Metabolite and macromolecule T1 and T2 relaxation times in the rat brain in vivo at 17.2T.

Abstract

To measure the T1 and T2 relaxation times of water, metabolites, and macromolecules in the rat brain in vivo at 17.2T and achieve absolute quantification of the neurochemical profile. Relaxation times were compared with values from the literature found at lower magnetic fields. (1) H NMR spectra were measured using a LASER localization sequence. T1 - and T2 -weighted spectra were analyzed using LCModel with an original parameterization of the macromolecule baseline. The T1 relaxation times of 20 metabolites and the T2 relaxation times of 16 singlets and J-coupled metabolites were measured. The mean T1 and T2 relaxation times for metabolites were 1721 ± 237 ms and 148 ± 53 ms, respectively. In addition, we measured the T1 and T2 relaxation times of 4 macromolecule resonance groups, their mean T1 and T2 relaxation times being 690 ± 100 ms and 37 ± 15 ms, respectively. Absolute quantification of 21 metabolites and 4 groups of macromolecule resonances was achieved with Cramer-Rao Lower Bounds below 5% for Cr, Gln, Glu, GPC, Ins, NAA, PCr, and Tau and below 25% for the remaining resonances. Comparison of our relaxation times to previously published values suggests a small increase of T1 values and a clear decrease of T2 values between 11.7 and 17.2T.