Material Modeling: Mixed-Effects Models

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Especially when it comes to arteries with atherosclerotic changes or to abdominal aortic aneurysm, the originally homogenous mechanical properties of arterial wall drastically changes to extremely heterogenous properties. Heterogeneity basically means that material parameters for the arterial wall, e.g. its thickness, the elastic behavior or its failure strength, change with location in the artery. With regard to arteries this definition even has to be widened: Arterial wall properties change with the patients and change locally within the individual patient.

Left, CT image of an AAA: Calcification can be easily identified using CT, since they feature high radiodensity and therefore are displayed in bright white color. Right, AAA wall samples: For AAAs, calcification is mostly adjacent to the luminal side of the arterial wall, introducing heterogeneous stiffening to the wall compound.

An increase in arterial stiffness is attributable to calcifications. We use patient-specific computed tomography (CT) and wall samples in order to find relations between radiodensity values provided by CT and actual sample stiffness. With these results, we are able to include patient-specific stiffness distributions in finite element simulations of abdominal aortic aneurysms (AAA), cartotid stenosis and aortic dissection.