This proposal is designed to investigate the central hypothesis that, once an aneurysm is diagnosed, the primary biomechanical determinant of rupture potential is the non-uniform arterial wall thickness, within the context of a dynamic assessment of aneurysm mechanics. Our overall goal is to address this hypothesis by predicting AAA risk of rupture on a patient-specific basis for subjects that will undergo elective repair and retrospectively examining ruptured aneurysms. The biomechanical environment of the native AAAs will be reproduced by non-invasively evaluating blood flow in the abdominal aorta, aneurysmal wall thickness and wall motion as it is mediated by the cardiac cycle. Dynamic indicators of AAA risk of rupture to be evaluated include peak wall stress, peak intra-aneurysmal sac pressure, and spatial and temporal changes in aneurysmal wall thickness. Retrospectively evaluating these indicators for ruptured aneurysms will provide a threshold for which future diagnosed AAAs can be measured against to assess their potential for mechanical failure in a clinical setting. These biomechanical and clinical endpoints will be assessed using standard computational and imaging techniques (fluid-structure interaction modeling, cine, phase-contrast and spin echo magnetic resonance imaging, computed tomography imaging, segmentation and reconstruction algorithms, particle image velocimetry, and soft tissue mechanics frameworks). In addition, (i) we propose a novel constitutive material model for the mechanical properties of the AAA wall based on a strain energy function for soft tissues that accounts for anisotropy and arrangement of a collagen fiber network;(ii) we have developed a new method for calculating the zero-pressure configuration of the abdominal aorta based on the pressurized geometry reconstructed from medical images;and (iii) we have developed a custom-based code for calculation of impedance-derived outflow boundary conditions from in vivo phase-contrast MRI data. This proposal represents a pilot study for the development of a methodology to specifically evaluate the biomechanics of AAAs dynamically within the context of assessing their rupture potential. Predicting the in vivo forces the diseased abdominal aorta is required to withstand will allow surgical management of AAA patients to be planned in a timely and cost-effective manner and tailored to prevent catastrophic events resulting from this dynamics, providing better care while improving the quality of life of the patients. The innovative nature of the proposed research is based not only on the non-invasive methodology, but also on the unprecedented validation of the numerical techniques used herein, and the application of patient-specific intraluminal flow conditions and arterial wall thickness measured at the time of patient examination. PUBLICE
This award will enable the development of a methodology for non-invasively estimating wall thickness in abdominal aortic aneurysms (AAAs) and assessing their rupture potential. We will combine clinical imaging with computational methods to reconstruct patient-specific aneurysms and evaluate the 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.
