SUPINE LUNG CLEARANCE OF TC-99M DTPA AND HMPAO AEROSOLS

The speed of Tc-99m DTPA/HMPAO radioaerosol clearance from the lungs t hat is represented as a slope from lungs to blood was measured in 23 m ale normal controls using commercial lung radioaerosol delivery units in the supine position in order to avoid the influences of gravity. Th e right lung was selected and three regions of interest were created f or equal subdivisions of the upper, middle, and lower third. The resul ts show that the clearance of Tc-99m DTPA/HMPAO aerosols in the upper lung is slowest. The differences between upper and lower lungs for Tc- 99m DTPA/HMPAO aerosol clearances are significant. The clearance of Tc -99m DTPA aerosols was significantly faster than those of Tc-99m HMPAO in any region. The authors conclude that, although the effect of grav ity disappears in the supine position in our study, the differences of aerosol clearance in different regions are still significant. Lipophi lic Tc-99m HMPAO aerosols were slower than those of hydrophilic Tc-99m DTPA, which suggests there are at least two different mechanisms.