Quantitative CT and visual emphysema scores: association with lung function decline

Abstract

Computed tomography (CT) visual emphysema score (VES) is a better predictor of mortality than single quantitative CT emphysema measurements in chronic obstructive pulmonary disease (COPD), but there are numerous CT measurements that reflect COPD-related disease features. The purpose of this study was to determine if linear combinations of quantitative CT measurements by principal component analysis (PCA) have a greater association with FEV₁ lower limit of normal (LLN) annualized change (ΔFEV₁) than VES in COPD. In this retrospective, longitudinal study, demographic, spirometry, and CT images were acquired. CT VES and quantitative analysis (VIDA Diagnostics Inc.) was performed; the low-attenuation-area-below-950HU (LAA₉₅₀), and 12 other quantitative CT measurements were investigated. PCA was used for CT feature extraction. Multiple linear regression models for baseline FEV₁ LLN and 6-year ΔFEV₁ were used to determine associations with VES and CT measurements. A total of 725 participants were analyzed (n=299 never-smoker, n=242 at-risk, n=184 COPD). Quantitative CT measures (LAA₉₅₀, PCA components) were independently statistically significant (p<0.05) in predicting baseline FEV₁ LLN, whereas VES was not statistically significant in any baseline models. When predicting 6-year ΔFEV₁, only VES was significant (p<0.05) in models with LAA₉₅₀ and PCA combination of emphysema measurements. In the model with PCA using all CT measurements predicting 6-year ΔFEV₁, VES (p=0.021) along with one PCA component (p=0.004) were statistically significant. PCA with a combination of CT measurements reflecting several different COPD-related disease features independently predicted baseline lung function and increased the relative importance of quantitative CT compared to VES for predicting lung function decline.