Department of Radiology and Biomedical Imaging, University of California, San Francisco, CA 94107, USA.
Med Phys. 2012 Apr;39(4):1893-903. doi: 10.1118/1.3689813.
Accurate quantification of bone microstructure plays a significant role in understanding bone mechanics and response to disease or treatment. High-resolution peripheral quantitative computed tomography (HR-pQCT) allows for the quantification of trabecular and cortical structure in vivo, with the capability of generating images at multiple voxel sizes (41, 82, and 123 μm). The aim of this study was to characterize the effect of voxel size on structural measures of trabecular and cortical bone and to determine accuracy in reference to micro-CT ([micro sign]CT), the gold standard for bone microstructure quantification.
Seventeen radii from human cadaver specimens were imaged at each HR-pQCT voxel size and subsequently imaged using [micro sign]CT. Bone density and microstructural assessment was performed in both the trabecular and cortical compartments, including cortical porosity quantification. Two distinct analysis techniques were applied to the 41 μm HR-pQCT data: the standard clinical indirect analysis and a direct analysis requiring no density or structural model assumptions. Analysis parameters were adjusted to enable segmentation and structure extraction at each voxel size.
For trabecular microstructural measures, the 41 μm HR-pQCT data displayed the strongest correlations and smallest errors compared to [micro sign]CT data. The direct analysis technique applied to the 41 μm data yielded an additional improvement in accuracy, especially for measures of trabecular thickness. The 123 μm data performed poorly, with all microstructural measures either having moderate or nonsignificant correlations with [micro sign]CT data. Trabecular densitometric measures showed strong correlations to [micro sign]CT data across all voxel sizes. Cortical thickness was strongly correlated with [micro sign]CT values across all HR-pQCT voxel sizes. The accuracy of cortical porosity parameters was highly dependent on voxel size; again, the 41 μm data was most strongly correlated. Measures of cortical density and pore diameter at all HR-pQCT voxel sizes had either weak or nonsignificant correlations.
This study demonstrates the effect of voxel size on the accuracy of HR-pQCT measurements of trabecular and cortical microstructure and presents parameters for HR-pQCT analysis at nonstandard resolutions. For all parameters measured, correlations were strongest at 41 μm. Weak correlations for porosity measures indicate that a better understanding of pore structure and resolution dependence is needed.
准确量化骨微结构对于理解骨力学以及对疾病或治疗的反应具有重要意义。高分辨率外周定量计算机断层扫描（HR-pQCT）允许在体内定量评估小梁和皮质结构，具有生成多种体素大小图像的能力（41、82 和 123μm）。本研究旨在描述体素大小对小梁和皮质骨结构测量的影响，并确定与骨微结构定量的金标准——微计算机断层扫描（micro-CT）[micro sign]CT 的准确性。
对 17 个人体尸体标本的每个 HR-pQCT 体素大小进行成像，然后使用[micro sign]CT 进行成像。在小梁和皮质骨腔室中进行骨密度和微观结构评估，包括皮质孔隙率的量化。对 41μm HR-pQCT 数据应用两种不同的分析技术：标准临床间接分析和无需密度或结构模型假设的直接分析。调整分析参数以实现每个体素大小的分割和结构提取。
对于小梁微观结构测量，与[micro sign]CT 数据相比，41μm HR-pQCT 数据显示出最强的相关性和最小的误差。应用于 41μm 数据的直接分析技术进一步提高了准确性，特别是对于小梁厚度的测量。123μm 数据表现不佳，所有微观结构测量要么与[micro sign]CT 数据具有中度相关性，要么无显著相关性。小梁密度测量在所有体素大小上均与[micro sign]CT 数据具有很强的相关性。皮质厚度与所有 HR-pQCT 体素大小的[micro sign]CT 值具有很强的相关性。皮质孔隙率参数的准确性高度依赖于体素大小；再次，41μm 数据的相关性最强。在所有 HR-pQCT 体素大小下，皮质密度和孔径的测量值要么相关性较弱，要么无显著相关性。
本研究表明体素大小对 HR-pQCT 测量小梁和皮质骨微观结构的准确性有影响，并提出了非标准分辨率下 HR-pQCT 分析的参数。在所测量的所有参数中，41μm 时相关性最强。孔隙率测量值的弱相关性表明需要更好地了解孔隙结构和分辨率依赖性。
