TECHNEGAS AND PERTECHNEGAS PARTICLE-SIZE DISTRIBUTION

Technegas and Pertechnegas are radioactive aerosols produced in a comm ercial generator and used for lung scintigraphy. The aerosols are prod uced by first evaporating to dryness standard technetium-99m generator eluate ((TCO4)-T-99m in normal saline) in a graphite crucible (the si mmer stage) and then heating this to 2500 degrees C (the ,,burn'' stag e). The aim of this work was to measure the particle size distribution s of these agents and relate this to regional lung deposition. Factors that may vary during production of the aerosol in routine use were in vestigated to determine whether they influenced the particle size. Act ivity size distributions were measured using a serial wire-screen diff usion battery. The Technegas size distribution was approximately log-n ormal with an activity median diameter of 158 nm and a geometric stand ard deviation of 1.5. The results for Pertechnegas were similar. The m edian size increased with the number of simmers and with the time from generation. The increase in size with the number of simmers is though t to be due to the increased salt content in the crucible prior to the ,,burn''. The predicted lung deposition is 37% in the alveolar region and 5% in the bronchial region. Significant changes in deposition are not predicted over the range of particle sizes measured.