The Quantitative Structural and Compositional Analyses of Degenerating Intervertebral Discs Using Magnetic Resonance Imaging and Contrast-Enhanced Micro-Computed Tomography.

The intervertebral disc (IVD) is susceptible to degenerative changes that are associated with low back pain. Murine models are often used to investigate the mechanistic changes in the development, aging, and diseased states of the IVD, yet the detection of early degenerative changes in structure is challenging because of the minute size of the murine IVDs. Histology is the gold standard for examining the IVD structure, but it is susceptible to sectioning artifacts, spatial biases, and requires the destructive preparation of the sample. We have previously demonstrated the feasibility of using Ioversol for the contrast-enhanced micro-computed tomography (microCT) to visualize and quantitate the intact healthy murine IVD. In this work, we demonstrate utility of this approach to monitor the longitudinal changes of in vitro nucleolytic- and mechanical injury- degeneration models of the murine discs and introduce novel quantitative metrics to characterize the structure and composition of the IVD. Moreover, we compared the imaging quality and quantitation of these in vitro models to magnetic resonance imaging (MRI) and histology. Stab puncture, trypsin injection, and collagenase injection all induced detectable and significant changes in structure and composition of the discs overtime. Compared to MRI and histology, contrast-enhanced microCT produced superior images that capture the degenerative progression in these models. Contrast-enhanced microCT was also capable of monitoring the structural deteriorations via the changes in disc height and volume, and novel the nucleus pulposus intensity/disc intensity (NI/DI) parameter provides a surrogate measure of proteoglycan composition (R = 0.96). Overall, this approach allows for the nondestructive monitoring of the structure and composition of the IVD at very high resolutions.