Radiation dose to the trachea from inhaled Oxygen-15 labelled carbon dioxide

This study was carried out to estimate the radiation dose to the trachea from inhalation of O-15 labelled CO/sub 2/ and to compare the findings with a report postulating significant fixation of O-15 CO/sub 2/ in the tracheal wall. Three volunteers were studied by transaxial PET imaging on the Therascan 3128. First, O-15 O/sub 2/ was used to image tracheal activity from the gas alone. This was followed by a study with O-15 CO/sub 2/. The radioactive gases were administered at 7 mCi/min and a flow of 70 ml/min to which 200 ml/min of medical air were mixed. Both studies were initiated at the start of tracer administration and consisted of twenty frames of 30 seconds duration. The procedure and observations are described in this paper. The O/sub 2/ curve rapidly reached a constant level whereas the CO/sub 2/ curve gradually increased until the supply was turned off. The authors dose estimate to the trachea from inhaled O-15 CO/sub 2/, amounts to 4 rads, about one sixth of the figure described by other investigators, for a typical 30 min study with an O-15 CO/sub 2/ supply of 4 mCi/min