Dynamic digital radiography–derived low signal area ratio for assessing emphysema and associated pulmonary vascular changes in COPD

Emphysema in chronic obstructive pulmonary disease (COPD) destroys alveolar walls together with the alveolar capillary bed, yet unenhanced computed tomography (CT) quantifies parenchymal change rather than perfusion. Dynamic digital radiography (DDR) generates perfusion-related maps from cardiac-synchronised changes in radiographic lung density without contrast material. In 40 prospectively enrolled patients with clinically stable COPD who underwent breath-hold DDR, inspiratory high-resolution CT and pulmonary function testing, we quantified a low signal area (LSA) ratio by histogram-based segmentation of DDR perfusion maps. The LSA ratio correlated with the percentage low attenuation volume at CT ( r s = 0.692), forced expiratory volume in 1 s ( r s = − 0.553) and diffusing capacity ( r s = − 0.436). Absolute pulmonary vessel volume showed no association with the LSA ratio, whereas vessel volume normalised to lung volume did ( r s = − 0.556); this association persisted after adjustment for emphysema extent (partial r = − 0.324) and for lung volume (partial r = − 0.517), although its confidence interval approached zero. When both CT measures were considered simultaneously, the LSA ratio was more strongly related to emphysema extent than to vessel volume. The LSA ratio therefore reflects emphysematous destruction predominantly, with an additional pulmonary vascular component that requires confirmation.