Assessment of pulmonary aerosol deposition and epithelial permeability in 99mTc-DTPA inhalation scintigram

Abstract

The degree of lung injury in bronchiolo-alveolar lesions may be quantitated from the pulmonary epithelial permeability estimated by 99mTc-DTPA (diethylene triamine penta acetate) aerosol inhalation scintigram. However, significant aerosol deposition sometimes occurs in the central airways and obscures the permeability change in the lung periphery. The radioaerosol deposition pattern and its effect on assessing the pulmonary epithelial permeability was studied. 99mTc-DTPA aerosol scintigraphy was performed in 47 patients with pulmonary fibrosis (PF), 12 patients with chronic obstructive pulmonary diseases (COPD), and 27 non-smoking and 17 smoking healthy volunteers. The scintigraphic images of the lungs were classified into 4 grades, 0; homogeneous distribution, 1; patchy distribution, 2; hot spots with partial defect, and 3; hot spots with little deposition in the lung field. The rate constant was used as a parameter for the permeability. The smokers and patients with PF showed increased kep values of 2.36 +/- 1.21%/min (mean +/- SD) and 2.49 +/- 1.29%/min as compared with the nonsmokers with 0.94 +/- 0.27%/min, respectively. The nonsmokers, smokers and 36 patients with PF were classified as deposition grade 0 or 1, suggesting good aerosol penetration to the lung periphery. All patients with COPD showed either grade 2 or 3 deposition. Aerosol deposition in the central airways can cause underestimation of the permeability because of the thicker lining layer in the bronchus than in the alveolus. In conclusion, the aerosol deposition pattern should be analyzed when the method is applied clinically to assess the permeability of the bronchiolo-alveolar epithelium.