基于三维医学影像的脑动脉瘤内血液流动的数值模拟

目的 利用数值模拟研究具有病人特异性的脑动脉瘤内的血液流动,为脑动脉瘤的破裂风险的评价和动脉瘤介入栓塞后复发风险的评价提供帮助。方法 从两例脑动脉瘤病人的3D-RA数据中重建动脉瘤几何模型,血液流变学模型选择假塑性非牛顿流体模型,利用商用CFD软件Fluent对两例动脉瘤内的血液流动进行数值模拟。结果 数值模拟给出了动脉瘤内的流线图、重要截面上的速度分布图、壁面上的切应力分布和压力分布图。并且绘制了在收缩期时刻动脉瘤颈部和瘤顶部各20个点上的壁面切应力和压力的变化情况。结论 血流动力学因素如流速、压力、壁面切应力、流动对壁面的冲击状况等因素与动脉瘤的生长和破裂密切相关,而由于脑动脉瘤形态各异、载瘤动脉与动脉瘤体的几何关系复杂,所以具有病人特异性的数值模拟对于研究动脉瘤破裂和复发风险具有重要价值。动脉瘤颈部的壁面切应力和壁面切应力的波动的变化规律并不相同,需要进一步研究壁面切应力的波动与脑动脉瘤生长与破裂之间的定量关系。     

个体化颈动脉瘤的血流动力学特性分析

目的构建个体化的流固耦合模型,计算分析不同血液特性对动脉瘤腔内血液动力学的影响,进一步探讨对脑动脉瘤破裂的影响。方法首先采集3D数字剪影图像构建动脉瘤模型,通过流体动力学计算方法分析在相同边界条件下,不同血流特性对颈动脉瘤动力学参数的影响。最后对简化颈动脉瘤实验模型进行粒子图像测试(particle image velocimetry,PIV)实验,以验证血流计算方法的可靠性。结果不同血流特性的流固耦合模型,在1个心动周期内,在相同时刻,瘤腔内的低速区域面积、瘤腔流线分布、壁面剪切力(wall shear stress,WSS)及动脉瘤壁面变形有较大的差异。通过PIV实验发现,在瘤腔内涡流位置随速度变化而变化,与模拟分析结果流动趋势相一致。结论两种血液特性差异较小,但非牛顿流体更加接近血液真实状态,数值结果将更接近真实流动状态。     

颅内动脉瘤径颈比对瘤体与分支血管血流动力学影响的数值模拟研究

动脉瘤的血流动力学是影响其生长与破裂的重要因素,尤其是形态学参数径颈比(aspect ratio,AR,瘤体长径/瘤颈宽度)对其血流动力学影响较大。本研究使用基于计算流体力学(computational fluid dynamics,CFD)技术的ANSYS 16.0软件包,数值仿真分析了不同径颈比对颅内动脉瘤瘤体与分支血管血流动力学的影响,为临床上制定合理的形态学与血流动力学指标来筛选高危的动脉瘤患者,并进行积极的干预治疗提供一定的理论依据。通过使用空间直角坐标系建立径颈比为3.33、2.5、2、1.67、1.43、1.25的理想颅内动脉瘤几何模型,分析和比较了包括血液流场与涡量分布、流速与流量、壁面压力、壁面切应力(wall shear stress,WSS)、瘤颈近远侧端与分支血管剪切应变率(shear strain rate,SSR)在内的血流动力学参数。数值模拟结果给出了动脉瘤与分支血管内的流线图、涡核图、压力分布云图、WSS分布云图以及随X轴变化的流速与压力峰值分布曲线。分析得出,径颈比决定瘤内血流模式,径颈比减小,瘤顶的流速与SSR增大,瘤壁上的压力与WSS增大,分支血管壁上的压力增大,且WSS/SSR瘤颈远侧端>WSS/SSR瘤颈近侧端>WSS/SSR分支血管中心,涡核区域由瘤体远侧壁增大至覆盖整个动脉瘤,但对分支血管内血流的阻碍作用减小。     

分支血管直径对颅内动脉瘤置入血流导向装置后血流动力学参数的影响

目的综合考虑血流导向装置(flow diverter,FD)置入对动脉瘤瘤体及分支血管的影响,为临床制定更加合理的FD栓塞颅内动脉瘤手术策略提供参考。方法基于计算流体动力学(computational fluid dynamics,CFD)方法,创新应用多孔介质模型模拟FD栓塞颅内分叉动脉瘤的过程。分析和比较不同分支血管直径条件下FD置入动脉瘤前后瘤体与分支血管血液流场、血流速度、壁面压力、壁面剪切力(wall shear stress,WSS)等血流动力学参数的变化。结果 FD置入改变动脉瘤内的血流动力学特征,血流速度减小,动脉瘤壁尤其是顶部压力减小,瘤颈口WSS增大,但瘤颈远侧端与近侧端WSS的差异减小。且不同分支血管直径对血流动力学特征改变的影响程度不同,直径越大,FD置入后流入分支血管内血流的减少量越大,但瘤体内血液流速与瘤顶压力的减少量越小,同时瘤颈部WSS增加量越小。结论分支血管直径越大,FD对动脉瘤的栓塞治疗效果与对血管粥样硬化的改善作用越差,越易造成分支闭塞或其他缺血性并发症的发生。此类情况下进行FD介入栓塞术尤其需要引起临床医师注意。     

蜿蜒型脑动脉瘤的血流动力学仿真

目的分析在一个心动周期中蜿蜒型脑动脉瘤的血液流动情形、压力和壁面切应力分布和变化情况。方法构建了二维理想化的蜿蜒型脑动脉瘤（有2个动脉瘤）几何模型。利用计算流体力学方法对生理性脉动流进行了数值仿真。选择6个相继的心动时刻来显示流腔内的流动。结果2个流腔内的流动情形和壁面切应力分布呈现相似的特征,而第2个动脉瘤的末端瘤口则呈现非常高的壁面切应力和很高的压力梯度,这将更易于导致动脉瘤的发展和破裂。结论血液流动特征可以帮助人们更好地理解在S形弯曲动脉上滋生的在体蜿蜒型动脉瘤的血流动力学特性。     

支架植入颅内蜿蜒型动脉瘤的血流动力学仿真

目的　构建蜿蜒型动脉瘤和弯曲支架三维有限元模型,研究支架植入动脉瘤后的血流动力学的变化。方法　通过CAD软件构建出几何实体模型,借助有限元软件利用计算流体力学方法,分别对无支架和有支架的蜿蜒型脑动脉瘤定常流动血流动力学进行数值模拟,分析在动脉瘤中植入内支架前后的瘤腔内流动情形、压力和壁面切应力分布的变化情况。结果　有支架动脉瘤模型上游瘤腔内的血流速度被大大削弱,圆顶突起处局部高压力明显减弱,在下游瘤腔沿壁面的压力也得到明显降低并且分布也均衡了很多,末端唇缘处局部高切应力消失了,出现的是较小且均衡的切应力。结论　有支架模型瘤腔内的流速明显减小,均衡的压力分布与瘤腔内减弱的流动速度是相互统一的,利于瘤腔内血栓的形成。     

支架植入颅内动脉瘤治疗效果的数值模拟研究

研究不同结构形状的血管支架用于治疗颅内动脉瘤后对血流动力学的影响。针对同一个体化颅内动脉瘤模型,设计了三种网丝截面相同、通透率近似相等、结构形状不同的支架。将这三种支架植入颅内动脉瘤模型,进行双向流固耦合数值模拟,分析血流速度、壁面切应力的变化情况。三种支架中,螺旋型支架对动脉瘤瘤腔内的血流旋涡改善效果最佳,对动脉瘤瘤颈和瘤顶部分较高的壁面切应力削弱也最明显;周期型支架的柔顺性优于其余两种类型的支架。螺旋型支架植入颅内动脉瘤的治疗效果最佳,但不适合几何形状复杂的血管,本研究也可为进一步优化支架结构提供依据。     

血管支架对颅内动脉瘤血液动力学的数值模拟

血管支架作为治疗颅内动脉瘤的新方法被广泛运用到临床中,而且越来越普遍。但由于某些支架植入后不能满足力学要求或对瘤内血液动力学无明显影响,反而更易形成血栓,造成动脉瘤破裂。本研究首先通过结构静力学分析比较矩形截面网格状支架和网丝编织成的圆形截面螺旋形支架的弯曲变形能力及扭转变形能力;然后将网格支架植入实际脑动脉瘤模型,进行流－固耦合模拟仿真,分析血流速度、壁面压力及壁面剪切力变化。结果表明：两种支架能够在不损失径向支撑力的情况下,提供良好的轴向顺应性,且网格状支架的变形能力高于螺旋状支架;支架植入后血液动力学各项指标明显降低。血管支架对颅内动脉瘤血液动力学有很大影响,可为临床治疗动脉瘤提供理论依据。     

基于MRA的个体化腹主动脉瘤计算机仿真

目的探讨基于MRA图像进行个体化腹主动脉瘤(abdominal aortic aneurysm,AAA)计算机仿真研究的可行性,并从血流动力学层面探讨AAA的发生、发展和破裂机制。方法基于AAA患者的MRA数据采用逆向建模法建立AAA的三维几何模型;采用FLUENT软件进行数值模拟,假设血管壁为刚性壁,血液为不可压缩牛顿流体,建立瞬态模型。将收敛之后的数据导入到CFD-Post中进行结果分析,输出心动周期内不同时刻的血流流线图、流速分布图、血管壁面切应力分布图以及压力分布图。结果AAA瘤颈处血液流动的方式以层流为主,瘤腔内血流以涡流、湍流为主,且在瘤体膨大处较明显;瘤颈处血液流速快于瘤腔,瘤腔大部分区域在整个心动周期内都处于较低的流速水平,且波动不明显,瘤腔内的高流速区域多位于入口血流直接延续的部位;射血期的壁面切应力的量值及其变化幅度均大于充盈期,壁面切应力较高的区域总是分布于瘤颈附近,瘤腔的切应力在整个心动周期内始终处于较低水平;瘤体的壁面压力量值及其分布范围在射血峰值(t=0.08 s)时最大。加速射血期的壁面压力及其变化范围均较减速射血期及充盈期大。结论基于MRA图像可建立个体化的AAA计算机仿真模型,通过计算机仿真得到的AAA内血流分布规律对AAA的研究和临床个体化的诊治有一定的帮助。     

腹主动脉瘤中定常流动的三维数值模拟

目的讨论定常流动情况下，三维腹主动脉瘤模型内的流动情况。方法应用三维非对称模型进行数值模拟。结果结果表明，在对称面上有一个涡而横截面上有两对涡的存在。壁面切应力在动脉瘤的出口处数值较高且变化大。结论流动和壁面切应力分布反应动脉瘤出口处为破裂的危险区域。     

支架治疗主动脉弓内侧动脉瘤的仿真研究

血管内支架是治疗主动脉弓动脉瘤的一种新技术。目前还没有人对具有局部突起的动脉瘤支架治疗血流动力学进行过研究。基于这样的事实,本仿真研究对主动脉弓内侧动脉瘤的支架治疗进行血流动力学分析。为便于比较,分别建立了有支架和无支架的主动脉弓动脉瘤模型。利用计算流体力学的方法对两个模型中的生理性血液流动进行了仿真。对流动情形、压力和壁面切应力分布进行了比较和分析,以便评价血管内支架对主动脉弓动脉瘤治疗的效果。结果表明,有支架的模型和无支架的模型,在瘤腔内的流动情形具有显著的不同。有支架模型瘤腔内的流动受到明显的抑制,特别是局部突起处的压力和壁面切应力大大地减小了。这些现象使我们有理由推断,血管内支架可以促进瘤腔内血栓的形成,并能减小动脉瘤破裂的危险。     

Quantification of particle residence time in abdominal aortic aneurysms using magnetic resonance imaging and computational fluid dynamics

Hemodynamic conditions are hypothesized to affect the initiation, growth, and rupture of abdominal aortic aneurysms (AAAs), a vascular disease characterized by progressive wall degradation and enlargement of the abdominal aorta. This study aims to use magnetic resonance imaging (MRI) and computational fluid dynamics (CFD) to quantify flow stagnation and recirculation in eight AAAs by computing particle residence time (PRT). Specifically, we used gadolinium-enhanced MR angiography to obtain images of the vessel lumens, which were used to generate subject-specific models. We also used phase-contrast MRI to measure blood flow at supraceliac and infrarenal locations to prescribe physiologic boundary conditions. CFD was used to simulate pulsatile flow, and PRT, particle residence index, and particle half-life of PRT in the aneurysms were computed. We observed significant regional differences of PRT in the aneurysms with localized patterns that differed depending on aneurysm geometry and infrarenal flow. A bulbous aneurysm with the lowest mean infrarenal flow demonstrated the slowest particle clearance. In addition, improvements in particle clearance were observed with increase of mean infrarenal flow. We postulate that augmentation of mean infrarenal flow during exercise may reduce chronic flow stasis that may influence mural thrombus burden, degradation of the vessel wall, and aneurysm growth.     

Simulation of abdominal aortic aneurysm growth with updating hemodynamic loads using a realistic geometry

Advances in modeling vascular tissue growth and remodeling (G&R) as well as medical imaging usher in a great potential for integrative computational mechanics to revolutionize the clinical treatment of cardiovascular diseases. A computational model of abdominal aortic aneurysm (AAA) enlargement has been previously developed based on realistic geometric models. In this work, we couple the computational simulation of AAA growth with the hemodynamics simulation in a stepwise, iterative manner and study the interrelation between the changes in wall shear stress (WSS) and arterial wall evolution. The G&R simulation computes a long-term vascular adaptation with constant hemodynamic loads, derived from the previous hemodynamics simulation, while the subsequent hemodynamics simulation computes hemodynamic loads on the vessel wall during the cardiac cycle using the evolved geometry. We hypothesize that low WSS promotes degradation of elastin during the progression of an AAA. It is shown that shear stress-induced degradation of elastin elevates wall stress and accelerates AAA enlargement. Regions of higher expansion correlate with regions of low WSS. Our results show that despite the crucial role of stress-mediated collagen turnover in compensating the loss of elastin, AAA enlargement can be accelerated through the effect of WSS. The present study is able to account for computational models of image-based AAA growth as well as important hemodynamic parameters with relatively low computational expense. We suggest that the present computational framework, in spite of its limitations, provides a useful foundation for future studies which may yield new insight into how aneurysms grow and rupture.     

Effect of Variation in Intraluminal Thrombus Constitutive Properties on Abdominal Aortic Aneurysm Wall Stress

The abdominal aortic aneurysm (AAA) is a degenerating disease for which the end stage is the rupture of the vessel wall. Accurate prediction of the stresses acting on the aneurysm tissue may be used to determine the actual risk of rupture of a specific aneurysm. To accomplish this, a correct constitutive model for the aneurysmal aortic wall and any intraluminal thrombus (ILT) present within it are needed. Our laboratory has previously reported the mechanical properties of ILT. The aim of this work is to investigate the reliability of using population-mean values of ILT constitutive parameters to estimate AAA wall stress distribution. For this, a three-dimensional asymmetric model of an aneurysm including ILT was generated and a parametric study was conducted varying ILT constitutive properties within a physiological range. Results show that the presence of any ILT reduces and redistributes the stresses in the aortic wall markedly. Maximum variation in the peak wall stresses for all the models analyzed was 5%. Adopting a nonhomogeneous ILT did not alter the stress distribution. On the basis of these results, we infer that population mean parameters for ILT material characteristics can be used to reasonably estimate the wall stresses in patient specific aneurysm models. © 2003 Biomedical Engineering Society. PAC2003: 8719Rr, 8719Xx, 8710+e     

基于个性化颈内动脉瘤模型的流固耦合分析

目的在考虑血管壁弹性条件下,分析颈内动脉血液流动和壁面切应力的分布特性,探讨动脉瘤破裂的生物力学因素。方法依据二维医学扫描图像构建三维个性化颈内动脉瘤模型。依据人体生理统计数据构建出血管壁模型。根据人体颈内动脉生理流动条件,利用有限体积法和有限元法模拟分析流固耦合作用下颈内动脉瘤中的血流动力学。结果在动脉瘤腔中有一个明显的涡旋存在,此涡旋流动的方向在心动周期内没有改变;在动脉瘤颈和动脉瘤壁面处存在一个壁面切应力值相对较大区域;在动脉瘤颈和动脉瘤顶有两个区域的Von Mises应力处于局部最大值。从材料强度角度考虑,这几个区域都是动脉瘤容易破裂的地方。结论通过流固耦合计算可以获得血管壁面应力分布特性,进而推断动脉瘤破裂的可能位置。     

The importance of parent artery geometry in intra-aneurysmal hemodynamics

We show the importance of arterial geometry in intra-aneurysmal hemodynamics. Using a new geometric parameterized saccular aneurysm model including parameters for parent artery shape and the configuration of the aneurysm in the parent artery, we performed a parametric computational fluid dynamics study. We examined lateral saccular aneurysm models with different aneurysm shapes (i.e., the ratio of aneurysm height to aneurysm neck diameter) and different configurations (i.e., the torsion angle of the aneurysm to the upstream part of the parent artery). The aneurysm lateral to the curve of the parent artery had significantly higher wall shear stress than the aneurysm inside or outside the curve of the artery, even with the same shape of the aneurysm. Our findings suggest the important role played by the configuration of the aneurysm relative to the parent artery in intra-aneurysmal hemodynamics.     

附带局部突起的主动脉弓动脉瘤的血流动力学仿真

目的：为了弄清楚顶部附带局部突起的主动脉弓动脉瘤的血流动力学特征，因为针这种动脉瘤的血流动力学目前还较少有人研究。方法：建立了理想化的动脉瘤模型。利用计算流体力学的方法对模型中的生理性血液流动进行了仿真。结果：对流动情形、压力和壁面切应力分布进行了分析，以便评价血流动力学对动脉瘤的发展和破裂的影响。来自动脉的血流对下游瘤口和瘤顶局部突起的冲击较大。瘤顶局部突起区域的压力较高。在瘤口和突起口部位的局部壁面切应力比其他地方的要高。结论：下游瘤口和瘤顶局部突起部位是动脉瘤扩展和破裂的危险区域。     

Fluid-structure interaction within realistic three-dimensional models of the aneurysmatic aorta as a guidance to assess the risk of rupture of the aneurysm.

Abdominal aortic aneurysm (AAA) disease is a degenerating process whose ultimate event is the rupture of the vessel wall. Rupture occurs when the stresses acting on the wall rise above the strength of the AAA wall tissue. The complex mechanical interaction between blood flow and wall dynamics in a three dimensional custom model of a patient AAA was studied by means of computational coupled fluid-structure interaction analysis. Real 3D AAA geometry is obtained from CT scans image processing. The results provide a quantitative local evaluation of the stresses due to local structural and fluid dynamic conditions. The method accounts for the complex geometry of the aneurysm, the presence of a thrombus and the interaction between solid and fluid. A proven clinical efficacy may promote the method as a tool to determine factual aneurysm risk of rupture and aid the surgeon to refer elective surgery patients.     

腹主动脉瘤应力模型的建立及其应用

本研究用螺旋CT扫描腹主动脉瘤获得的断层图像合成腹主动脉瘤几何模型，通过设定瘤壁组织生物力学参数和边界条件，使用有限元分析的方法分析腹主动脉瘤瘤壁的应力分布。结果标明，本例腹主动脉瘤应力峰值位于远端分叉部位，瘤体应力峰值位于后壁，均小于瘤壁的承受极限。本研究所得结果对腹主动脉瘤应力模型有助于分析个体化腹主动脉瘤的破裂部位和生长方向，对研究疾病进程提供依据。     

Abdominal aortic aneurysm and cytomegalovirus infection

Cytomegalovirus (CMV) has been implicated in the pathogenesis of atherosclerosis. Abdominal aortic aneurysm is regarded traditionally as a consequence of atherosclerosis. Several microorganisms have been suggested as possible contributing factors for the development of abdominal aortic aneurysm. The relevance of CMV in the processes underlying the development, expansion, and rupture of abdominal aortic aneurysm is unknown. The aim of the present study was to investigate whether CMV infection is related to abdominal aortic aneurysm rupture. One hundred nineteen patients with abdominal aortic aneurysm and 36 matched controls without abdominal aortic aneurysm were investigated prospectively by CMV serology. Patients with ruptured abdominal aortic aneurysm have similar levels of IgG antibodies against CMV as patients with nonruptured abdominal aortic aneurysm, small abdominal aortic aneurysm, and controls without abdominal aortic aneurysm. In conclusion, this study fails to demonstrate a connection between CMV infection and abdominal aortic aneurysm rupture.