Reduction of contamination risks during clinical studies with Technegas

During patient studies with the Technegas equipment in our department, we r egularly detected small to considerable contaminations of the operator and in the area surrounding the apparatus. These contaminations were found to b e of different origin: residual activity in the tubing from the apparatus t o the patient which diffuses after deconnection, residual activity and smal l particles of the destroyed carbon crucible in the apparatus which are dis persed during opening of the door of the gas preparation chamber, leakage a t the patient site during studies in uncooperative patients and a dysfuncti oning valve inside the apparatus. To reduce the contamination risks, we mad e some adaptations to the apparatus. In the first place, the dysfunctioning valve was replaced. In addition, a powerful air exhaust pump with an effic ient filter was installed. It was connected with (1) a newly installed tran sparent box in front of the door of the gas preparation chamber, (2) a dome on a flexible arm which can be positioned above the patient's face during the examination and (3) a nipple on which the mouthpiece can be placed afte r the study. After these adaptations, a study showed the absence of measura ble contamination on the clothing of the personnel handling the apparatus. Occasionally, considerable contamination was still measured on the gloves w orn during filling of the carbon boat with generator eluate, but only small contaminations (up to 9.25 kBq) were measured on the mouthmask worn by the operator during administration of the Technegas, This results in a maximum effective dose equivalent from activity deposited in the lungs of 0.008 mu Sv per study. The total body dose of the operator from external radiation for one Technegas examination was determined to be 2 mu Sv. The highest dos e rate was measured during filling of the crucible (0.2 mSv/h).