Evidence for the long-term biological distribution of Technegas particles.

Technegas is a suspension of structured graphite ellipsoids, between 5 and 20 nm in aerodynamic diameter and labelled, in a carrier gas of argon, with 99Tcm. Its emergence and rapidly expanding clinical usage (105,000 studies, 22 countries), as a unique dry insoluble microaerosol for diagnostic lung imaging, has prompted a review of reports of experiments on lung clearance with other aerosols. No direct comparison exists although it is clear that experimental inhalation insults which deliver to the alveoli a mass of material orders of magnitude greater than Technegas are well tolerated by human volunteers.