PRESS timings for resolving 13 C 4 ‐glutamate 1 H signal at 9.4 T: Demonstration in rat with uniformly labelled 13 C‐glucose

MRS of 13 C 4 ‐labelled glutamate ( 13 C 4 ‐Glu) during an infusion of a carbon‐13 ( 13 C)‐labelled substrate, such as uniformly labelled glucose ([U‐ 13 C 6 ]‐Glc), provides a measure of Glc metabolism. The presented work provides a single‐shot indirect 13 C detection technique to quantify the approximately 2.51 ppm 13 C 4 ‐Glu satellite proton ( 1 H) peak at 9.4 T. The methodology is an optimized point‐resolved spectroscopy (PRESS) sequence that minimizes signal contamination from the strongly coupled protons of N ‐acetylaspartate (NAA), which resonate at approximately 2.49 ppm. J ‐coupling evolution of protons was characterized numerically and verified experimentally. A ( TE 1 , TE 2 ) combination of (20 ms, 106 ms) was found to be suitable for minimizing NAA signal in the 2.51 ppm 1 H 13 C 4 ‐Glu spectral region, while retaining the 13 C 4 ‐Glu 1 H satellite peak. The efficacy of the technique was verified on phantom solutions and on two rat brains in vivo during an infusion of [U‐ 13 C 6 ]‐Glc. LCModel was employed for analysis of the in vivo spectra to quantify the 2.51 ppm 1 H 13 C 4 ‐Glu signal to obtain Glu C4 fractional enrichment time courses during the infusions. Cramér‐Rao lower bounds of about 8% were obtained for the 2.51 ppm 13 C 4 ‐Glu 1 H satellite peak with the optimal TE combination.