Accuracy of CT Pulmonary Artery Diameter for Pulmonary Hypertension in End-Stage COPD

Efficacy of computed tomography in diagnosing pulmonary hypertension: A systematic review and meta-analysis

Objective

This study seeks to evaluate the diagnostic value of computed tomography (CT) in pulmonary hypertension.

Method

PubMed, Embase, Scopus, and Web of Science databases were searched to obtain the relevant English literature, and the retrieval time until June 2022. The quality of the included studies is evaluated using the QUADAS-2 tool. The quality of the included studies was assessed, followed by a meta-analysis, analyze heterogeneity, summarize sensitivity and specificity, draw the comprehensive subject working characteristics (sROC) curve, calculate the area under the curve and conduct subgroup analysis and sensitivity analysis to find the source of the heterogeneity.

Results

A total of 12 articles were included, all with pulmonary artery diameter/liter aortic diameter >1 or 1 as the diagnostic criteria for pulmonary hypertension, and a total of 1,959 patients were included. Deek’s funnel plot analysis suggests that there is no significant publication bias (P = 0.102). The combined sensitivity was 0.652 (95% CI: 0.579, 0.719), combined specificity was 0.830 (95% CI: 0.796, 0.880), positive likelihood ratio was 3.837 (95% CI: 3.215, 4.579), negative likelihood ratio was 0.419 (95% CI: 0.346, 0.507), diagnostic odds ratio was 9.157 (95% CI: 6.748, 12.427) and area under the summary receiver operating characteristic (SROC) curve was 0.84 (95% CI: 0.81, 0.87).

Conclusion

The CT examination of pulmonary artery diameter/aortic artery hypertension is worthy of clinical application.

The Incidence and Prevalence of Pulmonary Hypertension in the COPD Population: A Systematic Review and Meta-Analysis

Purpose

Chronic obstructive pulmonary disease (COPD)-related pulmonary hypertension (PH) is one of the most common comorbidities of COPD, and often leads to a worse prognosis. Although the estimated prevalence and risk factors of COPD-related PH have been widely reported, these results have not been well integrated. This study aimed to review the worldwide incidence and prevalence of COPD-related PH and explore possible factors affecting its prevalence.

Patients and Methods

We searched four electronic databases (Web of Science, Embase, Cochrane, and MEDLINE) to identify all observational studies on the prevalence of COPD-related PH from database creation until July 20, 2021. Eligibility screening, quality assessment, and data extraction of the retrieved studies were independently conducted by two reviewers. Meta-analyses were performed to determine the prevalence of PH in the COPD population. Random-effects meta-regression model analyses were conducted to investigate the sources of heterogeneity.

Results

Altogether, 38 articles were included in the meta-analyses. The pooled prevalence was 39.2% (95% CI: 34.0–44.4, I² = 97.6%) for COPD-related PH. Subgroup analyses showed that the prevalence of PH increased with COPD severity, where the majority (30.2%) had mild PH and the minority had severe PH (7.2%). Furthermore, we found a significant regional difference in the prevalence of COPD-related PH (P = 0.000), which was the highest in Africa (64.0%) and the lowest in Europe (30.4%). However, stratified studies on other factors involving mean age, sex, enrolment time, participant recruitment settings, and PH diagnostic methods showed no significant differences in prevalence (P >0.05).

Conclusion

The global incidence of PH in the COPD population is very high, and there are significant regional and international variations. Patients with COPD should be screened for PH and contributing risk factors to reduce the burden on individuals and society.

Diagnostic value of computed tomography-based pulmonary artery to aorta ratio measurement in chronic obstructive pulmonary disease with pulmonary hypertension: A systematic review and meta-analysis

OBJECTIVE

We conducted a meta-analysis to systematic assess the diagnostic value of computed tomography (CT)-based pulmonary artery to aorta (PA:A) ratio measurement in COPD with pulmonary hypertension (COPD-PH).

METHODS

Published studies referring to diagnostic accuracy of PA:A ratio for COPD-PH were screened out from PubMed, Embase, Web of science, China National Knowledge databases (CNKI), Wan fang databases, and VIP databases. We used bivariate random-effects model to estimate pooled sensitivity (SEN), specificity (SPE), positive and negative likelihood ratios (PLR and NLR, respectively), and diagnostic odds ratios (DOR). Summary receiver operating characteristic (SROC) curves and area under the curve (AUC) were also calculated to summarize the aggregate diagnostic performance.

RESULTS

Nine eligible studies were included and the pooled SEN was 69% (95% CI: 59 ~ 78), SPE was 85% (95% CI: 77 ~ 90), PLR was 4.5 (95% CI: 2.8 ~ 7.5), and NLR was 0.36 (95% CI: 0.26 ~ 0.51), respectively. DOR reached 13.00 (95% CI: 6.00 ~ 28.00), and value of AUC was 0.84 (95% CI: 0.81 ~ 0.87). Subgroup analysis indicated that when the value of PA:A ratio was equal or greater than one (PA/A ≥ 1), the combined SEN, SPE, AUC, and DOR was 69%, 89%, 0.90, and 19.65, respectively.

CONCLUSIONS

PA:A ratio is helpful for appraisal of COPD-PH, and PA/A ≥ 1 possessed prominent diagnostic accuracy.

Clinical Effect of Pulmonary Artery Diameter/Ascending Aorta Diameter Ratio on Left Ventricular Reverse Remodeling in Patients With Dilated Cardiomyopathy

BACKGROUND

Many patients with dilated cardiomyopathy (DCM) progress to heart failure (HF), although some demonstrate left ventricular (LV) reverse remodeling (LVRR), which is associated with better outcomes. The pulmonary artery diameter (PAD) to ascending aortic diameter (AoD) ratio has been used as a prognostic predictor in patients with HF, although this tool's usefulness in predicting LVRR remains unknown.Methods and Results:Data from a prospective observational study of 211 patients diagnosed in 2000-2020 with DCM were retrospectively analyzed. Sixty-nine patients with New York Heart Association class I or II HF were included. LVRR was observed in 23 patients (33.3%). The mean LV ejection fraction (29%) and LV end-diastolic dimension (64.5 mm) were similar in patients with and without LVRR. The PAD/AoD ratio was significantly lower in patients with LVRR than those without (81.4% vs. 92.4%, respectively; P=0.003). The optimal PAD/AoD cut-off value for detecting LVRR was 0.9 according to the receiver operating characteristic curve analysis. Multivariate analysis identified a PAD/AoD ratio ≥0.9 as an independent predictor of presence/absence of LVRR. Cardiac events were significantly more common in patients with a PAD/AoD ratio ≥0.9 than those with a ratio <0.9, after a median follow up of 2.5 years (log-rank, P=0.007).

CONCLUSIONS

The PAD/AoD ratio can predict LVRR in patients with DCM.

Chest CT-derived pulmonary artery enlargement at the admission predicts overall survival in COVID-19 patients: insight from 1461 consecutive patients in Italy

OBJECTIVES

Enlarged main pulmonary artery diameter (MPAD) resulted to be associated with pulmonary hypertension and mortality in a non-COVID-19 setting. The aim was to investigate and validate the association between MPAD enlargement and overall survival in COVID-19 patients.

METHODS

This is a cohort study on 1469 consecutive COVID-19 patients submitted to chest CT within 72 h from admission in seven tertiary level hospitals in Northern Italy, between March 1 and April 20, 2020. Derivation cohort (n = 761) included patients from the first three participating hospitals; validation cohort (n = 633) included patients from the remaining hospitals. CT images were centrally analyzed in a core-lab blinded to clinical data. The prognostic value of MPAD on overall survival was evaluated at adjusted and multivariable Cox's regression analysis on the derivation cohort. The final multivariable model was tested on the validation cohort.

RESULTS

In the derivation cohort, the median age was 69 (IQR, 58-77) years and 537 (70.6%) were males. In the validation cohort, the median age was 69 (IQR, 59-77) years with 421 (66.5%) males. Enlarged MPAD (≥ 31 mm) was a predictor of mortality at adjusted (hazard ratio, HR [95%CI]: 1.741 [1.253-2.418], p < 0.001) and multivariable regression analysis (HR [95%CI]: 1.592 [1.154-2.196], p = 0.005), together with male gender, old age, high creatinine, low well-aerated lung volume, and high pneumonia extension (c-index [95%CI] = 0.826 [0.796-0.851]). Model discrimination was confirmed on the validation cohort (c-index [95%CI] = 0.789 [0.758-0.823]), also using CT measurements from a second reader (c-index [95%CI] = 0.790 [0.753;0.825]).

CONCLUSION

Enlarged MPAD (≥ 31 mm) at admitting chest CT is an independent predictor of mortality in COVID-19.

KEY POINTS

• Enlargement of main pulmonary artery diameter at chest CT performed within 72 h from the admission was associated with a higher rate of in-hospital mortality in COVID-19 patients. • Enlargement of main pulmonary artery diameter (≥ 31 mm) was an independent predictor of death in COVID-19 patients at adjusted and multivariable regression analysis. • The combined evaluation of clinical findings, lung CT features, and main pulmonary artery diameter may be useful for risk stratification in COVID-19 patients.

Imaging of pulmonary hypertension in adults: a position paper from the Fleischner Society

Pulmonary hypertension (PH) is defined by a mean pulmonary artery pressure greater than 20 mmHg and classified into five different groups sharing similar pathophysiologic mechanisms, haemodynamic characteristics, and therapeutic management. Radiologists play a key role in the multidisciplinary assessment and management of PH. A working group was formed from within the Fleischner Society based on expertise in the imaging and/or management of patients with PH, as well as experience with methodologies of systematic reviews. The working group identified key questions focusing on the utility of CT, MRI, and nuclear medicine in the evaluation of PH: a) Is noninvasive imaging capable of identifying PH? b) What is the role of imaging in establishing the cause of PH? c) How does imaging determine the severity and complications of PH? d) How should imaging be used to assess chronic thromboembolic PH before treatment? e) Should imaging be performed after treatment of PH? This systematic review and position paper highlights the key role of imaging in the recognition, work-up, treatment planning, and follow-up of PH.

Imaging of Pulmonary Hypertension in Adults: A Position Paper from the Fleischner Society

Pulmonary hypertension (PH) is defined by a mean pulmonary artery pressure greater than 20 mm Hg and classified into five different groups sharing similar pathophysiologic mechanisms, hemodynamic characteristics, and therapeutic management. Radiologists play a key role in the multidisciplinary assessment and management of PH. A working group was formed from within the Fleischner Society based on expertise in the imaging and/or management of patients with PH, as well as experience with methodologies of systematic reviews. The working group identified key questions focusing on the utility of CT, MRI, and nuclear medicine in the evaluation of PH: (a) Is noninvasive imaging capable of identifying PH? (b) What is the role of imaging in establishing the cause of PH? (c) How does imaging determine the severity and complications of PH? (d) How should imaging be used to assess chronic thromboembolic PH before treatment? (e) Should imaging be performed after treatment of PH? This systematic review and position paper highlights the key role of imaging in the recognition, work-up, treatment planning, and follow-up of PH. This article is a simultaneous joint publication in Radiology and European Respiratory Journal. The articles are identical except for stylistic changes in keeping with each journal's style. Either version may be used in citing this article. © 2021 RSNA and the European Respiratory Society. Online supplemental material is available for this article.

CT-Derived Pulmonary Artery Diameters to Preselect for Echocardiography in COPD Patients Eligible for Bronchoscopic Treatments

BACKGROUND

Currently, patients with COPD who are evaluated for bronchoscopic treatments are routinely screened for pulmonary hypertension (PH) and systolic left ventricle dysfunction by echocardiography.

OBJECTIVES

We evaluated the prevalence of PH and systolic left ventricle dysfunction in this patient group and investigated if the previously proposed CT-derived pulmonary artery to aorta (PA:A) ratio >1 and PA diameter measurements can be used as alternative screening tools for PH.

METHODS

Two hundred fifty-five patients were included in this retrospective analysis (FEV1 25%pred, RV 237%pred). All patients received transthoracic echocardiography and chest CT scans on which diameters of the aorta and pulmonary artery were measured at the bifurcation and proximal to the bifurcation.

RESULTS

Following echocardiography, 3 patients (1.2%) had PH and 1 (0.4%) had systolic left ventricle dysfunction. Using a PA:A ratio >1, only 10.3% of the patients with a right ventricular systolic pressure (RVSP) ≥35 mm Hg were detected and none of the patients with an RVSP >50 mm Hg were detected. Patients with an RVSP ≥35 mm Hg had significantly higher PA diameters (29.5 vs. 27.5 mm; p = 0.02) but no significantly different PA:A ratios. All patients with an RVSP >50 mm Hg had PA diameters >30 mm.

CONCLUSIONS

The prevalence of PH and systolic left ventricle dysfunction is low in this preselected cohort of patients with severe COPD. In this population, a PA:A ratio >1 is not a useful cardiac screening tool for PH. A PA diameter >30 mm could substitute for routinely performed echocardiography in the screening for PH in this patient group.

Pulmonary artery to ascending aorta ratio by echocardiography: A strong predictor for presence and severity of pulmonary hypertension

BACKGROUND

The pulmonary artery (PA) to ascending aorta diameter ratio (PA:A) has been evaluated in numerous studies analyzing cardiac magnetic resonance (CMR) and computed tomography (CT) data. Previously, no transthoracic echocardiography (TTE) cutoffs have been published. We sought to evaluate (1) the feasibility to image the pulmonary trunk in a prospective cohort, and (2) the ability of PA:A derived by TTE to predict pulmonary hypertension (PH).

METHODS

We performed a post-hoc analysis of a prospectively recruited consecutive cohort of patients referred to our tertiary center cardiology department due to suspicion for PH. Invasive hemodynamic assessment and quasi-simultaneous TTE was performed in all participants.

RESULTS

A total of 84 patients were included in the analysis, median age was 70.5 years (IQR 58-75), 46 (55%) were female. The PA was significantly wider in the PH group (28mm vs. 22.5mm, p<0.001) with a resulting median PA:A of 0.84 vs. 0.66 (p<0.001). Both PA diameter (r = 0.524 and r = 0.44, both p<0.001) and PA:A (r = 0.652 and 0.697, both p<0.001) significantly correlated with mPAP and with PVR, respectively. Area under the curve for the detection of PH was 0.853 (95%CI 0.739-0.967, p<0.001).

CONCLUSION

The PA can be visualized in almost all echocardiographic exams, especially when it is dilated. A view showing the pulmonary trunk should be included in every routine TTE. An increased PA:A should raise suspicion for PH and prompt further evaluation and follow-up examinations of these patients.

Differences in routes of guiding catheters for left coronary artery according to access sites assessed by the combined angiography-computed tomography system

Differences in guiding catheters (GCs) manipulations and selections among different access sites are currently unclear. We examined the differences in the routes of GCs for the left coronary artery (LCA) among the right radial, left radial, and femoral approaches. We used a combined angiography-computed tomography (CT) system that enabled to perform CT scans during percutaneous coronary intervention (PCI). We enrolled 88 patients who underwent CT scans during LCA PCI or percutaneous transluminal septal myocardial ablation. To evaluate the route of GCs, we analyzed the positions of the catheter's contact point on the contralateral aortic wall to the LCA ostium, which were expressed by the angle formed by the vertical line and the diagonal line from the GC shaft to the center of the aorta. The procedures were performed via the right radial in 47 cases, left radial in 20, and femoral approach in 21. The positions of the catheter's contact point were significantly different depending on the approaches (interquartile range - 3.7 [- 14.3 to 7.8], - 46.5 [- 76.9 to - 9.3], and - 30.7 [- 39.4 to - 22.4] degrees, respectively; p < 0.001). Multivariate analysis demonstrated that access sites and LCA ostium locations had significant impacts on the positions of the catheter's contact point. The routes of LCA GCs were different among the right radial, left radial, and femoral approaches.

Characteristics of Chronic Obstructive Pulmonary Disease Patients with Pulmonary Hypertension Assessed by Echocardiography in a Three-Year Observational Cohort Study

Background

Pulmonary hypertension (PH) is a major comorbidity of chronic obstructive pulmonary disease (COPD). However, the association of PH detected by echocardiography and COPD-related outcome in longitudinal follow-up has not been elucidated. In this study, we aimed to investigate the relationship between clinical characteristics of COPD patients with PH detected by echocardiography and various outcome parameters such as COPD exacerbation and health status over a three-year observation period.

Methods

In this observational study, we analyzed patients with COPD who underwent chest computed tomography and echocardiography at baseline (n = 183).

Results

The prevalence of PH was 21.9% (40 patients). The median estimated systolic pulmonary artery pressure in patients with PH was 38.8 mmHg. COPD patients with PH were older, had a lower body mass index, scored worse in the COPD Assessment Test and St. George's Respiratory Questionnaire, and exhibited a lower diffusing capacity of the lung for carbon monoxide in comparison to patients without PH. In computed tomography images, the percentages of low-attenuation areas (LAA%) and interstitial abnormalities were higher in COPD patients with PH than in those without PH. Higher values for LAA% (LAA ≥ 30%) and interstitial abnormalities independently increased the risk of PH. The ratio of main pulmonary diameter to aortic artery diameter was significantly correlated with estimated systolic pulmonary artery pressure. In the follow-up analysis, the frequency of exacerbations in three years was significantly higher in patients with PH compared to patients without PH.

Conclusion

In this study, we identified the clinical characteristics of COPD patients with PH detected by echocardiography. The presence of PH assessed by echocardiography was related to future COPD exacerbations and closely related to radiographical emphysema.

Diameter of the dilated main pulmonary artery in patients with pulmonary hypertension decreases after lung transplantation

PURPOSE

The pulmonary artery (PA) in patients with pulmonary hypertension (PH) becomes dilated. We analyzed the postoperative changes of the main PA after lung transplantation (LuTx).

METHODS

The subjects of this retrospective study were 68 LuTx recipients, divided into a PH group (n = 36) and a non-PH group (n = 32), based on preoperative right heart catheterization findings. The PA diameter was measured on chest computed tomography. We evaluated the correlation between the mean pulmonary arterial pressure (mPAP) and the main PA diameter and compared the main PA diameters before and 3 months after LuTx.

RESULTS

The main PA diameter was significantly correlated with the mPAP (r = 0.423, P < 0.001). Preoperatively, the mean main PA diameter in the PH group was significantly greater than that in the non-PH group. However, by 3 months after LuTx, the main PA diameter in the PH group had decreased significantly from 32.4 ± 6.7 to 26.9 ± 4.8 mm (P < 0.001), while that in the non-PH group had decreased minimally from 28.3 ± 4.9 to 26.4 ± 4.6 mm (P < 0.001), resulting in no significant difference in postoperative main PA diameters between the two groups.

CONCLUSIONS

The main PA diameter in recipients with PH was enlarged and correlated with the mPAP. The dilated main PA diameter in PH patients decreased shortly after LuTx.

Association between cardiovascular risk factors and the diameter of the main pulmonary artery in asymptomatic population in the Appalachian region

Background

Pulmonary artery (PA) diameter may be altered in association with cardiovascular (CV) risk factors as noted in aorta in systemic hypertension. The flow of blood from the right ventricle to the PA and all the way to the capillary level depends on the pulmonary vascular resistance and to a lesser extent compliance and impedance of the PA, which are the fundamental conduit for maintenance of the right heart hemodynamics. Our objective is to determine the association between CV risk factors and the main pulmonary artery (MPA) diameter.

Methods

The study population are asymptomatic individuals with no known diagnosis of CV diseases in central Appalachia (n=1,282). Adults aged 18 years or older were eligible for the screening if they were referred by a physician. For self-referral, only males aged ≥45 years and females aged ≥55 years were eligible. Unadjusted and adjusted linear regression analyses were performed.

Results

The mean MPA diameter was significantly higher among males compared to females (27.19±4.20 vs. 24.99±3.91 mm, P<0.0001). Participants with diabetes also had wider MPA diameter (26.79±4.56 mm) compared to those without diabetes (25.93±4.11 mm) (P=0.015). Further, hypertensive (26.42±4.15 vs. 25.71±4.21 mm, P=0.002) and obese (27.25±4.11 vs. 25.28±4.07 mm, P<0.0001) participants had significantly wider MPA diameter compared to non-hypertensive and non-obese participants, respectively. Multivariable model showed that age, sex and body mass index (BMI) were significantly associated with MPA diameter. A 1-year increase in age increased MPA diameter by 0.046 mm (P<0.0001). The diameter of MPA was wider among males by 2.16 mm compared to females (P<0.0001). Finally, with one unit increase in BMI, the MPA diameter increased by 0.16 mm (P<0.0001).

Conclusions

MPA diameter was significantly associated with age, sex, and BMI. Further prospective studies are needed to correlate computed tomography (CT) measurement of MPA diameter with pulmonary pressure as assessed by echocardiogram to diagnose pulmonary hypertension (PH).

Assessing pulmonary hypertension in COPD. Is there a role for computed tomography?

Pulmonary hypertension (PH) is a common complication of chronic obstructive pulmonary disease (COPD) and is associated with increased morbidity and mortality. Reference standard method to diagnose PH is right heart catheterization. Several non-invasive imaging techniques have been employed in the detection of PH. Among them, computed tomography (CT) is the most commonly used for phenotyping and detecting complications of COPD. Several CT findings have also been described in patients with severe PH. Nevertheless, CT analysis is currently based on visual findings which can lead to reproducibility failure. Therefore, there is a need for quantification in order to assess objective criteria. In this review, progresses in automated analyses of CT parameters and their values in predicting PH and COPD outcomes are presented.

Screening For Pulmonary Hypertension With Multidetector Computed Tomography Among Patients With Severe Aortic Stenosis Undergoing Transcatheter Aortic Valve Implantation

Aim: To assess the accuracy of multi-detector computed tomography (MDCT) derived pulmonary vessel measurements in predicting pulmonary hypertension (PH) among patients with severe symptomatic aortic stenosis (AS) undergoing transcatheter aortic valve implantation (TAVI).

Background: PH is common among patients with severe AS undergoing TAVI and is associated with adverse outcomes. MDCT is the imaging modality of choice to assess anatomical dimensions among patients selected for TAVI.

Methods: One hundred and thirty-nine patients with severe AS undergoing TAVI with both CT scans and right heart catheterizations (RHC) were included. CT diameters of the main pulmonary artery (MPA), right (RPA) and left (LPA), and ascending aorta (AA) were measured. The relationship between CT measurements and PA pressures assessing using RHC was tested with linear regression.

Results: The CT derived ratio of the diameter of the MPA to the diameter of the AA (PA/AA_ratio) correlated best with mean PA pressure (R² = 0.48) and PA systolic pressure (R² = 0.50). Receiver operating characteristic curve analysis showed that the PA/AA_ratio is a moderate predictor of PH (AUC 0.74, 95% CI 0.65–0.83, p < 0.0001) and that the optimal cut off point is 0.80 (sensitivity 56%, specificity 88%, positive predictive value 95.5%, negative predictive value 30.6% for PH).

Conclusions: Elderly patients with severe AS and PA/AA_ratio values ≥ 0.80 on MDCT are more likely to have PH but PH cannot be reliably excluded among such patients with lower PA/AA_ratio values.

CT measurements of central pulmonary vasculature as predictors of severe exacerbation in COPD

To identify a predictive value for the exacerbation status of chronic obstructive pulmonary disease (COPD) subjects, we evaluated the relationship between pulmonary vascular measurements on chest CT and severe COPD exacerbation.Six hundred three subjects enrolled in the COPDGene population were included and divided into nonexacerbator (n = 313) and severe exacerbator (n = 290) groups, based on whether they had an emergency room visit and/or hospitalization for COPD exacerbation. We measured the diameter of the main pulmonary artery (MPA) and ascending aorta (AA) at 2 different sites of the MPA (the tubular midportion and bifurcation) on both axial images and multiplanar reconstructions. Using multiple logistic regression analyses, we evaluated the relationship between each CT-measured pulmonary vasculature and exacerbation status.Axial and multiplanar MPA to AA diameter ratios (PA:AA ratios) at the tubular midportion and the axial PA:AA ratios at the bifurcation indicated significant association with severe exacerbation. The strongest association was found with the axial PA:mean AA ratio at the bifurcation (adjusted odds ratio [OR] = 12.53, 95% confidence interval [CI] = 2.35-66.74, P = .003) and the axial PA:major AA ratio at the tubular midportion (adjusted OR = 10.72, 95% CI = 1.99-57.86, P = .006). No differences were observed in the MPA diameter. Receiver operating characteristic analysis of these variables indicates that they may serve as a good predictive value for severe exacerbation (area under the curve, 0.77-0.78). The range of cut-off value for PA:AA ratio was 0.8 to 0.87.CT-measured PA:AA ratios at either the bifurcation or the tubular site, measured either on axial or multiplanar images, are useful for identification of the risk of severe exacerbation, and consequently can be helpful in guiding the management of COPD. Although CT measurement was used at the level of pulmonary bifurcation in previous studies, we suggest that future studies should monitor the tubular site of the MPA for maximum diagnostic value of CT in pulmonary hypertension or severe COPD exacerbation, as the tubular site of the MPA remains relatively constant on CT images.