Characterization of 99mTc-DTPA Aerosols for Lung Permeability Studies

Background: The interpretation of 99m Tc diethylenetriamine pentaacetate ( 99m Tc DTPA) aerosol clearance is based on the hypothesis that the 99m Tc-DTPA complex is not altered by the nebulization process. Objectives: To characterize (1) the radiochemical purity (RCP) of 99m Tc-DTPA and the stability of labeling after jet nebulization, and (2) the particle size distribution of the aerosol. Methods: RCP and stability – the aerosol was driven by oxygen, captured on filters which were eluted and RCP was checked by thin layer chromatography. Particle size distribution – the aerosol was generated using dry air (50 psi) at three different flow rates, i.e. 3 (1 run), 6 (4 runs) and 9 l·min –1 (4 runs). The mass median aerodynamic diameter (MMAD) and the geometric standard deviation (σg) were determined using a cascade impactor from the radioactivity counted on each stage. Results: The RCP was more than 95% in all cases. Mean MMAD (±SD) was 0.70 µm (±0.07) at 9 l·min –1 , 0.93 µm (±0.05) at 6 l·min –1 (p < 0.05) and 1.50 µm at 3 l·min –1 . Mean σg (±SD) was 2.02 (±0.08) at 9 l·min –1 , 2.00 (±0.16) at 6 l·min –1 and 1.90 at 3 l·min –1 . Conclusion: This study demonstrates (1) that the high RCP of 99m Tc-DTPA is not affected by jet nebulization, even when using oxygen at a high flow rate, and (2) that when using a flow rate between 6 and 9 l·min –1 , the MMAD remains optimal for peripheral lung deposition.