Measurements of [ 11 C]CO 2 in exhaled air with a positron-sensitive single-wire proportional counter after i.v. injection of [ 11 C]acetate

A positron-sensitive, large-window single-wire proportional counter was used for measurements of [ 11 C]CO 2 in exhaled air after i.v. injection of [ 11 C]acetate. The performance of the proportional counter was studied using Geant4 and Garfield simulation tools as well as experimentally by injections of known amounts of radioactive gas into the measuring volume. The proportional counter was found to be sensitive enough for measuring the low concentrations of [ 11 C]CO 2 in the air exhaled by patients after i.v. injection of an 11 C-labelled radiopharmaceutical. The limit of detection was 200 Bq/L for [ 11 C]CO 2 .