Part 2: Quantitative Proton T2 and Sodium Magnetic Resonance Imaging to Assess Intervertebral Disc Degeneration in a Rabbit Model

Study Design. Comparison of sodium concentration ([Na-23]) and proton T-2 relaxation time between normal and degenerated discs in a rabbit model. Objective. The purpose of this article was to evaluate quantitative [Na-23] and T-2 characteristics of discs associated with degenerative changes. Summary of Background Data. Intervertebral disc degeneration is a common chronic condition that may lead to back pain, limited activity, and disability. Noninvasive imaging method to detect early intervertebral disc degeneration is vital to follow disease progression and guide clinical treatment and management. Methods. Dual-tuned magnetic resonance imaging of rabbit discs was performed using 3T. Thirteen rabbits were included in the study; 6 control rabbits (24 normal discs) and 7 rabbits with annular puncture-induced disc degeneration (9 degenerated discs, 19 intact internal-control discs). Dual-tuned magnetic resonance imaging of discs was performed at baseline and 12-week poststab. [Na-23] and T-2 were measured and compared among 3 groups of discs. Results. The mean [Na-23] were 274.8 +/- 40.2 mM for the normal discs, 247.2 +/- 27.7 mM for the internal-control discs, and 190.6 +/- 19.1 mM for the degenerated discs. The corresponding T-2 for 3 groups were 97.1 +/- 12.1 ms, 93.7 +/- 11.9 ms, and 79.0 +/- 9.1 ms, respectively. The [Na-23] is highly correlated with the T-2 in the degenerated discs (r = 0.90, P < 0.01). The mean percent decreases from the normal to degenerated discs were in 30.6% in [Na-23] and 18.6% in T-2, whereas those from the internal-control to degenerated discs were 22.9% in [Na-23] and 15.6% in T-2. Conclusion. Although both [Na-23] and T-2 changes in discs were associated with the disc-punctured rabbits, greater change in [Na-23] is observed at 12-week poststab compared with T-2 change. Because T-2 and [Na-23] reflect different disc properties, performing both imaging under same condition will be helpful in the evaluation of disc degeneration.