UCSF

266 million individuals are diagnosed with intervertebral disc degeneration annually. Most of these individuals experience pain and reduced mobility, but some are asymptomatic. In contrast to age-related physiologic disc degeneration, pathologic disc degeneration is hypothesized to entail changes to the proteoglycan matrix within the disc. T1rho-weighted MR imaging has the ability to detect subtle changes in disc biochemistry, and may therefore discriminate between pathologic vs. physiologic disc degeneration. However, the contribution of individual biochemical changes to T1rho signals is unclear. Therefore, the goal of this study is to elucidate the individual roles of proteoglycan concentration and molecular weight on T1rho relaxation time. To do this, MRI phantoms with prescribed differences in the concentration and molecular weight of proteoglycan-mimicking dextrans were fabricated and imaged with T1rho-weighted MRI. Results showed that changing the dextran concentration changed T1rho relaxation times by up to 8 percent, while varying dextran size changed T1rho relaxation times by up to 47 percent. Proteoglycan fragmentation is an early marker of disc degeneration that precedes proteoglycan loss from the disc. Prior studies reported that T1rho relaxation times are correlated with disc proteoglycan content. Thus, our findings are important because they are the first to show that T1rho relaxation times are also sensitive to polysaccharide fragment size, and therefore T1rho relaxation times in the disc may reflect proteoglycan degradation in the very early stages of disc degeneration.