebrum. Comparison of manual and automatic placement using 8 OVS slices demonstrated consistent MRSI volume selection and comparable spectral quality with similar degree of lipid suppression and number of usable voxels. Automated positioning of 16 OVS slices enabled larger volume coverage, while maintaining similar spectral quality and lipid suppression. Atlas-based automatic prescription of short TE MRSI is expected to be advantageous for longitudinal and cross sectional studies