WHOLE-BODY RETENTION OF RADIOXENON

Abstract

The total-body retention of 127Xe [in humans], and its variation with time following short, nonequilibrium periods of inhalation, were measured in vivo to refine dosimetry calculations. Radioactivity in the chest region and in the recirculating Xe-air mixture was measured continuously during rebreathing of the gas mixture and in the first 5 min of the immediate gas-washout period using a scintillation camera and shielded NaI detector, respectively. subjects were then counted in a whole-body counter at varying time intervals until background levels were reached, usually in .apprx. 72 h. Five components of Xe clearance from the entire body were measured; they had biologic half-times [t1/2] of 21.7 .+-. 12.4 s, 3.05 .+-. 1.72 min, 0.40 .+-. 0.11 h and 2.71 .+-. 0.87 h, and a long-term component varied between 7.59 and 17.04 h. The t1/2 of the last component correlated highly with the percent of total-body fat. After 10 min inhalations of the Xe-air mixture, approximately 1/3 of the total Xe was transferred to the body tissues, extrapolated back to the start of gas washout. Of this amount, .apprx. 13% was associated with the slowest component of clearance.