Quantifying global-brain metabolite level changes with whole-head proton MR spectroscopy at 3T.

BACKGROUND AND PURPOSE: To assess the sensitivity of non-localized, whole-head1 H-MRS to an individual's serial changes in total-brain NAA, Glx, Cr and Cho concentrations - metabolite metrics often used as surrogate markers in neurological pathologies.

MATERIALS AND METHODS: In this prospective study, four back-to-back (single imaging session) and three serial (successive sessions) non-localizing, ~3min1 H-MRS (TE/TR/TI=5/104 /940ms) scans were performed on 18 healthy young volunteers: 9 women, 9 men: 29.9±7.6 [mean±standard deviation (SD)] years old. These were analyzed by calculating a within-subject coefficient of variation (CV=SD/mean) to assess intra- and inter-scan repeatability and prediction intervals. This study was Health Insurance Portability and Accountability Act compliant. All subjects gave institutional review board-approved written, informed consent.

RESULTS: The intra-scan CVs for the NAA, Glx, Cr and Cho were: 3.9±1.8%, 7.3±4.6%, 4.0±3.4% and 2.5±1.6%, and the corresponding inter-scan (longitudinal) values were: 7.0±3.1%, 10.6±5.6%, 7.6±3.5% and 7.0±3.9%. This method is shown to have 80% power to detect changes of 14%, 27%, 26% and 19% between two serial measurements in a given individual.

CONCLUSIONS: Subject to the assumption that in neurological disorders NAA, Glx, Cr and Cho changes represent brain-only pathology and not muscles, bone marrow, adipose tissue or epithelial cells, this approach enables us to quantify them, thereby adding specificity to the assessment of the total disease load. This will facilitate monitoring diffuse pathologies with faster measurement, more extensive (~90% of the brain) spatial coverage and sensitivity than localized1 H-MRS.