Characterization of non-linear material parameters of atherosclerotic arteries using numerical and experimental models.

摘要

Cardiovascular diseases are the leading cause of death worldwide. In most cases, cardiovascular diseases are caused by an underlying pathology: atherosclerosis. Numerical models are very helpful to study the biomechanics of atherosclerosis, assess the risks and more likely sites of rupture, to design and study the effect of interventions. Yet, the reliability of the simulations is directly dependent on the fidelity of the material properties, geometry and boundary conditions to represent the reality. However, data available to precisely model the mechanical behaviour of the plaque and its constituents are relatively limited, particularly for the inclusions.;The experimental part of the approach consists in extension-pressurization of the intact vessel. For different states of axial extension, the vessel is pressurized while intravascular ultrasound images are acquired at regular intervals. Then, the images are segmented to extract the contours of the different constituents. The contours from before the pressurization are use to build the geometry of finite element models. Simulations are run for different pressure values. The resulting deformed contours are compared to the contours extracted from the images for the same pressure values, to optimize the material parameters for the inclusion and for the wall layers. The comparison is defined in terms of circumferences and thicknesses.;The estimated material parameters for the gels were applied to predict the responses in uniaxial and biaxial tensions, to compare them to experimental data from tension testing of samples made of the same gels. The estimated parameter for the lard was compared to shear test measurements. The predictions were good (R2 ≥ 0.90) for deformations in the range and slightly over the range of those used for the optimisation process.;The main objective of this project is to propose a method to determine the non-linear material parameters for an inclusion and for the surrounding tissues of atherosclerotic medium arteries using numerical and experimental models. To evaluate the proposed method, a mock artery with a stenosis and a lipid inclusion was designed and fabricated with polyvinyl alcohol gel for each of the two wall layers, and animal fat (lard) for the inclusion. PVA gel has a non-linear elastic behaviour that can be described with a Money-Rivlin model.