Quantitative computed tomography and visual emphysema scores: association with lung function decline

Computed tomography (CT) visual emphysema score is a better predictor of mortality than single quantitative CT emphysema measurements in 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 forced expiratory volume in 1 s (FEV₁) lower limit of normal (LLN) annualised change (ΔFEV₁) than visual emphysema score in COPD.

In this retrospective, longitudinal study, demographic, spirometry and CT images were acquired. CT visual emphysema score and quantitative analysis were performed; low attenuation area <950 HU (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 visual emphysema score and CT measurements. A total of 725 participants were analysed (n=299 never-smokers, n=242 at-risk and n=184 COPD).

Quantitative CT measures (LAA₉₅₀ and PCA components) were independently statistically significant (p<0.05) in predicting baseline FEV₁ LLN, whereas visual emphysema score was not statistically significant in any baseline model. When predicting 6-year ΔFEV₁, only visual emphysema score 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, visual emphysema score (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 with visual emphysema score for predicting lung function decline.