In Vivo Measurement of Carbon-13 Labeling of Glutamate and Glutamine in Human Brain Using Proton Magnetic Resonance Spectroscopy

Abstract A single-step spectral editing 1H magnetic resonance spectroscopy (MRS) technique was used to measure fractional enrichments of glutamate and glutamine in the dorsal anterior cingulate cortex of five healthy volunteers after oral administration of [U-13C]glucose. Strong pseudo singlets of glutamate and glutamine were induced at an echo time of 56 ms using an always-on editing pulse at 2.12 ppm. At 113 ± 9 minutes after oral administration of [U-13C]glucose, fractional enrichment of glutamate was found to be 64 ± 5% with 1.7% within-subject coefficient of variation (CV) and fractional enrichment of glutamine was found to be 40 ± 10% with 11% within-subject CV. This study demonstrated that 13C labeling of both glutamate and glutamine can be measured with the high sensitivity and spatial resolution of proton MRS using a proton-only MRS technique with standard commercial hardware. Furthermore, it is now feasible to measure 13C labeling of glutamate and glutamine in limbic structures, which play major roles in behavioral and emotional responses and whose abnormalities are involved in many neuropsychiatric disorders.