Characterization of Normal and Degenerative Diskcovertebral Complexes Using Qualitative and Quantitative Magnetic Resonance Imaging at 4.7 T: Longitudinal Evaluation of Immature and Mature Rats

Purpose or Learning Objective: We assessed the feasibility of qualitative, semiquantitative, and multiparametric quantitative magnetic resonance imaging (MRI) using a three-dimensional (3D) ultrashort echo time (3D-UTE) sequence together with two-dimensional (2D)-T2 and 3D-T1 mapping sequences to evaluate normal and pathological diskcovertebral complexes (DVCs). We tested both mature and immature rats at 4.7 T. We assessed the diskc (nucleus pulposus [NP] and annulus fibrosus [AF]), vertebral end plate (cartilage end plate [CEP] and growth plate [GP]), and subchondral bone (SB), using a rat model of degenerative diskc disease (DDD).

Methods or Background: DDD was induced by percutaneous diskc trituration and collagenase injection of the tail. The animals were imaged at 4.7 T. The adjacent diskc served as the control. The MRI protocol consisted of 3D-UTE, 2D-T2, and 3D-T1 mapping sequences and was performed at baseline and each week (W) postoperatively for 2 weeks. Visual analysis and signal intensity measurements from the 3D-UTE images, as well as T2 and T1 measurements, were performed in all DVC portions. Histological analysis with hematoxylin and -eosin and Masson trichrome staining was performed following death euthanization of the rats at 2 weeks, and the results were compared with the MRI findings.

Results or Findings: Complete qualitative identification of the normal zonal anatomy of the DVC, including the AF, CEP, and GP, was achieved using the 3D-UTE sequence. Both the GP and the CEP were thicker in immature than in mature rats. Quantitative measurements of the signal-to-noise and contrast-to-noise ratios in the AF and NP enabled healthy DVCs to be distinguished from surgery-induced DDD, based on a significant increase in these values at 1- week post-surgery. The 2D-T2 mapping results showed a significant increase in the T2 values of the AF and a decrease in the values of the NP between the baseline and W1 and W2 postoperatively. In the 3D-T1 mapping, there was a significant decrease in the T1 values of the AF and NP between baseline and W1 and W2 postoperatively. This variation in T1 and T2 over time was consistent with the results of the 3D-UTE sequence.

Conclusion: Use of 3D-UTE sequence enabled a complete, robust, and reproductible visualization of DVC anatomy in both immature and mature rats under both normal and pathological conditions.

 

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Publication History

Article published online:
22 May 2024