A technique for simulating radionuclide images from the aerosol deposition pattern in the airway tree

Radionuclide imaging has provided much useful experimental data on aerosol deposition in the lung. Nevertheless, relatively little work has been carried out to validate the parameters derived from the technique and to relate the spatial information on deposition to position in the airway tree. This article describes a method of converting a defined distribution of deposition within the airway tree to the corresponding spatial distribution within a real lung shape and hence simulating the corresponding two- and three-dimensional images. The technique is applied to six different deposition distributions in a human subject, and parameters of total and regional deposition are derived from the images and compared with the actual values used in the simulation. In this initial application, both two- and three-dimensional methods assessed total lung activity accurately. The three- dimensional analysis gave an improved estimation of distribution of activity over that obtained from planar imaging. The technique should have considerable value in assessing the accuracy of radionuclide imaging of aerosol deposition and in interpreting image distributions in relation to the underlying distribution within the airway tree.