Simultaneous mass spectrometry and thermoconductivity measurements of end tidal xenon concentrations: A comparison

Studies in which the rate of local cerebral blood flow is determined by xenon enhanced computerized tomography require measurement of end tidal gas. A mass spectrometer and a thermoconductivity detector were compared in measuring the concentration of xenon in end tidal gas both in humans and in a clinically simulated (“breathing bag”) system. The experiments showed that the two instruments provided virtually identical results up to a rate of 18 breaths/min, at which rate recorded concentrations showed marginal degradation with the thermoconductivity detector. Given the absence of a significant difference in the ability of the mass spectrometer and the thermoconductivity detector to measure end tidal xenon concentration, the thermoconductivity detector appears to be a satisfactory alternative in studies measuring the rate of local cerebral blood flow by enhanced computerized tomography.