Computer Aided Angioplasty: Patient-specific arterial modeling and smooth 3D contact analysis of the stent-balloon-artery interaction

Balloon angioplasty is a well established interventional procedure. In a more general context, the procedure is known as percutaneous (through the skin) transluminal (within the lumen or artery) angioplasty (remodeling the artery) (PTA). It was shown to be an effective and inexpensive alternative to surgery. This interventional treatment is of great and steadily growing medical, economical and scientific interest. Although PTA has a high primary success rate, the long-term success is not satisfying. This is mainly due to re-narrowing of the vessel, also known as restenosis. This problem may be avoided with stents. A stent is a wire mesh tube which is delivered to the lesion site by means of a catheter and deployed with a balloon. It acts like a scaffold which aims to keep the arterial lumen open. Stents have been effective in reducing the elastic recoil and partly vascular remodeling, but they may lead to adverse effects such as neointima formation, late lumen loss and in-stent restenosis. However, almost all studies, which compare classical PTA with stented PTA, document that the patience rate with stenting has been slightly higher. Hence, vascular stents have gained wide popularity over the last several years. There are many types of stents with different characteristics, in different stages of clinical use and approval. PTA and stenting are both clearly mechanically-based treatments exposing the artery to non-physiological loadings and changes of their biomechanical environment. The motivation behind the project is the development of a computational environment which enables the simulation of the mechanical aspects of these interventional treatments. This should serve two purposes: (i) to study and deeper understand the short-term outcome of PTA with stenting by using a particular device set for a stenosis with arbitrary morphology, and (ii) to provide a virtual test bed to choose the optimal clinical devices for a specific stenosis. More particularly, the project focuses on: (i) the three-dimensional (3D) contact interaction of the involved medical devices (balloon catheter, stent) and the vessel wall. (ii) the post-angioplasty strain and stress environments, which may be correlated with restenosis (according to experimental trials tissue growth is related to high stress concentrations). (iii) the redistribution of the plaque components inside the wall during and after stenting. (iv) the stent design parameters and their influence on the outcome of the interventional procedure. The arising (initial) boundary-value problems are (approximately) solved with the finite element method, which employs nonlinear continuum mechanics as a fundamental basis. The interaction between the artery, the balloon catheter and the stent is simulated by means of a special contact algorithm, based on smooth surface representations. This addressed topic is of particular interest, since contact modeling between finite deformable bodies is still under scientific research. The approaches mentioned above have the potential to take all important nonlinearities and mechanical effects of the procedure into account.