基于 μCT 和 MDCT 的有限元模型预测骨强度：需要多少空间分辨率？

Prediction of bone strength by μCT and MDCT-based finite-element-models: how much spatial resolution is needed?

机构信息

Department of Radiology, Technische Universität München, Munich, Germany; Department of Radiology, University of California, San Francisco, CA, United States; Max Planck Institute for Extraterrestrial Physics, Garching, Germany.

Max Planck Institute for Extraterrestrial Physics, Garching, Germany.

出版信息

Eur J Radiol. 2014 Jan;83(1):e36-42. doi: 10.1016/j.ejrad.2013.10.024. Epub 2013 Nov 8.

DOI:10.1016/j.ejrad.2013.10.024

PMID:24274992

Abstract

OBJECTIVES

Finite-element-models (FEM) are a promising technology to predict bone strength and fracture risk. Usually, the highest spatial resolution technically available is used, but this requires excessive computation time and memory in numerical simulations of large volumes. Thus, FEM were compared at decreasing resolutions with respect to local strain distribution and prediction of failure load to (1) validate MDCT-based FEM and to (2) optimize spatial resolution to save computation time.

MATERIALS AND METHODS

20 cylindrical trabecular bone specimens (diameter 12 mm, length 15-20mm) were harvested from elderly formalin-fixed human thoracic spines. All specimens were examined by micro-CT (isotropic resolution 30 μm) and whole-body multi-row-detector computed tomography (MDCT, 250 μm × 250 μm × 500 μm). The resolution of all datasets was lowered in eight steps to ~ 2,000 μm × 2000 μm × 500 μm and FEM were calculated at all resolutions. Failure load was determined by biomechanical testing. Probability density functions of local micro-strains were compared in all datasets and correlations between FEM-based and biomechanically measured failure loads were determined.

RESULTS

The distribution of local micro-strains was similar for micro-CT and MDCT at comparable resolutions and showed a shift toward higher average values with decreasing resolution, corresponding to the increasing apparent trabecular thickness. Small micro-strains (εeff<0.005) could be calculated down to 250 μm × 250 μm × 500 μm. Biomechanically determined failure load showed significant correlations with all FEM, up to r=0.85 and did not significantly change with lower resolution but decreased with high thresholds, due to loss of trabecular connectivity.

CONCLUSION

When choosing connectivity-preserving thresholds, both micro-CT- and MDCT-based finite-element-models well predicted failure load and still accurately revealed the distribution of local micro-strains in spatial resolutions, available in vivo (250 μm × 250 μm × 500 μm), that thus seemed to be the optimal compromise between high accuracy and low computation time.

摘要

目的

有限元模型（FEM）是一种预测骨强度和骨折风险的有前途的技术。通常，使用技术上可获得的最高空间分辨率，但这在大体积的数值模拟中需要过多的计算时间和内存。因此，FEM 在降低分辨率方面进行了比较，以比较局部应变分布和失效载荷的预测，以（1）验证基于 MDCT 的 FEM，以及（2）优化空间分辨率以节省计算时间。

材料和方法

从老年福尔马林固定的人体胸椎中采集了 20 个圆柱形小梁骨标本（直径 12mm，长度 15-20mm）。所有标本均通过微 CT（各向同性分辨率 30μm）和全身多排探测器 CT（MDCT，250μm×250μm×500μm）进行检查。所有数据集的分辨率均降低了八个步骤，降至~2000μm×2000μm×500μm，并在所有分辨率下计算了 FEM。失效载荷通过生物力学测试确定。在所有数据集之间比较了局部微应变的概率密度函数，并确定了基于 FEM 的和生物力学测量的失效载荷之间的相关性。

结果

在可比分辨率下，微 CT 和 MDCT 的局部微应变分布相似，随着分辨率的降低，平均应变值升高，这与表观小梁厚度的增加相对应。小应变（εeff<0.005）可计算至 250μm×250μm×500μm。生物力学确定的失效载荷与所有 FEM 均呈显著相关，最高可达 r=0.85，并且随着分辨率的降低不会显著变化，但随着阈值的升高而降低，这是由于小梁连接性丧失所致。