In Vivo Assessment of AAA Biomechanics with Dynamic Wall Properties

Carnegie-Mellon University, Pittsburgh PA

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Abstract

[unreadable] DESCRIPTION (provided by applicant): Predicting the in vivo forces the diseased abdominal aorta is required to withstand will allow interventional management of AAA patients to be planned in a timely and cost-effective manner and tailored to prevent catastrophic events resulting from these forces, providing better care while improving the quality of life of the patients. Peak intraluminal pressure has been thought of as the most important patient-based variable predicting such forces, and thus the great majority of numerical modeling studies of AAA mechanics have been based on quasi-static finite element analysis (FEA) predictions. In such studies blood flow has been ignored and the aneurysm model is limited to a solid shell, ignoring in most cases the presence of intraluminal thrombus. We hypothesize that, once an aneurysm is formed, the primary biomechanical determinants of rupture potential are (i) the non-uniform arterial wall thickness of the AAA and (ii) the anisotropic nature of the AAA wall tissue. We therefore propose a novel anisotropic model for the aneurysmal wall that takes into account the orientation of collagen fibers in the tissue and the non-invasive detection of non-uniform AAA wall thickness. Coupled with the transient dynamics of blood flow within the abdominal aorta in the presence of intraluminal thrombus, we postulate this technique as a more accurate modeling approach for assessing AAA biomechanics than a traditional static, solid-only representation of the aneurysmal wall. The novelty of the proposed research is based not only on the non-invasive nature of the methodology, but also on the utilization of patient-specific intraluminal flow conditions measured in vivo at the time of patient examination and the development of a new constitutive mathematical model for the material characterization of the aneurysmal wall based on collagen distribution in the media. The long-term objective of this research is to develop a clinical tool that will accurately predict the risk of rupture of an individual AAA within the same day of the initial diagnosis of the disease. This proposal represents a pilot study for the development of such tool to specifically evaluate the biomechanics of AAAs with dynamic wall properties within the context of assessing their rupture potential. We intend to address this challenge by pursuing the following specific aims: (1) Acquisition of Vascular Geometry and Intraluminal Flow Characterization In Vivo. To perform a pilot (feasibility) study of the AAA population treated at Allegheny General Hospital based on the reconstruction of the abdominal aorta from CT and cine- MR diagnosis and time dependent blood flow rates and spatial distributions of the flow velocity measured by PC-MR; (2) Application of Constitutive Material Model and Evaluation of Abdominal Aortic Aneurysm Biomechanics. To apply a new constitutive anisotropic model for the AAA material characterization and to predict the flow dynamics and flow-induced wall stresses utilizing patient-based AAA computational models subject to fluid-structure interaction (FSI) numerical techniques applied with in vivo flow boundary conditions. PUBLIC HEALTH RELEVANCE: This award will enable the development of a methodology for non-invasively assessing the rupture potential of abdominal aortic aneurysms (AAAs). We will combine clinical imaging with computational methods to reconstruct a patient's aneurysm and evaluate its risk of rupture by means of computer prediction and validation of the forces exerted on the artery. This methodology is expected to greatly enhance the presurgical planning capabilities of vascular surgeries and endovascular therapies in the future management of cardiovascular diseases. [unreadable] [unreadable] [unreadable]