Introduction: Cervical spondylotic myelopathy (CSM) is a progressive degenerative disease of the spine that has significant clinical morbidity with significant variation in symptoms. Advanced imaging with magnetic resonance imaging (MRI) has largely been accepted as a tool to evaluate CSM. However, there are limitations on quality and predictability of clinical deterioration, as such MRI now only serves to confirm the diagnosis. Magnetization transfer (MT) is a technique based on the application of offresonance radio‐frequency pulses and observing their effects on MR images. MT contrast has been established as a marker of myelin integrity through its ability to measure the exchange of freely moving protons to large macromolecules. We sought to compare the magnetization ratio (MTR) in healthy subjects to CSM patients.
Materials and Methods: Seven healthy controls and ten patients with clinical and MRI imaging manifestations of CSM were identified by three board‐certified spine surgeons. The severity of CSM was assessed with the Nurick score. For imaging, transverse slices across the intervertebral discs of the cervical spine were acquired using a gradient echo sequence with and without an MT saturation pulse on a 3 Tesla Siemens Prisma scanner (TR = 300 ms, TE = 17 ms, flip angle = 30°, in‐plane resolution = 0.47x0.47 mm2). Image processing was performed using the Spinal Cord Toolbox. The MT1 and MT0 images were coregistered, and MTR images were calculated. A T2 anatomical image of the cervical spine, which was in alignment with MT images, was normalized to a standard spinal cord template (Figure 1A), and the output warping fields were used to transform the MT images to standard space and transform a spinal cord mask from standard to native space. Using the transformed mask, the mean MTR was calculated at each intervertebral disc level (Figure 1B).
Results: The mean MTR across all of the intervertebral disc levels was 34.8 ± 3.5 (mean ± standard deviation) for the controls and 30.4 ± 6.5 for the CSM patients. The CSM patients tended to have a lower mean MTR than the controls, but the difference was not significant (independent samples t‐test, p = 0.110)(Figure 2A). The mean MTR across all of the intervertebral disc levels was not significantly correlated to the Nurick score (Spearman's ρ = ‐0.489, p = 0.151)(Figure 2B). However, when focusing only at the intervertebral disc level with the lowest MTR for each subject, the mean MTR at this level was negatively correlated to the Nurick score (Spearman's ρ = ‐0.725, p = 0.018) (Figure 2C).
Conclusion: CSM patients tended to have decreased MTR indicating myelin degradation compared to our healthy subjects, and MTR was negatively correlated with the severity of CSM. MT MRI may have the potential to better detect structural changes in white matter than conventional T1 and T2 imaging techniques.