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CT-Based Pulmonary Artery Measurements for the Assessment of Pulmonary Hypertension

Posted Mar 31, 2014 Updated Apr 10, 2023
By Neal Corson PhD , Samuel G. Armato PhD , Zacariah E. Labby PhD , Christopher Straus MD , Adam Starkey , Mardi Gomberg-Maitl MD
12 min read

Rationale and Objectives

Pulmonary hypertension (PH) is a complex and fatal disease that is difficult to diagnose noninvasively. This study evaluated previously published computed tomography–based vessel measurement criteria and investigated the predictive power and diagnostic ability of the main pulmonary artery diameter (MPAD) and the ratio of MPAD to aorta diameter (rPA).

Materials and Methods

The database for this study consisted of 175 PH patients (for whom mean pulmonary artery pressure [mPAP] was known), 16 patients without PH but with known mPAP (non-PH patients), and 114 “normal” patients without known mPAP. The performance of previously published criteria, MPAD > 29 mm and rPA > 1, was determined. The relationship between vessel measurements and mPAP was evaluated through correlation and linear regression analysis. The ability of these measurements to discriminate between patients with and without PH was determined by receiver operating characteristic analysis.

Results

For discriminating between PH and “normal” patients, the sensitivity and specificity of the criterion MPAD > 29 mm were 0.89 (0.84–0.93) and 0.83 (0.76–0.90), respectively, and the sensitivity and specificity of the criterion rPA > 1 were 0.89 (0.85–0.94) and 0.82 (0.74–0.89), respectively. At a specificity of 0.95 in the task of separating PH and “normal” patients, the sensitivity of MPAD was 0.81 (0.72–0.90) and the sensitivity of rPA was 0.76 (0.66–0.85), but the specificity for both decreased when non-PH patients were included. For the combined PH and non-PH patient groups, the correlation between the vessel measurements and mPAP was significant but low, and the ability of the vessel measurements to predict mPAP was limited.

Conclusion

This study found that the sensitivity of previously published vessel criteria for identifying PH patients is high, but the specificity may not be high enough for routine use in a clinical patient population.

Pulmonary hypertension (PH) is a fatal disease that is not diagnosed early because patients typically present to their doctor with symptoms associated with advanced disease . PH has a wide range of etiologies and requires a complex clinical classification scheme . PH is classified into five groups. PH group 1, which is known as pulmonary arterial hypertension (PAH), includes idiopathic PAH and heritable PAH among others, and PH groups 2–5 include PH resulting from left heart disease, lung diseases and/or hypoxia, chronic thromboembolic disease, or unclear multifactorial mechanisms, respectively. A mean arterial pulmonary pressure (mPAP) > 25 mm Hg at rest or > 30 mm Hg with exercise as determined by right heart catheterization (RHC) is required but not sufficient to be diagnosed with PH because additional criteria must be met .

PH has nonspecific symptoms that make it difficult to diagnose noninvasively. Consequently, patient evaluation normally requires numerous diagnostic tests. The diagnostic evaluation of PH includes physical examination, electrocardiography, pulmonary function tests, blood gas analysis, ventilation/perfusion scan, echocardiography, and RHC with vasodilatory testing. Although RHC is the gold standard for the diagnosis of PH , it is an invasive procedure. Echocardiography is a noninvasive means to assess heart function and blood pressures, but the accuracy of the pressure measurements obtained through echocardiography is suboptimal because of differences when compared with RHC .

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Materials and methods

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Figure 1, Vessel measurements obtained from computed tomography scans. (a) The diameter of an enlarged pulmonary artery (PA) from an idiopathic pulmonary arterial hypertension patient (compare with the aorta [A] diameter). (b) An A and PA diameter from a “normal” patient.

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Statistics

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Results

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Table 1

Summary of Patient Demographic and Clinical Information

Patient Group Total Male/Female Mean Age (Range) (y) CT Scan Infused/Noninfused Mean mPAP (Range) (mm Hg) Mean PCWP (Range) (mm Hg) Mean BSA (m 2 ) PH 175 42/133 54 (14–86) 125/50 46 (15–78) 13 (1–45) 1.9 (1.3–2.6) Non-PH 16 5/11 57 (27–79) 11/5 18 (12–37) 10 (5–32) 1.9 (1.5–2.4) “Normal” 114 49/65 47 (13–83) 114/0 N/A N/A N/A

BSA, body surface area; CT, computed tomography; mPAP, mean pulmonary artery pressure; PCWP, pulmonary capillary wedge pressure; PH, pulmonary hypertension.

Table 2

Distribution of PH Patients ( n = 175) by Clinical Classification

Total Clinical Classification of PH 89 1. PAH IPAH/HPAH_n_ = 28 Associated with CTD_n_ = 36 Associated with portal hypertension_n_ = 13 Associated with congenital heart_n_ = 6 Other within PAH_n_ = 6 5 1′. PVOD and/or PCH 33 2. PHLHD 10 3. PH owing to lung diseases and/or hypoxia 19 4. CTEPH 19 5. PH with unclear multifactorial mechanisms Sarcoidosis_n_ = 17 Other_n_ = 2

CTD, connective tissue disease; CTEPH, chronic thromboembolic pulmonary hypertension; HPAH, heritable PAH; IPAH, idiopathic PAH; PAH, pulmonary arterial hypertension; PCH, pulmonary capillary hemangiomatosis; PHLHD, PH owing to left heart disease; PVOD, pulmonary veno-occlusive disease.

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Demographics

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Table 3

Vessel Measurements by Patient Group

Patient Group Total MPAD (mm) Mean ± SD (Range)P ∗ rPA Mean ± SD (Range)P ∗ Aorta (mm) Mean ± SD (Range)P ∗ PH 175 36.4 ± 6.68 (24.2–70.6) < .05 1.27 ± 0.28 (0.70–2.20) < .05 29.3 ± 4.37 (18.8–39.9) .2 Non-PH 16 28.6 ± 5.48 (17.7–35.6) 0.98 ± 0.17 (0.55–1.26) 29.4 ± 3.44 (22.9–36.1) “Normal” 114 24.9 ± 3.66 (17.7–34.0) 0.87 ± 0.13 (0.56–1.24) 29.0 ± 4.40 (17.3–44.3) “Normal” + non-PH 130 25.4 ± 4.08 (17.7–35.6) 0.88 ± 0.14 (0.55–1.26) 29.1 ± 4.28 (17.3–44.3)

Aorta, diameter of the aorta; MPAD, main pulmonary artery diameter; PH, pulmonary hypertension; rPA, ratio of MPAD to aorta diameter; SD, standard deviation.

MPAD and aorta were measured at the level of the bifurcation of the main pulmonary artery on the same computed tomography section. P values are based on Student t -test.

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Table 4

Sensitivity or Specificity (with 95% Confidence Intervals) Obtained from Application of the Previously Reported Vessel Measurement Criteria for PH Diagnosis to the Present Patient Cohort

Patient group Vessel Measurement Criteria MPAD > 29 mm rPA > 1 PH (sensitivity) 0.89 (0.84–0.93) 0.89 (0.85–0.94) “Normal” (specificity) 0.83 (0.76–0.90) 0.82 (0.74–0.89) “Normal” + non-PH (specificity) 0.79 (0.71–0.86) 0.79 (0.71–0.86)

MPAD, main pulmonary artery diameter; PH, pulmonary hypertension; rPA, ratio of MPAD to aorta diameter.

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Correlations and Linear Regression Analyses

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Table 5

Pearson/Spearman Correlation Coefficients Relating mPAP to Vessel Measurements for the Combined PH and non-PH Patient Groups and for Different PH Subgroups

Patient Group MPAD rPA PH + non-PH 0.34 ∗ /0.35 ∗ 0.40 ∗ /0.40 ∗ IPAH/HPAH 0.093/−0.14 0.034/−0.019 CTD 0.19/0.35 ∗ 0.12/0.20 PHLHD 0.32/0.35 ∗ 0.40 ∗ /0.30 CTEPH 0.43/0.49 ∗ 0.39/0.43

CTD, connective tissue disease; CTEPH, chronic thromboembolic pulmonary hypertension; HPAH, heritable PAH; IPAH, idiopathic PAH; MPAD, main pulmonary artery diameter; PAH, pulmonary arterial hypertension; PH, pulmonary hypertension; PHLHD, PH owing to left heart disease; rPA, ratio of MPAD to aorta diameter.

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Figure 2, Scatter plot of mean pulmonary artery pressure (mPAP) versus main pulmonary artery diameter (MPAD) for the combined pulmonary hypertension and non-pulmonary hypertension patient groups. Superimposed on the scatter plot is the line of regression from the linear model (MPAD) ( straight solid line ) with 95% prediction bands ( straight dashed lines ) and the line of regression from the linear-quadratic model (MPAD + MPAD 2 ) ( curved solid line ) with 95% prediction bands ( curved dashed lines ).

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Figure 3, Scatter plot of mean pulmonary artery pressure (mPAP) versus ratio of the main pulmonary artery diameter to the diameter of the aorta (rPA) for the combined pulmonary hypertension and non- pulmonary hypertension patient groups. Superimposed on the scatter plot is the line of regression for the linear model (rPA) ( solid line ) with 95% prediction bands ( dashed lines ).

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ROC Analyses

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Figure 4, Distributions of (a) measured main pulmonary artery diameter (MPAD) values and (b) measured main pulmonary artery diameter to the diameter of the aorta (rPA) values for the pulmonary hypertension (PH) patients and the “normal” patients.

Table 6

AUC Values (with 95% Confidence Intervals) Obtained from ROC Analysis Performed to Evaluate the Ability of Vessel Measurements to Distinguish between Different Patient Groups

Classification Task Vessel Measurement MPAD rPA PH versus “normal” 0.96 (0.94–0.98) 0.94 (0.91–0.96) PH versus “normal” + non-PH 0.94 (0.92–0.97) 0.92 (0.90–0.95) IPAH/HPAH versus “normal” 0.98 (0.94–1.00) 0.97 (0.93–1.00) CTD versus “normal” 0.92 (0.87–0.98) 0.88 (0.81–0.96) PHLHD versus “normal” 0.98 (0.95–1.00) 0.92 (0.86–0.98) CTEPH versus “normal” 0.96 (0.91–1.00) 0.95 (0.89–1.00)

AUC, area under the ROC curve; CTD, connective tissue disease; CTEPH, chronic thromboembolic pulmonary hypertension; HPAH, heritable PAH; IPAH, idiopathic PAH; MPAD, main pulmonary artery diameter; PAH, pulmonary arterial hypertension; PH, pulmonary hypertension; PHLHD, PH owing to left heart disease; ROC, receiver operating characteristic; rPA, ratio of MPAD to aorta diameter.

Figure 5, Empirical and proper binormal model (PBM) receiver operating characteristic curves for the ability of main pulmonary artery diameter (MPAD) ( top left : pulmonary hypertension [PH] vs “normal;” top right : PH vs “normal” + non-PH) and measured main pulmonary artery diameter to the diameter of the aorta (rPA) ( bottom left : PH vs “normal;” bottom right : PH vs “normal” + non-PH) to individually classify patients into two groups (those with PH and those without PH). AUC, area under the receiver operating characteristic curve; FPF, false-positive fraction (1-specificity); TPF, true-positive fraction (sensitivity).

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Table 7

Sensitivities (with 95% CI) Obtained at Specificities of 0.95 and 0.90 When MPAD and rPA Are Evaluated in the Task of Separating PH Patients from “Normal” Patients and PH Patients from the Combined Group of “Normal” Patients Plus non-PH Patients as Determined by the Proper Binormal ROC Curves

Classification Task Specificity Vessel Measurement MPAD rPA PH versus “normal” 0.95 0.81 (0.72–0.90) 0.76 (0.66–0.85) 0.90 0.88 (0.83–0.94) 0.83 (0.76–0.90) PH versus “normal” + non-PH 0.95 0.73 (0.62–0.84) 0.70 (0.60–0.80) 0.90 0.83 (0.76–0.91) 0.79 (0.71–0.87)

CI, confidence interval; MPAD, main pulmonary artery diameter; PH, pulmonary hypertension; rPA, ratio of MPAD to aorta diameter.

Table 8

Empirical Sensitivities and Vessel Measurement Thresholds Obtained at Specificities of Approximately 0.95 and 0.90 When MPAD and rPA Are Evaluated in the Task of Separating PH Patients from “Normal” Patients

Vessel Measurement Specificity PH versus “Normal” Sensitivity MPAD 0.95 MPAD > 31.0 mm 0.82 0.90 MPAD > 30.5 mm 0.85 rPA 0.95 rPA > 1.08 0.75 0.90 rPA > 1.04 0.81

MPAD, main pulmonary artery diameter; PH, pulmonary hypertension; rPA, ratio of MPAD to aorta diameter.

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Discussion

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Limitations

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Conclusion

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Acknowledgments

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Academic Radiology, Volume 21, Issue 4
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