2.12. Radiography and magnetic resonance imaging

The rats were conducted with radiography using an in vivo MS FX PRO imaging system (Bruker). The disc height was measured using the ImageJ 1.8 software and calculated using the disc height index (DHI) according to a previously described. ³⁰ The change of DHI was used to evaluate disc degeneration and calculated according to the formula: DHI % = post‐DHI/pre‐DHI × 100%. Post‐DHI was the post‐operation DHI and pre‐DHI was the pre‐operation DHI. Besides, magnetic resonance imaging (MRI) was performed using an MRI system (BRUKER BioSpec), and sagittal T2‐weighted images were used to assess the signal of the discs, indicating the change of water content. Pfirrmann grades based on the T2‐weighted section images were used to evaluate the degree of IDD as previously described. ³⁰