人眼有限元建模与仿真的研究进展

目的:眼组织生物力学、生物热传递、电磁场分布等生理病理信息在眼部疾病诊治中有重要意义。目前的成像和测量技术难于对以上眼的生理病理变化进行量化分析,有限元建模仿真的引入为这些信息的定量分析提供了可行方案。本文对近年来人眼有限元建模与仿真的研究进展进行综述。方法:首先介绍了眼有限元建模仿真的基本方法。接下来,采取由局部到整体、从前到后的结构顺序重点对眼有限元建模仿真的研究进展进行了归类总结,讨论了这些模型构建与仿真在眼科研究中的应用。结果:分析了有限元建模与仿真在角膜、虹膜、房水、晶状体、玻璃体、视神经乳头、巩膜等局部区域生理病理研究中的应用。分析了基于整体模型对眼部生物热传递和与外力相关的眼组织受力分析的研究现状。结论:人眼建模仿真的研究深化了对眼部生理学和病理学的认识。但由于眼组织生理参数和物理属性测定困难,有限元建模与仿真的运行环境特殊,分析过程复杂,难以推广至个体化的临床实时分析。人眼建模仿真研究重要的发展趋势是:融合先进的成像技术和参数化建模技术构建精细人眼整体形态模型;在体测量物理属性;对构建的模型赋予各向异性、非线性、粘弹性等属性,使模型属性更接近眼组织真实属性;将仿真结果与合理的动物实验相结合。     

肱骨远端三维有限元模型的建立及生物力学分析

背景：采用有限元分析法进行骨与关节的生物力学分析得到了广泛应用,但是关于肱骨远端的有限元分析较少,且所建模型粗糙,方法繁琐。 目的：建立肱骨远端的三维有限元模型,并模拟不同受力状态下的应力分布及应变特征。 方法：通过对正常成年男性肘关节的多排螺旋CT扫描,获得连续断层图片,导入Mimics医学建模软件生成实体模型后,应用大型通用有限元分析软件ANSYS 10.0,进行网格划分、材料属性赋值生成有限元模型。约束边界条件,模拟肱骨远端轴向受力,得出肱骨远端有限元模型上的应力分布与应变结果。 结果与结论：建立的肱骨远端有限元模型总单元数为6 292,总节点数为10 232。肱骨远端在轴向载荷状态下的应力集中主要位于内、外侧柱区域。提示建立的有限元模型精确度高,符合肱骨远端的临床特点,较好地模拟了肱骨远端的生物力学特性。     

建立全腰椎有限元接触模型

目的 应用自编软件和HyperMesh软件并结合接触理论建立全腰椎有限元模型。方法 以正常自愿者全腰椎节段螺旋CT扫描图像的基础,利用自编软件和HyperMesh软件,生成全椎体的骨性有限元模型,补充建立终板、关节突软骨、椎间盘及韧带等结构,建立全腰椎有限元分析模型。引入接触理论处理上下关节突之间的面面接触问题。结果所建模型几何外型较真实,组织结构更完整,外观表现更细腻。生理载荷下的模拟结果与体外生物力学实验结果更加吻合。结论 利用自编软件和HyperMesh软件可以提高有限元模型建立的速度和准确度,引入接触理论可提高有限元模型的可靠性和真实性。     

足部有限元模型的构建与验证

背景：目前国内所建的足部模型大部分是采用自动划分网格的四面体有限元模型,虽然四面体网格自动剖分技术给三维实体的有限元网格自动剖分带来了极大的方便,但力学性能较差。 目的：基于CT图片构建六面体网格足部有限元模型。 方法：选取中国正常男性人体足部的CT数据,利用Mimics软件对足部几何模型进行重构,运用NURBS 曲面的节点插入算法,对足部几何模型进行了细化,构建了具有较高生物仿真度的人体足部有限元模型,利用Pam-crash软件对模型进行了碰撞仿真分析。 结果与结论：仿真结果与尸体实验结果基本一致,证明模型可信。实验基于CT图片构建的六面体网格足部有限元模型,添加了足底肌肉、肌腱、皮肤等结构,更真实的反映了足部解剖学结构特征,进而提高了有限元模型的质量,更能有效地研究足部损伤机制,从而为提高汽车安全性设计提供参考依据。     

全膝关节假体三维有限元模型的建立

背景：由于全膝关节的结构形态具有运动复杂、受力复杂等特性,造成了数据采集,模型建立困难,影响了三维实体模型的准确性。 目的：建立全膝关节假体三维有限元模型。 方法：通过Microscribe G2三维定位扫描仪取得假体数据、Geomagic软件进行曲面拟合、导入大型有限元分析软件Abaqus6.7.2建立全膝关节假体三维有限元模型,对如何提高三维有限元模型的精确性,扩大模型的开放性以及提高建模效率,增加关节外科医师在建模过程中的参与性进行探讨。 结果与结论：通过Microscribe G2三维定位扫描仪取得假体数据、Geomagic软件进行曲面拟合、导入大型有限元分析软件Abaqus6.7.2建立了全膝关节假体三维有限元模型。与以往建模方法比较,该模块设计使模型更加精准,使用更灵活,简化了有限元前期处理过程,明显降低了建模难度,提高了建模效率,增加了模型的扩展形,并获得了更高的精度。     

腰椎智能医学图像建模系统的构建及精度检验

目的　构建腰椎智能医学图像建模系统，替代分析人员完成有限元建模过程中对腰椎活动度的繁复计算工作。 方法　利用python语言构建一个附和系统，包括录制程序与回放程序。通过Geomagic的偏差分析功能评估智能建模与人工建模二者的偏差分布，并分别构建腰椎的非线性有限元模型，验证模型对有限元分析结果的影响。 结果　本课题建立智能腰椎复位系统，成功构建腰椎体的三维模型。与人工建模进行偏差分析，超过98%的区域0偏差。有限元活动度存在些许差异，经配对t检验，差异无统计学意义（P=0.2）。 结论　利用智能建模系统构建的三维腰椎模型，精确度较高且对有限元分析结果未产生影响。     

基于Simpleware全颈椎三维有限元模型的构建与分析

目的 利用Simpleware软件构建全颈椎三维有限元模型,并对模型进行验证和分析,为探讨颈椎损伤机制提供可靠模型。方法 基于CT断层扫描图像,利用医学图像处理软件Simpleware、逆向工程软件Geomagic建立C1~7全颈椎三维实体模型,导入Hypermesh进行颈椎网格划分、添加韧带并引入小关节突接触关系等,建立C1~7全颈椎有限元模型,在ANSYS中模拟前屈、后伸、侧弯和轴向旋转工况下颈椎的生物力学性能。结果 建立的模型准确可靠,在前屈、后伸、侧弯和轴向旋转时,活动范围与文献中离体实验和有限元分析结果相近。椎间盘应力集中在椎体受压侧,C4/5最易产生应力集中。结论 建立的C1~7全颈椎有限元模型能够有效模拟颈椎的生物力学特性,为后续颈椎挥鞭样损伤的生物力学研究奠定良好的基础。     

基于CT数据的人体L3-L4腰椎节段的三维有限元建模和分析

目的 建立一个精确的人体L3-L4腰椎节段有限元模型,用于腰椎生物力学的研究.方法 基于可视人计划(visible human project,VHP)男性冷冻CT数据,通过Marchingcubes算法三维重建L3和L4椎骨的几何模型并转换为有限元网格,然后结合椎间盘和韧带的网格建立L3-L4节段的有限元网格.根据CT值设定材料特性建立有限元模型,施加压缩的边界条件进行有限元分析,并和参考模型的结果比较分析.结果 基于CT的L3-L4节段有限元模型比参考模型更符合腰椎的解剖结构.结论 基于CT的L3-L4节段有限元模型能够精确的描述腰椎解剖结构,保证有限元分析的准确性.     

人体脊柱动力学数值仿真分析模型建立及验证

目的 建立T2～L5胸腰椎有限元模型并验证其有效性,为探究脊柱冲击载荷下的动态响应特性及损伤机制提供数值模型支撑。方法 基于CT扫描图像数据建立T2～L5胸腰椎三维有限元模型;仿真分析施加不同力矩下(屈伸、旋转和侧弯工况)T12～L1段载荷-转角曲线,并与文献报道的数据进行对比;对T2～6、T7～11和T12～L5 3段脊柱有限元模型施加不同高度下的自由落体载荷并进行仿真分析,获得轴向力峰值和弯矩,并与文献报道的数据进行对比分析。结果 T12～L1段脊柱有限元模型受不同方向力矩发生最大转角在-2.24°～1.55°,与文献数据吻合良好。在不同跌落高度下,T2～6、T7～11和T12～L5 3段脊柱有限元模型的轴向峰值力分别为1.7～5.3、1.3～5.5、1.3～7.5 kN,均处于文献数据误差范围内;脊柱与椎间盘应力云图显示,椎体由外缘最先受力,椎间盘由髓核承受主要载荷,符合实际脊柱损伤发生机制。结论 所建立的T2～L5脊柱模型能够正确模拟不同工况下脊柱的生物力学行为特性,分析结果具有有效性。     

青少年脊柱侧弯全脊柱生物力学模型的构建及验证

背景:现阶段脊柱侧弯患者的生物力学模型过于简化,未建立完整的患者躯干骨骼-肌肉有限元模型,并缺少软组织力学特性的建模。目的:构建一个真实且具有详细解剖学结构的脊柱侧弯躯干有限元模型,并对其有效性进行验证。方法:选择1例11岁青少年脊柱侧弯患者,通过64排螺旋CT扫描获得.Dicom格式的原始数据,建立其躯干有限元模型,并进行有效性验证,将腰骶段模型和躯干模型的模拟结果分别与已公开发表的文献中实验结果进行对比验证。研究方案的实施符合鹤壁市人民医院的相关伦理要求(医院伦理批件号YK2019015)。结果与结论:(1)模型的建立:整个躯干有限元模型包括8 470 000余个单元,1 690 000余个节点;(2)腰骶段模型验证:建立的模型在屈伸、侧屈和扭转情况下的平均刚度分别为7.15,2.56,1.92 N·m/(°),该值介于文献报道的实验结果之间,加载结果与文献中的实验值一致;(3)躯干模型的验证:在3种束带张力(20,40和60 N)作用下,脊柱的应力值变化均介于文献报道的实验结果的中间;(4)构建的1例具有详细解剖学结构的青少年脊柱侧弯躯干生物力学模型,通过生物力学模型有效性验证,...     

Finite element analysis (FEA): Applying an engineering method to functional morphology in anthropology and human biology

A fundamental research question for morphologists is how morphological variation in the skeleton relates to function. Traditional approaches have advanced our understanding of form–function relationships considerably but have limitations. Strain gauges can only record strains on a surface, and the geometry of the structure can limit where they can be bonded. Theoretical approaches, such as geometric abstractions, work well on problems with simple geometries and material properties but biological structures typically have neither of these. Finite element analysis (FEA) is a method that overcomes these problems by reducing a complex geometry into a finite number of elements with simple geometries. In addition, FEA allows strain to be modelled across the entire surface of the structure and throughout the internal structure. With advances in the processing power of computers, FEA has become more accessible and as such is becoming an increasingly popular tool to address questions about form–function relationships in development and evolution, as well as human biology generally. This paper provides an introduction to FEA including a review of the sequence of steps needed for the generation of biologically accurate finite element models that can be used for the testing of biological and functional morphology hypotheses.     

Modeling the Human Mandible Under Masticatory Loads: Which Input Variables are Important?

Finite element analyses (FEA) that have simulated masticatory loadings of the human mandible differ significantly with regard to their basic input variables such as material properties, constraints, and applied forces. With sensitivity analyses it is possible to assess how the choice of different input values and the degree of model simplification affect FEA results. However, published FEA studies are rarely accompanied by sensitivity analyses so that the robusticity of their results is impossible to assess. Here, we conduct a sensitivity analysis with an FE model of a human mandible to quantify the relative importance of several modeling decisions: (1) the material properties assigned to the cancellous bone tissue; (2) the inclusion or not of the periodontal ligament; (3) the constraints at the joints and bite point; and (4) the orientation of applied muscle forces. We study the effects of varying these properties by analysing the strain magnitudes and directions across the model surface. In addition, we perform a geometric morphometric analysis of the deformation resulting from the loading of each model. The results show that the effects of altering the different model properties can be significant and that most effects are potentially large enough to cause problems for the biological interpretation of FEA results. We therefore recommend that researchers conduct more sensitivity analyses than at present to assess the robusticity of their FEA results and their biological conclusions. Anat Rec, 2012. © 2012 Wiley Periodicals, Inc.     

人在摔倒时股骨上端承载能力的有限元分析——(I)有限元分析模型及股骨失效准则的建立

摔跤后,骨折已成为老年人最严重的损伤之一。有限元分析被证实在股骨的结构分析中是一项非常有用的工具。我们建立了股骨上端的有限元模型,并基于有关文献中关于股骨密质骨和松质骨的强度实验数据建立了Hoffm an失效准则。有限元模型和失效准则用前人的实验结果进行了验证。结果表明:预测的松质骨失效载荷仅比实验值低0.5%,而密质骨失效载荷仅比实验值高4.2%。这说明我们建立的有限元模型结合Hoffm an失效准则将很好地预测人摔倒时股骨的承载能力。     

有限元分析中软组织力学参数的设定及验证

目的提供软组织超弹性材料参数并探讨优化方法,为有限元分析(finite element analysis,FEA)冲击研究中软组织显式求解的准确模拟提供参考。方法测定6具足底软组织标本抗压性能,以实验数据计算FEA材料参数,利用泊松比对材料参数进行优化。设置与体外实验相同工况的FEA模型进行模拟。利用实验及文献报道数据对模拟结果进行验证。结果软组织体外实验中力-位移曲线呈指数增长。FEA模拟与实验结果相比,压缩率≤45%时,结果相一致;在压缩率>45%时,材料泊松比愈接近0.5,FEA模拟的准确性越高。泊松比为0.497时,FEA模拟与体外实验结果有较强线性相关关系(R2=0.9923)。结论本研究中材料参数模拟效果良好。在较低压缩率下,计算结果与体外实验的结果相一致;在较高压缩率下,提高材料泊松比可增加FEA模拟准确性。     

生物主动脉瓣膜设计中的有限元分析模型

目的 为了更好地分析生物心脏瓣膜的应力分布及闭合性能,本研究提出一种新的有限元分析模型.方法 利用点点接触将瓣膜与支架的缝合点一一对应以模拟瓣膜实际缝制过程,建立将平面设计的瓣膜缝制到支架上的模型,从而形成缝制模型.而对照模型则直接建立瓣叶的理想三维几何结构.在两种模型的瓣叶上施加一定压力,进行有限元计算,将缝制模型与对照模型的应力分布情况进行对比,同时参照实际瓣膜的闭合情况对比上述两种模型的闭合形态.结果 缝制模型最大应力集中部位为瓣叶两翼,其瓣叶倾角及闭合形态分析均较可靠.结论有限元缝制模型可以为心脏瓣膜瓣叶性能分析提供比对照模型更精确的结果,从而为瓣叶形状的设计和优化提供指导依据.     

Caring for academic ophthalmology in Croatia

Like any other area of academic medicine in Croatia, academic ophthalmology has always been limited by or has depended on the factors outside the profession itself: during the communist regime, it was mostly political and ideological correctness of academic ophthalmologists, and today during the social and economic transition, it is the lack of finances, planning, and sophisticated technology. The four university eye clinics, which are the pillars of academic ophthalmology in Croatia, provide health care to most difficult cases, educate students, residents, and specialists, and do research. On the other hand, they lack equipment, room, and financial recognition. This ever growing imbalance between requirements imposed on academic ophthalmology today and its possibilities make it less and less attractive, especially in comparison with private practice. The possible solution lies in increasing the independence of ophthalmology from pharmaceutical industry and politics, especially in research and financial aspects.     

Young's Modulus and Load Complexity: Modeling Their Effects on Proximal Femur Strain

Finite element analysis (FEA) is a powerful tool for evaluating questions of functional morphology, but the application of FEA to extant or extinct creatures is a non‐trivial task. Three categories of input data are needed to appropriately implement FEA: geometry, material properties, and boundary conditions. Geometric data are relatively easily obtained from imaging techniques, but often material properties and boundary conditions must be estimated. Here we conduct sensitivity analyses of the effect of the choice of Young's Modulus for elements representing trabecular bone and muscle loading complexity on the proximal femur using a finite element mesh of a modern human femur. We found that finite element meshes that used a Young's Modulus between 500 and 1,500 MPa best matched experimental strains. Loading scenarios that approximated the insertion sites of hip musculature produced strain patterns in the region of the greater trochanter that were different from scenarios that grouped muscle forces to the superior greater trochanter, with changes in strain values of 40% or more for 20% of elements. The femoral head, neck, and proximal shaft were less affected (e.g. approximately 50% of elements changed by 10% or less) by changes in the location of application of muscle forces. From our sensitivity analysis, we recommend the use of a Young's Modulus for the trabecular elements of 1,000 MPa for the proximal femur (range 500–1,500 MPa) and that the muscular loading complexity be dependent on whether or not strains in the greater trochanter are the focus of the analytical question. Anat Rec, 301:1189–1202, 2018. © 2018 Wiley Periodicals, Inc.     

有限元分析在腰椎手法治疗中的生物力学研究进展

中医腰椎手法在腰痛等慢性损伤性腰椎病的疼痛治疗中有明显的临床优势,但其基础研究不足是限制手法进步的重要因素。利用有限元技术能够很好地模拟各类腰椎手法的力学状况,分析其作用机制,验证假说,规范手法操作,定量、定性和优化治疗方案,为手法治疗的基础研究提供有效的研究方法。通过回顾近年腰椎手法治疗的有限元研究,探讨不同腰椎手法对椎间盘、附属结构、脊柱负荷以及椎体力学稳定性的影响,结果发现目前关于腰椎手法的有限元研究有待于对模拟方法进行标准化和精确化,同时可进一步推广有限元的研究思路,更好地指导中医腰椎手法的临床运用。     

Masticatory loadings and cranial deformation in Macaca fascicularis: a finite element analysis sensitivity study

Biomechanical analyses are commonly conducted to investigate how craniofacial form relates to function, particularly in relation to dietary adaptations. However, in the absence of corresponding muscle activation patterns, incomplete muscle data recorded experimentally for different individuals during different feeding tasks are frequently substituted. This study uses finite element analysis (FEA) to examine the sensitivity of the mechanical response of a Macaca fascicularis cranium to varying muscle activation patterns predicted via multibody dynamic analysis. Relative to the effects of varying bite location, the consequences of simulated variations in muscle activation patterns and of the inclusion/exclusion of whole muscle groups were investigated. The resulting cranial deformations were compared using two approaches; strain maps and geometric morphometric analyses. The results indicate that, with bite force magnitude controlled, the variations among the mechanical responses of the cranium to bite location far outweigh those observed as a consequence of varying muscle activations. However, zygomatic deformation was an exception, with the activation levels of superficial masseter being most influential in this regard. The anterior portion of temporalis deforms the cranial vault, but the remaining muscles have less profound effects. This study for the first time systematically quantifies the sensitivity of an FEA model of a primate skull to widely varying masticatory muscle activations and finds that, with the exception of the zygomatic arch, reasonable variants of muscle loading for a second molar bite have considerably less effect on cranial deformation and the resulting strain map than does varying molar bite point. The implication is that FEA models of biting crania will generally produce acceptable estimates of deformation under load as long as muscle activations and forces are reasonably approximated. In any one FEA study, the biological significance of the error in applied muscle forces is best judged against the magnitude of the effect that is being investigated.     

Significance of flat epithelial atypia on mammotome core needle biopsy: Should it be excised?

The aim of this study was to determine the morphologic types, associations, and significance of flat epithelial atypia (FEA) with or without atypical ductal hyperplasia (ADH) in mammotome core needle biopsies. We evaluated the correlation of FEA in core biopsies with follow-up excision biopsies to predict the likelihood of upgrade to carcinoma. We also investigated the utility of Ki-67 in predicting which lesions were associated with carcinoma in the excisional biopsies. Core biopsies with a diagnosis of atypia were categorized as pure FEA, pure ADH, or both. The following parameters were recorded: indication for core biopsies, presence of microcalcifications, inflammation, and stromal changes. A total of 60 core biopsies from 56 patients were studied. Pure ADH, pure FEA, and concomitant FEA and ADH were seen in 13%, 23%, and 64% of core biopsies, respectively. The most common architectural pattern of FEA resembled blunt duct adenosis (52%), followed by cystically dilated ducts with secretions (38%) and apocrine features (10%). Chronic inflammation and stromal changes were noted in 29% and 36% of FEA, respectively. Excisional biopsies in 48 of 56 patients demonstrated ductal carcinoma in situ and/or invasive carcinoma in 10 patients (21%), lobular carcinoma in situ or atypical lobular hyperplasia in 5 (11%), residual ADH in 11 (23%), and no atypia in 24 patients (50%). Three (21%) of 14 pure FEA upgraded to ductal carcinoma in situ and/or invasive carcinoma on excisional biopsy. The staining for Ki-67 in FEA/ADH was similar regardless of whether they were upgraded to carcinoma or not. In summary, we found a strong association between FEA and ADH, which may reflect a biologic progression. Most FEAs have a low-power appearance of a well-circumscribed group of ducts. Chronic inflammation and stromal changes are present in a subset of cases. Flat epithelial atypia shows a risk of upgrade to carcinoma similar to that of ADH and, hence, should be recognized and warrants a follow-up excision.