¹H MRS in the rat brain under pentobarbital anesthesia: Accurate quantification of in vivo spectra in the presence of propylene glycol

Commercial solutions for pentobarbital anesthesia typically contain water, ethanol, and propylene glycol (PG). The last two are characterized by resonances that can affect the determination of metabolite concentrations from ¹H spectra. The purpose of the present study was to measure the concentration of metabolites in the rat brain in vivo under pentobarbital anesthesia using ¹H MRS. Resonances of PG, but not ethanol, were observed in the rat brain. Chemical shifts and J-coupling constants for PG were measured at 37°C and pH 7.1 and used for spectral simulation. Inclusion of the simulated PG spectrum in the basis set for LCModel analysis enabled accurate fitting of in vivo spectra. This work demonstrates that concentration of brain metabolites can be reliably measured using ¹H spectroscopy under pentobarbital anesthesia. The chemical shifts and J-coupling values reported here can be used to simulate the spectrum of PG at any field strength, with various pulse sequences.