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

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