超声弹性成像中的逆问题求解方法

超声弹性成像通常只能得到组织在外部压缩作用下的纵向应变分布.超声弹性成像逆问题的求解,即重建组织内部的弹性模量分布,具有重要的意义.本文提出一种利用组织的应力-应变关系和基于有限元分析的迭代计算方法,从组织的纵向应变分布重建出组织的弹性模量分布.对平面应变状态下的均匀组织内含一圆形异物的模型和弹性模量连续过渡的模型分别进行了计算机仿真.结果初步验证了该方法的可行性.     

采用径向压缩的超声弹性成像逆问题求解

超声弹性成像在前列腺的应用以及血管弹性成像中,组织压缩的方向是沿径向的.本文利用极坐标下的应力-应变关系,提出一种有限元迭代的方法,进行组织弹性模量分布的重建,即弹性成像逆问题的求解.采用扇形组织模型和环形组织模型两种模型进行了计算机仿真,分别用来模拟超声弹性成像在前列腺中的应用情形和血管弹性成像的情形.仿真结果表明了该方法的可行性.     

基于磁声耦合效应的电导率图像重建研究

磁声耦合成像技术利用电磁声三物理场耦合作用的原理,通过声检测方式重建电导率存在明显变化的组织轮廓,实现恶性肿瘤的早期检测。本文建立双层同心球模型,模拟被正常组织包裹的病变组织,利用声场中的时间反转法以及电磁场方程,求解组织中的电导率分布,研究了由检测声压计算电导率分布的重建算法,并进行了仿真分析。仿真结果显示重建的电导率分布图像在电导率边界处清晰可见,进而验证了应用磁声耦合成像对电导率边界进行功能成像的可行性,为恶性肿瘤的早期检测提供了一种新的功能成像方法。     

腰背部肌筋膜疼痛综合征激痛点的剪切波弹性模量研究

目的 通过剪切波弹性成像(SWE)技术研究肌筋膜疼痛综合征激痛点的弹性特征,探索弹性超声技术在肌筋膜疼痛综合征临床诊断中的应用价值.方法 对8例女性健康志愿者的8个正常点和15例女性肌筋膜疼痛综合征患者腰背部30个激痛点行弹性超声检查,分别获得正常点、激痛点病灶区及邻近区定量分析取样框(Q-box)内弹性模量的均值(Mean)、最小值(Min)、最大值(Max)及标准差(SD);比较正常点、激痛点病灶区及临近区的弹性模量差异,探索激痛点弹性模量与患者年龄、所在部位的关系.结果 激痛点病灶区弹性模量的均值、最小值、最大值、标准差显著高于邻近区及正常点,其差异具有统计学意义(P＜0.05);而邻近区与正常点的弹性模量差异无统计学意义(P＞0.05),两个年龄组和3个不同部位激痛点的弹性模量差异亦无统计学意义(P＞0.05).结论 剪切波弹性模量值可用于激痛点病灶区与临近区及正常组织的鉴别,为激痛点的定位提供了新方法,也为肌筋膜疼痛综合征的触诊提供了新依据,具有较高的临床应用价值和研究前景.     

超声弹性成像用于高强度聚焦超声损伤的检测

采用超声弹性成像的方法检测高强度聚焦超声在动物组织内产生的损伤.结果表明,聚焦超声的损伤在应变分布图(弹性图像)上表现为应变较小的区域,即损伤部位的弹性模量较周围组织的大,组织切片的损伤范围和大小也与应变分布图的结果一致.     

血管内超声弹性成像研究进展

自1997年有学者将组织力学属性测定与血管内超声成像结合以后,血管内超声弹性成像(IVUSE)技术的发展方兴未艾.IVUSE是利用血管自身的搏动产生腔内压差,通过分析压缩前后的超声图像获取血管和斑块的应变、弹性模量等弹性参数进行成像.介绍了血管内超声弹性成像技术的成像原理,并根据成像参数的不同对IVUSE分2大类介绍其计算方法和目前进展情况,最后对此技术的发展趋势进行了展望.     

基于医学影像的血管快速提取与可视化

在计算机辅助诊断系统中,血管的提取与可视化是血管研究的重要组成部分.本研究利用八叉树实现了血管的双阈值快速分割和边界距离场的快速计算;然后建立基于边界距离场的血管组织最大生成树,并提取感兴趣血管分支的树的主干,即该分支的中心路径,最后用基于图形处理器的三维纹理体绘制方法沿着路径显示血管虚拟内窥镜,用曲面重建方法显示该血管分支的相关信息.实验结果表明八叉树能有效的提高血管分割速度,并减少边界距离场的计算时间,体绘制算法和曲面重建方法能快速的显示血管组织的详细信息,为疾病诊断提供技术支持.     

基于原子力显微镜压痕技术的大鼠小梁网组织弹性模量测定

目的 探索基于原子力显微镜(atomic force microscope,AFM)压痕技术确定大鼠小梁网组织弹性模量的方法,为揭示小梁网组织力学特性与小梁网通道房水外流阻力之间的关系等研究奠定基础.方法 首先利用大鼠眼球组织切片获取大鼠小梁网组织与毗邻组织之间的距离信息和结构信息;其次利用AFM压痕实验获取角膜-角巩膜缘-小梁网-巩膜方向的弹性模量与相对位置的关系;最后综合对比以确定小梁网组织测试区域.结果 探索了一种基于原子力显微镜压痕实验定位小梁网组织并获取该组织弹性模量的方法,利用该方法获取了大鼠眼球鼻侧、颞侧、上侧、下侧4个位置处的小梁网组织弹性模量范围为300～600 Pa.结论 本研究给出了一种基于AFM压痕技术确定大鼠小梁网组织弹性模量的方法,该方法提供了AFM测试环境下小梁网组织区域的位置参考,优势在于可快速定位到大鼠小梁网组织区域.     

发射端频率复合弹性成像的仿真研究

目的 目前,有关频率复合技术能否提高弹性成像的信噪比以及对弹性图像性能的影响尚无文献报道,本研究对发射端频率复合技术应用于弹性成像进行了仿真研究.方法 仿真一50 mm×50 mm含2个圆形硬包容物的组织,2包容物直径均为10 mm且均匀分布在组织中轴线上,其弹性模量均为背景组织的10倍;然后仿真使用3.5,5,7.5 MHz频率探头对该组织区域分别进行准静态压缩弹性成像（组织压缩量为1%）;最后将3.5 MHz和5 MHz,3.5 MHz和7.5 MHz,3.5 MHz、5 MHz和7.5 MHz频率子图像分别进行复合.结果 复合前各子弹性图像的信噪比（SNRe）分别为8.42、9.62、10.73,对比度噪声比（CNRe）为11.35、14.82、18.37,轴向分辨率为9.83、9.82、9.81;复合后图像的信噪比分别为11.82、13.05、19.45,对比度噪声比为22.31、27.63、56.12,轴向分辨率为9.83、9.83、9.83.结论 复合后的图像比复合前各频率子图像的信噪比、对比度噪声比均有明显提高,轴向分辨率几乎没有损失;使用频率复合技术能有效改善弹性图像的性能,证实了发射端频率复合弹性成像技术的可行性.     

交联剂对脱细胞膀胱基质生物力学性能的影响

目的 研究不同交联剂对猪脱细胞膀胱基质的组织结构影响,并比较其生物力学性能,为盆底修复替代材料的选择提供依据.方法 采用表面活性剂+酶消化法去除新鲜猪膀胱的细胞成分,将脱细胞膀胱基质随机分为3组,A组经0.25％戊二醛交联,B组经0.625％京尼平交联,C组未交联.对各组材料进行HE染色,观察纤维的变化情况.使用生物力学性能测试系统检测抗拉强度、断裂伸长率、弹性模量,并进行统计学分析.结果 京尼平交联脱细胞膀胱基质后呈深蓝色,保持了天然组织构架的完整,纤维更加致密.戊二醛交联脱细胞膀胱基质后呈浅黄色,纤维排列紊乱且有断裂.新鲜猪膀胱经上述三种方法处理后,其弹性模量增大、断裂伸长率减小,而其中京尼平交联处理的脱细胞膀胱基质力学性能与新鲜膀胱组织更为相近.结论 京尼平交联的脱细胞膀胱基质组织结构的形态佳,同时较大限度地保留膀胱组织的力学性能,可能是较理想的盆底重建材料.     

Evaluation of an iterative reconstruction method for quantitative elastography

This paper describes an inverse reconstruction technique based on a modified Newton Raphson iterative scheme and the finite element method, which has been developed for computing the spatial distribution of Young's modulus from within soft tissues. Computer simulations were conducted to determine the relative merits of reconstructing tissue elasticity using knowledge of (a) known displacement boundary conditions (DBC), and (b) known stress boundary conditions (SBC). The results demonstrated that computing Young's modulus using knowledge of SBC allows accurate quantification of Young's modulus. However, the quality of the images produced using this reconstruction approach was dependent on the Young's modulus distribution assumed at the start of the reconstruction procedure. Computing Young's modulus from known DBC provided relative estimates of tissue elasticity which, despite the disadvantage of not being able to accurately quantify Young's modulus, formed images that were generally superior in quality to those produced using the known SBC, and were not affected by the trial solution. The results of preliminary experiments on phantoms demonstrated that this reconstruction technique is capable in practice of improving the fidelity of tissue elasticity images, reducing the artefacts otherwise present in strain images, and recovering Young's modulus images that possess excellent spatial and contrast resolution.     

组织工程修复关节软骨缺损的力学状态研究

背景：力学状态对软骨的正常生理有重要影响,若应力集中过大将造成人工软骨退变和原宿主软骨退化,影响治疗效果。目前的各种力学手段很难实现活体软骨力学状态测量,而有限元动态分析能有效地模拟修补后软骨的受力情况。 目的：通过有限元仿真研究组织工程修复膝关节软骨缺损后人工软骨和宿主软骨的力学状态。 方法：以人体膝关节软骨受滚压部分为研究对象,建立滚动运动下关节软骨的有限元模型。根据行走过程中股骨与胫骨间的滚压边界条件,对软骨在取不同弹性模量、不同压缩量、不同载荷速度及不同缺损大小的情况进行了滚压受力分析。 结果与结论：在滚压载荷下,植入人工软骨弹性模量和软骨压缩量的不同都使人工软骨和宿主软骨受到的Mises应力值变化,二者对修复缺损处软骨Mises应力分布的影响比较明显,是临床治疗软骨缺损和术后康复阶段值得注意的因素。模拟中使用的载荷速度和缺损大小对软骨应力值的影响不明显。当人工软骨弹性模量取某个值时,人工软骨和宿主软骨的Mises应力差别可以达到很小值,二者趋于吻合。应力差别还和个体宿主软骨的力学性能有关,据此,应针对不同病例选择最佳弹性模量的人工软骨植入。     

Shear modulus reconstruction in dynamic elastography: time harmonic case

This paper presents a direct inversion approach for reconstructing the elastic shear modulus in soft tissue from dynamic measurements of the interior displacement field during time harmonic excitation. The tissue is assumed to obey the equations of nearly incompressible, linear, isotropic elasto-dynamics in harmonic motion. A finite element discretization of the governing equations is used as a basis, and a procedure is outlined to eliminate the need for boundary conditions in the inverse problem. The hydrostatic stress (pressure) is also reconstructed in the process, and the effect of neglecting this term in the governing equations, which is common practice, is considered. The approach does not require iterations and can be performed on sub-regions of the domain resulting in a computationally efficient method. A sensitivity study is performed to investigate the detectability of abnormal regions of different size and shear modulus contrast from the background. The algorithm is tested on simulated data on a two-dimensional domain, where the data are generated on a very fine mesh to get a near exact solution, then downsampled to a coarser mesh that is similar to the spatial discretization of actual data, and noise is added. Results showing the effect of the hydrostatic stress term and noise are presented. A reconstruction using MR measured experimental data involving a tissue-mimicking phantom is also shown to demonstrate the algorithm.     

Microindentation test for assessing the mechanical properties of cartilaginous tissues

Mechanical properties of the fresh control, frozen, and vitrified cartilaginous (cartilage and meniscus) samples were measured by microindentation. Indentation depth, elastic modulus, and indentation yield strength were obtained from the microindentation loading curves. Indentation deformation behavior was studied using Hertz contact model. The stress distribution of cartilaginous tissues under indentation loading was analyzed by finite element technique. It was found that fresh tissue shows the lowest indentation depth and the highest elastic modulus and indentation yield strength, followed by vitrified and frozen tissues. The vitrified tissue shows slightly lower but comparable mechanical properties with control tissue. The vitrification technique used in this study can preserve live cells with superior mechanical properties that make it an ideal technique for use in orthopedic and other biomedical applications. The microindentation tests and corresponding analysis methods used in this study offer a simple way to evaluate the mechanical properties of cartilaginous tissues. It suits small sample sizes and it may be used for other biological tissues.     

Development of a mechanical testing assay for fibrotic murine liver

In this article, a novel protocol for mechanical testing, combined with finite element modeling, is presented that allows the determination of the elastic modulus of normal and fibrotic murine livers and is compared to an independent mechanical testing method. The novel protocol employs suspending a portion of murine liver tissue in a cylindrical polyacrylamide gel, imaging with a microCT, conducting mechanical testing, and concluding with a mechanical property determination via a finite element method analysis. More specifically, the finite element model is built from the computerized tomography (CT) images, and boundary conditions are imposed in order to simulate the mechanical testing conditions. The resulting model surface stress is compared to that obtained during mechanical testing, which subsequently allows for direct evaluation of the liver modulus. The second comparison method involves a mechanical indentation test performed on a remaining liver lobe for comparison. In addition, this lobe is used for histological analysis to determine relationships between elasticity measurements and tissue health. This complete system was used to study 14 fibrotic livers displaying advanced fibrosis (injections with irritant), three control livers (injections without irritant), and three normal livers (no injections). The moduli evaluations for nondiseased livers were estimated as 0.62 +/- 0.09 kPa and 0.59 +/- 0.1 kPa for indenter and model-gel-tissue (MGT) assay tests, respectively. Moduli estimates for diseased liver ranged from 0.6-1.64 kPa and 0.96-1.88 kPa for indenter and MGT assay tests, respectively. The MGT modulus, though not equivalent to the modulus determined by indentation, demonstrates a high correlation, thus indicating a relationship between the two testing methods. The results also showed a clear difference between nondiseased and diseased livers. The developed MGT assay system is quite compact and could easily be utilized for controlled evaluation of soft-tissue moduli as shown here. In addition, future work will add the correlative method of elastography such that direct controlled validation of measurement on tissue can be determined.     

The influence of the bone-implant interface stiffness on stress profiles surrounding Al2O3 and carbon dental implants

Dental implants have been used and studied for the replacement of missing teeth for many years. Finite element stress analysis (FESA) has previously been used in their evaluation to study the effect of various design parameters on induced stresses. A twodimensional FESA was used to evaluate the effect that the implant-bone interface elastic modulus has on the stress distribution around LTI carbon and aluminum oxide dental implants. The results of this investigation indicate that a soft tissue interface between implants and bone negates the effect of implant elastic modulus and results in stress profiles that were almost identical for the LTI carbon and aluminum oxide implants. This research was supported by NIH Grants DE 04653, DE 0041, and AM 0022, and VA Grant V629P-713.     

Stress analysis between implant prostheses with different moduli and surrounding bones北大核心

背景:应力遮挡效应会导致植入假体修复骨缺损手术失败,其主要原因是由于植入假体的弹性模量大于骨组织弹性模量。目的:分析植入假体弹性模量对应力分布的影响,寻求消除应力遮挡现象的方法。方法:通过CT扫描的方式获取实验犬与人体骨组织的模型,分别对其优化后进行梯度赋值,建立较为可靠的骨骼力学模型,并与植入假体组合后进行有限元仿真。首先,通过对比格犬骨骼模型和人体骨骼模型及其对应的植入假体进行有限元仿真,模拟了不同弹性模量对植入假体修复术后的应力和位移分布情况;其次,分析了较小弹性模量差仍会形成应力遮挡现象的原因,建立了骨骼模型及植入假体模型,确立了材料属性赋予方法;最后,验证了该模型及材料属性赋予方法的可行性,并通过随机选取受力点的方式,定量分析植入假体弹性模量与骨骼弹性模量之间的关系对应力遮挡形成的影响。结果与结论:通过梯度赋值法建立与骨骼力学性质更加接近的实验犬骨骼模型和人体骨骼模型,该方法重建的力学模型与真实骨骼的力学性质更为接近;通过有限元仿真力学测试证明,不同弹性模量植入假体对假体本身与周围骨骼间相对位移的影响较小;另外量化弹性模量对假体植入骨骼后对应力分布的影响,可为后续的相关研究提供帮助。     

鼻腔结构矫正手术对OSAHS患者上气道流场影响的数值分析

目的研究伴鼻腔结构异常的OSAHS患者经鼻腔结构矫正手术后,气道结构形态的改变对患者整个上气道流场分布以及软腭运动姿态的影响。方法基于患者手术前后CT影像学数据,建立上气道及软腭三维有限元模型,采用流固耦合的方法模拟手术前后上气道流场特性及软腭的运动情况。结果手术矫正了异常的鼻腔结构形态,鼻腔及整个上气道阻力明显下降。术后软腭的肥厚水肿明显缓解,其游离缘的运动幅度减小。软腭运动幅度随弹性模量的减小而增大。术后的模拟结果与文献报道的正常人实验与模拟结果接近。结论鼻腔结构矫正手术改变了上气道结构,影响了气流流场的分布和软腭的运动姿态;不同病理生理状态下,软腭弹性模量的变化对其运动姿态有影响。     

基于神经网络法反求耳结构弹性模量

目的通过耳结构的位移反算耳结构弹性模量。方法基于Patran软件建立耳结构有限元模型,使用Mat-lab建立计算耳结构反问题的BP神经网络。对耳结构有限元模型进行频率响应分析,得到鼓膜凸和镫骨足板的位移响应;把位移作为BP神经网络的输入、相对应的结构弹性模量作为输出,对网络进行训练。结果利用训练成熟的BP网络反算出耳结构的弹性模量,相对误差非常小。结论反算结果表明,所使用的反问题方法求解耳结构弹性模量是可行的,可为临床提供确定生物结构力学参数简捷有效的方法。