Measurement of nonlinear pO2 decay in mouse lungs using 3He-MRI.

Spatial and temporal variations in oxygen partial pressure ( pO2) during breath-hold can be exploited to obtain important regional parameters of lung function. In the course of apnea, the oxygen concentration is known to decay exponentially. Therefore, the initial pO2 ( p0) can be used to represent local ventilation, and the oxygen depletion time constant can characterize perfusion. The protocol, based on a nonlinear model of pO2 decay, was validated in six healthy mice. Parametric maps of p0 and oxygen depletion time constant were obtained for pure 3 He and 3 He/air mixture. The mean measured values of p0 were 77 � 9 mbar for the pure 3 He insufflation and 107 � 5 mbar for 3 He/air mixture, in agreement with the predefined p0 values: 75 � 15 mbar and 123 � 15 mbar, respectively. The mean measured oxygen depletion time constants were 6.5 � 0.2 s for pure 3 He and 7.1 � 0.8 s for the 3 He/air mixture, in agreement with physiology.