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Use of Anionic Contrast agent Magnetic Resonance Imaging (ACMRI) as a new technique for assessing intervertebral disc degeneration Levitz, Joshua Adam

Abstract

Glycosaminoglycan (GAG) depletion is a consistent sign of intervertebral disc degeneration, a cause of lower back pain. Anionic contrast agent MRI (ACMRI) has been able to quantify GAG loss in articular cartilage but it has not yet been tested in the intervertebral disc in a controlled setting. We assessed the feasibility of ACMRI to measure GAG depletion in porcine lumbar intervertebral discs. Three studies were undertaken. In study 1, we performed in-vitro dynamic diffusion MR imaging to assess the best method to ensure contrast agent uptake occurred in the disc. Signal intensity of discs bathed in contrast agent was measured at various points over a 10 hour scan. We determined that isolating the disc from the spine and manually exposing the cartilaginous endplates enhanced diffusion into the central nucleus. This result was used in our subsequent studies. Our second study assessed the ability of ACMRI to indirectly assess GAG concentration in the disc. In-vitro contrast agent uptake in healthy and GAG-degenerated discs was measured by calculating T1 times of disc tissue before and after contrast agent exposure. Using Analysis of Variance, we tested the null hypothesis that the magnitude of T1 after contrast uptake and the change in T1 from before to after contrast uptake (z.T1) was the same in healthy and GAG-depleted discs. The nucleus of degenerated specimens had significantly lower post-contrast T1 times and significantly larger AT1 than healthy discs. There were no significant differences found in the annulus of healthy and degenerated discs. In our final study, we designed a research protocol to correlate axial mechanical properties and ACMRI indices of healthy and GAG-degenerated discs. Loading repeatability tests revealed a one degree of rotational freedom rig, combined with facet joint removal will give reproducible results on repeated tests. Six specimens were tested, and compressive stiffness dropped more in GAG-degenerated discs. ACMRI may be useful in creating a new quantifiable scale of disc degeneration. It may also help in assessing the efficacy of disc therapeutic techniques, and to study the effect of GAG health on the in-vivo mechanics of the spine.

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Attribution-NonCommercial-NoDerivatives 4.0 International

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