Bronchopulmonary Shunts in Patients with Chronic Thromboembolic Pulmonary Hypertension: Evaluation with Helical CT and MR Imaging

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Abstract
OBJECTIVE. The purpose of our study was to compare differences in flow between the pulmonary and systemic circulations by assessing MR phase-contrast flow measurements and CT measurements of dilated bronchial arteries in patients with chronic thromboembolic pulmonary hypertension. MATERIALS AND METHODS. Seventeen patients were included in this study. MR phase-contrast flow measurements were used to calculate the net forward volumes in the right and left pulmonary arteries and in the ascending aorta. Single-detector helical CT scans were assessed for the presence of dilated bronchial arteries that could be delineated from the descending aorta to the mainstem bronchi. Their perpendicular cross-sectional area at the level of the main bronchi was measured using a double-threshold region of interest (≥100-3072 H). RESULTS. The mean net forward volume in the aorta was 44.6 mL per heartbeat (R-R interval) and in the pulmonary arteries, 30 mL per R-R interval. Thus, the mean difference was 14.6 mL per R-R interval; this value represents the shunt volume between the systemic arterial and pulmonary venous circulations. On CT, dilated bronchial arteries were depicted in all patients (mean, three arteries per patient). The mean cross-sectional area of the bronchial arteries was 0.19 cm2. Pearson's correlation coefficient (r) between cross-sectional area and shunt volume was 0.86 (p < 0.01). CONCLUSION. MR imaging was able to reveal substantial differences in flow between the systemic arterial and pulmonary venous circulations in patients with chronic thromboembolic pulmonary hypertension. These differences correlated well with the diameters of the bronchial arteries seen on helical CT. Furthermore, these differences resolved after pulmonary thromboendarterectomy. MR imaging enables the accurate estimation of flow in the bronchial arteries in patients with chronic thromboembolic pulmonary hypertension.