Effect of micro-computed tomography voxel size and segmentation method on trabecular bone microstructure measures in mice

Blaine A Christiansen

doi:10.1016/j.bonr.2016.05.006

Abstract

Micro-computed tomography (μCT) is currently the gold standard for determining trabecular bone microstructure in small animal models. Numerous parameters associated with scanning and evaluation of μCT scans can strongly affect morphologic results obtained from bone samples. However, the effect of these parameters on specific trabecular bone outcomes is not well understood. This study investigated the effect of μCT scanning with nominal voxel sizes between 6–30μm on trabecular bone outcomes quantified in mouse vertebral body trabecular bone. Additionally, two methods for determining a global segmentation threshold were compared: based on qualitative assessment of 2D images, or based on quantitative assessment of image histograms. It was found that nominal voxel size had a strong effect on several commonly reported trabecular bone parameters, in particular connectivity density, trabecular thickness, and bone tissue mineral density. Additionally, the two segmentation methods provided similar trabecular bone outcomes for scans with small nominal voxel sizes, but considerably different outcomes for scans with larger voxel sizes. The Qualitatively Selected segmentation method more consistently estimated trabecular bone volume fraction (BV/TV) and trabecular thickness across different voxel sizes, but the Histogram segmentation method more consistently estimated trabecular number, trabecular separation, and structure model index. Altogether, these results suggest that high-resolution scans be used whenever possible to provide the most accurate estimation of trabecular bone microstructure, and that the limitations of accurately determining trabecular bone outcomes should be considered when selecting scan parameters and making conclusions about inter-group variance or between-group differences in studies of trabecular bone microstructure in small animals.

Highlights

Micro-computed tomography is the gold standard for quantifying trabecular and cortical bone microarchitecture in small animal models (Bouxsein et al, 2010)
It was found that parameters such as trabecular thickness and connectivity density are strongly affected by scan voxel size, while other parameters such as trabecular number and trabecular separation are less dependent on voxel size
Micro-computed tomography scan voxel size strongly affected several trabecular bone parameters that are commonly reported in small animal studies

Summary

Introduction

Micro-computed tomography (μCT) is the gold standard for quantifying trabecular and cortical bone microarchitecture in small animal models (Bouxsein et al, 2010). There are numerous variables associated with the data acquisition, processing, and evaluation of μCT scans that can affect morphologic results obtained from bone samples. The voxel size for a μCT scan can strongly affect trabecular or cortical bone results if the voxel size is not appropriately small compared to the dimensions of the structure being measured (Kim et al, 2004). When analyzing small structures such as mouse trabeculae (20– 70 μm), which have dimensions on the same order as the smallest voxel size of most commercially available μCT systems (1–10 μm), voxel size can have significant effects on the results (Muller et al, 1996). If μCT scans are performed on live animals in vivo, long scan times and higher radiation dose become important concerns

Methods

Discussion

Conclusion