We investigated the relative clearance rates for 99mTc-labeled diethylenetriamine-pentaacetate (Tc-DTPA) and 113mIn-labeled DTPA (In-DTPA) when they were inhaled and deposited together within the lungs of same animal. Submicronic aerosols containing Tc-DTPA and In-DTPA were simultaneously generated by different nebulizers and collected within the same anesthetic bag. The combined aerosols were insufflated into piglets. Clearances for both compounds were measured simultaneously in normal lungs and when the lungs were damaged by intravenous oleic acid or by a presumed oxidant agent, intravenous or intratracheal phorbol myristate acetate (PMA). A medium-energy collimator and a computer-assisted gamma camera were used to calculate clearances. Correction was made for downscatter from the In photopeak into the Tc window. Marked lung injury occurred as evidenced by increases in lung water content and decreases in arterial PO2. The clearance of In-DTPA was slightly but significantly slower than for Tc-DTPA in each group of animals. The correlation (r = 0.93) between clearances for Tc-DTPA and In-DTPA was good, even though in vitro studies demonstrated that Tc-DTPA, but not In-DTPA, slowly dissociated at room and body temperatures. Oleic acid increased, but surprisingly, PMA had no effect on clearance rates for both In-DTPA and Tc-DTPA. We recommend continued use of Tc-DTPA for these measurements in view of its lower cost, requirement for only low-energy collimation, better imaging characteristics, and widespread availability. The overlap between control and injured lungs and the lack of increased clearance rates after PMA suggest this technique does not always detect acute lung injury.
View details for Web of Science ID A1989U606100038
View details for PubMedID 2663817