Peter Mortier Bifurcation stenting simulation the vessel IBi

Peter Mortier Bifurcation stenting simulation: the vessel IBi. Tech - bio. MMeda Ghent University, Belgium 2 FEops, Gent, Belgium 1

Virtual stent implantation in a patientbased bifurcation model

Stents induce different stress levels 0. 4 0. 3 0. 2 0. 1 0. 0 Circumferential stresses [MPa] Cypher Select Endeavor Taxus Liberté

How to … ? … create a virtual bifurcation model based on patient data? … incorporate realistic material properties for the vessel?

Step 1: 3 D-CA Images are illustrative Allura 3 D-CA (Philips) Possibility to export geometrical information (circles)

Step 2: Luminal surface generation Circles describing the lumen can be exported – Idealised (cross-sections often have a much more complex shape) – Limited geometrical information in the bifurcation region Mathematical surfaces were created (NURBS)

Step 3: Outer surface generation A wall thickness was assigned based on anatomical data * – Varying wall thickness – Alternative approach: using IVUS information (ANGUS**) * Holzapfel et al. , 2005, Am J Physiol Heart Circ Physiol ** Slager et al. , 2000, Circulation

Step 4: Discretization + layers The continuous model has to be split in discrete regions (or elements) – Finite Element Analysis (FEA) – Calculation of the displacements of the nodes

Step 4: Discretization + layers The continuous model has to be split in discrete regions (or elements) – Finite Element Analysis (FEA) – Calculation of the displacements of the nodes A structured grid or mesh can easily be divided in different layers

Alternative approach

Vessel wall mechanics Each of the arterial layers has a different composition, which leads to important differences in their mechanical behavior. Characterization of the mechanical behavior requires experimental testing of each tissue layer Courtesy Prof. G. Holzapfel

Experimental testing Courtesy Prof. G. Holzapfel The mechanical behavior can be quantified by imposing a displacement and measuring the reaction forces

Experimental testing Force Courtesy Prof. G. Holzapfel Displacement The mechanical behavior can be quantified by imposing a displacement and measuring the reaction forces Vascular tissue behaves non linear

Experimental testing Force Circumferential Courtesy Prof. G. Holzapfel Axial Displacement The mechanical behavior can be quantified by imposing a displacement and measuring the reaction forces Vascular tissue behaves non linear Mechanical behavior is direction-dependent (i. e. anisotropic)

Material model The experimentally measured behavior is then translated into a material model which is used by the simulation software:

Patient-based bifurcation model

Simulated insertion

Conclusions Patient-based bifurcation models – We need to automate some time-consuming steps in order to use these simulations for a large series of patients – The better the imaging techniques, the better the models Material modelling – Not all real-life phenomena are included (e. g. dissections) – Imaging might play a crucial role (accurate in-vivo determination of mechanical properties? )

Thank you! • Acknowledgements – – – Matthieu De Beule Denis Van Loo Benedict Verhegghe Yves Taeymans Patrick Segers Pascal Verdonck • Email: – peter. mortier@feops. com