Automated attenuation analysis of CT pulmonary angiography identifies peripheral hyperperfusion as a prognostic marker in non-surgical chronic thromboembolic pulmonary hypertension (CTEPH)
Vojtech Suchanek1, Roman Jakubicek2, Jan Hrdlicka3, Matej Novak3, Lubomir Stepanek4, Pavel Jansa5, Lukas Lambert1
Contributions: (I) Conception and design: V Suchanek, R Jakubicek, P Jansa, L Lambert; (II) Administrative support: L Lambert; (III) Provision of study materials or patients: P Jansa; (IV) Collection and assembly of data: P Jansa, L Lambert; (V) Data analysis and interpretation: V Suchanek, R Jakubicek, J Hrdlicka, M Novak, P Jansa, L Lambert; (VI) Manuscript writing: All authors; (VII) Final approval of manuscript: All authors.
Background: Risk stratification in patients with chronic thromboembolic pulmonary hypertension (CTEPH) relies mainly on functional testing and imaging-based structural assessment. The aim of this study was to investigate the prognostic significance of automated regional attenuation analysis on computed tomography pulmonary angiography (CTPA) as a surrogate of perfusion abnormalities.
Methods: We analyzed 52 consecutive patients diagnosed with CTEPH. Patients underwent either surgical [pulmonary endarterectomy (PEA), n=21] or non-surgical treatments [balloon pulmonary angioplasty (BPA) and/or pharmacotherapy, n=31]. Parameters derived from CTPA, including automated lung attenuation analysis and clinical metrics, were correlated with survival outcomes over a median follow-up of 5.0 years.
Results: During follow-up, 19 patients (36.5%) died. In the non-surgical group, predictors of survival derived from CTPA included diameter of the ascending aorta [hazard ratio (HR) =1.37, P=0.013] and right atrial area (HR =1.17, P=0.007). Automated attenuation analysis demonstrated that a higher proportion of hyperemic parenchyma in the middle and peripheral regions of the right middle and both lower lobes was associated with increased mortality (HR from 1.38 to 1.69 and P from 0.002 to 0.027). Oligemic parenchyma in similar regions was protective (HR from 0.72 to 0.74 and P from 0.010 to 0.015). In the surgical group, no significant predictors were identified.
Conclusions: Automated, region-specific attenuation analysis of CTPA provides quantitative prognostic information in non-surgically treated CTEPH patients. Increased peripheral hyperperfusion in the right middle and lower lobes was associated with decreased survival. We hypothesize that hyperperfusion in these regions may reflect neovascularization and the development of peripheral collaterals.
Keywords: Chronic thromboembolic pulmonary hypertension (CTEPH); pulmonary embolism; computed tomography; image processing
Submitted Aug 13, 2025. Accepted for publication Feb 02, 2026. Published online Feb 26, 2026.
doi: 10.21037/qims-2025-1753
Introduction
Chronic thromboembolic pulmonary hypertension (CTEPH) is a rare progressive complication that develops in 3.4% of patients after acute pulmonary embolism with a poor outcome if untreated (1). CTEPH is a result of persistent organized thrombi in the pulmonary artery tree, scarring, and flow compromise, which ultimately lead to clinical symptoms of right heart failure and death. Secondary microvasculopathy driven by pathologic vasoconstriction and hyperproliferation of endothelial cells and vessel wall collagen matrix, which establishes at the level of arterioles and venules, has a substantial impact on prognosis and outcome even after surgical treatment (2).
In the diagnostic workup, computed tomography pulmonary angiography (CTPA) along with echocardiography, ventilation/perfusion (V/Q) scan, right heart catheterization and pulmonary angiography is used to assess the distribution and extent of pathological changes in the pulmonary arteries and parenchyma (3-5). According to previous studies, there are measurable parameters on CTPA associated with treatment outcome in patients with CTEPH—the pulmonary artery to ascending aorta diameter ratio, left-to-right ventricle diameter ratio, and pulmonary artery diameter (3,6). The prognostic value of attenuation changes in the pulmonary parenchyma as a surrogate indicator of perfusion abnormalities has not been fully explored yet (7,8).
The aim of this study was to quantify perfusion changes in lung parenchyma on CTPA of patients with known CTEPH and correlate them with outcomes of surgical and non-surgical treatment methods to extend the understanding of hemodynamics in structurally altered pulmonary vasculature and its implications for patients’ prognosis. We present this article in accordance with the STROBE reporting checklist (available at https://qims.amegroups.com/article/view/10.21037/qims-2025-1753/rc).
Methods
The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by the Ethics Committee of the General University Hospital in Prague (No. 198/22 S-IV; 24/11/2022) and individual consent for this retrospective analysis was waived.
Patient population
Consecutive patients diagnosed with CTEPH between 1st January 2018 and 31st December 2018 at the General University Hospital in Prague were included (7,9). The exclusion criteria were incomplete follow-up data (at least 1 year follow-up or endpoint), malignancy, interstitial lung disease, and the unavailability of submillimeter slices from CTPA. Patients underwent a comprehensive workup, including V/Q scan, CTPA, echocardiography, right heart catheterization, pulmonary angiography, cardiopulmonary exercise testing, pulmonary function and laboratory tests. The choice of treatment [pulmonary endarterectomy (PEA) or non-surgical procedures—balloon pulmonary angioplasty (BPA) and/or pharmacotherapy] was noted.
CTPA
Briefly, as previously reported, CTPAs were performed prior to the initiation of treatment on 256-slice CT scanner (iCT Brilliance, Philips, Best, The Netherlands) in a breath-hold spiral craniocaudal acquisition triggered by bolus tracking in the pulmonary artery and reconstructed in 0.9-mm slices with 50% overlap. For further details, see references (5,7). Two radiologists (J.H., M.N.) with 4 and 9 years of cardiovascular imaging experience measured parameters listed in Table S1 on a diagnostic workstation (Philips IntelliSpace Portal v.10, CT viewer). The measurements from both radiologists were averaged. Both radiologists were blinded to patients’ outcomes.
Automated attenuation analysis of lung parenchyma
The fully automated analysis was implemented in Python 3.12 as described previously (7). The trained Total Segmentator network was used to segment the lungs and lung segments (10). Lungs were automatically divided into central, middle, and peripheral regions relative to the distance from the pleura to the hilum by thirds. Three individual Gaussian distributions representing three compartments (high = hyperemic, medium = normal, low = oligemic) were fitted to the lung attenuation histogram of both lungs using variational Bayesian estimation, a Gaussian mixture model (11,12). A relative proportion of hyperemic and oligemic compartments representing pathology in each lung lobe and region was calculated and used in further analysis. The software was made available on GitHub (https://github.com/JakubicekRoman/lung_CTPA.git) (7).
Statistical analysis
R and SPSS v. 19 (IBM Corp., Armonk, NY) were used for data analysis. The values were represented as mean ± standard deviation or median [interquartile range (IQR)] according to distribution (D’Agostino normality test). The Grubbs test and data plots were used to detect outliers. Cox proportional hazards calculation, regression (stepwise forward likelihood ratio model), analysis of optimal cutpoints, and plotting of Kaplan-Meier graphs were performed using the survival and survminer libraries in R. Hazard ratios (HRs) for attenuation analysis were calculated per 10% increase. For a two-tailed distribution, alpha =0.05, beta =0.2, equal proportions, and relative hazard of 2, the number of events needed was calculated to be 16. A P value below 0.05 was considered significant.
Results
The final study cohort comprised 52 patients diagnosed with CTEPH (mean age, 65.2±13 years, 27 men) (7). Patients were treated by PEA (21 patients), or non-surgical procedures (31 patients)—16 were treated with BPA, and 15 received pharmacotherapy only. The median follow-up duration was 5.0 years (IQR, 2.8–5.4 years). At the end of the study period, 33 patients were alive, 19 deceased. There were no significant differences between the surgical and non-surgical groups in demographic or functional parameters (Table S1).
In the surgical group, no significant predictors of survival were found. In the non-surgical group, significant functional predictors included cardiac output (HR =0.52, P=0.032), cardiac index (HR =0.14, P=0.012), and mixed venous oxygen saturation (SvO2; HR =0.93, P=0.012). Hazards derived from CTPA in the non-surgical group included diameter of the ascending aorta (HR =1.37, P=0.013) and right atrial area (HR =1.17, P=0.007, Table 1). From the automated lung analysis, several significant prognostic parameters in the non-surgical group were apparent: proportion of hyperemic parenchyma in the middle and peripheral parts of the right middle lobe and lower lung lobes (HR from 1.38 to 1.69 and P from 0.002 to 0.027), oligemic parenchyma in the middle and peripheral part of the right middle lobe (HR =0.72 and 0.74, P=0.010 and P=0.015, respectively) and oligemic parenchyma in the central part of the left upper lobe (HR =1.66, P=0.004, Figures 1,2, Table 2). Cutpoints were identified to divide the non-surgical group into two strata with favorable and unfavorable prognosis, resulting in significance between <0.001 and 0.044 (Figure 3, Table S2).
Table 1
| Variable | Non-surgical treatment | Surgical treatment | |||
|---|---|---|---|---|---|
| HR | P value | HR | P value | ||
| Basic characteristics | |||||
| Age (years) | 1.07 | 0.043 | 1.00 | 0.918 | |
| Height (cm) | 0.99 | 0.816 | 1.00 | 0.976 | |
| Weight (kg) | 0.98 | 0.189 | 1.00 | 0.928 | |
| BMI (kg/m2) | 0.89 | 0.111 | 1.00 | 0.975 | |
| BSA (m2) | 0.26 | 0.299 | 0.97 | 0.985 | |
| Functional parameters | |||||
| 6MWD (m) | 0.99 | 0.052 | 1.00 | 0.456 | |
| ProBNP (ng/L) | 1.00 | 0.241 | 1.00 | 0.171 | |
| PAMP (mmHg) | 1.00 | 0.633 | 1.00 | 0.966 | |
| PCWP (mmHg) | 1.10 | 0.344 | 0.83 | 0.186 | |
| CO (L/min) | 0.52 | 0.032 | 0.96 | 0.943 | |
| CI [L/(min·m2)] | 0.14 | 0.012 | 1.22 | 0.878 | |
| PVR (wood) | 1.09 | 0.215 | 1.11 | 0.549 | |
| SaO2 (%) | 0.97 | 0.255 | 1.08 | 0.662 | |
| SvO2 (%) | 0.93 | 0.012 | 0.96 | 0.524 | |
| CTPA measurements | |||||
| AA diameter† | 1.37 | 0.013 | 1.14 | 0.057 | |
| PA diameter† | 1.17 | 0.198 | 0.85 | 0.405 | |
| PA to AA aorta ratio | 0.05 | 0.170 | 0.03 | 0.081 | |
| RV diameter† | 1.06 | 0.190 | 1.11 | 0.264 | |
| RA area† | 1.17 | 0.007 | 1.06 | 0.199 | |
| RV to LV diameter | 1.43 | 0.480 | 1.08 | 0.958 | |
†, indexed to BSA. 6MWD, 6-minute walking distance; AA, ascending aorta; BMI, body mass index; BSA, body surface area; CI, cardiac index; CO, cardiac output; CTPA, computed tomography pulmonary angiography; HR, hazard ratio; LV, left ventricle; PA, pulmonary artery; PAMP, mean pulmonary arterial pressure; PCWP, pulmonary capillary wedge pressure; proBNP, brain natriuretric peptide prohormone; PVR, pulmonary vascular resistance; RA, right atrium; RV, right ventricle; SaO2, arterial oxygen saturation; SvO2, mixed venous oxygen saturation.
Table 2
| Anatomy | Component | Non-surgical treatment | Surgical treatment | |||
|---|---|---|---|---|---|---|
| HR† | P value | HR† | P value | |||
| Right upper lobe | ||||||
| Central | Hyperemic | 1.18 | 0.068 | 0.82 | 0.294 | |
| Oligemic | 0.99 | 0.957 | 1.8 | 0.135 | ||
| Middle | Hyperemic | 1.25 | 0.277 | 0.85 | 0.731 | |
| Oligemic | 0.82 | 0.230 | 1.07 | 0.792 | ||
| Peripheral | Hyperemic | 1.38 | 0.172 | 0.82 | 0.655 | |
| Oligemic | 0.84 | 0.317 | 0.94 | 0.743 | ||
| Right middle lobe | ||||||
| Central | Hyperemic | 1.18 | 0.098 | 0.79 | 0.462 | |
| Oligemic | 0.76 | 0.066 | 1.34 | 0.142 | ||
| Middle | Hyperemic | 1.38 | 0.027 | 1.27 | 0.772 | |
| Oligemic | 0.72 | 0.010 | 1.17 | 0.514 | ||
| Peripheral | Hyperemic | 1.69 | 0.008 | 2.44 | 0.354 | |
| Oligemic | 0.74 | 0.015 | 0.97 | 0.900 | ||
| Right lower lobe | ||||||
| Central | Hyperemic | 1.31 | 0.056 | 1.08 | 0.641 | |
| Oligemic | 0.82 | 0.262 | 0.9 | 0.709 | ||
| Middle | Hyperemic | 1.65 | 0.002 | 1.06 | 0.803 | |
| Oligemic | 0.83 | 0.189 | 0.88 | 0.615 | ||
| Peripheral | Hyperemic | 1.54 | 0.008 | 1.06 | 0.844 | |
| Oligemic | 0.79 | 0.138 | 0.90 | 0.668 | ||
| Left upper lobe | ||||||
| Central | Hyperemic | 0.93 | 0.479 | 1.08 | 0.637 | |
| Oligemic | 1.66 | 0.004 | 0.48 | 0.231 | ||
| Middle | Hyperemic | 1.03 | 0.850 | 1.07 | 0.812 | |
| Oligemic | 1.27 | 0.250 | 0.68 | 0.211 | ||
| Peripheral | Hyperemic | 1.31 | 0.297 | 1.14 | 0.757 | |
| Oligemic | 0.95 | 0.787 | 0.86 | 0.515 | ||
| Left lower lobe | ||||||
| Central | Hyperemic | 1.02 | 0.802 | 0.97 | 0.841 | |
| Oligemic | 0.67 | 0.643 | 0.90 | 0.826 | ||
| Middle | Hyperemic | 1.12 | 0.332 | 0.97 | 0.895 | |
| Oligemic | 0.54 | 0.140 | 0.90 | 0.709 | ||
| Peripheral | Hyperemic | 1.33 | 0.076 | 0.90 | 0.694 | |
| Oligemic | 0.67 | 0.108 | 1.01 | 0.959 | ||
†, HR per 10% increase. CTPA, computed tomography pulmonary angiography; HR, hazard ratio.
In multivariate Cox regression analysis, left upper lobe central oligemia and right middle lobe peripheral hyperemia conferred an HR of 2.26 in the non-surgical group with a model significance of <0.001.
Discussion
In the present study, the prognostic significance of parameters derived from CTPA, both by measurement and by automated analysis of attenuation of lung parenchyma, was analyzed. In patients who underwent PEA, no predictors were found, while in non-surgical patients, predictors of outcome were identified among functional parameters, morphological CTPA parameters, and from the automated analysis of attenuation of pulmonary parenchyma. Notably, the increased proportion of hyperemic parenchyma in the peripheral and middle part of the right middle and lower lobes was the strongest predictor of poor prognosis, along with decreased proportion of oligemic parenchyma.
PEA is considered the gold standard treatment for patients with central to segmental disease and good performance status, with a mortality rate of 3% in expert centers, conferring the best long-term outcomes (13). In the operated group, no predictors of survival were identified. This is consistent with previous studies, where only postoperative mean pulmonary artery pressure (PAMP) was the only consistantly identified predictor of survival, additionally with preoperative New York Heart Association (NYHA) class (14-16).
BPA is a less invasive percutaneous treatment more suitable for diseases with a peripheral distribution and for patients with comorbidities or other risk factors (17,18). Pharmacotherapy has its role in the management of patients with contraindication to invasive treatment or as a part of a multimodality approach in which PEA and BPA can be sequentially performed to treat both central and peripheral disease (13). In patients undergoing non-surgical therapy, functional and hemodynamic parameters such as NYHA class, right atrial pressure and 6 minute walking distance were reported as independent predictors of survival (16,19,20). Further predictors included pulmonary vascular resistance (PVR), PAMP, SvO2 and cardiac index (20,21). In inoperable CTEPH, treatment with BPA and riociguat (Adempas) are known to improve survival (22). While these prognostication parameters remain essential, they do not directly reflect regional lung perfusion, which is a key pathophysiological hallmark in CTEPH.
Previously, CTPA was used to predict residual pulmonary hypertension after PEA, showing that a lower aortopulmonary index resulted in a lower risk (23). Even though sole diameter of the pulmonary artery is considered a risk factor, in our study, neither of these parameters proved to be a significant hazard in either the surgical or non-surgical groups (24).
A comprehensive analysis of CTPA features with regard to survival was performed by Abdulaal et al. (6), who reported that the presence of mosaic perfusion was associated with improved survival. They were the first to report that aortic diameter predicted worse outcomes in patients treated by PEA, which was apparent in our study only in non-surgical patients. Right-to-left ventricular ratio, a hallmark of right heart overload, conferred a non-significant hazard in the non-surgical group of our study.
To our knowledge, this is the first study to analyze pulmonary perfusion based on automated analysis of attenuation in different regions of the lung in CTEPH patients. These parameters may help identify high-risk patients who might benefit from intensified therapy and may also aid in therapeutic decision-making or serve as imaging biomarkers in longitudinal monitoring. While the use of this algorithm is not yet implemented in the routine clinical pathway, its potential to complement existing prognostic tools is promising and warrants future integration into clinical workflows to enhance patient stratification and individualized management.
Our findings challenge the traditional emphasis on perfusion defects (oligemia) in CTEPH and suggest that abnormally increased perfusion, probably due to neovascularization and collateral formation, may represent maladaptive compensatory mechanisms (25). This interpretation aligns with recent observations by Remy-Jardin et al., who proposed that such hyperperfusion may reflect the development of peripheral systemic and systemic-to-pulmonary collaterals. We hypothesize that the hyperperfused regions in the peripheral segments of the right middle and lower lobes are attributable to this pathophysiological process. Notably, these collateral vessels can be visualized on CTPA, as convincingly illustrated by Remy-Jardin et al. using high-resolution images obtained from a photon-counting computed tomography (CT) scanner (Figure 4) (8).
Study limitations
Several limitations of this study should be acknowledged. First, it is a single-center study that reflects survival in the local cohort and may not be extrapolated. Second, in a single-vendor study using high-end CT scanner, attenuation of the pulmonary parenchyma is not a direct measure of its perfusion. However, it has been shown that in CTEPH, areas with mosaic attenuation correlate with those of high iodine content on dual-energy CT (26). Third, the retrospective nature of this single-center study has potential for selection bias. Fourth, although contrast-to-noise ratio was not directly measured, its potential influence is likely mitigated by the use of the Gaussian mixture model, which is inherently robust to variability in attenuation values. Fifth, the number of patients, especially in the surgical subgroup limits the power to detect smaller effect sizes. Last, the prognostic markers were evaluated on a single uniform dataset, which warrants prospective validation in a larger cohort with the aim of confirming its prognostic value and assessing its reproducibility across different CT vendors and acquisition protocols including iodine mapping to better characterize perfusion abnormalities and their relationship to clinical outcomes.
Conclusions
This study highlights the prognostic utility of CTPA-derived parameters, including innovative automated attenuation analysis, which showed that in non-surgical patients, hyperemic regions in the periphery of the right middle and lower lobes were associated with decreased survival. We hypothesize that hyperperfusion in these regions may result from neovascularization and the development of peripheral collaterals.
Acknowledgments
None.
Footnote
Reporting Checklist: The authors have completed the STROBE reporting checklist. Available at https://qims.amegroups.com/article/view/10.21037/qims-2025-1753/rc
Data Sharing Statement: Available at https://qims.amegroups.com/article/view/10.21037/qims-2025-1753/dss
Funding: This work was supported by
Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://qims.amegroups.com/article/view/10.21037/qims-2025-1753/coif). L.L. serves as an unpaid editorial board member of Quantitative Imaging in Medicine and Surgery. The other authors have no conflicts of interest to declare.
Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by the Ethics Committee of the General University Hospital in Prague (No. 198/22 S-IV; 24/11/2022) and individual consent for this retrospective analysis was waived.
Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.
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