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

Abstract

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