Comparison of T 1 relaxation times of the neurochemical profile in rat brain at 9.4 tesla and 14.1 tesla

Knowledge of T 1 relaxation times can be important for accurate relative and absolute quantification of brain metabolites, for sensitivity optimizations, for characterizing molecular dynamics, and for studying changes induced by various pathological conditions. 1 H T 1 relaxation times of a series of brain metabolites, including J‐coupled ones, were determined using a progressive saturation (PS) technique that was validated with an adiabatic inversion‐recovery (IR) method. The 1 H T 1 relaxation times of 16 functional groups of the neurochemical profile were measured at 14.1T and 9.4T. Overall, the T 1 relaxation times found at 14.1T were, within the experimental error, identical to those at 9.4T. The T 1 s of some coupled spin resonances of the neurochemical profile were measured for the first time (e.g., those of γ‐aminobutyrate [GABA], aspartate [Asp], alanine [Ala], phosphoethanolamine [PE], glutathione [GSH], N‐acetylaspartylglutamate [NAAG], and glutamine [Gln]). Our results suggest that T 1 does not increase substantially beyond 9.4T. Furthermore, the similarity of T 1 among the metabolites (∼1.5 s) suggests that T 1 relaxation time corrections for metabolite quantification are likely to be similar when using rapid pulsing conditions. We therefore conclude that the putative T 1 increase of metabolites has a minimal impact on sensitivity when increasing B 0 beyond 9.4T. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.