Aortic hemodynamics in health and disease: validation of fluid structure interaction simulations against 4D flow magnetic resonance imaging

Understanding the complex interplay between morphologic and hemodynamic features in the human aorta is critical for risk stratification and individualized treatment planning.  In this talk, we describe methods for patient specific fluid structure interaction (FSI) simulations in the healthy and diseased aorta. We validate simulations against in vitro 4D flow MRI in both cases.  First, we compare performance of the reduced unified continuum method for FSI against 4D-flow MRI using a compliant phantom of the healthy aorta with matched material properties. We extract high-resolution anatomical and hemodynamic information from an in vitro mock circulatory system. To accurately reflect experimental conditions, we implemented in-plane vascular motion, viscoelastic external tissue support and vascular tissue prestressing. Validation is demonstrated through close quantitative agreement in pressures, lumen area changes, pulse wave velocity, and early systolic velocities, as well as qualitative agreement in late systolic flow structures.  Second, we examine diseased aortic hemodynamics in patient specific models of type-B aortic dissection. We evaluate the effects of entry and exit tear size by comparing Abritrary Lagrangian Eulerian FSI simulations with in vitro 4D-flow MRI. A baseline patient-specific 3D-printed model and two variants with modified tear size (smaller entry tear, smaller exit tear) were embedded into a flow- and pressure-controlled setup to perform MRI. Results showed well-matched complex flow patterns between 4D-flow MRI and FSI simulations. Compared to the baseline model, false lumen flow volume decreased with either a smaller entry tear or smaller exit tear. True to false lumen pressure difference increased with a smaller entry tear and became negative with a smaller exit tear. This work establishes quantitative and qualitative effects of entry or exit tear size on hemodynamics in aortic dissection, with particularly notable impact observed on false lumen pressurization. In both studies, FSI simulations demonstrate acceptable qualitative and quantitative agreement with flow imaging, supporting its deployment in clinical studies.