Radioaerosol lung imaging - history and pharmaceuticals

The first use of a radioactive tracer to study lung function was made by Knipping and others in 1955. They used radioactive 133Xe (xenon) gas as an inhalation agent in a patient with lung cancer and found that distal to a tumor no radioactivity was detected indicating no ventilation although chest x-rays appeared as if there was active ventilation. Subsequently with advance in technology a number of radioactive gases such as 81mKr (krypton) and cyclotron produced 15O2 (oxygen), 11C (carbon) and 13N2 (nitrogen) became available to assess regional lung function. The advantages of these gases are manifold, but their utility is mostly limited due to high cost. An alternative to the use of radioactive gases to study regional ventilation is the use of particulate radioactive aerosol. Radioaerosol inhalation lung imaging technique was developed in 1965 almost simultaneously by Taplin and others and Pircher and others just 2 years following Taplin's invention of 131I-MAA for perfusion lung imaging. Their main aim was to use 131I-human serum albumin (HSA), and 99mTc-HSA, 131I-rose bengal, 197Hg-chlormerodrin and colloidal 198Au as agents for radioaerosol generation, and Taplin himself preferred 198Au colloids for serial studies from economical reasons. Already in 1965, however, Taplin said that the best agent would be 99mTc-HSA. Pircher used 131I-HSA aerosol. Taplin already noted at that time that the inhaled aerosol was removed from the lungs mainly by ciliary action and that it was not absorbed either from the lungs or the intestine. Anyway it is noteworthy that the idea of radioaerosol inhalation lung imaging was proposed soon after the advent of perfusion lung imaging. Besides 131I-HSA and colloidal 198Au, the following agents have been or are currently being used. The superiority of 99mTC over other radioisotopes used in the past is beyond dispute