Assessing the effect of anesthetic gas mixtures on hyperpolarized C-13 pyruvate metabolism in the rat brain

Purpose To determine the effect of altering anesthetic oxygen protocols on measurements of cerebral perfusion and metabolism in the rodent brain. Methods Seven rats were anesthetized and underwent serial MRI scans with hyperpolarized [1-C-13]pyruvate and perfusion weighted imaging. The anesthetic carrier gas protocol used varied from 100:0% to 90:10% to 60:40% O-2:N2O. Spectra were quantified with AMARES and perfusion imaging was processed using model-free deconvolution. A 1-way ANOVA was used to compare results across groups, with pairwise t tests performed with correction for multiple comparisons. Spearman's correlation analysis was performed between O-2% and MR measurements. Results There was a significant increase in bicarbonate:total C-13 carbon and bicarbonate:C-13 pyruvate when moving between 100:0 to 90:10 and 100:0 to 60:40 O-2:N2O % (0.02 +/- 0.01 vs. 0.019 +/- 0.005 and 0.02 +/- 0.01 vs. 0.05 +/- 0.02, respectively) and (0.04 +/- 0.01 vs. 0.03 +/- 0.01 and 0.04 +/- 0.01 vs. 0.08 +/- 0.02, respectively). There was a significant difference in C-13 pyruvate time to peak when moving between 100:0 to 90:10 and 100:0 to 60:40 O-2:N2O % (13 +/- 2 vs. 10 +/- 1 and 13 +/- 2 vs. 7.5 +/- 0.5 s, respectively) as well as significant differences in cerebral blood flow (CBF) between gas protocols. Significant correlations between bicarbonate:C-13 pyruvate and gas protocol (rho = -0.47), mean transit time and gas protocol (rho = 0.41) and C-13 pyruvate time-to-peak and cerebral blood flow (rho = -0.54) were also observed. Conclusions These results demonstrate that the detection and quantification of cerebral metabolism and perfusion is dependent on the oxygen protocol used in the anesthetized rodent brain.