Differentiating acute from chronic pulmonary thromboembolism: a preliminary study using dual-layer CT

The aim of this study was to evaluate the actual values and ranges of conventional and spectral parameters in pulmonary thromboembolism (PE) and assess their potential for distinguishing acute PE (APE) from chronic PE (CPE) using dual-layer CT (DLCT). This retrospective study included 52 patients with central PE diagnosed with CT pulmonary angiography (CTPA) using DLCT. Patients were categorized into APE and CPE groups. Conventional and spectral parameters including Hounsfield unit (HU) and electron density (ED) values were measured at the thrombus and pulmonary trunk on both pre- and post-contrast images. Additionally, in vitro experiments were conducted to generate clots of varying compositions. Apart from D-dimer levels, no significant clinical differences were found between APE and CPE groups. APE showed significantly higher mean HU and ED values than CPE on both unenhanced and enhanced images (both p < 0.001). Thrombus enhancement, using true non-contrast (TNC) values as a reference, was similar between groups. APE showed greater variability in HU and ED values, whereas CPE consistently demonstrated lower values across all imaging phases. Unenhanced HU and ED values provided better discrimination than post-contrast values, with high AUCs ( p < 0.05). The in vitro findings were consistent with these observations and may provide a plausible explanation for the compositional differences between APE and CPE. APE showed higher HU and ED values than CPE. Conventional and spectral CT parameters could help differentiate APE from CPE, reflecting distinct thrombus compositions.