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Comparison of T1 relaxation times of the neurochemical profile in rat brain at 9.4 tesla and 14.1 tesla

Knowledge of T1 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. 1H T1 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 1H T1 relaxation times of 16 functional groups of the neurochemical profile were measured at 14.1T and 9.4T. Overall, the T1 relaxation times found at 14.1T were, within the experimental error, identical to those at 9.4T. The T1s 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 T1 does not increase substantially beyond 9.4T. Furthermore, the similarity of T1 among the metabolites (∼1.5 s) suggests that T1 relaxation time corrections for metabolite quantification are likely to be similar when using rapid pulsing conditions. We therefore conclude that the putative T1 increase of metabolites has a minimal impact on sensitivity when increasing B0 beyond 9.4T. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.