Institute of Lightweight Design and Structural Biomechanics, Vienna University of Technology, Gusshausstrasse 27-19, A-1040, Vienna, Austria.
Med Phys. 2011 May;38(5):2602-8. doi: 10.1118/1.3582946.
The accuracy of QCT-based homogenized finite element (FE) models is strongly related to the accuracy of the prediction of bone volume fraction (BV/TV) from bone mineral density (BMD). The goal of this study was to establish a calibration methodology to relate the BMD computed with QCT with the BV/TV computed with micro-CT (microCT) over a wide range of bone mineral densities and to investigate the effect of region size in which BMD and BV/TV are computed.
Six human vertebral bodies were dissected from the spine of six donors and scanned submerged in water with QCT (voxel size: 0.391 x 0.391 x 0.450 mm3) and microCT (isotropic voxel size: 0.018(3) mm3). The microCT images were segmented with a single level threshold. Afterward, QCT-grayscale, microCT-grayscale, and microCT-segmented images were registered. Two isotropic grids of 1.230 mm (small) and 4.920 mm (large) were superimposed on every image, and QCT(BMD) was compared both with microCT(BMD) and microCT(BV/TV) for each grid cell.
The ranges of QCT(BMD) for large and small regions were 9-559 mg/cm3 and -90 to 1006 mg/cm3, respectively. QCT(BMD) was found to overestimate microCT(BMD). No significant differences were found between the QCT(BMD)-microCT(BV/TV) regression parameters of the two grid sizes. However, the R2 was higher, and the standard error of the estimate (SEE) was lower for large regions when compared to small regions. For the pooled data, an extrapolated QCTBMD value equal to 1062 mg/ cm3 was found to correspond to 100% microCT(BV/TV).
A calibration method was defined to evaluate BV/TV from QCTBMD values for cortical and trabecular bone in vitro. The QCT(BMD-microCT(BV/TV) calibration was found to be dependent on the scanned vertebral section but not on the size of the regions. However, the higher SEE computed for small regions suggests that the deleterious effect of QCT image noise on FE modelling increases with decreasing voxel size.
基于定量 CT（QCT）的均匀有限元（FE）模型的准确性与从骨密度（BMD）预测骨体积分数（BV/TV）的准确性密切相关。本研究的目的是建立一种校准方法，将 QCT 计算的 BMD 与微 CT（microCT）计算的 BV/TV 相关联，范围为广泛的骨矿物质密度，并研究计算 BMD 和 BV/TV 时区域大小的影响。
从 6 名供体的脊柱中解剖出 6 个人类椎体，在水中用 QCT（体素大小：0.391 x 0.391 x 0.450 mm3）和 microCT（各向同性体素大小：0.018(3) mm3）进行扫描。使用单个灰度级阈值对 microCT 图像进行分割。此后，对 QCT 灰度、microCT 灰度和 microCT 分割图像进行配准。将 1.230 毫米（小）和 4.920 毫米（大）的两个各向同性网格叠加在每个图像上，并为每个网格单元比较 QCT（BMD）与 microCT（BMD）和 microCT（BV/TV）。
大区域和小区域的 QCT（BMD）范围分别为 9-559 mg/cm3 和-90 至 1006 mg/cm3。发现 QCT（BMD）高估了 microCT（BMD）。两种网格尺寸的 QCT（BMD）-microCT（BV/TV）回归参数之间没有显著差异。然而，与小区域相比，大区域的 R2 更高，估计的标准误差（SEE）更低。对于汇总数据，发现外推的 QCTBMD 值等于 1062 mg/ cm3 对应于 100% microCT（BV/TV）。
定义了一种校准方法，用于评估体外皮质骨和小梁骨的 QCTBMD 值的 BV/TV。QCT（BMD-microCT（BV/TV）校准被发现依赖于扫描的椎骨节段，但不依赖于区域的大小。然而，对于小区域计算的更高 SEE 表明，QCT 图像噪声对 FE 建模的有害影响随着体素尺寸的减小而增加。
