The three dimensional (3D) distribution of inhaled [C-11]-labeled triamcinolone acetonide or [C-11]-TAA was measured using Positron Emission Tomography (PET) to maximize accuracy. Regional analysis was first done to emulate gamma scintigraphy with arbitrary regions such as inner, mid- and outer lung, bronchi, trachea etc., and determining regional ratios or penetration indices. In this work, to improve upon the analytical usefulness and objectivity of the results, PET data were mapped onto 23 airway generations following the general framework of a methodology using Single Photon Emission Computed Tomography (SPECT) reported by Fleming et al. Quantitative PET scan distributions of [C-11]-TAA in the lungs of healthy volunteers from an MDI administration were obtained at several time points after drug administration to explore both distribution patterns and decay kinetics. Deposition on conducting airways (generations 1~14) is greater than on acinar airways (generation 15~23) for the initial impact, but the distribution pattern slowly changes with a modest distal shift of distribution maxima from conducting towards acinar airways with time. Implications of these results for improving lung models for aerosol deposition and the design of drug formulations using PET are discussed.
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