Digital volume correlation can be used to estimate local strains in natural and augmented vertebrae: An organ-level study

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.

Precision of Digital Volume Correlation Approaches for Strain Analysis in Bone Imaged with Micro-Computed Tomography at Different Dimensional Levels

“…To overcome to the first limitation, we suggest to publish in the public domain the images used to test the DVC precision in the different publications. We started this process in previous studies (Palanca et al, 2016;Tozzi et al, 2017;Palanca et al, 2017a) and we suggest that also future publications should share the input datasets or use the published images as benchmark. The reader is encourage to look at the figshare links in the acknowledgments for the complete or partial datasets used in the presented studies and contact the corresponding author for the complete datasets.…”

“…In particular, the previously examined datasets consist in results from trabecular and cortical bone scanned with μCT (Dall ' Ara et al, 2014;Palanca et al, 2015) and with synchrotron light μCT (SRμCT) (Palanca et al, 2017a), from vertebral bodies with and without injected biomaterial scanned with μCT (Palanca et al, 2016;Tozzi et al, 2017), and mice tibiae scanned with SRμCT (Palanca et al, 2017a). Moreover, two new datasets from SRμCT scans of trabecular bone and biomaterials and from in vivo and ex vivo μCT scans of the mouse tibia were included in this study.…”

“…μCT Scans of Natural and Augmented Porcine Vertebral Bodies (Palanca et al, 2016;Tozzi et al, 2017) Ten thoracic vertebral bodies were extracted from spines of pigs killed for alimentary purposes. In this case, ethics approval was not required as per institutional and national guidelines.…”

Micro Finite Element models of the vertebral body: Validation of local displacement predictions

“…The DVC grid is then converted into an 8-noded hexahedral mesh, the displacement field measured from DVC is imposed to the mesh as boundary conditions and is then imported to an FE software package ( ANSYS ® Academic Research, Release 15.0) to compute the strain field. A NS equal to 48voxels (approximately 1872μm) was chosen as the best compromise between precision and spatial resolution of the DVC approach (precision errors below 3.7μm for displacements [40] and approximately 100μɛ for strains [41]).…”

Digital Volume Correlation: Review of Progress and Challenges

“…Let us note that there are few comparisons between local and global approaches to DVC [122,137,169,93,168]. Overall, it is found that the measurement uncertainties are of the same order of magnitude when the total number of kinematic unknowns are similar.…”