A Proof of Concept of a Non-Invasive Image-Based Material Characterization Method for Enhanced Patient-Specific Computational Modeling

PURPOSE: Computational models of cardiovascular structures rely on their accurate mechanical characterization. A validated method able to infer the material properties of patient-specific large vessels is currently lacking. The aim of the present study is to present a technique starting from the flow-area (QA) method to retrieve basic material properties from magnetic resonance (MR) imaging. METHODS: The proposed method was developed and tested, first, in silico and then in vitro. In silico, fluid-structure interaction (FSI) simulations of flow within a deformable pipe were run with varying elastic modules (E) between 0.5 and 32 MPa. The proposed QA-based formulation was assessed and modified based on the FSI results to retrieve E values. In vitro, a compliant phantom connected to a mock circulatory system was tested within MR scanning. Images of the phantom were acquired and post-processed according to the modified formulation to infer E of the phantom. Results of in vitro imaging assessment were verified against standard tensile test. RESULTS: In silico results from FSI simulations were used to derive the correction factor to the original formulation based on the geometrical and material characteristics. In vitro, the modified QA-based equation estimated an average E = 0.51 MPa, 2% different from the E derived from tensile tests (i.e. E = 0.50 MPa). CONCLUSION: This study presented promising results of an indirect and non-invasive method to establish elastic properties from solely MR images data, suggesting a potential image-based mechanical characterization of large blood vessels

Energetic and Hemodynamic Characteristics of Paravalvular Leak Following Transcatheter Aortic Valve Replacement

Transcatheter aortic valve replacement (TAVR) has emerged as an alternative treatment for inoperable and high risk patients with severe symptomatic aortic stenosis. TAVR short and medium term results are very promising, however paravalvular leak (PVL) post-TAVR still represents a significant complication. PVL post-TAVR is shown to be an independent predictor of short-term and long-term mortality. Despite, its importance and prevalence, with a wide range of reported incidences, only few studies addressed the PVL after TAVR. In the present study, first, the mathematical lumped parameter model is used to model the simplified circulatory system in presence of PVL and to evaluate the performance of TAVR by computing the variation of the left ventricle stroke work (LVSW) under several pre-TAVR and post-TAVR conditions. Results show that in a large majority of cases, TAVR significantly reduced LVSW. However, in cases with pre-existing aortic stenosis conditions with trace/mild aortic regurgitation, it did not significantly reduce LVSW or even led to an increase. Second, a three-dimensional (3D) computational fluid dynamics (CFD) simulation is performed in order to investigate the effect of PVL on the diastolic flow-field characteristics post-TAVR. Results show that PVL leads to significant disturbances in blood flow, which characterized by high speed jets, coherent structures and markedly elevated shear stress on both sides of the implanted aortic leaflets, which could promote a more rapid degeneration of the valve leaflets. Results could be useful in understating the hemodynamics of PVL post-TAVR and estimating some important parameters, which could not be obtained during the medical assessment (e.g. wall shear stress). Also, they could be a help in the process of choosing the appropriate valve for TAVR procedure, based on comparing the pre and post TAVR different scenarios