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

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 degrees C from separate 100 mm solutions of inositol (Ins), choline-containing compounds (Cho), N-acetyl-aspartate (NAA) and creatine. Simulations of T(1) 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 T(1)s within the same brain volume. The same order from shortest to longest T(1) (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 T(1) is inversely proportional to molecular weight. For all individual metabolites, T(1) increased from occipital grey to parietal white to frontal white matter. This study demonstrates that, in spectra acquired with TR near 1 s, T(1) weightings are substantially different for metabolites within a single tissue and also for the same metabolites in different tissues.