Toward an in vivo neurochemical profile: Quantification of 18 metabolites in short-echo time ¹H NMR spectra of the rat brain

Localized in vivo H-1 NMR spectroscopy was performed with 2-ms echo time in the rat brain at 9.4 T, Frequency domain analysis with LCModel showed that the in vivo spectra can be explained by 18 metabolite model solution spectra and a highly structured background, which was attributed to resonances with fivefold shorter in vivo T-1 than metabolites. The high spectral resolution (full width at half maximum approximately 0.025 ppm) and sensitivity (signal-to-noise ratio approximately 45 from a 63-mu L volume, 512 scans) was used for the simultaneous measurement of the concentrations of metabolites previously difficult to quantify in H-1 spectra. The strongly represented signals of N-acetylaspartate, glutamate, taurine, myo-inositol, creatine, phosphocreatine, glutamine, and lactate were quantified with Cramer-Rao lower bounds below 4%. Choline groups, phosphorylethanolamine, glucose, glutathione, gamma-aminobutyric acid, N-acetylaspartylglutamate, and alanine were below 13%, whereas aspartate and scyllo-inositol were below 22%. Intra-assay variation was assessed from a time series of 3-min spectra, and the coefficient of variation was similar to the calculated Cramer-Rao lower bounds. Interassay variation was determined from 31 pooled spectra, and the coefficient of variation for total creatine was 7%. Tissue concentrations were found to be in very good agreement with neurochemical data from the literature