Quantitative in vivo 1H spectroscopic imaging of metabolites in the early postnatal mouse brain at 17.6 T

Object  Early postnatal brain maturation is closely connected to local changes of metabolite levels. Spatially resolved in vivo ¹H NMR spectroscopic imaging is applied to follow absolute changes of brain metabolites in early postnatal mouse brain. Materials and methods  A short echo time semi LASER (localization by adiabatic selective refocusing) chemical shift imaging (CSI) sequence incorporating weighted k-space averaging was implemented at high magnetic field (17.6 T). In vivo measurements were carried out on postnatal days 5, 8, 12, 16, and 20. In vivo relaxation times T ₁ and T ₂ were measured using variable repetition times or a CPMG sequence, respectively, combined with LASER single voxel localization. Results  Spectra were obtained with a spatial resolution of (1 × 1) mm² in a 1.5 mm slice as early as postnatal day 5. Maturational changes of absolute metabolite concentrations of major metabolites were calculated in four different brain regions. A significant increase of N-acetylaspartate (NAA), total creatine (tCr), and glutamate/glutamine (Glx) concentration was paralleled by a decrease of taurine (Tau) concentration with age (P < 0.05). Differences between brain regions were found for NAA, tCr, and Tau (P < 0.05). Furthermore, in vivo T ₁ and T ₂ of the four major brain metabolites in adult mice are reported. Conclusion  The implemented semi LASER CSI sequence allows following regional changes of metabolite levels. It is suitable for investigation of local differences in brain metabolism and development.