Longitudinal inter- and intra-individual human brain metabolic quantification over 3 years with proton MR spectroscopy at 3 T.

The longitudinal repeatability of proton MR spectroscopy ((1) H-MRS) in the healthy human brain at high fields over long periods is not established. Therefore, we assessed the inter- and intra-subject repeatability of (1) H-MRS in an approach suited for diffuse pathologies in 10 individuals, at 3T, annually for 3 years. Spectra from 480 voxels over 360 cm(3) (∼30%) of the brain, were individually phased, frequency-aligned, and summed into one average spectrum. This dramatically increases metabolites' signal-to-noise-ratios while maintaining narrow linewidths that improve quantification precision. The resulting concentrations of the N-acetylaspartate, creatine, choline, and myo-inositol are: 8.9 ± 0.8, 5.9 ± 0.6, 1.4 ± 0.1, and 4.5 ± 0.5 mM (mean ± standard-deviation). the inter-subject coefficients of variation are 8.7%, 10.2%, 10.7%, and 11.8%; and the longitudinal (intra-subject) coefficients of variation are lower still: 6.6%, 6.8%, 6.8%, and 10%, much better than the 35%, 44%, 55%, and 62% intra-voxel coefficients of variation. The biological and nonbiological components of the summed spectra coefficients of variation had similar contributions to the overall variance.