Metabolic modelling and time-resolved mapping of glucose oxidative metabolism in rats brain by indirect deuterium detection with ¹ H-FID-MRSI at 9.4T

This study exploits newly developed dynamic indirect 1H-[2H]-FID-MRSI at 9.4 T, combined with a dedicated metabolic model, to enable regional and quantitative characterization of glucose oxidative metabolism flux in the rat brain with minimal metabolic assumptions, by measuring both 2H-labelled Glx turnover and pool size along a controlled 2H-Glc infusion protocol. Seven rats underwent dynamic 2D 1H-FID-MRSI during a 2-h infusion of [6,6’-2H₂] glucose. Consecutive 13-min acquisitions quantified Glx-C4 1H-signal decay, converted to 2H-Glx concentrations using baseline metabolite pool sizes. A four-pool kinetic model including 2H-label loss was fitted to regional turnover curves to estimate oxidative flux (Vgt) and pyruvate dilution (Kdil). Model performance and parameter robustness were assessed with Monte-Carlo simulations. In vivo 2H-Glx turnover showed a saturated exponential rise (~ 60 min), with a labelling plateau higher in striatum (1.85 μmol/g) than hippocampus (1.55 μmol/g). Metabolic modelling provided region-specific oxidative fluxes: Vgt = 0.53 ± 0.15 μmol/g/min (hippocampus) and Vgt = 0.81 ± 0.12 μmol/g/min (striatum), with consistent Kdil across regions. Simulations confirmed a good model robustness in retrieving Vgt over a large range of experimental conditions. This work shows the potential of indirect dynamic 1H-[2H]-FID-MRSI for quantitative metabolic flux mapping of cerebral glucose oxidative metabolism.