Discordant findings between krypton-81m gas and Tc-99m labeled ultrafine aerosol lung ventilation SPECT in two patients with idiopathic pulmonary fibrosis.

Technegas, a newly developed ultra-fine dry dispersion of Tc-99m labeled carbon with a particle size of approximately 5 nm to 20 nm, possesses the properties for lung ventilation imaging using SPECT. The authors observed a discrepancy between krypton-81m gas and technegas lung ventilation SPECT in two patients with idiopathic pulmonary fibrosis who demonstrated heterogeneously decreased distribution of technegas without regions of high count density (focal hot spots) of tracer in their lungs in spite of the almost homogenous distribution of krypton-81m gas. This finding could be explained by the duration of radioactive gas inhalation. Technegas lung ventilation SPECT images reflected lung ventilation with tidal breathing. Conversely, Kr-81m gas lung ventilation SPECT images reflected not only lung ventilation, but also lung volumes. These two radioactive agents for lung ventilation SPECT show different findings.