Non-Invasive Evaluation of Pulmonary Artery Stenosis in Congenital Heart Disease Patients Using Phase Contrast MRI

Branch pulmonary artery (PA) stenosis is a significant congenital heart defect causing elevated pulmonary blood pressure, trans-stenotic pressure drop, and abnormal differential blood flow to the lungs. We propose combined pressure-flow diagnostic parameters, pressure drop coefficient (CDP) and normalized energy loss (Ē_loss) for improved delineation of stenosis severity. In extension to our previous benchtop experimental study, we performed in vitro experiments using phase contrast magnetic resonance imaging (PC MRI) to evaluate the diagnostic parameters and stenosis severity non-invasively.

Subject-specific branch PA test sections representing the main, left, and right PAs (MPA, LPA, and RPA) with a discrete LPA stenosis were manufactured from medical images using additive manufacturing. Three clinically-relevant stenosis severities, 70% area stenosis (AS), 80% AS, and 90% AS, were evaluated at 2 LPM cardiac output under pathophysiologic hemodynamics generated using a mock circulatory loop. 2D (all severities) and 3D (only 70% AS) PC MRI scans were performed to compute the velocity (or flow) and derived pressure drop across the PA test section. The CDP_LPA and ${\overline{E}}_{loss,LPA}$ were evaluated for the three stenosis severities using MRI measurements and compared against results from the benchtop study.

The CDP_LPA increased with an increase in LPA stenosis severity [70% AS: 11 (2D PC), 11.5 (3D PC); 80% AS: 34.6; 90% AS: 154.2]. These values resulted in an absolute difference of within 107 (2D PC) and 3 (3D PC) compared to the benchtop values. Interestingly, the CDP_LPA computed by all three methods (benchtop, 2D and 3D PC MRI) showed distinct and non-overlapping ranges for each stenosis severity [70% AS: 11.0-14.5; 80% AS: 34.6-60.7; and 90% AS: 154.2-261.6]. The ${\overline{E}}_{loss,LPA}$ (absolute) generally increased with an increase in LPA stenosis severity, except for 90% [70% AS: - 435 mJ per Q_LPA (2D PC), - 376 mJ per Q_LPA (3D PC); 80% AS: - 945 mJ per Q_LPA; 90% AS: - 933 mJ per Q_LPA (Q_LPA-LPA flow rate)].

The CDP_LPA demonstrates an improved diagnostic capability over ${\overline{E}}_{loss,LPA}$ in accurately delineating unilateral PA stenosis severity. Further, PC MRI is a comprehensive and safe clinical modality for the non-invasive diagnosis of branch PA stenosis.