Quantitative analysis of technegas SPECT: Evaluation of regional severity of emphysema

The purpose of this study was to quantify the regional severity of emphysem a by 3-dimensional fractal analysis of technegas (Tc-99m-carbon particle ra dioaerosol) SPECT images. Methods: Technegas SPECT was performed on 22 pati ents with emphysema. The lungs were delineated using 4 cutoff levels (15%, 20%, 25%, and 30% of the maximal pixel radioactivity), and the total number of pixels was measured in the areas surrounded by the contours obtained wi th each cutoff level. We calculated fractal dimensions from the relationshi p between the total number of pixels and cutoff levels transformed into log arithms. Fractal dimension for total or regional lung was defined as the se verity of emphysema. Results: Total lung fractal dimension (T-FD), upper lu ng fractal dimension (U-FD), and lower lung fractal dimension (L-FD) for pa tients with emphysema were 1.84 +/- 0.46 (mean +/- SD), 2.22 +/- 0.61, and 1.77 +/- 0.49, respectively. U-FD was significantly greater than was L-FD. Patients with the ratio of U-FD to L-FD of <1.16 had a significantly greate r percentage forced vital capacity (FVC) than did patients with the ratio o f >1.16. Patients with an L-FD of <1.8 had a significantly greater forced e xpiratory volume in 1 s (FEV1)/FVC than did patients with that of >1.8. No significant difference was found between patient groups stratified by U-FD. Conclusion: The regional severity of emphysema was well shown by these fra ctal dimensions.