An analytical technique to recover the third dimension in planar imaging of inhaled aerosols--2 estimation of the deposition per airway generation.

An analytical algorithm has been recently described for converting planar scintigraphic images of aerosol distributions in the lungs to an equivalent three-dimensional (3D) representation. The recovery of the volumetric information has opened up to planar imaging the possibility of measuring aerosol deposition per airway generation. This paper investigates the accuracy and precision of the generation analysis achievable with planar imaging using simulation. Typical generation parameters--such as the bronchial and conducting airway deposition fractions (BADF and CADF)--have been derived. The accuracy of the technique has been measured by the coefficient of variation (COV) of the estimates from the known values used in the simulation. The results have also been compared to those obtained from 3D imaging (single photon emission computed tomography or SPECT). Finally, the technique has been applied to two aerosol studies conducted on a healthy volunteer, to demonstrate its implementation on clinical data. The accuracy of the BADF and CADF estimates from planar imaging were 42% and 41%, respectively; the corresponding values from SPECT were 32% and 22%. In conclusion, approximate estimates of airway distribution parameters can be derived from planar imaging. However, the errors are significantly higher than with SPECT.