Dual-layer dual-energy CT characterization of thrombus composition in acute pulmonary embolism and chronic thromboembolic pulmonary hypertension

To evaluate dual-layer dual-energy computed tomography (dlDECT)-based characterization of thrombus composition for differentiation of acute pulmonary embolism (PE) and chronic thromboembolic pulmonary hypertension (CTEPH). This retrospective single center cohort study included 49 patients with acute PE and 33 patients with CTEPH who underwent CT pulmonary angiography on a dlDECT from 06/2016 to 06/2022. Conventional images), material specific images (virtual non-contrast [VNC], iodine density overlay [IDO], electron density [ED]), and virtual monoenergetic images (VMI_50KeV) were analyzed. Regions-of-interest (ROIs) were manually placed in pulmonary artery thrombi, and morphological imaging characteristics for acute and chronic PE were assessed. Area under the receiver operating characteristics curve (AUC) of ROI measurements, morphological imaging features, and their combination in distinguishing between acute PE and CTEPH were evaluated. Compared to PE, thrombi in patients with CTEPH had lower attenuation on conventional images (Median [inter-quartile range]: 40 [35-47] HU vs 64 [52-83] HU) and VMI_50keV reconstructions (59 [46-72] HU vs 101 [80-123] HU) as well as decreased iodine uptake (IDO: 0.5 [0.2-1.0] vs 1.2 [0.5-1.8]; p for all < 0.001). Conventional images and VMI_50keV reconstructions were the most accurate for differentiating between acute and chronic thrombi (conventional: AUC 0.92, 95% CI 0.86-0.98; VMI_50keV: AUC 0.91, 95% CI 0.85-0.97). Main pulmonary artery (MPA) diameter combined with thrombus attenuation significantly increased the AUC compared to MPA diameter alone (p = 0.002 respectively). Thrombi in patients with CTEPH exhibit lower attenuation and reduced contrast enhancement. Analyzing attenuation in pulmonary thrombi may add diagnostic information to established morphological parameters in differentiating acute PE from CTEPH.