作者想感谢梅奥诊所的材料和结构测试核心, 他们在进行骨折测试时的技术支持。此外, 我们还要感谢拉梅什 Raghupathy 和 Ian Gerstel 在梅奥诊所任职期间协助编写 dic 方案的剧本和具体细节, 以及明尼苏达大学的维克多 Barocas 研究小组底层开源软件, 它执行数字图像相关应变计算的核心11。这项研究由 Grainger 基金会的 Grainger 创新基金资助。

所有实验都是通过机构审查委员会的批准进行的。这些样本是从解剖学研究实验室合作获得的. 
 1. 准备用于测试的标本 <ol> <li> 在 RT 中解冻股骨 24 h. </li>
	<li> 当股骨在队列中进行测试时, 取出在冻结前应用的任何包装, 用干毛巾擦拭股骨, 去除残余水分、脂肪堆积或软组织。将较大的大转子放入一个带有骨水泥的预制铝杯中. </li>
	<li> 用一个盒子尽可能多地容纳微粒, 用白色的塑料底漆喷涂骨头, 以达到一种薄而均匀的涂层。注意用一层均匀的油漆覆盖骨, 以获得最佳的对比度, 并与股骨表面有很强的附着力. 
	注意: 未测量厚度. </li>
	<li> 让油漆干燥至少5分钟。这是很重要的, 以避免与斑点滴的意外混合2节. </li>
	<li> 用湿布包裹骨头以避免组织干燥. </li>
</ol> 2。斑点进程 <ol> <li> 近似地, 将1部分水添加到2部分的油漆中, 以便在骨骼上进行最佳斑点。将水逐渐 (为更好的混合物) 添加到丙烯酸漆中使其成为黑色. </li>
	<li> 在黑色颜料的调色板上蘸一把干净的牙刷, 以吸收颜色并轻拂画笔, 使白色涂层上的黑色斑点. </li>
	<li> 让油漆干5分钟, 然后再继续. </li>
</ol> 3。图像采集 <ol> <li> 在机械试验机上插入准备好的有斑点的股骨, 方法是将远端装入夹具, 并拧紧两个螺钉以固定试样. </li>
	<li> 调整两个高强度放电光反射器, 使股骨表面达到尽可能高的光照, 同时避免相机图像中的反射。请在3节中快速执行以下步骤, 以避免在测试之前对样品进行不必要的加热. </li>
	<li> 减少前、后视图的光圈高速摄像机镜头, 使整个区域的股骨在视野中的兴趣集中. </li>
	<li> 调整光线反射器以进一步改善光照, 同时减少眩光. </li>
	<li> 将图像采集软件设置为捕获6000帧/秒和 #160; 分辨率为 1024年 x 512 像素。设置接收到12288的触发信号后要获取的帧总数。当从测试系统接收到触发信号时, Arm 高速视频软件用于图像采集。测试完成后, 视频驻留在照相机和 #39 的缓冲区内存中. </li>
	<li> 使用图像采集软件, 通过指定所需的路径和文件名并单击和 #34, 将视频保存到磁盘中; 保存和 #34;。准备在 5-40 分钟之间等待此过程的完成, 这取决于要保存的帧数. </li>
</ol> 4。图像准备 <ol> <li> 为股骨的正面和背面视图创建单独的工作目录 </li>
	<li> 使用视频分析软件打开适当的高速视频录制, 并记下关键帧参考号码在 1) 开始 加载帧执行器移动, 和 2) 在 断开事件后立即帧 . </li>
	<li> 要从高速视频缩减未压缩的 TIFF 图像序列, 请打开并运行 #34; mov_frames. #34; 在相关的股骨侧的工作目录中编写脚本. 
	<ol> <li> 在结果对话框中, 输入步骤4.2 中标识的结束帧编号, 步骤大小为 25-40。单击并 #34; 提取帧和 #34; 检查工作目录以确保正确提取了 tiff 文件. </li>
	</ol> </li> </ol> 5。有限元网格创建 <ol> <li> 使用外部有限元啮合程序创建有限元网格。用有限元法计算了差分位移矢量的2D 应变。将初始提取的 *. tiff 图像导入有限元软件预处理作为样条创建的模板. </li>
	<li> 查找两个容易识别位于帧的相反角的图像中的信讬点, 并记录它们的 X 和 Y 坐标 (这些将最终用于步骤 6.1)。根据有限元软件用于导入 *. tiff 图像的约定, 这些坐标是任意的。这些点的坐标将用于在步骤6.2 中将有限元网格的节点与视频图像的相应像素进行注册. </li>
	<li> 在图像编辑软件中, 打开导入到有限元软件预处理器中的同一图像, 并记录与步骤5.2 中标识的点相关联的像素的 X 和 Y 方向值。这些最终将在步骤6.1 中使用. </li>
	<li> 在 #34; 草图和 #34; 有限元啮合程序的模块, 使用样条工具勾勒出表示感兴趣区域的闭合剖面。验证区域是不是太大, 这样, 骨骼的表面会在骨折前由于旋转而移动到区域之外. </li>
	<li> 准备在步骤5.4 中创建的闭合截面, 通过在菜单和 #34 下播种全局网格大小为 1 mm 的边缘进行啮合; 种子部件实例和 #34;. </li>
	<li> 下 #34; 分配网格控件和 #34;, 将元素形状设置为四边形. </li>
	<li> 将已关闭的分区网格. </li>
	<li> 将网格导出为由节点坐标和元素定义组成的网格数据库的 ASCII 文件. </li>
	<li> 在文本编辑器中打开所生成的有限元素输入文件, 将包含节点编号的节点块复制到一个新的文本文件中, 并将其另存为和 #34; nodes.txt 和 #34;。重复执行元素块并将新的文本文件保存为和 #34; elements.txt 和 #34;. </li>
</ol> 6。将 FE 网格与高速视频图像进行注册, 并进行数字图像相关分析 <ol> <li> 在新会话内, 创建2元素行向量, 称为 ab1 和 ab2 , 并使用步骤5.2 中标识的值. px1 和 px2步骤5.3 中标识的值, 方法是在命令行上键入这些向量名称。将工作区保存为和 #34;p oints #34;... </li>
	<li> 运行脚本和 #34; convert_imagesize #34; 用提取的高速视频图像对有限元网格中的点进行注册. </li>
	<li> 运行脚本和 #34; rrImageTrackGui #34;。加载第一个图像 (和 #34;p 01.tif 和 #34;) 并输入作为要处理的图像总数提取的最后一个. tiff 文件的编号. </li>
	<li> 加载在步骤5.7 中创建的网格, 方法是确保将网格选项设置为 #34; 从文件和 #34 中读取; 然后单击并 #34; 接受和 #34;。有限元网格应出现在骨骼图像上. </li>
	<li> 根据跟踪参数的下列准则指定跟踪值, 并单击和 #34;P roceed 和 #34; (请记住, 参数值是图像大小、纹理和变形量, 需要进行测试仔细的个案基础上). 
	<ol> <li> 使用起始内核大小21。内核大小, n, 是大小 of n x n 窗口 (其中 n 是奇数) 的像素, 用于互相关, 并确定该区域的变形向量将用于应变计算. </li>
		<li> 使用起始子像素大小4。亚像素的大小, m, 是大小的 (2 米 + 1) x (2 m + 1) 子的亚像素变形计算通过假设均匀应变在该子. </li>
		<li> 使用起始平滑系数2。平滑系数是在计算应变之前, 在履带位置的位移场上平滑应用的量. </li>
		<li> 使用起始 maxMove 系数 10. maxMove 因子是任何节点相对于其相邻和 #39 的轨迹, 可以远离其轨迹的最大像素数。这有助于避免严重的变形跟踪. </li>
		<li> 使用起始 smoothGrid 系数15。smoothGrid 因子是用于平滑处理的网格大小 (比跟踪节点的网格略粗). </li>
	</ol> </li> <li> 选择一个具有显著对比度的参考线, 同时避免带有眩光或模糊的区域。通过单击和 #34 检查此点; 检查导轨和 #34; 并验证相关峰值是否强 (至少是振幅的两倍) 与它的邻居相比。单击和 #34; 接受和 #34; #34;P erform 跟踪和 #34; 当满足时。这可以是一个冗长的计算过程, 其中差分位移计算的时序图像序列. </li>
	<li> 步骤6.6 完成后, 单击并 #34; 动画和 #34;。动画完成后, 单击并 #34; 写入应变 (后处理软件) 和 #34;, 输入 * exe, 然后选择 writeStrainRR_simple 11 。这将计算菌株。关闭 GUI. </li>
</ol> 7。位移和应变数据的后处理 <ol> <li> 获取应变 与 帧数、运行和 #34; analyzeFailurePrecursor 和 #34; 从命令行到步长大小的输入参数 (选择 20-30)。峰值将意味着骨损伤, 最大的峰值将对应于接近全球骨衰竭的框架. </li>
	<li> 创建应变、运行和 #34 的影片文件; makeMovies 和 #34; 从命令窗口中使用参数 (numVars、endstep、标志). 
	注意: 参数 numVars 定义为 1-3 是位移, 4-6 是 xx , yy , 和 xy 应变分量, 7 和 #38; 8 是两个主要和冯米塞斯应变, 9 是应变能。参数 endstop 是要包含在影片中的最后一个框架。
	<ol> <li> 将可选参数标志设置为 1, 以便仅为 numVars 参数指定的实体和0创建所有变量的影片. </li>
	</ol> </li> </ol> 8。对结果进行微调和细化 <ol> <li> 如果 DIC 跟踪给出了糟糕的结果, 如不连续的应变场, 这是在连续体力学假设之外, 确定发生了什么以及为什么跟踪失败。重复6节, 特别注意跟踪参数的调整。第二个选项可能是返回到有限元软件, 并创建一个更均匀和可能更细的网格. </li>
	<li> 如果 dic 跟踪给出了合理的结果, 则为 dic 创建更精细的图像系列。使用步骤4.2 中的关键帧参考编号和视频的相应帧速率, 在断裂试验中确定三不同的感兴趣制度的帧间距, 并记住这些点应移动不超过6帧之间的像素. 
	注: 对于测试的初始段, 当应变在股骨缓慢上升时, 帧间距将相对较大 (例如, 对于 100 mm/秒的位移率, 此部分的帧间距为3333和 #956; s)。对于更接近于断裂框架的中间部分, 应变增加得更快, 需要更小的帧间距 (1667 和 #956; s 用于 100 mm/秒的位移率)。在断裂前的最后部分, 帧间距在最小 (16.7 和 #956; s 在100毫米/秒的位移率). </li>
	仅用于文档用途的 <li> 可选: 使用步骤8.2 中的信息, 在名为 "和 #34 的 ASCII 文件中创建格式化数据项; steps.txt 和 #34; 包含每个帧间距的一行数据。每行的格式将是该制度的起始帧, 该框架由要跳过的帧数 (基于步骤 8.2) 分隔, 然后是该制度的最终框架 ( 即 和 #160; #34 的格式; 1:20:200 和 #34; 将指示提取软件提取帧1到帧200的步骤 20). 
	<ol> <li> 紧接该指定之后, 插入一个选项卡并指定图像提取号码范围 (用于和 #34; 1:20:200 和 #34; 例如, 完整的行指定将是和 #34; 1:20:200 和 #60;P ress 选项卡和 #62; 1:11 和 #34; 没有引文)。对其他两个测试机制重复, 以便在 #34 中有三行信息; steps.txt 和 #34; 文件。此文件用作记录如何从原始的高速视频中提取图像. </li>
	</ol> </li> <li> 在该对话框中指定多个帧间距制度时, 再次运行 mov_Frames. m 代码。输入步骤8.2 中标识的帧号和步长, 以确定在 "工具和 #39" 对话框中预期的开始、完成和帧跳过参数。请确保在新目录中执行此项, 否则将覆盖原始图像. </li>
	<li> 重复6和7节, 并查看改进结果。每个股骨可能需要不同的额外的迭代, 这取决于骨折事件的性质, 斑点图案和照明。重复步骤6.5 时, 将设置保持不变, 除非将 maxMove 减少到 6 (从 10). </li>
</ol>

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作者没有相关的披露。

我们介绍了一个协议, 以一致准备在骨折试验期间的高对比度成像的股骨样本, 然后用于估计全场应变分布的 DIC。这个协议确保了适当的对比纹理黑色跟踪斑点对坚实的白色背景的骨骼表面。根据该协议, 我们成功地复制了八十九股骨的 DIC 分析的应变估计。
DIC 是一种光学方法, 它涉及在高速摄像机拍摄的一系列图像上放置一个网格, 并使用互相关算法跟踪帧之间的像素亮度变...

数字图像相关 (DIC) 是一种图像后处理方法, 用于在目前的协议中估计的全场表面应变的尸体股骨试验标本从时序图像中获得的机械断裂试验。该技术在1980的实验应力分析中首次被开发和应用, 并在近几年的使用中迅速增加1,2,3。它有几个关键的优势超过传统的方法安装应变计的结构, 包括增加空间分布的应变场, 更精细的测量长度通过增加相机分辨率, 并避免问题的应变计粘合或合规性。生物组织 DIC 的一个主要优势, 如骨骼, 是它可以应用于不规则的几何图形, 包括高度异构的材料属性4,5。它的主要缺点是传统的应变采集方法是, 它需要昂贵的高速摄像机的足够分辨率的测量区域的利益, 以实现足够的空间和时间采样准确估计应变场。
从骨折 DIC 分析得到的时间应变场的初步应用是验证 QCT/有限元模型中的应变估计5。这种验证是许多骨科研究小组的重点, 主要利用远程测量的力量和位移从负载细胞和位移传感器6,7,8。此外, 骨折图像分析的断裂模式已与这些远程测量结合起来, 作为进一步的模型验证9。最近, 应用 DIC 法对股骨近端断裂和裂纹扩展的有限元模型进行了验证, 并对其进行了10。利用模型与实验之间的应变相关性, 对近股骨的计算模型的有效性有了更深入的把握, 进一步提高了 QCT/有限元诊断方法在临床上的应用效果。
这项工作解释了详细的协议, 以纳入必要的步骤, DIC 分析在断裂试验的近端股骨。该程序包括在骨表面喷涂白色涂料的骨准备步骤, 然后在骨骼干白表面斑点黑点, 利用高速视频获取具有足够空间和时间分辨率的图像的方法摄像机, 以及我们用于计算这些图像中的应变场的过程和工具。我们还解释了一些可能影响测量质量的警告。

<table><tbody><tr><td>Krylon plastic primer white</td><td>Krylon, Peoria, AZ, USA</td><td>N/A</td><td>Used as a base coat for a smooth white finish on bone surface</td></tr><tr><td>Water-based acrylic white and black paint&amp;nbsp;</td><td>Plaid Enterprises (Ceramcoat), Norcross, GA, USA</td><td>N/A</td><td>Paint source for white and black colors</td></tr><tr><td>Mixing bowl</td><td>Not specific (generic)</td><td>N/A</td><td>Used to mix and prepare paint</td></tr><tr><td>Foam brush</td><td>Linzer Products, Wyandanch, NY, USA</td><td>N/A</td><td>Used to apply paint on bone surface</td></tr><tr><td>Toothbrush</td><td>Colgate-Palmolive, New York, NY, USA</td><td>Firm bristle</td><td>Used to apply appropriate size and distribution of speckling pattern</td></tr><tr><td>Hygenic Orthodontic Resin (PMMA)</td><td>Patterson Dental, St Paul, MN, USA</td><td>H02252</td><td>Controlled substance and can be purchased with proper approval</td></tr><tr><td>Kenmore Freezer</td><td>Sears Holdings, Hoffman Estates, IL, USA</td><td>N/A</td><td>Used to maintain a -20&lt;sup&gt;o&lt;/sup&gt;C storage enviroment for bone specimens</td></tr><tr><td>Physiologic Saline (0.9% Sodium Chloride)</td><td>Baxter Healthcare, Deerfield, IL, USA</td><td>NDC 0338-0048-04</td><td>Used for keeping specimens hydrated</td></tr><tr><td>Scalpels and scrapers</td><td>Aspen Surgical (Bard-Parker), Caledonia, MI, USA&amp;nbsp;</td><td>N/A</td><td>Used to remove soft tissue from bone specimens</td></tr><tr><td>Fume Hood</td><td>Hamilton Laboratory Solutions, Manitowoc, WI, USA</td><td>70532</td><td>Used for ventilation when preparing PMMA for potting of specimens</td></tr><tr><td>Lighting units</td><td>ARRI, Munich, Germany</td><td>N/A</td><td>Needed for illumination of target for image capture</td></tr><tr><td>High-speed video camera</td><td>Photron Inc., San Diego, CA, USA</td><td>Photron Fastcam APX-RS&amp;nbsp;</td><td>Used to capture the high speed video recordings of the fracture events</td></tr><tr><td>Photron FASTCAM Imager and Viewer</td><td>Photron Inc., San Diego, CA, USA</td><td>Ver.3392(x64)</td><td>Used to record and view the high speed video recordings</td></tr><tr><td>Camera lens</td><td>Zeiss, Oberkochen, Germany</td><td>Zeiss Planar L4/50 ZF Lens</td><td>Needed for appropriate image resolution</td></tr><tr><td>ABAQUS CAE</td><td>Dassault System&amp;egrave;s, Waltham, MA, USA</td><td>Versions 6.13-4</td><td>Used for defining region of interest and creating finite element mesh</td></tr><tr><td>MATLAB</td><td>Mathworks, Natick, MA, USA</td><td>Version 2015b</td><td>Used for image processing and DIC analysis</td></tr><tr><td>TecPlot</td><td>TecPlot Inc., Bellevue, WA</td><td></td><td>Used for post processing of strain fields</td></tr><tr><td>Strain Calculator Software</td><td>Victor Barocas Research Group, University of Minnesota, Minneapolis, MN, USA</td><td>http://license.umn.edu/technologies/20130022_robust-image-correlation-based-strain-calculator-for-tissue-systems</td><td>Used to calculate strain field</td></tr><tr><td>mov_frames.m</td><td>Matlab script, Mayo Clinic, Rochester, MN,USA</td><td>N/A</td><td>Used to downsample uncompressed images from high speed video files</td></tr><tr><td>convert_imagesize.m</td><td>Matlab script, Mayo Clinic, Rochester, MN,USA</td><td>N/A</td><td>Used to register image pixel coordinates with mesh coordinates</td></tr><tr><td>rrImageTrackGui.m</td><td>Matlab script, Mayo Clinic, Rochester, MN,USA</td><td>N/A</td><td>Used to perform the image cross-correlation to obtain deformations and run Strain Calculator</td></tr><tr><td>analyzeFailurePrecursor.m</td><td>Matlab script, Mayo Clinic, Rochester, MN,USA</td><td>N/A</td><td>Used to track the peak strain components temporally</td></tr><tr><td>makeMovies.m</td><td>Matlab script, Mayo Clinic, Rochester, MN,USA</td><td>N/A</td><td>Used to create portable *.avi movies of the deformation components, strain components, principal strains, von Mises strain, and strain energy</td></tr></tbody></table>

a method to estimate cadaveric femur cortical strains during fracture testing using digital image correlation

本协议描述了利用数字图像相关技术对从机械测试中获得的尸体股骨表面的高速视频图像中的皮层应变进行估计的方法。这种光学方法要求在一个坚实的白色背景上有许多对比的信讬标记的纹理, 以准确地跟踪表面变形, 因为载荷被应用到试样上。在测试之前, 在相机视图的兴趣表面被涂上了一个水性白色底漆, 并允许干燥几分钟。然后, 黑色的油漆在白色的背景上仔细地斑点, 特别考虑到水滴的均匀大小和形状。照明是精心设计和设置这样, 有最好的对比, 这些标记, 同时尽量减少反射通过使用过滤器。图像是通过高速视频捕获1.2万帧/秒获得的。提取之前和包括骨折事件的关键图像, 并在经过特定区域的详细询问窗口中的连续帧之间进行变形估计。这些变形然后被用来计算表面应变在断裂试验期间。应变数据是非常有用的识别骨折开始在股骨, 并最终验证的股骨近端骨折强度模型从定量计算 Tomography-based 有限元分析 (QCT)。

在斑点过程之前, 股骨是从多余的脂肪和软组织清洗, 和大转子是盆栽在一个铝杯。在酯 (PMMA) 凝固过程中, 骨头被用盐水浸泡过的布料包裹, 以避免组织干燥。一旦 PMMA 固化后, 在喷涂(图 1)之前, 再次对骨骼进行清洗。然后, 用水性塑料白颜色喷涂或刷骨表面。干燥后, 白色表面上有黑色斑点, 在白色背景上有一个随机的黑点图案(<stro...

Watch this Scientific Journal Video about A Method to Estimate Cadaveric Femur Cortical Strains During Fracture Testing Using Digital Image Correlation at JoVE.com

A Method to Estimate Cadaveric Femur Cortical Strains During Fracture Testing Using Digital Image Correlation

在该协议中, 使用数字图像相关技术对骨折试验中的股骨表面应变进行估计。该方法的新颖性包括在股骨表面上应用高对比度随机散斑图、精心指定的光照、高速视频捕捉以及应变计算的数字图像相关分析。

基于数字图像相关的骨折检测中股骨皮质应变的估算方法

This protocol describes the method using digital image correlation to estimate cortical strain from high speed video images of the cadaveric femoral ...

a-method-to-estimate-cadaveric-femur-cortical-strains-during-fracture

Universidad de Cartagena UDEC

Research

JoVE Journal

Bioengineering

7.3K 次观看.  Mayo Clinic. 在该协议中, 使用数字图像相关技术对骨折试验中的股骨表面应变进行估计。该方法的新颖性包括在股骨表面上应用高对比度随机散斑图、精心指定的光照、高速视频捕捉以及应变计算的数字图像相关分析。

视频: A Method to Estimate Cadaveric Femur Cortical Strains During Fracture Testing Using Digital Image Correlation

Full-field Strain Measurements for Microstructurally Small Fatigue Crack Propagation Using Digital Image Correlation Method

A novel measurement approach is used to reveal the cumulative deformation field at a sub-grain level and to study the influence of microstructure on the growth of microstructurally small fatigue cracks. The proposed strain field analysis methodology is based on the use of a unique pattering technique with a characteristic speckle size of approximately 10 &#181;m. The developed methodology is applied to study the small fatigue crack behavior in body centered cubic (bcc) Fe-Cr ferritic stainless steel with a relatively large grain size allowing a high spatial measurement accuracy at the sub-grain level. This methodology allows the measurement of small fatigue crack growth retardation events and associated intermittent shear strain localization zones ahead of the crack tip. In addition, this can be correlated with the grain orientation and size. Thus, the developed methodology can provide a deeper fundamental understanding of the small fatigue crack growth behavior, required for the development of robust theoretical models for the small fatigue crack&#160;propagation in polycrystalline materials.

Microstructurally small fatigue crack growth behavior is investigated using a novel methodological approach combining crack growth rate measurement and strain-field analysis to reveal the cumulative deformation field at sub-grain level.

基于数字图像相关的微结构小疲劳裂纹扩展的全场应变测量

A novel measurement approach is used to reveal the cumulative deformation field at a sub-grain level and to study the influence of microstructure on the ...

科研

工程学

Intermediate Strain Rate Material Characterization with Digital Image Correlation

The mechanical response of a material under dynamic load is typically different than its behavior under static conditions; therefore, the common quasistatic equipment and procedures used for material characterization are not applicable for materials under dynamic loads. The dynamic response of a material depends on its deformation rate and is broadly categorized into high (i.e., greater than 200/s), intermediate (i.e., 10&#8722;200/s) and low strain rate regimes (i.e., below 10/s). Each of these regimes calls for specific facilities and testing protocols to ensure the reliability of the acquired data. Due to the limited access to high-speed servo-hydraulic facilities and validated testing protocols, there is a noticeable gap in the results at the intermediate strain rate. The current manuscript presents a validated protocol for the characterization of different materials at these intermediate strain rates. Strain gauge instrumentation and digital image correlation protocols are also included as complimentary modules to extract the utmost level of detailed data from every single test. Examples of raw data, obtained from a variety of materials and test setups (e.g., tensile and shear) is presented and the analysis procedure used to process the output data is described. Finally, the challenges of dynamic characterization using the current protocol, along with the limitations of the facility and methods of overcoming potential problems are discussed.

Here we present a methodology for the dynamic characterization of tensile specimens at intermediate strain rates using a high-speed servo-hydraulic load frame. Procedures for strain gauge instrumentation and analysis, as well as for digital image correlation strain measurements on the specimens, are also defined.

数字图像相关的中间应变率材料表征

The mechanical response of a material under dynamic load is typically different than its behavior under static conditions; therefore, the common ...

A Simple Critical-sized Femoral Defect Model in Mice

While bone has a remarkable capacity for regeneration, serious bone trauma often results in damage that does not properly heal. In fact, one tenth of all limb bone fractures fail to heal completely due to the extent of the trauma, disease, or age of the patient. Our ability to improve bone regenerative strategies is critically dependent on the ability to mimic serious bone trauma in test animals, but the generation and stabilization of large bone lesions is technically challenging. In most cases, serious long bone trauma is mimicked experimentally by establishing a defect that will not naturally heal. This is achieved by complete removal of a bone segment that is larger than 1.5 times the diameter of the bone cross-section. The bone is then stabilized with a metal implant to maintain proper orientation of the fracture edges and allow for mobility. 
Due to their small size and the fragility of their long bones, establishment of such lesions in mice are beyond the capabilities of most research groups. As such, long bone defect models are confined to rats and larger animals. Nevertheless, mice afford significant research advantages in that they can be genetically modified and bred as immune-compromised strains that do not reject human cells and tissue.
Herein, we demonstrate a technique that facilitates the generation of a segmental defect in mouse femora using standard laboratory and veterinary equipment. With practice, fabrication of the fixation device and surgical implantation is feasible for the majority of trained veterinarians and animal research personnel. Using example data, we also provide methodologies for the quantitative analysis of bone healing for the model.

Animal models are frequently employed to mimic serious bone injury in biomedical research. Due to their small size, establishment of stabilized bone lesions in mice are beyond the capabilities of most research groups. Herein, we describe a simple method for establishing and analyzing experimental femoral defects in mice.

一个简单的临界尺寸股骨缺损模型小鼠

While bone has a remarkable capacity for regeneration, serious bone trauma often results in damage that does not properly heal. In fact, one tenth of all ...

医学

Measuring Local Tissue Strains in Tendons via Open-Source Digital Image Correlation

There is considerable scientific interest in understanding the strains that tendon cells experience in situ and how these strains influence tissue remodeling. Based on this interest, several analytical techniques have been developed to measure local tissue strains within tendon explants during loading. However, in several cases, the accuracy and sensitivity of these techniques have not been reported, and none of the algorithms are publicly available. This has made it difficult for the more widespread measurement of local tissue strains in tendon explants. Therefore, the objective of this paper was to create a validated analysis tool for measuring local tissue strains in tendon explants that is readily available and easy to use. Specifically, a publicly available augmented-Lagrangian digital image correlation (ALDIC) algorithm was adapted for measuring 2D strains by tracking the displacements of cell nuclei within mouse Achilles tendons under uniaxial tension. Additionally, the accuracy of the calculated strains was validated by analyzing digitally transformed images, as well as by comparing the strains with values determined from an independent technique (i.e., photobleached lines). Finally, a technique was incorporated into the algorithm to reconstruct the reference image using the calculated displacement field, which can be used to assess the accuracy of the algorithm in the absence of known strain values or a secondary measurement technique. The algorithm is capable of measuring strains up to 0.1 with an accuracy of 0.00015. The technique for comparing a reconstructed reference image with the actual reference image successfully identified samples that had erroneous data and indicated that, in samples with good data, approximately 85% of the displacement field was accurate. Finally, the strains measured in mouse Achilles tendons were consistent with the prior literature. Therefore, this algorithm is a highly useful and adaptable tool for accurately measuring local tissue strains in tendons.

Measuring Local Tissue Strains in Tendons via Open-Source Digital Image Correlation

This paper describes an open-source digital image correlation algorithm for measuring local 2D tissue strains within tendon explants. The accuracy of the technique has been validated using multiple techniques, and it is available for public use.

通过开源数字图像相关 测量 肌腱中的局部组织应变

There is considerable scientific interest in understanding the strains that tendon cells experience in situ and how these strains influence tissue ...

Imaging of the Microstructural Failure Mechanism in the Human Hip

Imaging the bone microstructure under progressively increasing loads allows for observing the microstructural failure behavior of bone. Here, we describe a protocol for obtaining a sequence of three-dimensional microstructural images of the entire proximal femur under progressively increasing deformation, causing clinically relevant fractures of the femoral neck. The protocol is demonstrated using four femora from female donors aged 66-80 years at the lower end of bone mineral density in the population (T-score range = &#8722;2.09 to &#8722;4.75). A radio-transparent compressive stage was designed for loading the specimens replicating a one-leg stance, while recording the applied load during&#160;micro-computed tomography (micro-CT) imaging. The field of view was 146 mm wide and 132 mm high, and the isotropic pixel size was 0.03 mm. The force increment was based on finite-element predictions of the fracture load. The compressive stage was used to apply the displacement to the specimen and enact the prescribed force increments. Sub-capital fractures due to opening and shear of the femoral neck occurred after four to five load increments. The micro-CT&#160;images and the reaction force measurements were processed to study the bone strain and energy absorption capacity. Instability of the cortex appeared at the early loading steps. The subchondral bone in the femoral head displayed large deformations reaching 16% before&#160;fracture, and a progressive increase in the support capacity up to&#160;fracture. The deformation energy linearly increased with the displacement up to&#160;fracture, while the stiffness decreased to near-zero values immediately before&#160;fracture. Three-fourths of the fracture energy was taken by the specimen during the final 25% force increment. In conclusion, the protocol developed revealed a remarkable energy absorption capacity, or damage tolerance, and a synergic interaction between the cortical and trabecular bone at an advanced donor age.

The protocol enables the measurement of the deformation of the bone microstructure in the entire proximal human femur and its toughness by combining large-volume micro-CT scanning, a custom-made compressive stage, and advanced image processing tools.

人髋关节微观结构失效机制的成像

Imaging the bone microstructure under progressively increasing loads allows for observing the microstructural failure behavior of bone. Here, we describe ...

Proximal Cadaveric Femur Preparation for Fracture Strength Testing and Quantitative CT-based Finite Element Analysis

Cadaveric fracture testing is routinely used to understand factors that affect proximal femur strength. Because ex vivo biological tissues are prone to lose their mechanical properties over time, specimen preparation for experimental testing must be performed carefully to obtain reliable results that represent in vivo conditions. For that reason, we designed a protocol and a set of fixtures to prepare the femoral specimens such that their mechanical properties experienced minimal changes. The femora were kept in a frozen state except during preparation steps and mechanical testing. The relevant clinical measures of total hip and femoral neck bone mineral density (BMD) were obtained with a clinical dual X-ray absorptiometry (DXA) bone densitometer, and the 3D geometry and distribution of bone mineral were obtained using CT with a calibration phantom for quantitative estimations based on the greyscale values. Any possible bone disease, fracture, or the presence of implants or artifacts affecting the bone structure, was ruled out with X-ray scans. For preparation, all bones were carefully cleaned of excess soft tissue, and were cut and potted at the internal rotation angle of interest. A cutting fixture allowed the distal end of the bone to be cut off leaving the proximal femur at a desired length. To allow positioning of the femoral neck at prescribed angles during later CT scanning and mechanical testing, the proximal femoral shafts were potted in polymethylmethacrylate (PMMA) using a fixture designed specifically for desired orientations. The data collected from our experiments were then used for validation of quantitative computed tomography (QCT)-based finite element analysis (FEA), as described in a different protocol. In this manuscript, we present the protocol for the precise bone preparation for mechanical testing and subsequent QCT/FEA modeling. The current protocol was successfully applied to prepare about 200 cadaveric femora over a 6-year time period.

We present a robust protocol on how to carefully preserve and prepare cadaveric femora for fracture testing and quantitative computed tomography imaging. The method provides precise control over input conditions for the purpose of determining relationships between bone mineral density, fracture strength, and defining finite element model geometry and properties.

近端股骨尸制备基于CT的断裂强度测试和定量的有限元分析

Cadaveric fracture testing is routinely used to understand factors that affect proximal femur strength.  Because ex vivo biological tissues are prone to ...

In Vivo Quantification of Hip Arthrokinematics during Dynamic Weight-bearing Activities using Dual Fluoroscopy

Several hip pathologies have been attributed to abnormal morphology with an underlying assumption of aberrant biomechanics. However, structure-function relationships at the joint level remain challenging to quantify due to difficulties in accurately measuring dynamic joint motion. The soft tissue artifact errors inherent in optical skin marker motion capture are exacerbated by the depth of the hip joint within the body and the large mass of soft tissue surrounding the joint. Thus, the complex relationship between bone shape and hip joint kinematics is more difficult to study accurately than in other joints. Herein, a protocol incorporating computed tomography (CT) arthrography, three-dimensional (3D) reconstruction of volumetric images, dual fluoroscopy, and optical motion capture to accurately measure the dynamic motion of the hip joint is presented. The technical and clinical studies that have applied dual fluoroscopy to study form-function relationships of the hip using this protocol are summarized, and the specific steps and future considerations for data acquisition, processing, and analysis are described.

In Vivo Quantification of Hip Arthrokinematics during Dynamic Weight-bearing Activities using Dual Fluoroscopy

Dual fluoroscopy accurately captures in vivo dynamic motion of human joints, which can be visualized relative to reconstructed anatomy (e.g., arthrokinematics). Herein, a detailed protocol to quantify hip arthrokinematics during weight-bearing activities of daily living is presented, including the integration of dual fluoroscopy with traditional skin marker motion capture.

在维沃 使用双氟镜检查进行动态负重活动时臀部关节肌学的量化

Several hip pathologies have been attributed to abnormal morphology with an underlying assumption of aberrant biomechanics. However, structure-function ...

Using Digital Image Correlation to Characterize Local Strains on Vascular Tissue Specimens

Characterization of the mechanical behavior of biological and engineered soft tissues is a central component of fundamental biomedical research and product development. Stress-strain relationships are typically obtained from mechanical testing data to enable comparative assessment among samples and in some cases identification of constitutive mechanical properties. However, errors may be introduced through the use of average strain measures, as significant heterogeneity in the strain field may result from geometrical non-uniformity of the sample and stress concentrations induced by mounting/gripping of soft tissues within the test system. When strain field heterogeneity is significant, accurate assessment of the sample mechanical response requires measurement of local strains. This study demonstrates a novel biomechanical testing protocol for calculating local surface strains using a mechanical testing device coupled with a high resolution camera and a digital image correlation technique. A series of sample surface images are acquired and then analyzed to quantify the local surface strain of a vascular tissue specimen subjected to ramped uniaxial loading. This approach can improve accuracy in experimental vascular biomechanics and has potential for broader use among other native soft tissues, engineered soft tissues, and soft hydrogel/polymeric materials. In the video, we demonstrate how to set up the system components and perform a complete experiment on native vascular tissue.

We describe the use of digital image correlation to characterize the local surface strain field on vascular tissue samples subjected to uniaxial tensile testing. These measurements facilitate precise quantification of the sample mechanical response and the generation of constitutive stress-strain relations.

利用数字图像相关表征的血管组织标本本地菌株

Characterization of the mechanical behavior of biological and engineered soft tissues is a central component of fundamental biomedical research and ...

生物学

Assessment of Bone Fracture Healing Using Micro-Computed Tomography

Micro-computed tomography (&#181;CT) is the most common imaging modality to characterize the three-dimensional (3D) morphology of bone and newly formed bone during fracture healing in translational science investigations. Studies of long bone fracture healing in rodents typically involve secondary healing and the formation of a mineralized callus. The shape of the callus formed and the density of the newly formed bone may vary substantially between timepoints and treatments. Whereas standard methodologies for quantifying parameters of intact cortical and trabecular bone are widely used and embedded in commercially available software, there is a lack of consensus on procedures for analyzing the healing callus. The purpose of this work is to describe a standardized protocol that quantitates bone volume fraction and callus mineral density in the healing callus. The protocol describes different parameters that should be considered during imaging and analysis, including sample alignment during imaging, the size of the volume of interest, and the number of slices that are contoured to define the callus.

Micro-computed tomography (&#181;CT) is a non-destructive imaging tool that is instrumental in assessing bone structure in preclinical studies, however there is a lack of consensus on &#181;CT procedures for analyzing the bone healing callus. This study provides a step-by-step &#181;CT protocol that allows the monitoring of fracture healing.

使用显微计算机断层扫描评估骨折愈合

Micro-computed tomography (&#181;CT) is the most common imaging modality to characterize the three-dimensional (3D) morphology of bone and newly formed ...

Quantitative Strain Mapping of an Abdominal Aortic Aneurysm

Source: Hannah L. Cebull1, Arvin H. Soepriatna1, John J. Boyle2 and <a href="https://jove.unicartagenaproxy.elogim.com/author/Craig+J._Goergen">Craig J. Goergen</a>1 
1Weldon School of Biomedical Engineering, Purdue University, West Lafayette, Indiana
2Mechanical Engineering &#38; Materials Science, Washington University in St. Louis, St Louis, Missouri
The mechanical behavior of soft tissues, such as blood vessels, skin, tendons, and other organs, are strongly influenced by their composition of elastin and collagen, which provide elasticity and strength. The fiber orientation of these proteins depends on the type of soft tissue and can range from a single preferred direction to intricate meshed networks, which can become altered in diseased tissue. Therefore, soft tissues often behave anisotropically on the cellular and organ level, creating a need for three-dimensional characterization. Developing a method for reliably estimating strain fields within complex biological tissues or structures is important to mechanically characterize and understande disease. Strain represents how soft tissue relatively deforms over time, and it can be described mathematically through various estimations.
Acquiring image data over time allows deformation and strain to be estimated. However, all medical imaging modalities contain some amount of noise, which increases the difficulty of accurately estimating in vivo strain. The technique described here successfully overcomes these issues by using a direct deformation estimation (DDE) method to calculate spatially varying 3D strain fields from volumetric image data.
Current strain estimation methods include digital image correlation (DIC) and digital volume correlation. Unfortunately, DIC can only accurately estimate strain from a 2D plane, severely limiting the application of this method. While useful, 2D methods such as DIC have difficulty quantifying strain in regions that undergo 3D deformation. This is because out-of-plane motion creates deformation errors. Digital volume correlation is a more applicable method that divides the initial volume data into regions and finds the most similar region of the deformed volume, thereby reducing out-of-plane error. However, this method proves to be sensitive to noise and requires assumptions about the mechanical properties of the material.
The technique demonstrated here eliminates these issues by using a DDE method, thus making it very useful in the analysis of medical imaging data. Furthermore, it is robust to high or localized strain. Here we describe the acquisition of gated, volumetric 4D ultrasound data, its conversion into an analyzable format, and the use of a custom Matlab code to estimate 3D deformation and corresponding Green-Lagrange strains, a parameter that better describes large deformations. The Green-Lagrange strain tensor is implemented in many 3D strain estimation methods because it allows for F to be calculated from a Least Squares Fit (LSF) of the displacements. The equation below represents the Green-Lagrange strain tensor, E, where F and I represent the deformation gradient and second order identity tensor, respectively.
<img alt="Equation 1" src="/files/ftp_upload/10480/10480eq1v2.jpg" /> (1)

4-D Ultrasound &amp; Quantitative Strain Mapping in Abdominal Aortic Aneurysm

腹部主动脉瘤的定量应变图谱

Source: Hannah L. Cebull1, Arvin H. Soepriatna1, John J. Boyle2 and Craig J. Goergen1 
1Weldon School of Biomedical Engineering, Purdue University, West ...

基于数字图像相关的骨折检测中股骨皮质应变的估算方法

摘要

探索更多视频

此视频中的章节

基于数字图像相关的微结构小疲劳裂纹扩展的全场应变测量

数字图像相关的中间应变率材料表征

一个简单的临界尺寸股骨缺损模型小鼠

通过开源数字图像相关测量肌腱中的局部组织应变

人髋关节微观结构失效机制的成像

近端股骨尸制备基于CT的断裂强度测试和定量的有限元分析

在维沃使用双氟镜检查进行动态负重活动时臀部关节肌学的量化

利用数字图像相关表征的血管组织标本本地菌株

使用显微计算机断层扫描评估骨折愈合

腹部主动脉瘤的定量应变图谱

基于数字图像相关的骨折检测中股骨皮质应变的估算方法

摘要

探索更多视频

此视频中的章节

基于数字图像相关的微结构小疲劳裂纹扩展的全场应变测量

数字图像相关的中间应变率材料表征

一个简单的临界尺寸股骨缺损模型小鼠

通过开源数字图像相关 测量 肌腱中的局部组织应变

人髋关节微观结构失效机制的成像

近端股骨尸制备基于CT的断裂强度测试和定量的有限元分析

在维沃 使用双氟镜检查进行动态负重活动时臀部关节肌学的量化

利用数字图像相关表征的血管组织标本本地菌株

使用显微计算机断层扫描评估骨折愈合

腹部主动脉瘤的定量应变图谱

通过开源数字图像相关测量肌腱中的局部组织应变

在维沃使用双氟镜检查进行动态负重活动时臀部关节肌学的量化