Reproducibility of the Determination of 13C-Labeling of Glutamate and Glutamine in the Human Brain Using selPOCE-MRS at 7 T Upon [U-13C]-Labeled Glucose Infusion

Glutamate (Glu) is the major excitatory neurotransmitter in the central nervous system. The measurement of Glu/glutamine (Gln) neurotransmitters in the brain provides valuable insights into the dynamic aspects of neuroenergetics and neurotransmitter cycles and can be accomplished through the detection of 13C-labeling of Glu and Gln during the administration of 13C-labeled glucose. Our goal is to evaluate the reproducibility of selective proton-observed, carbon-edited (selPOCE) MRS at 7 T for the detection of 13C-labeled Glu and Gln in the human brain. Data of three healthy participants, who were scanned twice at 7 T while undergoing [U-13C]-glucose infusion for 120 min, were used to detect 13C-labeled Glu and Gln in the brain, using selPOCE-STEAM-MRS. There was a rapid increase of plasma glucose 13C fractional enrichment (FE) during the first 20 min of infusion, followed by a steady state of plasma glucose 13C FE until the end of the [U-13C]-glucose infusion. The time courses of 13C-labeling of Glu and Gln were similar for test/retest. The test/retest variability was 15.8% for 13C-Glu and 33.3% for 13C-Gln. Knowing the variability of these readings using selPOCE-STEAM-MRS can inform the application to future studies on disease-specific alterations in Glu/Gln cycling.