High-resolution human cervical spinal cord imaging at 7T

We present high-resolution anatomical imaging of the cervical spinal cord in healthy volunteers at the ultrahigh field of 7T with a prototype four-channel radiofrequency coil array, in comparison with 3-T imaging of the same subjects. Signal-to-noise ratios at both field strengths were estimated using the rigorous Kellman method. Spinal cord cross-sectional area measurements were performed, including whole-cord measurements at both fields and gray matter segmentation at 7T. The 7-T array coil showed reduced sagittal coverage, comparable axial coverage and the expected significantly higher signal-to-noise ratio compared with equivalent 3-T protocols. In the cervical spinal cord, the signal-to-noise ratio was found by the Kellman method to be higher by a factor of 3.5 with the 7-T coil than with standard 3-T coils. Cervical spine imaging in healthy volunteers at 7T revealed not only detailed white/gray matter differentiation, but also structures not visualized at lower fields, such as denticulate ligaments, nerve roots and rostral-caudal blood vessels. Whole-cord cross-sectional area measurements showed good agreement at both field strengths. The measurable gray/white matter cross-sectional areas at 7T were found to be comparable with reports from histology. These pilot data demonstrate the use of higher signal-to-noise ratios at the ultrahigh field of 7T for significant improvement in anatomical resolution of the cervical spinal cord, allowing the visualization of structures not seen at lower field strength, particularly for axial imaging.