Quantitative magnetic resonance imaging of enzymatically induced degradation of the nucleus pulposus of intervertebral discs

Study Design. The structural integrity of the nucleus pulposus (NP) of intervertebral discs was targeted by enzyme-specific degradations to correlate their effects to the magnetic resonance (MR) signal. Objective. To develop quantitative MR imaging as an accurate and noninvasive diagnostic tool to better understand and treat disc degeneration. Summary of Background Data. Quantitative MR analysis has been previously shown to reflect not only the disc matrix composition, but also the structural integrity of the disc matrix. Further work is required to identify the contribution of the structural integrity versus the matrix composition to the MR signal. Methods. The bovine coccygeal NPs were injected with either enzyme or buffer, incubated at 37 C as static, unloaded and closed 3-disc segments, and analyzed by a 1.5-Tesla MR scanner to measure MR parameters. Results. Collagenase degradation of the NP significantly decreased the relaxation times, slightly decreased the magnetization transfer ratio, and slightly increased the apparent diffusion coefficient. Targeting the proteoglycan and/or hyaluronan integrity by trypsin and hyaluronidase did not significantly affect the MR parameters, except for an increase in the apparent diffusion coefficient of the disc after trypsin treatment. Conclusions. Our results demonstrate that changes in the structural integrity of matrix proteins can be assessed by quantitative MR.