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

Most in vivo ¹³C NMR spectroscopy studies in the brain have been performed using ¹H decoupling during acquisition. Decoupling 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 ¹³C label from ¹³C-labeled glucose into brain amino acids can be monitored accurately using localized ¹³C NMR spectroscopy without the application of ¹H 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, ¹³C MMR 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 ¹³C NMR spectra in humans at varied brain locations (not only the occipital lobe) and at very high magnetic fields above 4 Tesla.