Department of Aerospace and Mechanical Engineering, University of Notre Dame, Notre Dame, IN 46556, USA.
Bone. 2011 Mar 1;48(3):443-50. doi: 10.1016/j.bone.2010.10.160. Epub 2010 Oct 15.
Conventional methods used to image and quantify microdamage accumulation in bone are limited to histological sections, which are inherently invasive, destructive, two-dimensional, and tedious. These limitations inhibit investigation of microdamage accumulation with respect to volumetric spatial variation in mechanical loading, bone mineral density, and microarchitecture. Therefore, the objective of this study was to investigate non-destructive, three-dimensional (3-D) detection of microdamage accumulation in human cortical bone using contrast-enhanced micro-computed tomography (micro-CT), and to validate micro-CT measurements against conventional histological methods. Unloaded controls and specimens loaded in cyclic uniaxial tension to a 5% and 10% reduction in secant modulus were labeled with a precipitated BaSO₄ stain for micro-CT and basic fuchsin for histomorphometry. Linear microcracks were similarly labeled by BaSO₄ and basic fuchsin as shown by backscattered electron microscopy and light microscopy, respectively. The higher X-ray attenuation of BaSO₄ relative to the bone extracellular matrix provided enhanced contrast for the detection of damage that was otherwise not able to be detected by micro-CT prior to staining. Therefore, contrast-enhanced micro-CT was able to nondestructively detect the presence, 3-D spatial location, and accumulation of fatigue microdamage in human cortical bone specimens in vitro. Microdamage accumulation was quantified on segmented micro-CT reconstructions as the ratio of BaSO₄ stain volume (SV) to total bone volume (BV). The amount of microdamage measured by both micro-CT (SV/BV) and histomorphometry (Cr.N, Cr.Dn, Cr.S.Dn) progressively increased from unloaded controls to specimens loaded to a 5% and 10% reduction in secant modulus (p < 0.001). Group means for micro-CT measurements of damage accumulation were strongly correlated to those using histomorphometry (p < 0.05), validating the new methods. Limitations of the new methods in the present study included that the precipitated BaSO₄ stain was non-specific and non-biocompatible, and that micro-CT measurements exhibited greater variability compared to conventional histology. Nonetheless, contrast-enhanced micro-CT enabled non-destructive imaging and 3-D spatial information, which are not possible using conventional histological methods.
传统的用于成像和量化骨微损伤积累的方法仅限于组织学切片，这些方法具有内在的侵袭性、破坏性、二维性和繁琐性。这些限制抑制了对微损伤积累与体积空间变化的机械载荷、骨矿物质密度和微结构的关系的研究。因此，本研究的目的是利用增强对比度的微计算机断层扫描（micro-CT）来研究非破坏性的、三维（3-D）的人皮质骨微损伤积累的检测，并验证 micro-CT 测量值与传统的组织学方法的一致性。未加载的对照样本和在循环单轴拉伸下加载至割线模量降低 5%和 10%的样本用沉淀的 BaSO₄ 染色剂进行 micro-CT 标记，并用碱性品红进行组织形态计量学标记。线性微裂纹也用 BaSO₄ 和碱性品红进行了类似的标记，分别通过背散射电子显微镜和光学显微镜显示。与骨细胞外基质相比，BaSO₄ 的更高 X 射线衰减提供了增强的对比度，以便在染色之前用 micro-CT 检测到否则无法检测到的损伤。因此，对比增强的 micro-CT 能够非破坏性地检测出体外人皮质骨样本中疲劳微损伤的存在、3-D 空间位置和积累。微损伤积累通过分割的 micro-CT 重建中的 BaSO₄ 染色体积（SV）与总骨体积（BV）的比值来定量。用 micro-CT（SV/BV）和组织形态计量学（Cr.N、Cr.Dn、Cr.S.Dn）测量的微损伤量从未加载的对照样本逐渐增加到割线模量降低 5%和 10%的样本（p < 0.001）。微损伤积累的 micro-CT 测量的组平均值与组织形态计量学的平均值具有很强的相关性（p < 0.05），验证了新方法的有效性。本研究中，新方法的局限性包括沉淀的 BaSO₄ 染色剂是非特异性的、非生物相容性的，以及 micro-CT 测量值与传统组织学相比具有更大的变异性。尽管如此，对比增强的 micro-CT 能够实现非破坏性的成像和 3-D 空间信息，而这是传统的组织学方法无法实现的。
