Ethanol in human brain by magnetic resonance spectroscopy: Correlation with blood and breath levels, relaxation, and magnetization transfer

Background: proton magnetic resonance spectroscopy (H-1 MRS) allows measure ment of alcohol in the human brain after alcohol consumption. However, the quantity of alcohol that can be detected in the brain by H-1 MRS pulse sequ ences has been controversial, with values ranging from about 24% to 94% of the temporally concordant blood alcohol concentrations. The quantitation of brain alcohol is critically affected by the kinetics of alcohol uptake and elimination, by the relaxation times of the protons that give rise to the brain alcohol signal, and by the specifics of both pulse sequence timing an d radio frequency pulse applications. Methods: We investigated these factors in 20 light-drinking subjects after oral administration of approximately 0.85 g/kg body weight of alcohol by lo calized H-1 MRS and measurements of blood and breath alcohol concentrations obtained at the same time. Specifically, we measured transverse and longit udinal relaxation times of brain alcohol and its signal saturation on appli cation of on- or off-resonance radio frequency pulses. All H-1 MRS measurem ents were performed at a time after brain and blood alcohol concentrations had equilibrated. Results: H-1 MRS measures of brain alcohol were correlated highly with both breath and blood alcohol concentrations after equilibration in brain tissu e. The measured H-1 MRS relaxation times of brain alcohol were shorter than given in previous reports that were limited by smaller subject numbers, im proper use of H-1 MRS methods, and estimates rather than measurements. The brain alcohol signal decreased by about 30% on application of on- or off-re sonance saturation pulses. Conclusions: H-1 MRS allows direct measurement of brain alcohol, formerly o nly possible indirectly through inferences from breath alcohol levels. Quan titation of brain alcohol levels need to take into account measured relaxat ion times and alcohol signal attenuation due to presence and timing of stan dard radio frequency MRS pulses. Saturation experiments give evidence for t he existence of more than one compartment of brain alcohol characterized by different molecular environments. They suggest that a fraction of brain al cohol is invisible to H-1 MRS.