Introduction

In close collaboration with Erasmus Medical Center in Rotterdam, Femto Engineering is investigating the possibility of including the orientation and location of fibres in a finite element model of arteries. The purpose of these simulations is to predict possible rupture of tissue in case of atherosclerosis.

Problem definition

Atherosclerosis is the accumulation of inflammatory cells and fatty material in the artery wall. Rupture of atherosclerotic plaques, which are formed by this process, is the main cause of the majority of sudden heart attacks and stroke. Finite element models of atherosclerotic arteries can be used to compute the stress distribution in plaques and possibly predict potential plaque rupture. The future goal is to evaluate the mechanical stress distribution in atherosclerotic arteries quickly and reliably using this technique. The models will provide medical personnel with more information on plaque vulnerability and enable them to decide whether to operate on a patient or not.

Approach

Until now atherosclerotic plaque components were modelled assuming isotropic material behaviour. However, with biomedical imaging techniques it has been demonstrated that the plaque tissue contains fibrous material with a preferred orientation that depends on the location within the plaque. The presence of these fibres will greatly influence the mechanical behaviour of the plaque and thus the accuracy of the model. Being so, it is important to find a way to include the orientation and location of the fibres in the finite element models that are used to compute the stress distribution in the plaque.

Using MRI scanning techniques, Erasmus MC is able to extract the fibre location and orientation from arteries and plaques. This data is processed by Femto Engineering to create a ‘meshable’ geometry. It is important that this process does not simplify the actual, complex shape of the plaque. The geometry is then separated into the most important arterial components, each with individual material properties.

Conclusion

An anisotropic material model namely the Holzapfel-Gasser-Ogden model is able to simulate the characteristic material behaviour of plaque components. This model is used for the fibrous parts of the artery and plaque. For some arteries it suffices to define a single fibre family with one or more dominant directions per component. However, most atherosclerotic plaques show a more complex fibre structure. For these plaques the fibre structure must be defined per element. In view of the intended purpose of the FEA results, Femto Engineering is looking into automating the processes that generate the geometry and retrieve fibre structure.