Quantitative CT Evaluation in Patients with Combined Pulmonary Fibrosis and Emphysema: Correlation with Pulmonary Function

Rationale and Objectives: The purpose of this study was to evaluate the correlations between objective quantitative computed tomography (Cl) measurements of the extent of emphysematous and fibrotic lesions and the results of pulmonary function tests (PFTs) in patients with combined pulmonary fibrosis and emphysema (CPFE). Materials and Methods: This study involved 43 CPFE patients who underwent CT and PFTs. The extent of emphysematous lesions was obtained by calculating the percentage of low attenuation area (%LAA) values lower than -950 Hounsfield units (HU). Fibrotic lesions were defined as high attenuation area (HAA) using thresholds with pixels between 0 and -700 HU, and the extent of fibrosis was obtained by calculating the percentage of HAA (%HAA). The correlations of %LAA and %HAA with PFTs were evaluated by the Spearman rank correlation coefficients and multiple linear regression analysis. Results: A significant negative correlation was found between %HAA and diffusing capacity of the lung for carbon monoxide (DLco) % predicted (p = -0.747; P < .001), whereas no significant correlation was found between %LAA and DLco %predicted. On multiple linear regression analysis, although the %HAA and %LAA were independent contributors to DLco %predicted, the predictive power of %HAA was superior to that of %LAA. Conclusions: In CPFE, the extent of fibrosis has a more significant impact on DLco than emphysema.