In vivo and in vitro deformation and strain measurements in human bone and intervertebral disc using MRI based digital volume correlation (DVC)

Abstract

Digital volume correlation (DVC) is emerging as a standard tool for calculating three-dimensional (3D) deformation and strain in biological tissues. To date, DVC has been used extensively in combination with micro computed tomography (micro-CT), synchrotron radiation micro-CT, and clinical CT for strain measurement in trabecular bone, cortical bone, whole bone, and at bone-implant interfaces. However, limited number of studies investigated internal strains within soft biological tissues using CT-based DVC, possibly due to the difficulties of soft tissue visualisation with CT. Additionally, the radiation associated with clinical CT is a limitation that reduces its suitability for use on patients. Using DVC based on MRI may allow non-invasive strain measurements in both soft and hard tissues. The aim of this PhD was to use DVC with MRI for ex vivo strain measurement within human intervertebral disc (IVD) and in vivo strain measurement within human bone and joint. During this PhD, a framework was established to measure strains within human IVDs. Consequently, this technique was used to evaluate the effect of degeneration on the internal strains and the mechanism of failure in human IVDs. Findings identified that degenerate IVDs had higher (p<0.05) axial strains (58% higher), maximum 3D compressive strains (43% higher), and maximum 3D shear strains (41% higher) in comparison to the non-degenerate IVDs, mainly in the lateral and posterior annulus. Subsequently, MRI sequences and DVC settings were optimised to develop a novel clinical MRI-based DVC technique for in vivo deformation and strain measurement in human bone. This technique was implemented to compute in vivo human ankle joint kinematics and tibiotalar joint contact strains. The findings suggested a possible correlation between the sites of peak strains and the location of osteochondral lesions of the talus. In conclusion, DVC was successfully used for ex vivo deformation and strain calculations within human IVDs, and in vivo deformation and strain measurements in human bone and joint. In the future, further development of these techniques may lead to a novel, non-invasive diagnostic tool with the potential to be widely used in clinical settings.