Strength through structure: visualization and local assessment of the trabecular bone structure

Abstract

Abstract. The visualization and subsequent assessment of the inner human bone structures play an important role for better understanding the disease-or drug-induced changes of bone in the context of osteoporosis giving prospect for better predictions of bone strength and thus of the fracture risk of osteoporotic patients. In this work, we show how the complex trabecular bone structure can be visualized using µCT imaging techniques at an isotropic resolution of 26 µm. We quantify these structures by calculating global and local topological and morphological measures, namely Minkowski functionals (MFs) and utilizing the (an-)isotropic scaling index method (SIM) and by deriving suitable texture measures based on MF and SIM. Using a sample of 151 specimens taken from human vertebrae in vitro, we correlate the texture measures with the mechanically measured maximum compressive strength 7 Author to whom any correspondence should be addressed. New Journal of Physics 10 (2008) 1250101367-2630/08/125010+18$30.00 © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft 2 (MCS), which quantifies the strength of the bone probe, by using Pearson's correlation coefficient. The structure parameters derived from the local measures yield good correlations with the bone strength as measured in mechanical tests. We investigate whether the performance of the texture measures depends on the MCS value by selecting different subsamples according to MCS. Considering the whole sample the results for the newly defined parameters are better than those obtained for the standard global histomorphometric parameters except for bone volume/total volume (BV/TV). If a subsample consisting only of weak bones is analysed, the local structural analysis leads to similar and even better correlations with MCS as compared to BV/TV. Thus, the MF and SIM yield additional information about the stability of the bone especially in the case of weak bones, which corroborates the hypothesis that the bone structure (and not only its mineral mass) constitutes an important component of bone stability. Contents

Simulating Bone Atrophy and Its Effects on the Structure and Stability of the Trabecular Bone

“…For our study we chose 17 specimens of young (50 < age < 70) patients with high maximum compressive strength (MCS > 70 Newton (N)) out of a data set (Räth et al, 2008) of 151 cylindrical specimens with a diameter of 8 mm and a length of 14 mm, which were harvested from 73 thoracic and 78 lumbar human vertebrae. The resulting µCT grey-value images with isotropic spatial resolution of 26 µm were segmented using a low-pass filter by convolving the image with a Gaussian kernel with standard deviation 0.8 and support of 1 to remove noise and a fixed global threshold equal to 22% of the maximal grey value to extract the mineralised bone phase (Hildebrand et al 1999).…”

“…We calculate isotropic and anisotropic scaling indices (SIM) (Räth & Morfill 1997;Monetti et al 2004;Müller et al 2006;Räth et al 2008) as measures to characterize the complex trabecular network and its degree of alignment relative to a preferential direction. Generally, scaling indices represent one way to estimate the local scaling properties of a ndimensional point set.…”

“…Having these highly resolved data at hand it now becomes possible to perform a differential analysis of both the structural and the mechanical properties of the trabecular bone. We determine the local structure of the trabecular network by calculating isotropic (α) and anisotropic scaling indices (α x ,α y ,α z ) (Räth et al, 2008). These measures have been proven to be able to discriminate rod-from sheet-like structures and to quantify the alignment of structures with respect to a preferential direction as e.g.…”

The Locally Adapted Scaling Vector Method: A New Tool for Quantifying Anisotropic Structures in Bone Images

“…This method, which is a variant of the Scaling Index Method Monetti et al, 2003;Müller et al, 2006), differs from previous approaches where only an average global directionality on images was considered (Monetti et al, 2004). Recently, the SIM has been applied to µ-CT images of trabecular bone (Monetti et al, 2007;Räth et al, 2008;Monetti et al, 2009) where it was demonstrated that the use of directional information allows identifying the most important load-bearing bone substructures. As shown below, any suitable method to estimate directions in 2D or 3D can be coupled to this structure characterization procedure.…”

Scaling Index Method (SIM): A Novel Technique for Assessment of Local Topological Properties of Porous and Irregular Structures

“…In our present paper we use specimens of cancellous bone as a typical example of such a tissue. We base our numerical analysis on 151 µCT images of trabecular network taken from the human vertebrae as previously described in Räth et al, 2008. The scans were acquired for the central 6 mm in length of the specimen using a µCT scanner (Scanco Medical, Bassersdorf, Switzerland).…”