Absolute and lung volume-normalized deep learning-derived pulmonary vascular measures in idiopathic pulmonary fibrosis: distinct clinical associations and the role of lung volume in prognosis.

Introduction: Idiopathic pulmonary fibrosis (IPF) has an unpredictable course and poor outcome, and lung function-based risk stratification remains incomplete. Whether absolute and lung volume-normalized deep learning-derived CT pulmonary vascular measurements show distinct associations with disease severity and mortality in patients with IPF remains unclear. Methods: In this dual-center retrospective study, 118 adults with newly diagnosed IPF, including 57 from the Italian cohort and 61 from the French cohort, underwent baseline chest CT analyzed with a deep learning-based quantitative pipeline combining lung parenchyma (whole lung volume, WLV; fibrosis extent) and pulmonary vascular metrics (total blood volume, TBV; and derived BV Results: Compared with controls, IPF patients had lower WLV and higher absolute TBV. Relative TBV (normalized to WLV) correlated strongly with fibrosis, while absolute TBV showed weaker associations. Relative vascular metrics inversely related to baseline lung function, whereas absolute TBV showed no significant association. Baseline TBV, BV Conclusion: Normalized and absolute pulmonary vascular metrics capture different aspects of IPF, with normalized measures associated with fibrosis burden and functional impairment, while absolute vascular volumes were associated with mortality, although this association was substantially attenuated after accounting for WLV. Absolute vascular volume may therefore partly reflect preserved lung volume rather than an independent prognostic effect. Prospective validation is warranted.