In Vivo Assessment of AAA Biomechanics with Dynamic Wall Properties

描述（由申请人提供）：预测患病腹主动脉需要承受的体内力将允许以及时和具有成本效益的方式计划AAA患者的介入管理，并针对这些力进行定制，以防止由这些力导致的灾难性事件，提供更好的护理，同时改善患者的生活质量。峰值腔内压力被认为是预测此类力的最重要的基于患者的变量，因此，绝大多数AAA力学的数值建模研究都是基于准静态有限元分析（FEA）预测。在这些研究中，血流被忽略，动脉瘤模型仅限于固体壳体，在大多数情况下忽略了腔内血栓的存在。我们假设，一旦动脉瘤形成，破裂可能性的主要生物力学决定因素是（i）AAA的动脉壁厚度不均匀和（ii）AAA壁组织的各向异性。因此，我们提出了一种新的各向异性模型的腹主动脉瘤壁，考虑到组织中的胶原纤维的方向和非侵入性检测不均匀的AAA壁厚度。再加上腔内血栓存在时腹主动脉内血流的瞬态动力学，我们假设该技术是一种比传统的静态、仅实体的动脉瘤壁表示更准确的评估AAA生物力学的建模方法。所提出的研究的新奇不仅基于方法的非侵入性，而且基于在患者检查时在体内测量的患者特异性管腔内流动条件的利用，以及基于介质中胶原蛋白分布的血管壁材料表征的新的本构数学模型的开发。本研究的长期目标是开发一种临床工具，该工具将在疾病初步诊断的同一天内准确预测单个AAA破裂的风险。该提案代表了一项试点研究，用于开发此类工具，以在评估其破裂潜力的背景下专门评估具有动态壁特性的AAA的生物力学。我们打算通过追求以下具体目标来应对这一挑战：（1）体内血管几何形状和管腔内流动表征的采集。基于CT和电影- MR诊断的腹主动脉重建以及PC-MR测量的时间依赖性血流速率和流速空间分布，对在Allegheny General Hospital接受治疗的AAA人群进行初步（可行性）研究;（2）本构材料模型的应用和腹主动脉瘤生物力学评价。将一种新的各向异性本构模型应用于AAA材料表征，并利用基于患者的AAA计算模型预测流动动力学和流动诱导壁应力，该计算模型受体内流动边界条件下应用的流体-结构相互作用（FSI）数值技术的影响。公共卫生相关性：该奖项将有助于开发一种非侵入性评估腹主动脉瘤（AAA）破裂可能性的方法。我们将结合联合收割机临床成像与计算方法来重建病人的动脉瘤，并通过计算机预测和验证施加在动脉上的力来评估其破裂的风险。这种方法有望大大提高未来心血管疾病管理中血管外科手术和血管内治疗的术前规划能力。

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.