Michigan State University MSU Engineering Mechanical Engineering

Computational Modeling of Abdominal Aortic Aneurysm

Shahrokh Zeinali-Davarani
Summary of Research

1) Identification of material properties of arterial wall
Vascular mechanical homeostasis is one of the key assumptions in vascular adaptation models. For models based on medical images, it is a challenging task to prescribe material (constitutive) and geometric (wall thickness, anisotropy) parameters such that homeostatic condition is maintained. In this project, we have developed an inverse technique such that, first, material parameters are estimated (by fitting mechanical test data) and then using an optimization technique, the distributions of geometric parameters are found accounting for both vascular homeostasis and geometric requirements.

Optimal distribution of thickness (left) and collagen fiber orientation (right).

2) Testing different hypothesis of vascular mechanical homeostasis
Existance of a prefered mechanical homeostatic state in arteries is well-accepted. But it is a matter of debate whether which mechanical parameter\form of parameters is responsible for vascular homeostasis and needs to be considered in modeling approaches. Using the developed inverse technique, we seek to discriminate between different hypotheses of homeostasis in terms of the consequent optimized distribution of parameters for different arteries.
Optimal distribution of thickness (a, b) and collagen fiber orientation (c, d)

using different stress-based hypotheses for an internal iliac artery model.

3) Simulation of Image-Based Abdominal Aortic Aneurysm (AAA)
Simulation of AAA growth and remodeling (G&R) provides an opportunity to study changes in biomechanical parameters and the evolution of wall mechanical properties (and shear stress if coupled with hemodynamic simulation) during growth. As a step towards patient-specific modeling of AAA, we have extended models of stress-mediated vascular G&R to include image-based FE models and simulated AAAs by inducing damage to elastin.

Variety of damage shapes for elastin (left column) and consequent forms of growth

and stress distibutions after G&R (right column). The arrows indicate the regions of elevated stress during AAA expansion.

Selected publications:
-Zeinali-Davarani S., Baek S., 2012, Medical image-based simulation of abdominal aortic aneurysm growth. Mechanics Research Communications, in press

-Zeinali-Davarani S., Raguin L.G., Baek, S., 2011, An inverse optimization approach toward testing different hypotheses of vascular homeostasis using image-based models, International Journal of Structural Changes in Solids, 3, 33-45

-Zeinali-Davarani S., Raguin L. G., Vorp D.A. Baek S. 2011. Identification of in vivo material and geometric parameters of a human aorta: toward patient-specific modeling of abdominal aortic aneurysm. Biomech Model Mechanobiol, 10, 689-699

- Zeinali-Davarani S., Sheidaei A., Baek S. 2011. A finite element model of stress-mediated vascular adaptation: application to abdominal aortic aneurysms. Comput Methods Biomech Biomed Eng, 9, 803-817

- Zeinali-Davarani S., Choi J., Baek S. 2009. On parameter estimation for biaxial mechanical behavior of arteries. J Biomech, 42, 524-530.

Last update: Feb, 2012

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