Post-euthanasia micro-computed tomography–based strain analysis is able to represent quasi-static in vivo behavior of whole vertebrae

Abstract

Three-dimensional image-based strain measurement in whole bones allows representation of physiological, albeit quasi-static, loading conditions. However, such work to date has been limited to specimens postmortem. The main purpose of this study is to verify the efficacy of deformable image registration of post-euthanasia strain to characterize the in vivo mechanical behavior of rat vertebrae. A micro-computed tomography–compatible custom loading device was used to apply 75 N load to a three-level caudal motion segment of a healthy rat. Loaded and unloaded micro-computed tomography scans were acquired in vivo and post-sacrifice. A micro-computed tomography–based deformable image registration algorithm was used to calculate vertebral strains live and post-euthanasia. No significant difference was found in the in vivo strains (−0.011 ± 0.001) and ex vivo strains (−0.012 ± 0.001) obtained from the comparisons of loaded and unloaded images (p = 0.3). Comparisons between unloaded–unloaded and loaded–loaded scans yielded significantly lower axial strains, representing the error of the method. Qualitatively, high strains were observed adjacent to growth plate regions in evaluating the loaded–unloaded images. Strain patterns in the loaded–loaded and unloaded–unloaded scans were inconsistent as would be expected in representing noise. Overall, live and dead loaded to unloaded comparisons yielded similar strain patterns and magnitudes. Point-wise differences in axial strain fields also supported this observation. This study demonstrated a proof of concept, suggesting that post-euthanasia micro-computed tomography–based strain analysis is able to represent the in vivo quasi-static behavior of rat tail vertebrae.