T2 Relaxation Times of Intervertebral Disc Tissue Correlated With Water Content and Proteoglycan Content

Study Design. Human and bovine cadaver study in which biochemical measurements and magnetic resonance (MR) imaging of intervertebral discs were correlated. Objective. To measure the correlations between T-2 relaxation time with water and proteoglycan (PG) content of intervertebral discs. Summary of Background Data. Measuring T-2 relaxation times may provide an accurate noninvasive method of detecting changes in disc water content and biochemistry due to aging or degeneration. Previous studies to validate the use of T-1 or T-2 relaxation times of intervertebral disc tissue have used MR relaxometers, lower field strength imagers, and in 1 case a 1.5-T imager. The dependence of T-2 relaxation times on water and PG content needs further validation in high field clinical MR imagers. Methods. Multiecho MR images were obtained in 14 calf and 5 human cadaver discs. T-2 relaxation times were calculated voxel by voxel for nucleus and anulus regions by fitting the decay of the signal intensity to an exponential model. Water and PG content were measured in samples of nucleus and anulus corresponding to the location of the T-2 measurements. T-2 relaxation times for calf and human specimens were correlated with water or PG content by regression analysis. Results. T-2 relaxation times correlated significantly with water content in human nucleus pulposus, human anulus fibrosus, and calf anulus. T-2 relaxation time correlated significantly with PG content only in the calf anulus. When the human and calf nucleus and anulus specimens were combined, T-2 relaxation times correlated strongly with water (R-2 = 0.81, P < 0.001) and less strongly with PG (R-2 = 0.57, P < 0.001) content. Conclusion. T-2 relaxation times of intervertebral disc anulus fibrosus and nucleus pulposus correlate strongly with water content and weakly with PG content.