In Vivo Assessment of AAA Biomechanics with Dynamic Wall Properties

描述(申请人提供)：预测患病腹主动脉需要承受的体内压力将使AAA患者的介入治疗能够以及时和具有成本效益的方式进行规划，并量身定做，以防止由这些力量导致的灾难性事件，在改善患者生活质量的同时提供更好的护理。腔内最大压力一直被认为是预测这种力的最重要的患者变量，因此绝大多数AAA力学的数值模拟研究都是基于准静态有限元分析(FEA)的预测。在这样的研究中，血流被忽略了，动脉瘤模型被限制在实心壳内，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动脉壁厚度的不均匀和(Ii)AAA壁组织的各向异性。因此，我们提出了一种新的动脉瘤壁各向异性模型，该模型考虑了组织中胶原纤维的取向和对不均匀的AAA壁厚的非侵入性检测。结合动脉内血栓存在时腹主动脉内血流的瞬时动力学，我们认为这项技术是一种比传统的静态的、仅实体的动脉瘤壁表示法更准确的AAA生物力学建模方法。这项研究的新颖性不仅基于该方法的非侵入性，还基于在患者检查时在体内测量的患者特定的腔内血流条件的利用，以及基于胶原蛋白在介质中的分布为基础的用于动脉瘤壁材料表征的新的本构数学模型的开发。这项研究的长期目标是开发一种临床工具，能够在疾病首次诊断的同一天内准确预测单个AAA破裂的风险。这项建议代表了一项初步研究，旨在开发这种工具，在评估AAA破裂潜力的背景下，具体评估具有动态室壁特性的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)在活体中获取血管几何和腔内血流特征。对在阿勒格尼综合医院接受治疗的AAA患者进行一项初步(可行性)研究，其基础是根据CT和电影-MR诊断重建的腹主动脉，以及PC-MR测量的随时间变化的血流速度和血流速度的空间分布；(2)腹主动脉动脉瘤生物力学本构模型的应用和评价。将新的本构各向异性模型应用于AAA材料的表征，并利用基于患者的AAA计算模型，结合体内流动边界条件，应用流体-结构相互作用(FSI)数值技术来预测流动动力学和流动诱导的壁应力。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。我们将结合临床成像和计算方法来重建患者的动脉瘤，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风险。这一方法有望极大地提高血管手术和血管内治疗在未来心血管疾病管理中的术前规划能力。

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.