Ex vivo evaluation of intervertebral disc mechanics using diffusion-weighted imaging on the 7 T MR : effect of degeneration

Structural changes that occur with intervertebral disc (IVD) degeneration have been established. However, there has been a major challenge in differentiating changes that occur solely due to aging from those that might be considered pathological; uncertainty still exists regarding the exact anatomic and physiologic basis for several clinical symptoms. Diffusion-weighted imaging techniques in MRI have emerged as a potential method to further our understanding of the effects of degeneration on the mechanical behaviour of the intervertebral disc. This thesis describes three stages of work: first, a force measurement system was developed to measure forces acting on the intervertebral disc in the MRI environment using Fibre Bragg Grating sensors. Secondly, a loading rig was designed that applied loading conditions simulating postures of the spine (supine, standing, flexion, and extension) to lumbar cadaveric specimens, and an imaging protocol was developed to obtain ADC measurements within defined regions of the disc. ADC values were then compared in these regions between loading conditions. In the final stage, a device was designed to apply compressive strain to annulus fibrosus tissue samples. In this part of the study, the relationship between ADC values and both compressive strain and degenerative state were evaluated. We successfully developed a load measurement system, which was then used to record forces acting on the disc during diffusion imaging. We found ADC values to be significantly higher in the NP than the AF; no change in ADC values was observed between different regions of the AF, regardless of applied load. Further, we found no change in ADC between any of the four loading conditions within any region of the disc. In samples of AF tissue, we found no change to ADC with increasing compressive strain, regardless of degenerative level. A significant decrease in ADC values was found between severely degenerated discs and both mild and moderately degenerated discs. These results expand our understanding of the limitations of ADC measurements to detect changes to mechanical behaviour of the disc, and may help guide the direction of future studies towards other avenues of investigation of disc mechanics.Applied Science, Faculty ofBiomedical Engineering, School ofGraduat