Quantitative study on water and glycosaminoglycan contents based on T2 relaxation time of intervertebral disks.

BACKGROUND: Water and glycosaminoglycan (GAG) are essential for intervertebral disk biomechanics and their loss marks early degeneration, yet the quantitative relationship between T2 relaxation time and contents of water and GAG remains unclear due to low-resolution sampling. PURPOSE: To establish the quantitative relationships between T2 relaxation time and key biochemical components of intervertebral disk (water and GAG). METHODS: Five fresh bovine caudal spine segments were sectioned into 13 anatomical zones for high spatial resolution sampling and spatially-matched analysis. Multi-echo MR images were obtained on a 3T MR imaging scanner and the T2 relaxation time was calculated, and biochemical assay for water content (tissue volume fraction) and GAG content (%dry weight) were conducted. The quantitative relationships between T2 relaxation time and water content, T2 relaxation time and GAG content were established using linear regression and validated. RESULTS: T2 relaxation time, water content, and GAG content showed a similar spatial distribution pattern within the IVD, with highest values in the central nucleus pulposus and decreasing toward the peripheral annulus fibrosus. T2 relaxation time correlated significantly with water content (R2 = 0.8, p < 0.05), T2 relaxation time correlated significantly with GAG content (R2 = 0.74, p < 0.05). CONCLUSION: The water content and GAG content could be predicted relatively accurately based on the T2 relaxation time through quantitative models.