Evidence of ¹³C-lactate oxidation in the human brain from hyperpolarized ¹³C-MRI

Purpose: To test the hypothesis that lactate oxidation contributes to the (13)13 C-bicarbonate signal observed in the awake human brain using hyperpolarized (13)13 C MRI.Methods: Healthy human volunteers (N = 6) were scanned twice using hyperpolarized (13)13 C-MRI, with increased radiofrequency saturation of (13)13 C-lactate on one set of scans. (13)13 C-lactate, (13)13 C-bicarbonate, and (13)13 C-pyruvate signals for 132 brain regions across each set of scans were compared using a clustered Wilcoxon signed-rank test.Results: Increased (13)13 C-lactate radiofrequency saturation resulted in a significantly lower (13)13 C-bicarbonate signal (p = 0.04). These changes were observed across the majority of brain regions.Conclusion: Radiofrequency saturation of (13)13 C-lactate leads to a decrease in (13)13 C-bicarbonate signal, demonstrating that the (13)13 C-lactate generated from the injected (13)13 C-pyruvate is being converted back to (13)13 C-pyruvate and oxidized throughout the human brain.