Characterization of Tc-99m-DTPA aerosols for lung permeability studies

Background: The interpretation of Tc-99m diethylenetriamine pentaacetate (T c-99m DTPA) aerosol clearance is based on the hypothesis that the Tc-99m-DT PA complex is not altered by the nebulization process. Objectives: To chara cterize (1) the radiochemical purity (RCP) of Tc-99m-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 oxy gen, captured on filters which were eluted and RCP was checked by thin laye r chromatography. Particle size distribution - the aerosol was generated us ing dry air (50 psi) at three different flow rates, i.e. 3 (1 run), 6 (4 ru ns) and 9 l.min(-1) (4 runs). The mass median aerodynamic diameter (MMAD) a nd the geometric standard deviation (sigmag) were determined using a cascad e impactor from the radioactivity counted on each stage. Results: The RCP w as more than 95% in all cases. Mean MMAD (+/-SD) was 0.70 mum (+/-0.07) at 9 l.min(-1), 0.93 mum (+/-0.05) at 6 l.min(-1) (p < 0.05) and 1.50 <mu>m at 3 l.min(-1). Mean sigmag (+/-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 dem onstrates (1) that the high RCP of Tc-99m-DTPA is not affected by jet nebul ization, even when using oxygen at a high flow rate, and (2) that when usin g a flow rate between 6 and 9 l.min(-1), the MMAD remains optimal for perip heral lung deposition. Copyright (C) 2001 S. Karger AG, Basel.