Reproducibility of Metabolic Mapping Using 2D Multi‐Slice Short‐TE and GABA‐Edited Spin‐Echo MRSI at 3T in a Single Protocol

MRSI is a non-invasive tool for mapping metabolic distributions in multi-focal or other diseases where the location of abnormalities may be uncertain. High-concentration metabolites can be investigated at 3T using non-edited MRSI, whereas lower-concentration metabolites, such as GABA, typically require specialized editing techniques because of spectral overlap. This study reports on the reproducibility of a protocol containing both co-localized short-TE and GABA-edited multi-slice spin-echo 2D MRSI. Multi-slice, short-TE (TE 20 ms) and GABA-edited (TE 68 ms) MRSI at a nominal spatial resolution of 2.2 cm³ was performed twice (7 to 14 days apart) at 3T on 11 healthy volunteers (age range 7 to 43 years). Data analysis was performed in the "Osprey" software package, including retrospective motion compensation, consensus-recommended processing, and linear-combination modeling. Metabolite estimates for six metabolites were quantified relative to total creatine (tCr) and water in 14 regions of interest. Reproducibility was assessed using intra- and inter-subject coefficients of variation. Short-TE MRSI metabolite estimates for total N-acetylaspartate (tNAA), tCr, total choline (tCho), myo-inositol (mI), and the sum of glutamate and glutamine (Glx) were found to be highly reproducible for both creatine- and water-referenced concentration estimates, with 77% of the regions of interest meeting the quality-control criteria for both visits and 96% for at least one visit. Average intra-subject CVs were 5.8% and 4.8%, and inter-subject CVs were 11.1% and 9.7% for water-referenced and tCr-referenced estimates, respectively. For GABA+ (GABA + macromolecules) estimates, 46% of the voxels of interest met quality-control criteria for both visits, and 82% for at least one visit. In the remaining datasets, the average intra-subject CVs were 13.5% for both quantification methods, and the inter-subject CVs were 13.5% and 16.9% for water-referenced and creatine-referenced estimates, respectively. 3T-MRSI sequences can achieve reproducible mapping with extended brain coverage of five major metabolites (tNAA, tCr, tCho, mI, and Glx). Reproducibility assessment for GABA+ mapping remains challenging, with 18% of the data being rejected in at least one visit, but it yielded acceptable reproducibility in datasets that met quality control criteria in both visits (46%).