Relationships between diffusing capacity for carbon monoxide (D_LCO), and quantitative computed tomography measurements and visual assessment for chronic obstructive pulmonary disease

Purpose To evaluate the relationships between D_LCO, and Quantitative CT (QCT) measurements and visual assessment of pulmonary emphysema and to test the relative roles of visual and quantitative assessment of emphysema. Materials and methods The subjects included 199 current and former cigarette smokers from the COPDGene cohort who underwent inspiratory and expiratory CT and also had diffusing capacity for carbon monoxide corrected for alveolar volume (D_LCO/V_A). Quantitative CT measurements included % low attenuation areas (%LAA-950ins = voxels ≤-950 Hounsfield unit (HU), % LAA, and % LAA), mean CT attenuation and 15th percentile HU value on inspiratory CT, and %LAA (voxels ≤-856 HU on expiratory CT). The extent of emphysema was visually assessed using a 5-point grading system. Univariate and multiple variable linear regression analyses were employed to evaluate the correlations between D_LCO/V_A and QCT parameters and visual extent of emphysema. Results The D_LCO/V_A correlated most strongly with 15th percentile HU (R² = 0.440, p < 0.001) closely followed by % LAA_-950ins (R² = 0.417, p < 0.001) and visual extent of emphysema (R² = 0.411, p < 0.001). Multiple variable analysis showed that visual extent of emphysema and 15th percentile HU were independent significant predictors of D_LCO/V_A at an R² of 0.599. Conclusions 15th percentile HU seems the best parameter to represent the respiratory condition of COPD. Visual and Quantitative CT assessment of emphysema provide complementary information to QCT analysis.