Novel strategy for cerebral 13C MRS using very low RF power for proton decoupling

One of the major difficulties of in vivo 13C MRS is the need to decouple the large, one-bond, 1H-13C scalar couplings in order to obtain useful signal-to-noise ratios (SNRs) and spectral resolution at magnetic field strengths that are accessible to clinical studies. In this report a new strategy for in vivo cerebral 13C MRS is proposed. We realized that the turnover kinetics of glutamate (Glu) C5 from exogenous [2-(13)C]glucose (Glc) is identical to that of Glu C4 from exogenous [1-(13)C]Glc. The carboxylic/amide carbons are only coupled to protons via very weak long-range 1H-13C scalar couplings. As such, they can be effectively decoupled at very low RF power. Therefore, decoupling of the large 1H-13C scalar couplings can be avoided by the use of [2-(13)C]Glc. An additional advantage of this strategy is the lack of contamination from subcutaneous lipids because there are no overlapping fat signals in the vicinity of the Glu C5 and glutamine (Gln) C5 peaks. The feasibility of this strategy was demonstrated using 13C MRS on rhesus monkey brains at 4.7T.