Ouyang X, Majumdar S, Link T M, Lu Y, Augat P, Lin J, Newitt D, Genant H K
Department of Radiology, University of California, San Francisco 94143, USA.
Med Phys. 1998 Oct;25(10):2037-45. doi: 10.1118/1.598391.
The measurement of bone microstructure as well as bone mineral density may improve the estimation of bone strength. Cubic specimens (N = 26, 12 mm X 12 mm X 12 mm) of human cadaver vertebrae were cut along three orthogonal anatomic orientations, i.e., superior-inferior (SI), medial-lateral (ML), and anterior-posterior (AP). Contact radiographs of the bone cubes along all three orientations were obtained and then digitized by a laser scanner with pixel size of 50 microns x 50 microns. The specimens were tested in compression along the 3 orthogonal orientations and the Young's modulus (YM) was calculated for each direction. Quantitative computed tomography (QCT) was used to obtain a measure of trabecular bone mineral density (BMD). Global gray level thresholding and local thresholding algorithms were used to extract the trabecular bone network. Apparent trabecular bone fraction (ABV/TV), mean intercept length (I.TH), mean intercept separation (I.SP), and number of nodes (N.ND) were measured from the extracted trabecular network. Fractal dimension (Fr.D) of the trabecular bone texture was also measured. Paired t-tests showed that the mean values of each texture parameter (except ABV/TV) and of YM along the SI direction were significantly different (p < 0.05) from those along the ML and AP direction. However, the mean values along the ML and AP directions were not significantly different. Multivariate regression of YM as a function of the texture parameters and BMD showed that without adjusting for the effect of BMD, YM was significantly explained by all the texture parameters (R2 = 0.2-0.6). When BMD was included in the regression, although the variations in YM of ML, AP, and SI orientations could be explained by BMD alone, some of the texture parameters did improve the overall prediction of the biomechanical properties, while, some parameters such as ABV/TV and Fr.D in the ML orientation showed a more significant overall effect in explaining mechanical strength than did BMD. In conclusion, trabecular texture parameters correlated significantly with BMD and YM. Trabecular texture parameters from projectional radiographs reflect the anisotropy of trabecular structure. Quantitative radiographic assessment of trabecular structure using fine-detail radiography can potentially improve the estimation of bone strength.
骨微结构以及骨密度的测量可能会改善对骨强度的评估。将人类尸体椎骨的立方体标本（N = 26，12毫米×12毫米×12毫米）沿三个正交解剖方向切割，即上下方向（SI）、内外方向（ML）和前后方向（AP）。获取沿所有三个方向的骨立方体的接触式X线照片，然后通过像素尺寸为50微米×50微米的激光扫描仪进行数字化处理。沿三个正交方向对标本进行压缩测试，并计算每个方向的杨氏模量（YM）。使用定量计算机断层扫描（QCT）来获取小梁骨矿物质密度（BMD）的测量值。使用全局灰度阈值化和局部阈值化算法来提取小梁骨网络。从提取的小梁网络中测量表观小梁骨分数（ABV/TV）、平均截距长度（I.TH）、平均截距间距（I.SP）和节点数（N.ND）。还测量了小梁骨纹理的分形维数（Fr.D）。配对t检验表明，每个纹理参数（ABV/TV除外）以及沿SI方向的YM平均值与沿ML和AP方向的平均值有显著差异（p < 0.05）。然而，沿ML和AP方向的平均值没有显著差异。将YM作为纹理参数和BMD的函数进行多变量回归分析表明，在不调整BMD影响的情况下，所有纹理参数均能显著解释YM（R2 = 0.2 - 0.6）。当将BMD纳入回归分析时，虽然ML、AP和SI方向上YM的变化可以仅由BMD解释，但一些纹理参数确实改善了生物力学性能的整体预测，而在ML方向上，一些参数如ABV/TV和Fr.D在解释机械强度方面显示出比BMD更显著的整体效果。总之，小梁纹理参数与BMD和YM显著相关。投影X线照片中的小梁纹理参数反映了小梁结构的各向异性。使用高分辨率X线摄影对小梁结构进行定量放射学评估可能会改善对骨强度的评估。
