Abstract
Purpose Although functional MRI is widely applied in the brain, fMRI of the spinal cord is more technically demanding. Proximity to the vertebral column and lungs results in strong spatial inhomogeneity and temporal fluctuations in B0. Increasing field strength enables higher spatial resolution and improved sensitivity to BOLD signal, but amplifies the effects of B0 inhomogeneity. In this work, we present the first stimulus task fMRI in the spinal cord at 7 T. Further, we compare the performance of single-shot and multi-shot 2D EPI protocols, as they differ in sensitivity to spatial and temporal B0 inhomogeneity.
Methods The cervical spinal cords of 11 healthy volunteers were scanned at 7 T using single-shot 2D EPI at 0.75 mm in-plane resolution and multi-shot 2D EPI at 0.75 and 0.6 mm in-plane resolutions. For each protocol, the BOLD response to thirteen 10-second noxious thermal stimuli applied to the right thumb was acquired in a 10-minute fMRI run. Image quality, temporal SNR, and BOLD activation (percent signal change and z-stat) at both individual- and group-level were evaluated between the protocols.
Results Temporal SNR was highest in single-shot and multi-shot 0.75 mm protocols. In group-level analyses, activation clusters appeared in all protocols in the ipsilateral dorsal quadrant at the expected C6 neurological level. In individual-level analyses, activation clusters at the expected level were detected in some, but not all subjects and protocols. Single-shot 0.75 mm generally produced the highest mean z-statistic, while multi-shot 0.60 mm produced the best-localized activation clusters and the least geometric distortion. Larger than expected within-subject segmental variation of BOLD activation along the cord was observed.
Conclusion Group-level sensory task fMRI of the cervical spinal cord is feasible at 7 T with single-shot or multi-shot EPI. The best choice of protocol will likely depend on the relative importance of sensitivity to activation versus spatial localization of activation for a given experiment.
Highlights First stimulus task fMRI results in the spinal cord at 7 T
Single-shot 0.75 mm 2D EPI produced the highest mean z-statistic
Multi-shot 0.60 mm 2D EPI provided the best-localized activation and least distortion
Group-level sensory task fMRI of the spinal cord is feasible at 7 T
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
Disclosures: All authors state that they have no conflicts of interest.
Preliminary results from this manuscript have previously been presented in the following conference abstracts:
Seifert AC, Vannesjo SJ. Spatial Specificity of BOLD Signal in the Spinal Cord at 7T Using a Noxious Thermal Stimulus. Proceedings of the International Society for Magnetic Resonance in Medicine 2020:1168.
Seifert AC, Vannesjo SJ. Comparison of Physiological Noise Models for Thermal Stimulus fMRI in the Cervical Spinal Cord at 7T. Proceedings of the International Society for Magnetic Resonance in Medicine 2022:1462.
Author name for co-author Falk Eippert was modified to remove the incorrect middle initial.
