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Abstract
The rate at which inhaled aerosol of 99mTc-diethylenetriamine pentaacetate (DTPA)
leaves the lung by diffusion into the vascular space can be measured with a gamma
camera or simple probe. In normal humans, 99mTc-DTPA clears from the lung with a half
time of about 80 minutes. Many acute and chronic conditions that alter the integrity
of the pulmonary epithelium cause an increased clearance rate. Thus cigarette smoking,
alveolitis from a variety of causes, adult respiratory distress syndrome (ARDS), and
hyaline membrane disease (HMD) in the infant have all been shown to be associated
with rapid pulmonary clearance of 99mTc-DTPA. Rapid clearance is also promoted by
increased lung volume and decreased surfactant activity. Although the mechanism of
increased clearance in pathological states is not known, the 99mTc-DTPA lung-clearance
technique has great potential clinically, particularly in patients at risk from ARDS
and HMD and in the diagnosis and follow-up of alveolitis.