应用于头部损伤生物力学研究的三维有限元模型发展概况

在交通事故中,头部损伤因其高发率和高致命率成为最严重的损伤.为了研究头部损伤,出现了一系列诸如物理试验、动物试验及尸体试验等研究方法.近年来,随着计算生物力学的发展,人体头部的有限元模型逐渐成为研究头部损伤生物力学的重要工具,文中就头部有限元模型的发展过程及最新进展进行了较为全面的综述,并探讨了该领域未来需要研究的问题.     

基于有限元模型的人体头部尺寸对颅内响应影响的探讨

本研究借助第5和第95百分位中国人头部有限元模型,通过对比小尺寸头部和大尺寸头部在相同载荷下的加速度、颅内压力和剪应力,来说明头部尺寸对其生物力学响应存在着较大的影响。在此基础上,本研究还进一步通过将大尺寸模型换算到小尺寸,将小尺寸模型换算到大尺寸,探讨了尺寸缩放方法在用于考虑头部尺寸的生物力学研究中的合理性。研究结果表明现有的采用相同头部损伤准则(HIC)值评估不同尺寸头部损伤有一定的局限性,并为更加科学地评判不同尺寸头部损伤提供了新的理论依据。     

头部钝器损伤实验与仿真分析

目的　为了研究头部在钝器作用下的生物力学响应及损伤机理。 方法　利用CT图像数据和MRI图像数据对头部骨骼与内部软组织进行几何重建,然后画分网格,构建颅脑有限元模型。另一方面,对连于躯干的头部标本进行10 m/s的低速冲击,测试冲击部位接触力、顶部应变及冲击的对侧（枕部）加速度。把构建的有限元模型导入MADYMO软件进行相同条件下模拟仿真,从输出模块里输出相应部位的结果。 结果　仿真结果表明模型的头部接触力、顶部应变、对撞侧加速度与头部标本冲击实验测得值能较好吻合。 结论　建立的头部有限元模型及采用的仿真方法可满足头部钝器损伤的仿真研究需要。     

基于有限元法的人类头部损伤生物力学的模拟分析

根据正常头部螺旋CT扫描影像，通过对CT扫描影像的图像处理，利用计算机辅助工程技术，采用单元网格划分和三维重构技术，开发、建立了三维的人类头部有限元计算模型。应用本模型模拟颅脑在直接碰撞中的生物力学问题。计算模型比较真实地反映了头颅实际碰撞实验中的物理反应，比较忠实地再现了某些实验的结果，如头部撞击合力和脑压力/强等。同时，脑压力，强的分布再次证实了经典的撞击压-对撞压产生理论。本研究的计算模型可为进一步的头部损伤生物力学研究提供一种新的工具。     

6岁儿童头部有限元模型的构建与验证

借助6岁儿童医用头部CT扫描图片,通过图像分析处理,提取几何参数,重构生成三维几何模型。对几何模型进行有限元前处理,构建了一个6岁儿童头部有限元模型。模型中包含颅骨、骨缝、脑脊液、大脑、小脑、脑干、脑室等各个器官,共有44 886个节点,11 675个壳单元,37 482个六面体单元。.各器官材料属性采用来自参考文献的数据。仿真分析计算中,力加载时窗为11 ms时,模型的CPU计算时长低于1 h。采用Nahum尸体实验数据与仿真结果进行对比。仿真分析结果显示:成人头部撞击时撞击压与对撞压的形成规律同样适用于儿童头部碰撞。在7 900 N力作用下,尸体头部撞击侧最大压应力为140 kPa,对撞侧最大压应力为-60 kPa,而儿童头部的值分别为220.2 kPa和-135.2 kPa;在HIC值均为775的作用下,成人头部撞击侧和对撞侧最大压应力分别为140 kPa和-60 kPa,而儿童头部的值分别为160 kPa和-89 kPa。这表明,在相同作用力或HIC值下与成人相比,儿童头部更容易受到损伤。     

6岁儿童行人-汽车碰撞中碰撞角度对头部损伤的影响

目的应用符合欧洲新车安全评鉴协会(the European New Car Assessment Programme,Euro NCAP)要求的6岁儿童行人有限元模型,探究不同碰撞角度对儿童头部损伤的影响。方法应用符合Euro NCAP技术公告(TB024)并且具有详细解剖学结构的6岁儿童行人有限元模型,设置4组行人-汽车碰撞仿真试验,探究不同碰撞角度下儿童头部损伤情况。人体头部质心初始位置在车的纵向中心线上,轿车初速度为40 km/h,轿车分别与人体右侧、前侧、左侧、后侧碰撞(即0°、90°、180°、270°)。比较不同碰撞角度下运动学差异和头部碰撞响应,同时分析面骨和颅骨的损伤情况。结果通过分析儿童行人头部接触力、头部质心合加速度、头部质心相对于车的合速度、头部损伤标准(head injury criterion,HIC_(15))、面骨骨折情况以及颅骨应力分布发现,背面、正面碰撞下儿童头部骨折及发生脑组织损伤的风险大于侧面碰撞,其中背面碰撞下儿童行人头部损伤风险最高,侧面碰撞下儿童行人头部损伤风险最低。结论背面碰撞下儿童行人头部损伤风险最大,研究结果对行人-汽车碰撞评估和防护装置研发具有重要的应用价值。     

建立人体头颈动力学有限元模型和验证

目的建立符合解剖结构的头颈三维动力学有限元模型,研究冲击力作用下头颈部动力学响应。方法采用中国成年男性志愿者颈部CT扫描图像,获取颈椎三维点云数据,通过有限元前处理软件ICEM-CFD和Hyper Mesh建立颈部有限元模型。模型包括椎骨、椎间盘、小关节、韧带和软骨等组织,结合已建立并验证的头部有限元模型,装配成具有详细解剖结构的人体头颈部有限元模型。结果模型参考公开发表的头颈部轴向冲击实验数据进行验证,其颈部变形、头部加速度、接触力曲线以及损伤部位与实验数据吻合较好。结论动力学三维有限元模型可用于汽车安全、运动学损伤等领域人体头颈部的动态响应和损伤机制研究。     

儿童头部有限元模型研究进展

头部损伤是导致儿童死亡与伤残的重要原因,对儿童头部损伤生物力学的深入研究意义重大。近年来,通过构建真实的儿童头部有限元模型来研究儿童头部损伤的方法日益成熟,逐步代替了尸体实验、动物实验以及物理实验。对儿童头部有限元模型的年龄特点、构建方法、模型应用以及发展趋势等进行较为全面的综述,并对该领域还有待研究的内容以及未来的发展方向做出展望。     

碳素纤维床CT值对头部肿瘤放疗计划剂量分布的影响

目的:定量分析碳素纤维床CT值对头部肿瘤放疗计划剂量分布的影响。方法:在Varian Eclipse 13.6计划系统中建立9种不同CT值的碳素纤维床和均匀圆柱水模体模型,并将圆柱水模体放置于碳素纤维床中间,在10 cm[×]10 cm射野下,采用6 MV X射线机架在0°~180°之间以10°为间隔行等中心照射,计算不同CT值的碳素纤维床的吸收剂量差异系数。选取头部肿瘤患者15例,以Eclipse计划系统提供的默认CT值碳素纤维床为基础,设计放疗计划,并将该计划保存为模板计划。随后将模板计划移植至其余8种不同CT值的碳素纤维床图像中,不进行通量优化,重新计算剂量分布。记录9种不同CT值碳素纤维床计划的D2%、D50%、D98%、CI、HI以及GI。结果:在-700 HU至-300 HU内,随着Panel Surface CT值的增加,吸收剂量差异系数逐渐减小;在-1 000 HU至-900 HU内,随着Panel Interior CT值的增加,吸收剂量差异系数逐渐增大。默认CT值的碳素纤维床计划与其他8种碳素纤维床计划的D2%、D50%、D98%,以及GI差异具有统计意义（P<0.05）,而HI则无统计学差异（P>0.05）。结论:物理师在设计放疗计划时,应根据实测治疗床的CT值构建碳素纤维床模型。     

跳伞着陆过程中膝关节损伤的有限元研究

目的利用膝关节有限元模型和模拟跳伞着陆实验数据,对半蹲式跳伞着陆过程进行数值模拟,并分析膝关节损伤的机理。方法对16名健康志愿者进行半蹲式模拟跳伞实验,跳落高度分别为0.32m,0.52m和0.72m。基于核磁共振成像建立人体膝关节的三维有限元模型,采用实验测得的膝关节运动学和地面反力数据对跳伞着陆过程进行数值模拟。结果关节内组织的应力水平随着跳落高度的增加而增加,外侧半月板和关节软骨承受了较大的载荷,前交叉韧带和内侧副韧带在屈膝角度达到最大时产生明显的应力集中。结论跳伞着陆的高速冲击是造成关节损伤的直接原因,外侧关节软骨和半月板更易受到损伤,前交叉韧带和内侧副韧带较易在屈膝幅度最大时发生撕裂。     

自适应有限元真实头模型的构造研究

有限元真实头模型在脑电计算领域中起到了重要的作用。本文提出了一种根据MRI图像构造自适应有限元真实头模型的方法,针对引起误差的关键部分自动进行细化,提高了建模的效率。本文给出了根据实际MRI图像生成的一个真实头有限元模型,并且分析了自适应细化前后的效果。     

Importance of partitioning membranes of the brain and the influence of the neck in head injury modelling

A head injury model consisting of the skull, the CSF, the brain and its partitioning membranes and the neck region is simulated by considering its near actual geometry. Three-dimensional finite-element analysis is carried out to investigate the influence of the partitioning membranes of the brain and the neck in head injury analysis through free-vibration analysis and transient analysis. In free-vibration analysis, the first five modal frequencies are calculated, and in transient analysis intracranial pressure and maximum shear stress in the brain are determined for a given occipital impact load.     

Effects of head size and morphology on dynamic responses to impact loading

Head responses subjected to impact loading are studied using the finite element method. The dynamic responses of the stress, strain, strain energy density and the intracranial pressure govern the intracranial tissues and skull material failures, and therefore, the traumatic injuries. The objectivity and consistency of the prevailing head traumatic injury criteria, i.e., the energy absorption, the gravity centre acceleration and the head injury criterion (HIC), are examined with regard to the head dynamic responses. In particular, the structural intensity (STI) (the vector representation of energy flow rate) is calculated and discussed. From the simulations, the STI, instead of the gravity centre acceleration, the HIC and the energy absorption criteria, is found to be consistent with the dynamic response quantities. The different local skull curvatures at impact have a marginal effect whereas the locations of the impact loadings have significant effects on the dynamics responses or the head injury. The STI also shows the failure patterns.     

急性颅脑损伤患者血清SICAM-1和CRP检测的临床意义

目的:探讨了急性颅脑损伤患者血清细胞间粘附分子-1(SICAM-1)和C反应蛋白(CRP)水平及其临床意义。方法:应用ELISA法和免疫法对33例急性颅脑损伤患者进行了血清SICAM-1和CRP水平检测,并与35名正常健康人作比较。结果:急性颅脑损伤患者血清中SICAM-1和CRP水平非常显著地高于正常人组(P<0.01),尤以重型组为甚。结论:测定急性颅脑损伤患者血清中SICAM-1和CRP水平对了解病情,并有助于预后判断。     

颅脑有限元模型的研究进展及应用

有限元法(finite element method,FEM)是随着电子计算机的发展而迅速发展起来的一种数值分析方法,同时也是一种比较先进的生物力学研究方法。FEM早期应用于工程科学技术领域,近几年来,生物医学工程领域已经广泛应用FEM进行脑方面的研究。随着交通、运输业的发展,颅脑损伤发生的概率越来越高,严重威胁着人类的身体健康。通过建立颅脑有限元模型,可以很好地研究颅脑损伤的生物力学机制。总结颅脑有限元模型的建立、发展和应用,并对未来的研究方向进行展望。     

Biomechanics of Traumatic Brain Injury: Influences of the Morphologic Heterogeneities of the Cerebral Cortex

Traumatic brain injury (TBI) can be caused by accidents and often leads to permanent health issues or even death. Brain injury criteria are used for assessing the probability of TBI, if a certain mechanical load is applied. The currently used injury criteria in the automotive industry are based on global head kinematics. New methods, based on finite element modeling, use brain injury criteria at lower scale levels, e.g., tissue-based injury criteria. However, most current computational head models lack the anatomical details of the cerebrum. To investigate the influence of the morphologic heterogeneities of the cerebral cortex, a numerical model of a representative part of the cerebral cortex with a detailed geometry has been developed. Several different geometries containing gyri and sulci have been developed for this model. Also, a homogeneous geometry has been made to analyze the relative importance of the heterogeneities. The loading conditions are based on a computational head model simulation. The results of this model indicate that the heterogeneities have an influence on the equivalent stress. The maximum equivalent stress in the heterogeneous models is increased by a factor of about 1.3–1.9 with respect to the homogeneous model, whereas the mean equivalent stress is increased by at most 10%. This implies that tissue-based injury criteria may not be accurately applied to most computational head models used nowadays, which do not account for sulci and gyri.     

Finite-element models of the human head

A review is presented of the existing finite-element (FE) models for the biomechanics of human head injury. Finite element analysis can be an important tool in describing the injury biomechanics of the human head. Complex geometric and material properties pose challenges to FE modelling. Various assumptions and simplifications are made in model development that require experimental validation. More recent models incorporate anatomic details with higher precision. The cervical vertebral column and spinal cord are included. Model results have been more qualitative than quantitative owing to the lack of adequate experimental validation. Advances include transient stress distribution in the brain tissue, frequency responses, effects of boundary conditions, pressure release mechanism of the foramen magnum and the spinal cord, verification of rotation and cavitation theories of brain injury, and protective effects of helmets. These theoretical results provide a basic understanding of the internal biomechanical responses of the head under various dynamic loading conditions. Basic experimental research is still needed to determine more accurate material properties and injury tolerance criteria, so that FE models can fully exercise their analytical and predictive power for the study and prevention of human head injury.     

A planar finite element model of bolus containment in the oral cavity

As individuals age, one of the objective changes that occurs in the oropharyngeal swallow is the development of a delay between bolus entry into the pharynx and the initiation of airway protection mechanisms. For longer delays, this phenomenon is sometimes referred to as "premature spillage," and it has been suggested that such spillage, which is a risk factor for dysphagia, may be associated with pre-swallow lingual gestures, or "tongue pumping." The goal of the current study was to develop a simplified two-dimensional computational model of the oropharynx to simulate the containment of a Newtonian fluid bolus within the oral cavity in response to a given pattern of lingual gestures for different viscosities. An arbitrary Lagrangian-Eulerian simulation was performed using the commercial finite element software package, LS-Dyna. It was found that for a given lingual motion, higher viscosity Newtonian boluses, consistent with those offered therapeutically, were able to be contained within the simulated oral cavity while a lower viscosity bolus would be "spilled," suggesting a potential mechanisim by which thickened liquids may reduce aspiration. Although the current data must be validated with more realistic, three-dimensional geometric information and for a wider range of bolus rheologies, they represent an exciting first step towards realistic modeling of oropharyngeal bolus flow.