Localization of a Xenon 133 bolus using a gamma camera during the closing volume measurement

The 'closing volume' concept has mainly been developed since the work of Dollfuss et al. (1967): these authors have shown that, when a normal subject inhales a bolus of 133Xe at residual volume, this bolus locates preferentially in the upper lung; during the subsequent expiration they observed a rise of Xe concentration measured at the mouth, at the very end of the vital capacity, due to the asynchronism of the opening and closure of distal airways. We have aimed at defining more accurately the location of the radioactivity, using a gamma camera, instead of superposed counters. Doing so, one increases the counting points, and the parametric image obtained pictures the concentration distribution of intrapulmonary Xenon more accurately than could be done by counters. In the 8 normal subjects studied, the highest concentration of the radio isotope was found in the half upper part of the lung fields; the boundary is clean cut with an upward concavity, the concentration in the lower part of the lung fields being nearly nul