Biomechanical Analysis of Aortic Aneurysm Failure to Find Out the Important Factors

本课题的目的是在体外获得动脉瘤壁的力学特性，从MRI图像上无创地测量患者动脉瘤的三维形态，并通过对动脉瘤壁的运动和应力分析，建立预测动脉瘤破裂危险区域的模型。得到以下结果.从患者的腰骶部切除的样本用于双向拉伸测试。这台机器是我们实验室新研制的。动脉瘤病变组织的硬度高于正常组织。弹性模量越高的试件，其各向异性力学性能越高.利用MRI图像成功地建立了人体胸椎的三维有限元模型。在该模型中，主动脉壁被假设为薄膜，各向同性，舒张压和收缩压之间的大线性变形。主动脉弓的额侧和背侧是动脉瘤形成的主要部位。此外，动脉瘤的位置和形状对最高应力值和应力分布有重要和显著的影响.通过测量MRI图像上主动脉壁的变形，计算出患者动脉瘤周围的应变和应力。结果表明，正常人主动脉弓额壁周围应变较大。在颅内动脉瘤患者中，观察到动脉瘤周围外壁侧的大变形。根据目前的结果，我们将开发新的系统，从MRI图像快速构建有限元模型，并研究更精确的颅内动脉瘤壁的力学特性。

The aim of this project are to obtain mechanical properties of aneurysmal wall in vitro, to noninvasively measure the three dimensional shape of aneurysms for patients from MRI images, and to make models to predict the dangerous regions for aneurysm failure from the motion and stress analyses of aneurysmal wall. The following results were obtained.1. The specimen excised form the aneurysmal region of patients was used for the biaxial tensile testing. The machine was newly developed in our laboratory. The diseased specimen from aneurysm was stiffer than normal tissues. The specimens with the higher elastic moduli were the higher anisotropic mechanical properties.2. Three dimensional finite element model was successfully composed from MRI images for human thoracic aortas. In this model, the aortic wall was assumed to be thin membrane, isotropic, large linear deformation between diastolic and systolic pressures. The stress concentration was found in the frontal and dosal sides of aortic arch where aneurysm formation is frequently observed. Further, the location and shapes of the aneurysm had important and significant effects on the highest stress values and the stress distribution.3. The strain and stress were calculated around the aneurysm of patients by measuring the deformation of aortic wall in MRI images. The results showed us that the strain was large around the frontal walls of aortic arch in healthy normal person. In aneurysmal patients, the large deformation to the outer wall side around the aneurysms was observed.According to the present results, we will develop the new system to rapidly construct the finite element model from the MRI images and study more precise mechanical properties of aneurysmal walls.