Systemic - pulmonary collateral supply evaluation using intra-aortic computed tomography angiography: Comparison of shunt with lung perfused blood volume by dual-energy computed tomography and clinical severity of chronic thromboembolic pulmonary hypertension

概要

Background (研究背景):
Chronic thromboembolic pulmonary hypertension (CTEPH) is a life-threatening disease. The lung perfused blood volume (PBV) images generated by dual-energy computed tomography (DECT) provide a convincing detection of the pulmonary perfusion defect for CTEPH. The systemic-pulmonary collateral supply generates in the occluded lung area. Exposure to high-pressure systemic circulation may result in pulmonary vasculature abnormalities. However, no radiological study has established the relationship between the degree of collateral flow and the clinical severity in CTEPH. Besides, the relationship between the degree of collaterals and the pulmonary perfusion defects remains uncertain.

Aims (研究目的):
We assumed that the CT values of the enhanced pulmonary vessels after intra-aortic injection of contrast media may reflect the degree of systemic-pulmonary collaterals. Therefore, we aim to assess whether the degree of contrast enhancement in the pulmonary vasculature, identified by intra-aortic CT angiography, is associated with the clinical severity of CTEPH and the pulmonary perfusion defects reflected by lung PBV images from DECT exams.

Methods (研究方法):
Twenty-four patients with inoperable CTEPH underwent both intra-aortic CT angiography and intravenous dual-energy CT (DECT) angiography within a 3-month interval. Intra-aortic CT angiography, with an injection of contrast media from the ascending aorta, was acquired with a 9-second scan delay. The Hounsfield units (HU) of the pulmonary trunk (PT), 18 segmental pulmonary arteries (PAs) and pulmonary veins (PVs) were measured. The difference of HU between PTs and PAs or PVs was defined as segmental-based HUdiff-PA and HUdiff-PV, respectively, as the parameter to quantify the vascular enhancement. On the patient base, the mean HUdiff-PA, mean HUdiff-PV and numbers of significantly enhanced PAs and PVs were calculated for each patient. Lung PBV images were generated from intravenous DECT angiography data. Segmental pulmonary perfusion defect scores were evaluated and summarized into patient-based lung PBV scores. Pearson’s or Spearman’s correlation coefficients were used in evaluating the correlation between patient-based enhancement parameters (mean HUdiff-PA, mean HUdiff-PV, numbers of significantly enhanced PAs and PVs) and clinical severity parameters or lung PBV scores. The correlation between segmental-based enhancement parameters and pulmonary perfusion defect scores was evaluated using Spearman’s correlation coefficient. Within-subject laterality was evaluated using paired t-test.

Results (研究結果):
On the patient-base, mean HUdiff-PV was correlated with mean pulmonary arterial pressure (PAP) (r = 0.52, p < 0.01), systolic PAP (r = 0.46, p = 0.02), cardiac output (CO) (r = - 0.41, p = 0.05) and lung PBV score (r = 0.43, p = 0.04); while number of significantly enhanced PVs was correlated with mean PAP (r = 0.54, p < 0.01), systolic PAP (r = 0.51, p= 0.01), pulmonary vascular resistance (r = 0.54, p < 0.01), and lung PBV score (r = 0.50, p = 0.01). On the segmental base, HUdiff-PV was correlated with segmental pulmonary perfusion defect scores (r = 0.45, p < 0.01). No correlation was found between the PA enhancement parameters and the pulmonary perfusion defect parameters or clinical severity parameters. Both systemic collaterals reflected by pulmonary vascular enhancement and the pulmonary perfusion defects showed a right lung dominance in CTEPH patients.

Conclusion (結論):
Intra-arterial CT angiography could demonstrate heterogeneous enhancement, reflecting systemic-pulmonary collaterals in CTEPH. The mean HUdiff-PV and the number of significantly enhanced PVs may be useful for estimating the clinical severity and lung perfusion defects of CTEPH. Our findings provide a better understanding of the hemodynamic changes in CTEPH and insights into the management of CTEPH patients.