Task Activation Results in Regional ¹³ C-Lactate Signal Increase in the Human Brain

Hyperpolarized- ¹³ C magnetic resonance imaging (HP- ¹³ C MRI) was used to image changes in ¹³ C-lactate signal during a visual stimulus condition in comparison to an eyes-closed control condition. Whole-brain ¹³ C-pyruvate, ¹³ C-lactate and ¹³ C-bicarbonate production was imaged in healthy volunteers (N=6, ages 24-33) for the two conditions using two separate hyperpolarized ¹³ C-pyruvate injections. BOLD-fMRI scans were used to delineate regions of functional activation. ¹³ C-metabolite signal was normalized by ¹³ C-metabolite signal from the brainstem and the percentage change in ¹³ C-metabolite signal conditions was calculated. A one-way Wilcoxon signed-rank test showed a significant increase in ¹³ C-lactate in regions of activation when compared to the remainder of the brain ( p = 0.02, V = 21). No significant increase was observed in ¹³ C-pyruvate ( p = 0.11, V = 17) or ¹³ C-bicarbonate ( p = 0.95, V = 3) signal. The results show an increase in ¹³ C-lactate production in the activated region that is measurable with HP- ¹³ C MRI.