Assessing the reliability of hippocampal single-voxel proton magnetic resonance spectroscopy through intra-class effect decomposition

BackgroundThe hippocampus is crucial for learning, memory, and stress regulation but is vulnerable to biological and environmental influences that compromise its structural and metabolic integrity. Proton magnetic resonance spectroscopy (MRS) enables in vivo quantification of hippocampal neurochemistry, yet the absolute and relative reliability of these measures has rarely been systematically evaluated.MethodsWe assessed absolute and relative reliability in hippocampal metabolite estimates acquired with single-voxel MRS using a semi-adiabatic localization by adiabatic selective refocusing (semi-LASER) sequence at 3 T. Nineteen healthy adults (8 male; mean age = 40.9 ± 16.9 years) underwent four measurements across two consecutive days, with one session including an extended acquisition. Absolute reliability was quantified using within-subject coefficients of variation (CVs), and relative reliability was estimated with the Intra-Class Effect Decomposition (ICED) framework, which partitions variance into true-score, day-specific, session-specific, and residual components.ResultsDespite high absolute reliability (CVs ≈ 4–7%), ICED indicated that relative reliability was generally poor to fair, with only myo-inositol, total choline, and total creatine reaching good intraclass correlation coefficients (ICCs; 0.60–0.70). Increasing the number of transients improved spectral precision, reflected in higher signal-to-noise ratio and lower Cramér–Rao lower bounds, but did not enhance relative reliability.ConclusionsHippocampal metabolite quantification at 3 T showed high absolute but limited relative reliability, indicating that improved signal precision does not guarantee higher relative reliability. These findings highlight the need for methodological refinement, including automated voxel placement and advanced shimming, to improve the suitability of hippocampal MRS for longitudinal and individual-difference research.