Proton T1 relaxation times of cerebral metabolites differ within and between regions of normal human brain

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Abstract
Saturation recovery spectra (STEAM) were acquired at 1.5 T with 7 TRs ranging from 530 to 5000 ms and a constant TE of 30 ms in voxels (7.2 ml) located in occipital grey, parietal white and frontal white matter (10 subjects each location). Spectra were also acquired at 7, 21 and 37°C from separate 100 mm solutions of inositol (Ins), choline‐containing compounds (Cho), N‐acetyl‐aspartate (NAA) and creatine. Simulations of T1 fits with 2, 3 and 7 TRs demonstrated that at typical SNR there is potential for both inaccurate and biased results. In vivo, different metabolites had significantly different T1s within the same brain volume. The same order from shortest to longest T1 (Ins, Cho, NAA, creatine) was found for all three brain regions. The order (Ins, NAA, creatine, Cho) was found in the metabolite solutions and was consistent with a simple model in which T1 is inversely proportional to molecular weight. For all individual metabolites, T1 increased from occipital grey to parietal white to frontal white matter. This study demonstrates that, in spectra acquired with TR near 1 s, T1 weightings are substantially different for metabolites within a single tissue and also for the same metabolites in different tissues. Copyright © 2003 John Wiley & Sons, Ltd.