Impact of calcifications on patient-specific wall stress analysis of abdominal aortic aneurysms |
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Authors: | A Maier M W Gee C Reeps H-H Eckstein W A Wall |
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Institution: | (1) Department of Biomedical Engineering, 1136 Seamans Center, College of Engineering, The University of Iowa, Iowa City, IA 52242-1527, USA;(2) Departments of Surgery and Bioengineering, University of Pittsburgh, Pittsburgh, PA 15219, USA |
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Abstract: | As a degenerative and inflammatory desease of elderly patients, about 80% of abdominal aortic aneurysms (AAA) show considerable
wall calcification. Effect of calcifications on computational wall stress analyses of AAAs has been rarely treated in literature
so far. Calcifications are heterogeneously distributed, non-fibrous, stiff plaques which are most commonly found near the
luminal surface in between the intima and the media layer of the vessel wall. In this study, we therefore investigate the
influence of calcifications as separate AAA constituents on finite element simulation results. Thus, three AAAs are reconstructed
with regard to intraluminal thrombus (ILT), calcifications and vessel wall. Each patient-specific AAA is simulated twice,
once including all three AAA constituents and once neglecting calcifications as it is still common in literature. Parameters
for constitutive modeling of calcifications are thereby taken from experiments performed by the authors, showing that calcifications
exhibit an almost linear stress–strain behavior with a Young’s modulus E ≥ 40 MPa. Simulation results show that calcifications exhibit significant load-bearing effects and reduce stress in adjacent
vessel wall. Average stress within the vessel wall is reduced by 9.7 to 59.2%. For two out of three AAAs, peak wall stress
decreases when taking calcifications into consideration (8.9 and 28.9%). For one AAA, simulated peak wall stress increases
by 5.5% due to stress peaks near calcification borders. However, such stress singularities due to sudden stiffness jumps are
physiologically doubtful. It can further be observed that large calcifications are mostly situated in concavely shaped regions
of the AAA wall. We deduce that AAA shape is influenced by existent calcifications, thus crucial errors occur if they are
neglected in computational wall stress analyses. A general increase in rupture risk for calcified AAAs is doubted. |
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