Task activation results in regional 13C-lactate signal increase in the human brain

Hyperpolarized-C-13 magnetic resonance imaging (HP-C-13 MRI) was used to image changes in C-13-lactate signal during a visual stimulus condition in comparison to an eyes-closed control condition. Whole-brain C-13-pyruvate, C-13-lactate and C-13-bicarbonate production was imaged in healthy volunteers (N = 6, ages 24-33) for the two conditions using two separate hyperpolarized C-13-pyruvate injections. BOLD-fMRI scans were used to delineate regions of functional activation. C-13-metabolite signal was normalized by C-13-metabolite signal from the brainstem and the percentage change in C-13-metabolite signal conditions was calculated. A one-way Wilcoxon signed-rank test showed a significant increase in C-13-lactate in regions of activation when compared to the remainder of the brain (p=0.02p=0.02). No significant increase was observed in C-13-pyruvate signal (p=0.11p=0.11) or C-13-bicarbonate signal (p=0.95p=0.95). The results show an increase in C-13-lactate production in activated regions that is measurable with HP-C-13 MRI.