Purpose
In 2004, Boumezbeur et al proposed a simple yet powerful approach to detect the metabolism of 13C‐enriched substrates in the brain. Their approach consisted of dynamic 1H‐MRS, without a 13C radiofrequency (RF) channel, and its successful application was demonstrated in monkeys. Since then, this promising method has yet to be applied rigorously in humans. In this study, we revisit the use of dynamic 1H‐MRS to measure the metabolism of 13C‐enriched substrates and demonstrate its application in the human brain.
Methods
In healthy participants, 1H‐MRS data were acquired dynamically before and following a bolus infusion of [1‐13C] glucose. Data were acquired on a 3T clinical MRI scanner using a short‐TE SPECIAL sequence, with regions of interest in both anterior and posterior cingulate cortex. Using simulated basis spectra to model signal changes in both 12C‐bonded and 13C‐coupled resonances, the acquired spectra were fit in LCModel to obtain labeling time courses for glutmate and glutamine at both C4 and C3 positions.
Results
Presence of the 13C label was clearly detectable, owing to the pronounced effect of heteronuclear (13C‐1H) scalar coupling on the observed 1H spectra. A decrease in signal from 12C‐bonded protons and an increase in signal from 13C‐coupled protons were observed. The fractional enrichment of Glu‐C4, (Glu+Gln)‐C4, and (Glu+Gln)‐C3 at 30 minutes following infusion of [1‐13C] glucose was similar in both regions: 11% to 13%, 9% to 12% and 3% to 5%, respectively.
Conclusion
These preliminary results confirm the feasibility of the use of dynamic 1H‐MRS to monitor 13C labeling in the human brain, without a 13C RF channel.