[Pulmonary distribution of 99mTc-technegas--a comparative study of radioactive inert gases]

99mTc-technegas (99mTc-gas), which consists of fine particles, is produced in carbon crucibles burned at 2500 degrees C. On this study, the particle size of 99mTc-gas was measured and the pulmonary distribution of 99mTc-gas was assessed in 28 patients with various pulmonary diseases. Most particles were 5-30 nm in diameter as determined by electron microscopy. In a clinical study, about 37 MBq of 99mTc-gas was inhaled three times during deep breathing in a sitting position. In a comparative study with radioactive inert gases (133Xe, 81mKr), 99mTc-gas showed a similar distribution to the inert gas in most patients, although some with obstructive disease showed hot spots in the lung fields. In patients with severe obstructive change, marked deposits of 99mTc-gas was noted in the central airways, but 99mTc-gas penetrated to the peripheral lung field. This result suggests that 99mTc-gas can be used to evaluate ventilatory function even in patients with chronic obstructive pulmonary diseases.