On-line measurement of exhaled [C-11]CO2 during PET

The purpose of this study was to develop and evaluate a system for the cont inuous on-line measurement of expired (CO2)-C-11 during C-11 PET studies. M ethods: A detector system was developed that allowed continuous sampling of expired air during PET. Healthy volunteers (n = 4) underwent PET with [C-1 1]CO2 during which expired air, tomographic tissue activity, and blood data were collected. The measured expired-air (CO2)-C-11 radioactivity time cou rses were filtered, and an envelope was extracted and compared with the tim e course of (CO2)-C-11/(HCO3-)-C-11 in blood. Results: Good agreement was f ound between the shapes of the expired-air envelope and the time course in blood, enabling quantitative calibration against discrete blood samples. Co nclusion: A system for the continuous monitoring of expired radioactivity d uring PET has been developed and evaluated with [C-11]CO2. This monitoring enables the quantitative continuous measurement of (CO2)-C-11/(HCO3-)-C-11 in blood.