Quantitative analysis of pulmonary emphysema: three-dimensional fractal analysis of single-photon emission computed tomography images obtained with a carbon particle radioaerosol

Abstract

Objective: The purpose of this study was to quantify the heterogeneous distribution of a carbon particle radioaerosol in the lungs of patients with pulmonary emphysema using single-photon emission computed tomography (SPECT) and fractal analysis.

Subjects and methods: Ventilation SPECT was performed on 19 patients with pulmonary emphysema, seven patients with suspected pulmonary emphysema, and 14 healthy volunteers. We delineated the lungs using five cutoff levels (15%, 20%, 25%, 30%, and 35% of the maximal pixel radioactivity) and measured the total number of pixels in the areas surrounded by the contours obtained with each cutoff level. We calculated fractal dimensions from the relationship between the total number of pixels and cutoff levels transformed into logarithms.

Results: The fractal dimensions increased with the severity of pulmonary emphysema. The fractal dimensions for patients with pulmonary emphysema, patients with suspected pulmonary emphysema, and healthy volunteers were 2.03+/-0.61 (mean +/- SD), 0.77+/-0.09, and 0.59+/-0.06, respectively. A significant difference (p < .0005) in the fractal dimension was found when any of these three groups was compared with any other group of subjects.

Conclusion: Three-dimensional quantitative evaluation of the emphysematous lung was possible using SPECT and fractal analysis. Our results suggest that fractal analysis can quantify the heterogeneity of the distribution of a carbon particle radioaerosol in the lung. Fractal analysis appears to be applicable for routine clinical use because it is simple and the fractal dimensions can be obtained easily without using special software.