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。     

基于多孔介质模型的血流导向装置栓塞颅内动脉瘤的敏感性

目的 应用计算流体力学（computational fluid dynamics, CFD）技术模拟不同血流导向装置（flow diverter, FD）参数对血流动力学的影响,为术前制定合理治疗策略提供可行方法。方法 运用多孔介质模型模拟FD置入动脉瘤的过程,针对特定FD（Tubridge）计算其自身特有的多孔介质动量源参数（渗透率、惯性阻力）初始值。比较不同动量源参数值（初始值80%、90%、100%、110%、120%）情况下血流速度、壁面剪切应力（wall shear stress, WSS）、体积流量、瘤顶压力等血流动力学参数的变化,并进行多孔介质模型针对病人特异性颅内动脉瘤（intracranial aneurysm, IA）血流动力学参数的敏感性分析。结果 IA各血流动力学参数对多孔介质模型渗透率的敏感性为：载瘤动脉WSS＞瘤体WSS＞瘤顶压力,而各参数均对惯性阻力的敏感性较低。结论 应用多孔介质模型能够通过选择不同的渗透率参数模拟不同FD金属覆盖率（metal coverage, MC）,对不同MC的FD进行建模需要调整特定的渗透率设置。     

血流导向装置与弹簧圈联合治疗巨型颅内动脉瘤的数值模拟研究现状

血管内弹簧圈(coil)栓塞治疗因创伤小、恢复快等优点成为目前普遍应用的颅内动脉瘤治疗手段。近年来血流导向装置(flow diverter,FD)作为颅内动脉瘤血管内治疗技术的重大突破,主要体现为从动脉瘤囊内填塞到载瘤动脉重塑治疗理念的转变,为巨型颅内动脉瘤的治疗带来了全新的方法。文章首先介绍了FD与弹簧圈的数值模拟方法,然后列出常见的影响动脉瘤治疗效果的形态学与血流动力学参数,详细说明了FD孔率、弹簧圈填塞率与壁面切应力对改善瘤囊内血流动力学的重要作用,最后结合FD与弹簧圈治疗颅内动脉瘤的特征,通过数值模拟的方法对比了二者的治疗效果。结果显示使用FD治疗巨型颅内动脉瘤具有一定的优越性,但更多的研究表明FD联合疏松弹簧圈栓塞治疗时,动脉瘤的延迟破裂率与复发率更低。结论进一步说明了FD与弹簧圈栓塞巨型颅内动脉瘤的发展方向。     

利用非均匀格Boltzmann方法研究支架对颅内动脉瘤血流动力学的影响

目的研究截面为不同旋转角度的三角形支架对颅内动脉瘤血流动力学的影响。方法采用非均匀格子Boltzmann方法对支架区域进行局部加细,并结合曲边界处理格式对置入支架的颅内动脉瘤进行数值模拟。通过对动脉瘤内流动形态、瘤口速度、瘤内速度减小量等动力学参量的分析,探讨不同旋转角度支架用于治疗颅内动脉瘤的效果。结果在减小瘤内血流速度方面,旋转角为180°的三角形截面支架效果最好,无旋转的三角形截面支架引起的速度减少量最小。在孔隙率较低情况下,截面为不同旋转角度的三角形支架起到效果差异较小。结论非均匀格子Boltzmann方法结合曲边界处理格式可以较准确地研究动脉瘤血流动力学特性,为支架的设计提供参考依据,并为临床介入治疗法提供一定的指导。     

利用非均匀格子Boltzmann方法研究支架对颅内动脉瘤血流动力学的影响

目的研究截面为不同旋转角度的三角形支架对颅内动脉瘤血流动力学的影响。方法采用非均匀格子Boltzmann方法对支架区域进行局部加细,并结合曲边界处理格式对置入支架的颅内动脉瘤进行数值模拟。通过对动脉瘤内流动形态、瘤口速度、瘤内速度减小量等动力学参量的分析,探讨不同旋转角度支架用于治疗颅内动脉瘤的效果。结果在减小瘤内血流速度方面,旋转角为180°的三角形截面支架效果最好,无旋转的三角形截面支架引起的速度减少量最小。在孔隙率较低情况下,截面为不同旋转角度的三角形支架起到效果差异较小。结论非均匀格子Boltzmann方法结合曲边界处理格式可以较准确地研究动脉瘤血流动力学特性,为支架的设计提供参考依据,并为临床介入治疗法提供一定的指导。     

先天性心脏病相关性肺动脉高压血流动力学特异性研究

目的先天性心脏病相关性肺动脉高压(pulmonary arterial hypertension related to congenital heart disease,PAH-CHD)是肺动脉血流动力学异常所致的一种疾病。研究肺循环血流动力学特异性,有助于了解PAH-CHD发生发展的生物力学因素。方法对5例PAH-CHD患儿和5例无PAH(Non-PAH)的先天性心脏病患儿通过临床及影像资料收集,重建三维血管模型,利用计算流体动力学模拟肺动脉血液流动,对比分析肺动脉血流动力学相关速度流线、壁面剪切力(wall shear stress,WSS)及单位体表面积平均能量损失(·E)差异。结果血流动力学相关指标显示,PAH-CHD患儿左右肺动脉分支处流速和WSS明显升高,主肺动脉处WSS明显降低,·E呈显著增加趋势且与肺动脉直径及入口流量呈明显正相关。结论 PAH-CHD患儿较Non-PAH患儿肺动脉分支处流速和WSS明显升高,主肺动脉WSS降低,·E增加,表明这些血流动力学因素与PAH-CHD密切相关,是临床评估PAH-CHD的潜在血流动力学指标。     

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。     

颅内动脉瘤夹闭手术的血流动力学数值分析

本文利用计算流体力学(CFD)方法对颅内动脉瘤夹闭手术前后血液流场进行三维数值模拟,根据血流动力学对手术方案的可行性进行预估。采用逆向工程软件Mimics对临床CT图像进行三维数字化重构,结合相关脉动血流量,模拟心动周期不同时刻的血流动力学细节。通过计算得到了模型手术前后在心动周期不同时刻的速度场、壁面剪切应力场、压力场的分布特征,对比分析手术前后分叉处的血流速度、壁面剪切应力、壁面压力变化,结果显示术后的血流速度与壁面剪切力显著提高,而壁面压强则明显降低。     

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。     

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。     

Investigation of intracranial aneurysm hemodynamics following flow diverter stent treatment

Flow diverters (FDs) are high density meshed stents designed to reduce blood flow into intra-cranial aneurysms. Though the FD is one of many intracranial aneurysm (IA) treatments, FD implantation may also result in the growth and rupture of residual aneurysms. The purpose of this research is to investigate the effect of FD implantation on IA hemodynamics. Computational fluid dynamics (CFD) was conducted to analyze dynamic and resistance forces after FD deployment. Simulation results for the successful case (patient A) showed that FD flow resistance force was higher than dynamic force. This indicated that the FD provided sufficient resistance to reduce flow into the aneurysm. As a result, flow velocity magnitude at the aneurysm neck was reduced by 95%. On the other hand, the flow velocity magnitude at the aneurysm neck was reduced by about 50% for the unsuccessful case (patient B). The reason was that the flow resistance force at the aneurysm neck section was calculated to be lower than the flow driving force. In order to completely occlude the aneurysm, a higher resistance FD stent is to be required to suppress the dynamic forces. Patient-specific hemodynamic simulations offer means of quantitative estimation FD treatment outcomes.     

Blood flow dynamics in patient-specific cerebral aneurysm models: the relationship between wall shear stress and aneurysm area index

Hemodynamics plays an important role in the progression and rupture of cerebral aneurysms. The temporal and spatial variations in wall shear stress (WSS) within the aneurysmal sac are hypothesized to be correlated with the growth and rupture of the aneurysm. The current work describes the blood flow dynamics in 34 patient-specific models of saccular aneurysms located in the region of the anterior and posterior circulation of the circle of Willis. The models were obtained from three-dimensional rotational angiography image data and blood flow dynamics was studied under a physiologically representative waveform of inflow. The three-dimensional continuity and momentum equations for unsteady laminar flow were solved with commercial software using non-structured fine grid sizes. The vortex structure, the wall pressure, and the WSS showed large variations, depending on the morphology of the artery, size of the aneurysm, and form. A correlation existed between the mean WSS on the aneurysmal sac for lateral unruptured and ruptured aneurysms with an aneurysm surface index, which is defined as the ratio between the aneurysm area and the artery area at model inlet, respectively.     

支架置入前脑动脉瘤血流场的特性分析

BACKGROUND: Cerebral aneurysm is a kind of mortal hemangioma, and its treatments such as endovascular embolization and clipping both cause high postoperative recurrence rate and mortality. So the stent implantation for cerebral aneurysm is coming into being. OBJECTTVE: To evaluate the hemodynamic parameters after stent implantation into cerebral aneurysm and to provide a novel feasible strategy for clinical treatment. METHODS: A retrospective analysis was preformed based on the CT image data of 11 patients with cerebral aneurysm from the Affiliated Hospital of Xinjiang Medical University. Firstly, the flexible and solid model of cerebral aneurysm was established by the MIMICS and reverse engineering. Secondly, the matching stent model was implanted into the cerebral aneurysm, and then the blood flow structure of cerebral aneurysm was analyzed by the fluid dynamics theory and the Fluent with the method of two-way flow solid coupling. Finally, comparative analysis of the kinetic parameters of cerebral aneurysm before and after implantation, including wall pressure, blood velocity, path line of the blood flow, wall shear stress, wall deformation was conducted, and blood flow characteristics after stent implantation were analyzed under different entrance velocity. RESULTS AND CONCLUSION: After implantation, the wall surface pressure was reduced about 61.1%; the blood flow velocity around the stent and the inside of the cerebral aneurysm was decelerated obviously; under setting 2 000 lines of blood flow, the number of path line of blood flow into the cerebral aneurysm reduced about 75.0%, the maximum wall shear stress decreased about 79.3%, and the maximum wall deformation reduced to a lower level. The entrance velocity was respectively v1=0.1 m/s, v2=0.2 m/s, v3=0.3 m/s and the wall pressure was in a gradient ascent; the wall shear stress increased with the velocity, meanwhile, τzou (left neck of aneurysm) <τzhong (aneurysm )< τyou (right neck of aneurysm). The path lines of blood flow mainly concentrated in the top of the aneurysm, and the blood velocity markedly affected the surface deformation. These results indicate that main hemodynamic parameters are obviously improved after stent implantation into cerebral aneurysm, and the blood velocity should never be neglectful in the treatment process.     

CFD modeling of blood flow following coil embolization of aneurysms

In case of coil embolization of a giant or a multilobular aneurysm, it is difficult to fill an aneurysm sac completely with coils, therefore, partial blocking of an aneurysm sac is inevitable. Blood flow characteristics, which may influence embolization process of an aneurysm, are affected by the locations of coils for partially blocked aneurysms. Blood flow fields inside an aneurysm are also influenced by the geometry of a parent vessel. In order to suggest the coil locations effective for aneurysm embolization, the blood flow fields of lateral aneurysm models were analyzed for different coil locations and parent vessel geometries. Flow rate into an aneurysm sac from a parent vessel (inflow rate) and wall shear stress were also calculated. Inflow rates were smaller and low wall shear regions were larger in the distal neck blocked model comparing to the dome blocked models. In the distal neck blocked model, inflow volume was smaller by 31% (straight parent vessel model) and 34% (curved parent vessel model) comparing to other models. The time averaged values of normalized low wall shear regions were 4% and 12% greater in the distal neck blocked models with a straight and a curved parent vessel, respectively. Since smaller inflow and low wall shear stress provide hemodynamic environment promoting thrombus embolization, distal neck should be the effective coil location for aneurysm embolization.     

Vortex Phenomena in Sidewall Aneurysm Hemodynamics: Experiment and Numerical Simulation

We carry out high-resolution laboratory experiments and numerical simulations to investigate the dynamics of unsteady vortex formation across the neck of an anatomic in vitro model of an intracranial aneurysm. A transparent acrylic replica of the aneurysm is manufactured and attached to a pulse duplicator system in the laboratory. Time-resolved three-dimensional three-component velocity measurements are obtained inside the aneurysm sac under physiologic pulsatile conditions. High-resolution numerical simulations are also carried out under conditions replicating as closely as possible those of the laboratory experiment. Comparison of the measured and computed flow fields shows very good agreement in terms of instantaneous velocity fields and three-dimensional coherent structures. Both experiments and numerical simulations show that a well-defined vortical structure is formed near the proximal neck at early systole. This vortical structure is advected by the flow across the aneurysm neck and impinges on the distal wall. The results underscore the complexity of aneurysm hemodynamics and point to the need for integrating high-resolution, time-resolved three-dimensional experimental and computational techniques. The current work emphasizes the importance of vortex formation phenomena at aneurysmal necks and reinforces the findings of previous computational work and recent clinical studies pointing to links between flow pulsatility and aneurysm growth and rupture.     

Patient-specific flow analysis of brain aneurysms at a single location: comparison of hemodynamic characteristics in small aneurysms

The purpose of this study is to examine and compare the hemodynamic characteristics of small aneurysms at the same anatomical location. Six internal carotid artery-ophthalmic artery aneurysms smaller than 10 mm were selected. Image-based computational fluid dynamics (CFD) techniques were used to simulate aneurysm hemodynamics. Flow velocity and wall shear stress (WSS) were also quantitatively compared, both in absolute value and relative value using the parent artery as a baseline. We found that flow properties were similar in ruptured and unruptured small aneurysms. However, the WSS was lower at the aneurysm site in unruptured aneurysms and higher in ruptured aneurysms (P < 0.05). Hemodynamic analyses at a single location with similar size enabled us to directly compare the hemodynamics and clinical presentation of brain aneurysms. The results suggest that the WSS in an aneurysm sac can be an important hemodynamic parameter related to the mechanism of brain aneurysm growth and rupture.     

Intraaneurysmal flow changes affected by clip location and occlusion magnitude in a lateral aneurysm model

In order to study the flow dynamic changes inside an aneurysm sac due to the partial occlusion of the aneurysm neck, velocity fields were measured using a particle image velocitimeter (PIV) in in vitro aneurysm models under the physiological flow waveform. Lateral aneurysm models arising from the curved parent vessel with different occlusion ratios and sites-e.g. no clip, 50% proximal and distal clip, and 75% proximal and distal clip-were tested. Reduced inflow and intraaneurysmal velocities may provide a better hemodynamic environment for aneurysm embolization. Comparing inflow rates and averaged intraaneurysmal velocities in the proximal and the distal clip model, they were lower in the distal clip model in cases of 50% neck occlusion, but they were lower in the proximal clip model in cases of 75% occlusion. These results suggest that clipping sites for reduced inflow and intraaneurysmal flow velocities may differ for different residual neck sizes. Less effective inflow blocking in the 75% distally clipped model may be due to the curvature of the parent artery. Therefore, not only the residual neck size and clipping site but the geometry of parent vessel significantly affect the flow fields inside the aneurysm, and subsequently the success of the aneurysm treatment.     

Quantitative Effects of Coil Packing Density on Cerebral Aneurysm Fluid Dynamics: An <Emphasis Type="Italic">In Vitro</Emphasis> Steady Flow Study

Over the past 15 years, coil embolization has emerged as an effective treatment option for cerebral aneurysms that is far less invasive than the long-standing convention of surgical clipping. However, aneurysm recurrence after coil embolization is not uncommon: recurrence rates as high as 50% have been reported in the literature. One factor that may contribute to recurrence after coiling is residual flow into the aneurysmal sac. At present, there is limited quantitative knowledge of the relationship between coil packing density and aneurysmal inflow. We present an in vitro fluid dynamic study of basilar tip aneurysm models that elucidates this relationship. At physiologically normal flow rates, we found that a packing density of 28.4% decreased aneurysmal inflow by 31.6% in a wide-neck model, and that a packing density of 36.5% decreased aneurysmal inflow by 49.6% in a narrow-neck model. Results also indicated that coiling reduced aneurysmal inflow more significantly at lower parent vessel flow rates, and that coiling reduced neck-plane velocity magnitudes more significantly for narrow-neck aneurysms. Our study provides novel quantitative information that could ultimately contribute to improved outcomes for patients with cerebral aneurysms by enabling more effective coil embolization.     

Computational hemodynamics in cerebral aneurysms: the effects of modeled versus measured boundary conditions

Modeling of flow in intracranial aneurysms (IAs) requires flow information at the model boundaries. In absence of patient-specific measurements, typical or modeled boundary conditions (BCs) are often used. This study investigates the effects of modeled versus patient-specific BCs on modeled hemodynamics within IAs. Computational fluid dynamics (CFD) models of five IAs were reconstructed from three-dimensional rotational angiography (3DRA). BCs were applied using in turn patient-specific phase-contrast-MR (pc-MR) measurements, a 1D-circulation model, and a physiologically coherent method based on local WSS at inlets. The Navier-Stokes equations were solved using the Ansys?-CFX? software. Wall shear stress (WSS), oscillatory shear index (OSI), and other hemodynamic indices were computed. Differences in the values obtained with the three methods were analyzed using boxplot diagrams. Qualitative similarities were observed in the flow fields obtained with the three approaches. The quantitative comparison showed smaller discrepancies between pc-MR and 1D-model data, than those observed between pc-MR and WSS-scaled data. Discrepancies were reduced when indices were normalized to mean hemodynamic aneurysmal data. The strong similarities observed for the three BCs models suggest that vessel and aneurysm geometry have the strongest influence on aneurysmal hemodynamics. In absence of patient-specific BCs, a distributed circulation model may represent the best option when CFD is used for large cohort studies.