Assessing the effect of anesthetic gas mixtures on hyperpolarized C 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]pyruvate and perfusion weighted imaging. The anesthetic carrier gas protocol used varied from 100:0% to 90:10% to 60:40% O :N O. 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 % and MR measurements.

Results: There was a significant increase in bicarbonate:total C carbon and bicarbonate: C pyruvate when moving between 100:0 to 90:10 and 100:0 to 60:40 O :N O % (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 pyruvate time to peak when moving between 100:0 to 90:10 and 100:0 to 60:40 O :N O % (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 pyruvate and gas protocol (ρ = -0.47), mean transit time and gas protocol (ρ = 0.41) and C pyruvate time-to-peak and cerebral blood flow (ρ = -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.