Abstract
Accurate measurement of local strain in heterogeneous and anisotropic bone tissue is fundamental to understand the pathophysiology of musculoskeletal diseases, to evaluate the effect of interventions from preclinical studies, and to optimize the design and delivery of biomaterials. Digital volume correlation (DVC) can be used to measure the three-dimensional displacement and strain fields from micro-Computed Tomography (µCT) images of loaded specimens. However, this approach is affected by the quality of the input images, by the morphology and density of the tissue under investigation, by the correlation scheme, and by the operational parameters used in the computation. Therefore, for each application the precision of the method should be evaluated. In this paper we present the results collected from datasets analyzed in previous studies as well as new data from a recent experimental campaign for characterizing the relationship between the precision of two different DVC approaches and the spatial resolution of the outputs. Different bone structures scanned with laboratory source µCT or Synchrotron light µCT (SRµCT) were processed in zero-strain tests to evaluate the precision of the DVC methods as a function of the subvolume size that ranged from 8 to 2500 micrometers. The results confirmed that for every microstructure the precision of DVC improves for larger subvolume size, following power laws. However, for the first time large differences in the precision of both local and global DVC approaches have been highlighted when SRµCT or in vivo µCT images were used instead of conventional ex vivo µCT. These findings suggest that in situ mechanical testing protocols applied in SRµCT facilities should be optimized in order to allow DVC analyses of localized strain measurements. Moreover, for in vivo µCT applications DVC analyses should be performed only with relatively course spatial resolution for achieving a reasonable precision of the method. In conclusion, we have extensively shown that the precision of both tested DVC approaches is affected by different bone structures, different input image resolution and different subvolume sizes. Before each specific application DVC users should always apply a similar approach to find the best compromise between precision and spatial resolution of the measurements.
Highlights
This paper investigates comprehensively the precision of two digital volume correlation (DVC) approaches that can be used to measure the full three-dimensional (3D) displacement and strain fields of heterogeneous materials
Even though previously other studies have investigated the precision of Digital volume correlation (DVC) methods, in this paper for the first time we report data obtained from five datasets acquired from different bone structures, scanned with three different techniques, and analyzed with two different DVC approaches, providing the most comprehensive dataset available in the literature to date
If a threshold of 200 με is accepted, the corresponding spatial resolution can be found when images from synchrotron light μCT (SRμCT) are used for cortical bone (33 μm for BoneDVC), for trabecular bone (96 μm for BoneDVC, 128 μm for DaVis-direct correlation (DC)), as well as for trabecular bone with biomaterials (117 μm for DaVis-DC)
Summary
This paper investigates comprehensively the precision of two digital volume correlation (DVC) approaches that can be used to measure the full three-dimensional (3D) displacement and strain fields of heterogeneous materials. To evaluate the effect of mechanical stimuli (Birkhold et al, 2017), aging (Razi et al, 2015), musculoskeletal pathologies (e.g., osteoporosis imbalances the bone homeostasis toward reabsorption) (Badilatti et al, 2016), or interventions to treat them (Levchuk et al, 2014), the local mechanical properties on the different bone structural units (BSUs, i.e., trabeculae or osteons) need to be accurately quantified over the whole bone Another example is the study of the effect of biomaterials such as injectable bone cements (Danesi et al, 2016) or systems of screws and plates on the bone mechanical properties and fracture healing (Widmer Soyka et al, 2013), where the constructs need to bio-integrate with the tissue and provide mechanical integrity to the organ. It should be noted that the models have to be rigorously validated (Anderson et al, 2007; Jones and Wilcox, 2008) for prediction of both apparent (Schileo et al, 2008; Wolfram et al, 2010; Zysset et al, 2013; Schwiedrzik et al, 2016) and local (Zauel et al, 2006; Chen et al, 2017; Costa et al, 2017; Gustafson et al, 2017) properties before their application
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