Treatment effect of balloon pulmonary angioplasty in chronic thromboembolic pulmonary hypertension quantified by automatic comparative imaging in computed tomography pulmonary angiography

Abstract

Objectives: Balloon

pulmonary angioplasty (BPA) in patients with inoperable chronic thromboembolic

pulmonary hypertension (CTEPH) can have variable outcomes. To gain more insight

into this variation, we designed a method for visualizing and quantifying changes in pulmonary perfusion by automatically comparing CT pulmonary angiography (CTPA) before and after BPA treatment. We validated these quantifications of perfusion changes against hemodynamic changes measured with right-heart catheterization (RHC). Materials and Methods: We studied 14 consecutive CTEPH patients (12 females; age:70.5 ± 24), who underwent CTPA and RHC, before and after BPA. Post-treatment images were registered to pre-treatment CT scans (using the Elastix toolbox) to obtain corresponding locations. Pulmonary vascular trees and their centerlines were detected using a graph-cuts method and a distance transform method, respectively. Areas distal from vessels were defined as pulmonary parenchyma. Subsequently, the density changes within the vascular centerlines and parenchymal areas were calculated and corrected for inspiration level differences. For visualization, the densitometric changes were displayed in color-coded overlays. For quantification, the median and inter-quartile range (IQR) of the density changes in the vascular and parenchymal areas (ΔVD and ΔPD) were calculated. The recorded changes in hemodynamic parameters, including changes in systolic, diastolic, mean pulmonary artery pressure (ΔsPAP, ΔdPAP and ΔmPAP, respectively) and vascular resistance (ΔPVR), were used as reference assessments of the treatment effect. Spearman’s correlation coefficients were employed to investigate the correlations between changes in perfusion and hemodynamic changes. Results: Comparative imaging maps showed distinct patterns in perfusion changes among patients. Within pulmonary vessels, the IQR of ΔVD correlated significantly with ΔsPAP (R=‑0.58, p=0.03), ΔdPAP (R=‑0.71, p=0.005), ΔmPAP (R=‑0.71, p=0.005) and ΔPVR (R=‑0.77, p=0.001). In the parenchyma, the median of ΔPD had significant correlations with ΔdPAP (R=‑0.58, p=0.030) and ΔmPAP (R=‑0.59, p=0.025). Conclusions: Comparative imaging analysis in CTEPH patients offers insight into differences in BPA treatment effect. Quantification of perfusion changes provides non-invasive measures that reflect hemodynamic changes.