OBJECTIVES: This work aimed to develop an automated method for quantifying the distribution and severity of perfusion changes on CT pulmonary angiography (CTPA) in patients with chronic thromboembolic pulmonary hypertension (CTEPH) and to assess their associations with clinical parameters and expert annotations. MATERIALS AND METHODS: Following automated segmentation of the chest, a machine-learning model assuming three distributions of attenuation in the pulmonary parenchyma (hyperemic, normal, and oligemic) was fitted to the attenuation histogram of CTPA images using Bayesian analysis. The proportion of each component, its spatial heterogeneity (entropy), and center-to-periphery distribution of the attenuation were calculated and correlated with the findings on CTPA semi-quantitatively evaluated by radiologists and with clinical function tests. RESULTS: CTPA scans from 52 patients (mean age, 65.2 ± 13.0 years; 27 men) diagnosed with CTEPH were analyzed. An inverse correlation was observed between the proportion of normal parenchyma and brain natriuretic propeptide (proBNP, ρ = -0.485, p = 0.001), mean pulmonary arterial pressure (ρ = -0.417, p = 0.002) and pulmonary vascular resistance (ρ = -0.556, p < 0.0001), mosaic attenuation (ρ = -0.527, p < 0.0001), perfusion centralization (ρ = -0.489, p = < 0.0001), and right ventricular diameter (ρ = -0.451, p = 0.001). The entropy of hyperemic parenchyma showed a positive correlation with the pulmonary wedge pressure (ρ = 0.402, p = 0.003). The slope of center-to-periphery attenuation distribution correlated with centralization (ρ = -0.477, p < 0.0001), and with proBNP (ρ = -0.463, p = 0.002). CONCLUSION: This study validates an automated system that leverages Bayesian analysis to quantify the severity and distribution of perfusion changes in CTPA. The results show the potential of this method to support clinical evaluations of CTEPH by providing reproducible and objective measures. KEY POINTS: Question This study introduces an automated method for quantifying the extent and spatial distribution of pulmonary perfusion abnormalities in CTEPH using variational Bayesian estimation. Findings Quantitative measures describing the extent, heterogeneity, and distribution of perfusion changes demonstrate strong correlations with key clinical hemodynamic indicators. Clinical relevance The automated quantification of perfusion changes aligns closely with radiologists' evaluations, delivering a standardized, reproducible measure with clinical relevance.
COVID-19 associates with a hypercoagulant state and an increased risk for venous thromboembolic events (VTEs). Whether severe COVID-19 infection requiring extracorporeal membrane oxygenation (ECMO) support might lead to chronic pulmonary perfusion abnormalities and chronic thromboembolic pulmonary disease/hypertension remains unclear. The purpose of this study was to evaluate chronic pulmonary perfusion abnormalities in long-term survivors of COVID-19-related severe acute respiratory distress syndrome (ARDS) treated by ECMO at our institution. Pulmonary perfusion was examined by ventilation/perfusion (V/Q) single-photon emission computed tomography or V/Q planar scintigraphy at least 3 months after ECMO explantation, comorbidities and incidence of thromboembolic events were recorded as well. Of 172 COVID-19 patients treated by ECMO for severe COVID-19 pneumonia between March 2020 and November 2021, only 80 were successfully weaned from ECMO. Of those, 37 patients were enrolled into the present analysis (27% female, mean age 52 years). Median duration of ECMO support was 12 days. In 24 (65%) patients VTE was recorded in the acute phase (23 patients developed ECMO cannula-related deep vein thrombosis, 5 of them had also a pulmonary embolism, and one thrombus was associated with a central catheter). The median duration between ECMO explantation and assessment of pulmonary perfusion was 420 days. No segmental or larger mismatched perfusion defects were then detected in any patient. In conclusion, in long-term survivors of COVID-19-related ARDS treated by ECMO, no persistent pulmonary perfusion abnormalities were detected although VTE was common.
