Hemodynamics of Coarctation of the Aorta - 4D Flow MRI Based Modeling Approach.*

Coarctation of the aorta (COA) is one of the most common congenital heart defects. It is characterized by a narrowing in the aortic arch or proximal descending aorta. Treatment procedures for COA include surgery, intravascular stent placement, and balloon angioplasty. However, the selection criteria for the optimal treatment strategy are not well defined, and interventionalists often rely on their preference rather than patient-specific conditions. 1 in 3 COA patients have post-interventional secondary complications, likely due to suboptimal treatment.

4D Flow MRI is a diagnostic imaging technique capable of measuring time-resolved 3D blood velocities within a volumetric acquisition region. Numerous studies have used 4D Flow MRI to evaluate patient-specific blood flow information in COA. 4D Flow MRI has high potential to be used as a tool for treatment planning, however, imaging on its own provides no predictive capabilities. Image-based computational fluid dynamics (CFD) and in vitro modeling can be used to complement medical imaging, such as virtually testing and simulating interventions. A major challenge hindering image-based CFD from achieving widespread clinical adoption is its high computational cost. This calls for reduced order modeling strategies.

In-vivo 4D Flow MRI was performed in  pediatric patients before and after COA repair following an IRB-approved HIPAA-compliant protocol. The thoracic aorta was segmented, and centerlines were generated using semi-automatic software Mimics (Materialise NV, Leuven, Belgium). Flow rates at the ascending aorta (AAo), brachiocephalic (BCA), left common carotid (LCCA), left subclavian arteries (LSA), and descending aorta (DAo) were obtained using EnSight (Ansys, Inc., Canonsburg, PA, USA). Information from in vivo 4D Flow MRI was used to generate anatomical models to perfrom CFD and to construct anatomically realistic models. Particle image Velocimetry (PIV) data was acquired in the fabricated models to validate the CFD and in vitro 4D Flow aquisitions. Diffirent flow dynamics metrics calculated with all methodologies were compared for all the cases. This study provides a comprehensive flow dynamics characterization of aortic coarctation.