Abstract
Digital Volume Correlation (DVC) has become popular for measuring the strain distribution inside bone structures. A number of methodological questions are still open: the reliability of DVC to investigate augmented bone tissue, the variability of the errors between different specimens of the same type, the distribution of measurement errors inside a bone, and the possible presence of preferential directions. To address these issues, five augmented and five natural porcine vertebrae were subjected to repeated zero-strain micro-CT scan (39μm voxel size). The acquired images were processed with two independent DVC approaches (a local and a global one), considering different computation sub-volume sizes, in order to assess the strain measurement uncertainties. The systematic errors generally ranged within ±100 microstrain and did not depend on the computational sub-volume. The random error was higher than 1000 microstrain for the smallest sub-volume and rapidly decreased: with a sub-volume of 48 voxels the random errors were typically within 200 microstrain for both DVC approaches. While these trends were rather consistent within the sample, two individual specimens had unpredictably larger errors. For this reason, a zero-strain check on each specimen should always be performed before any in-situ micro-CT testing campaign. This study clearly shows that, when sufficient care is dedicated to preliminary methodological work, different DVC computation approaches allow measuring the strain with a reduced overall error (approximately 200 microstrain). Therefore, DVC is a viable technique to investigate strain in the elastic regime in natural and augmented bones.
Highlights
Digital Volume Correlation (DVC) has been used to explore the full-field displacement and strain distribution inside specimens from 3D images (Bay et al, 1999; Grassi and Isaksson, 2015; Roberts et al, 2014)
The aim of this work was to quantify the measurement uncertainties of different DVC approaches applied to augmented bones at the organ-level
As no robust alternative reference method is available for measuring internal strains, repeated scans of vertebrae were shared between our institutions in a sort of round-Robin test
Summary
Digital Volume Correlation (DVC) has been used to explore the full-field displacement and strain distribution inside specimens from 3D images (Bay et al, 1999; Grassi and Isaksson, 2015; Roberts et al, 2014). Depending on the nature of the tissue type under investigation and on the voxel size of the input images, the accuracy of strain measurements can range between 300 and 794 microstrain, while the precision between 69 and 630 microstrain (Roberts et al, 2014). All these studies showed how the performance of DVC depends on the natural texture of the specimen (i.e. histomorphometric parameters in trabecular bone), and how DVC is suitable to examine the pre- and post-yield deformation in bone (Liu and Morgan, 2007; Tozzi et al, 2016b)
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