Evaluation of a newly developed 2D parametric parenchymal blood flow technique with an automated vessel suppression algorithm in patients with chronic thromboembolic pulmonary hypertension undergoing balloon pulmonary angioplasty

Aim: To evaluate the feasibility of two-dimensional parametric parenchymal blood flow (2D-PPBF) to quantify perfusion changes in the lung parenchyma following balloon pulmonary angioplasty (BPA) for treatment of chronic thromboembolic pulmonary hypertension.

Materials and methods: Overall, 35 consecutive interventions in 18 patients with 98 treated pulmonary arteries were included. To quantify changes in pulmonary blood flow using 2D-PPBF, the acquired digital subtraction angiography (DSA) series were post-processed using dedicated software. A reference region of interest (ROI; arterial inflow) in the treated pulmonary artery and a distal target ROI, including the whole lung parenchyma distal to the targeted stenosis, were placed in corresponding areas on DSA pre- and post-BPA. Half-peak density (HPD), wash-in rate (WIR), arrival to peak (AP), area under the curve (AUC), and mean transit time (MTT) were assessed. The ratios of the reference ROI to the target ROI (HPD_parenchyma/HPD_inflow, WIR_parenchyma/WIR_inflow; AP_parenchyma/AP_inflow, AUC_parenchyma/AUC_inflow, MTT_parenchyma/MTT_inflow) were calculated. The relative differences of the 2D-PPBF parameters were correlated to changes in the pulmonary flow grade score.

Results: The pulmonary flow grade score improved significantly after BPA (1 versus 3; p<0.0001). Likewise, the mean HPD_parenchyma/HPD_inflow (-10.2%; p<0.0001), AP_parenchyma/AP_inflow (-24.4%; p=0.0007), and MTT_parenchyma/MTT_inflow (-3.5%; p=0.0449) decreased significantly, whereas WIR_parenchyma/WIR_inflow (+82.4%) and AUC_parenchyma/AUC_inflow (+58.6%) showed a significant increase (p<0.0001). Furthermore, a significant correlation between changes of the pulmonary flow grade score and changes of HPD_parenchyma/HPD_inflow (ρ=-0.21, p=0.04), WIR_parenchyma/WIR_inflow (ρ=0.43, p<0.0001), AP_parenchyma/AP_inflow (ρ=-0.22, p=0.03), AUC_parenchyma/AUC_inflow (ρ=0.48, p<0.0001), and MTT_parenchyma/MTT_inflow (ρ=-0.39, p<0.0001) could be observed.

Conclusion: The 2D-PPBF technique is feasible for the quantification of perfusion changes following BPA and has the potential to improve monitoring of BPA.