Purpose: Imaging of the cervical spine in functional positions has so far been limited to conventional X-ray examinations or the scarcely available open magnetic resonance imaging (MRI). An MRI compatible positioning device allows MRI examinations in various positions and even in motion. In combination with high-resolution T2-weighted MRI it allows detailed functional imaging of the cervical spine and nerve roots. To evaluate the utility of this method a population of patients from a clinical study was examined 5 years after anterior cervical discectomy and fusion (ACDF).
Methods: A total of 32 patients (median age 51.5 years, 15 female, 17 male) were examined after a median interval of 64.3 months from ACDF including 16 patients with a titanium cage and 16 with autologous bone graft. The prototype of an MR compatible positioning device (NeuroSwing) was used for MRI of the cervical spine in functional positions on a 1.5 T MRI unit (Siemens Avanto). A real-time true fast imaging with steady-state precession (FISP) sequence [6 mm, TR 704, TE 1.3 ms, matrix 256 x 207, field of view (FoV) 22 cm] was used for monitoring of flexion up to 45° and extension up to 40° or until patient discomfort. A sagittal T2 sampling perfection with application optimized contrast using different flip angle evolution sequence (SPACE sequence, 0.9 mm isotropic voxels, TR 1770, TE 186 ms, matrix 320 x 318, FoV 28 cm) and an axial true FISP sequence (3 mm slices, TR 194, TE 1.9 ms, matrix 256 x 256, FoV 22 cm) were used for imaging in the end positions.
Results: Using the motorized positioning device and a real-time true FISP sequence, imaging of the cervical spine in flexion and extension motion was possible in a quality suitable to observe changes in the alignment of vertebral bodies, the width of the spinal canal and the spinal cord itself. The 3D T2-weighted SPACE sequence yielded high quality and resolution images in the maximum flexion and extension positions. Compared to primary axial T2 true FISP slices, axial reconstructions of the T2 SPACE sequence were found to be clearly less affected by metal artifacts with the additional benefit of multiplanar and transforaminal reconstructions.
Conclusions: The combination of a mechanical positioning device and a high-resolution 3D T2-weighted sequence (SPACE) on a conventional 1.5 T MRI allows kinematic imaging of the cervical spine as well as high-resolution imaging in the end positions, even in the presence of metal implants. In this proof of concept study a good visualization of narrowing of the spinal canal in functional positions could be achieved, showing the potential of MRI in functional positions for clinical and research applications.