Quantitative CT‐derived vessel metrics in idiopathic pulmonary fibrosis: A structure–function study

BACKGROUND AND OBJECTIVE: This study aimed to investigate whether quantitative lung vessel morphology determined by a new fully automated algorithm is associated with functional indices in idiopathic pulmonary fibrosis (IPF). METHODS: A total of 152 IPF patients had vessel volume, density, tortuosity and heterogeneity quantified from computed tomography (CT) images by a fully automated algorithm. Separate quantitation of vessel metrics in pulmonary arteries and veins was performed in 106 patients. Results were evaluated against readouts from lung function tests. RESULTS: Normalized vessel volume expressed as a percentage of total lung volume was moderately correlated with functional indices on univariable linear regression analysis: forced vital capacity (R(2) = 0.27, P < 1 × 10(−6)), diffusion capacity for carbon monoxide (DL(CO); R(2) = 0.12, P = 3 × 10(−5)), total lung capacity (TLC; R(2) = 0.45, P < 1 × 10(−6)) and composite physiologic index (CPI; R(2) = 0.28, P < 1 × 10(−6)). Normalized vessel volume was correlated with vessel density but not with vessel heterogeneity. Quantitatively derived vessel metrics (and artery and vein subdivision scores) were not significantly linked with the transfer factor for carbon monoxide (K(CO)), and only weakly with DL(CO). On multivariable linear regression analysis, normalized vessel volume and vessel heterogeneity were independently linked with DL(CO), TLC and CPI indicating that they capture different aspects of lung damage. Artery–vein separation provided no additional information beyond that captured in the whole vasculature. CONCLUSION: Our study confirms previous observations of links between vessel volume and functional measures of disease severity in IPF using a new vessel quantitation tool. Additionally, the new tool shows independent linkages of normalized vessel volume and vessel heterogeneity with functional indices. Quantitative vessel metrics do not appear to reflect vasculopathic damage in IPF.