Characterization of Ovine Intervertebral Disc Health Across the Lifespan: Relationships Between Quantitative MRI, Radiological, Histological, Biochemical, and Biomechanical Assessments.

Background: Intervertebral disc (IVD) degeneration contributes significantly to chronic low back pain and represents a major clinical challenge. Quantitative MRI (qMRI) techniques offer the potential to assess biochemical and structural disc changes noninvasively, but its use has been slow to be incorporated into studies utilizing spontaneous large animal models. This study characterizes qMRI-derived biomarkers of IVD degeneration across the lifespan in a clinically relevant ovine model. Methods: Ex vivo thoracolumbar spine segments from 10 sheep (13-130 months old) were assessed using 3T MRI, including T2, T2*, T1ρ, adiabatic T1ρ, adiabatic T2ρ, and ADC mapping. Relaxation times were compared with Pfirrmann grade, disc height index, biomechanical testing, GAG/water content, and histological scores. Results: T2 and T2* values in the nucleus pulposus (NP) were negatively correlated with age, Pfirrmann grade, and histological degeneration, and positively correlated with GAG and water content. T2 relaxation times in the annulus fibrosus (AF) were inversely related to biomechanical stiffness, whereas T2* relaxation times in the NP were positively associated. Strong inter-metric correlations were observed between most qMRI measures, but aT1ρ and ADC showed more distinct profiles. Conclusion: These findings support the sensitivity of qMRI in detecting regional and age-related IVD changes and reinforce its utility for noninvasive disc assessment in translational models of degeneration.