Emphysema quantification by combining percentage and size distribution of low-attenuation lung regions

OBJECTIVE. The purpose of this study was to investigate efficacy of two types of emphysema quantification: percentage of low-attenuation lung regions (%LA); and size distribution of these regions. On a log-log plot, cumulative frequency-size distribution of low-attenuation lung regions can be fitted by a straight line whose slope (D) has been reported to reflect diffusing capacity. In this study, % LA and D were compared with pulmonary function test (PFT) parameters, especially with ratio of diffusing capacity of carbon monoxide to effective alveolar ventilation (i.e., DL_CO/VA). MATERIALS AND METHODS. Thin-section unenhanced CT images were acquired from 30 patients (25 men, five women; mean [SD] age, 70.1 ± 12.1 years), of whom 25 had received diagnosis of COPD, and %LA and D were calculated at 20 thresholds, ranging from -995 to -900 HU. To determine utility of % LA and D, we used Pearson's correlation for emphysema quantification and PFT. Significance of the coefficients was determined with Bonferroni correction ( p < 0.0025). Finally, the relationships between emphysema quantification and DL _CO/VA were examined by linear models and Akaike information criterion (AIC). RESULTS. The correlation coefficients for %LA and DL_CO/VA were statistically significant at all the thresholds (optimal coefficient, -0.761). The correlation coefficients for D and DL_CO/VA were statistically significant at the thresholds from -945 to -900 HU (optimal coefficient, -0.646). AIC values showed that the most accurate prediction of DL_CO/VA was obtained by the model incorporating both %LA and D. CONCLUSION. Both %LA and D showed significant correlation with DL _CO/VA. Combining %LA and D resulted in more accurate evaluation of DL_CO/VA than did using % LA or D alone.