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