Fixation, retention and exhalation of carrier-free 11C-labeled carbon monoxide by man.

Carrier-free 11C-labeled carbon monoxide was produced by proton irradiation of a nitrogen gas flow target via the 14N(p, alpha)11C process followed by on-line reduction of the predominantly formed 11C-carbon dioxide with a yield of 0.4 mCi/muAmin. After appropriate quality control about 2 mCi of carrier-free 11C-carbon monoxide in 500 ml on nitrogen gas were inhaled by test subjects in one breath. The 11C-activity distribution was then followed in vivo by scanning above thorax, head, liver, thigh and os sacrum; simultaneously the 11c-activity of the blood was also followed by batch measurement. The data indicate that part of the 11C-activity migrates from the blood into the intercellular space, while another part is exhaled. The 11C-activity leaves the individual organs with a biological half-life ranging from about 120 to 200 min, a time which is short as compared to the one observed for 51Cr-labeled erythrocytes. A radio gas chromatographic analysis of the exhaled air showed that the 11C-activity leaves the body exculsively in the form of 11C-labeled carbon monoxide. Consequently, metabolism of the 11CO into 11CO2 or other compounds can be excluded.