Investigating brain metabolism at high fields using localized 13C NMR spectroscopy without 1H decoupling

Most in vivo C-13 NMR spectroscopy studies in the brain have been performed using H-1 decoupling during acquisition. Decoupiing imposes significant constraints on the experimental setup (particularly for human studies at high magnetic field) in order to stay within safety limits for power deposition. We show here that incorporation of the C-13 label from C-13-labeled glucose into brain amino acids can be monitored accurately using localized 13 C NMR spectroscopy without the application of H-1 decoupling. Using LCModel quantification with prior knowledge of one-bond and multiple-bond J(CH) coupling constants, the uncertainty on metabolites concentrations was only 35% to 91% higher (depending on the carbon resonance of interest) in undecoupled spectra compared to decoupled spectra in the rat brain at 9.4 Tesla. Although less sensitive, C-13 NMR without decoupling dramatically reduces experimental constraints on coil setup and pulse sequence design required to keep power deposition within safety guidelines. This opens the prospect of safely measuring C-13 NMR spectra in humans at varied brain locations (not only the occipital lobe) and at very high magnetic fields above 4 Tesla.