Larsson David, Luisier Benoît, Kersh Mariana E, Dall'ara Enrico, Zysset Philippe K, Pandy Marcus G, Pahr Dieter H
Institute of Lightweight Design and Structural Biomechanics, Vienna University of Technology, Guβhausstrasse 27-29, 1040, Vienna, Austria,
Ann Biomed Eng. 2014 May;42(5):950-9. doi: 10.1007/s10439-014-0983-y. Epub 2014 Jan 29.
The aim of this study was to develop a GST-based methodology for accurately measuring the degree of transverse isotropy in trabecular bone. Using femoral sub-regions scanned in high-resolution peripheral QCT (HR-pQCT) and clinical-level-resolution QCT, trabecular orientation was evaluated using the mean intercept length (MIL) and the gradient structure tensor (GST) on the HR-pQCT and QCT data, respectively. The influence of local degree of transverse isotropy (DTI) and bone mineral density (BMD) was incorporated into the investigation. In addition, a power based model was derived, rendering a 1:1 relationship between GST and MIL eigenvalues. A specific DTI threshold (DTI thres) was found for each investigated size of region of interest (ROI), above which the estimate of major trabecular direction of the GST deviated no more than 30° from the gold standard MIL in 95% of the remaining ROIs (mean error: 16°). An inverse relationship between ROI size and DTI thres was found for discrete ranges of BMD. A novel methodology has been developed, where transversal isotropic measures of trabecular bone can be obtained from clinical QCT images for a given ROI size, DTI thres and power coefficient. Including DTI may improve future clinical QCT finite-element predictions of bone strength and diagnoses of bone disease.
本研究的目的是开发一种基于梯度结构张量（GST）的方法，用于准确测量小梁骨的横向各向异性程度。利用高分辨率外周定量CT（HR-pQCT）和临床级分辨率定量CT扫描的股骨亚区域，分别在HR-pQCT和定量CT数据上使用平均截距长度（MIL）和梯度结构张量（GST）评估小梁方向。研究纳入了局部横向各向异性程度（DTI）和骨密度（BMD）的影响。此外，推导了一个基于幂的模型，得出GST与MIL特征值之间的1:1关系。对于每个研究的感兴趣区域（ROI）大小，都发现了一个特定的DTI阈值（DTI thres），在该阈值以上，GST的主要小梁方向估计在95%的其余ROI中与金标准MIL的偏差不超过30°（平均误差：16°）。对于离散的BMD范围，发现ROI大小与DTI thres之间存在反比关系。已经开发出一种新方法，对于给定的ROI大小、DTI thres和幂系数，可以从临床定量CT图像中获得小梁骨的横向各向同性测量值。纳入DTI可能会改善未来临床定量CT对骨强度的有限元预测和骨疾病的诊断。
