A comparison between monodisperse Tc-99m-labeled aerosol particles and Kr-81m for the assessment of lung function

A quantitative method for study of the penetration and clearance of inhaled particles (5-micron Tc-99m-labeled polystyrene) in the human lung is described and compared with a Kr-81m technique for ventilation imaging. Volunteer healthy subjects and patients with chronic obstructive airway disease (COAD) were studied. Following inhalation of radioaerosol, data were recorded by a gamma-camera/computer system over a period of 6 hr. An aerosol penetration index (API) measures the proportion of aerosol reaching the peripheral region of the lung relative to that deposited in the larger central airways. A significant difference in the mean values of API for both groups was observed. Aerosol clearance rates from the whole lung and from central, intermediate and peripheral compartments of each lung field were studied. The healthy group showed a total clearance rate consistent with data from earlier work; the patients with COAD showed no clearance over the same period. Some healthy subjects were smokers, and differences in their penetration and clearance rates were evident, in spite of normal results from their conventional pulmonary function tests and Kr-81m ventilation studies. The aerosol technique, if carefully controlled, can be a more sensitive index for early lung abnormality than Kr-81m ventilation imaging.