From a Voxel to Maps: A Comparative Study of sLASER SVS and 3D-CRT-FID-MRSI at 3 T and 7 T.

Magnetic resonance spectroscopy (MRS) enables non-invasive assessment of brain metabolites and is commonly implemented using single-voxel spectroscopy (SVS) or magnetic resonance spectroscopic imaging (MRSI). This study directly compares the reproducibility of SVS-based semi-localization by adiabatic selective refocusing (sLASER) and 3D-Concentric Ring Trajectory-based Free Induction Decay MRSI (3D-CRT-FID-MRSI) at 3T and 7T in the same cohort of healthy participants. To explore MRSI's capabilities for regional metabolite quantification and reproducibility assessment, three masking strategies were applied. Additionally, two spatial averaging approaches for MRSI, averaging before vs. after spectral fitting, were evaluated. Coefficients of variation (CV) and voxel-wise correlation analyses were used to assess intra-subject and inter-session reproducibility. Results showed good-to-excellent reproducibility across both techniques, with SVS generally providing lower CVs at 7T, while MRSI outperformed SVS in several metabolites at 3T. MRSI allowed tissue-specific analysis, with lower CVs observed in WM compared to GM, especially at 7T. Although MRSI reproducibility was slightly reduced at 7T likely due to longer scan times and lack of prospective motion correction, the spatial coverage and retrospective region analysis makes it an attractive alternative to SVS for many brain regions. This study demonstrates that both sLASER and CRT-FID-MRSI provide reproducible metabolite measurements at 3T and 7T. The findings highlight MRSI's advantages for retrospective multi-regional and tissue-specific analysis, facilitating its integration into future clinical research.