Introduction: Dual energy CT imaging allows the estimation of relative parenchymal iodine concentration in different parts of the lung- a marker that is used to detected perfusion defects in pulmonary thromboembolic disease. Vascular pruning has also been proposed as a marker of pulmonary vascular disease in thromboembolic disease. In this study we examine the trends in measurements from the iodine maps and vascular reconstructions from a cohort of patients with dual energy CT imaging.
Methods: DECTs with complete original information performed on the Siemens platform were retrospectively identified. Voxel values were extracted from the iodine maps sampled at 0.8mm thickness, inside of the lung, with the vasculature removed. The pulmonary vasculature was reconstructed, and the arterial and venous vasculature was labeled using a convolutional neural network. Measures of pulmonary blood volume were then extracted, including BV5 (vessels <5mm2 in cross-section), BV10, and total pulmonary blood vessel volume (TBV) for both the arterial and venous systems. The BV5/TBV and BV10/TBV ratio, markers of pruning, were extracted from the CT.
Results: 29 patients without thromboembolic disease, 18 patients with CTEPH and 13 patients with CTED were identified for total of 60 subjects. There was a trend towards decreased mean normalized voxel value between the patients with CTEPH and controls, but no difference in the standard deviation of voxel values. There was increasing arterial vascular pruning going from controls (aBV10/TBV 0.65), CTED (aBV10/TBV 0.63) and CTEPH (aBV10/TBV 0.55). Within the CTEPH cohort where PVR values were available, the median and standard deviation of voxel values and venous BV10/TBV correlated with PVR.
Conclusions: Vascular volume and voxel iodine based statistics derived from dual energy imaging may provide complimentary information about vascular remodeling and perfusion abnormalities in pulmonary thromboembolic disease and can both be derived from dual energy CT imaging.