Purpose: Quantitative MRI is currently being tested as an early and non-invasive diagnostic tool of disc problems prior to the appearance of symptoms. The aim of the present study was to determine the effects of cyclic loading and enzymatic digestion on quantitative MRI, biochemical composition, and mechanical properties of intervertebral disc tissue. Methods: Bovine tail segments consisting of three discs were subjected to 16h of cyclic compression loading (50N–300N–50N at 1Hz) or left unloaded for 16h while in saline solution at 37°C. Prior to loading, the nucleus pulposus were injected with either a trypsin or buffer solution. MR examinations were carried out in a 1.5T Siemens` Avanto system to measure T1 and T2 relaxation times, magnetization transfer ratio (MTR), and trace of the apparent diffusion coefficient (TrD). The nucleus pulposus and annulus fibrosus were dissected and analyzed for contents of water, glycosaminoglycan, total collagen, and denatured collagen. Cylindrical nucleus pulposus and annulus fibrosus tissue plugs were harvested, prepared, and tested under confined compression to measure compressive modulus (HA) and hydraulic permeability (k). ANOVA and linear regression analyses were performed (p< 0.05). Results: Loading decreased the T1, T2, and TrD of NP while it increased MTR. Only water content in the nucleus pulposus was significantly influenced by loading. T1, water content, and k of the annulus fibrosus tissue were significantly reduced with loading.|Enzymatic treatment of the nucleus pulposus had no effect on its MR properties, but increased the percent of denatured collagen and thus decreased HA. None of the biochemical, mechanical, and MR parameters of the annulus fibrosus changed with trypsin treatment. Conclusions: Dynamic loading of the disc segments for 16h decreased the permeability of both disc tissues. This was consistent with the measured drop in tissue hydration and was observed as a decrease in T1. Targeted trypsin digestion of the nucleus pulposus was confirmed with no detectable changes in the biochemical, biomechanical, or MR properties of the annulus fibrosus. Future studies will address additional quantitative MR parameters such as T1-rho, a higher strength magnet, and different enzymatic treatments. Funding: Other Education Grant Funding Parties: Canadian Institutes of Health Research, McGill William Dawson Scholar Award, and Whitaker Foundation

Introduction Fluid dynamics in the intervertebral disc plays an important role in the overall mechanical function as well as nutritional supply for both the annulus fibrosis (AF) and the nucleus pulposus (NP). The apparent diffusion coefficient of water in intervertebral discs has been suggested to be related to the matrix composition as well as the structural integrity of the disc. Methods Lesions were created in two intervertebral lumbar discs in 18 in-bred Sprague Dawley rats (approved by Animal Ethics Committee) using a 14G hypodermic syringe to induce degenerative change as described by Sobajima et al (. 1. ). Regenerative treatment involved the injection of multipotent stem cells isolated from the olfactory mucosa. These cells were injected either at the time of creation of the lesion or six weeks after creation of the lesion. MRI experiments were undertaken at 25.0 ± 0.1 °C on a Bruker Avance NMR spectrometer (Bruker Bio-Spin, Rheinstetten, Germany) using a 7.0T vertical bore magnet system, equipped with a 1.1 T m-1 (110 G cm-1) gradient set and 15 mm ‘birdcage’ RF resonator. Specimens for testing were immersed in physiological saline inside a 15 mm NMR. Both multi echo and diffusion weighted images were acquired with a recycle time TR = 2 s and 8 averages using a 0.7 mm slice thickness, a field of view (FOV) of ca. 15 × 15 mm and a 128 × 128 matrix. For multi echo experiments the echo time was 5 ms with 64 echoes and for DT imaging a diffusion gradient duration δ = 2 ms and diffusion delay Δ = 12 ms. The diffusion tensor was calculated from the seven requisite diffusion-weighted images using in-house Matlab® code (The Mathworks, Natick, MA) written for the purpose. Results Preliminary results of the multi echo images indicate that intervertebral disc degradation results in observable differences in the T2 of the NP ((mean/SD (ms)) control disc (63.2/3.4), untreated (49.5/1.4) and treated (49.7/3.4)). Diffusion tensor results show isotropic diffusion in the NP with anisotropic diffusion in the AF and observable differences in magnitude. Discussion The use of high resolution MRI has been shown to provide a useful tool for quantifying the effects of regenerative treatments for degenerative disc disease