Functional MR Imaging of the Cervical Spinal Cord by Use of Median Nerve Stimulation and Fist Clenching

Abstract

BACKGROUND AND PURPOSE: Findings of blood oxygen level–dependent (BOLD) functional MR (fMR) imaging of the cervical spinal cord, obtained by using a fist-clenching motor task, have been sporadically reported. Because spinal activation by sensory stimuli has a potential at least equal to that of fist clenching, its feasibility was assessed. Whether stimulation of the median nerve could evoke an fMR imaging response at 1.5 T in the cervical spinal cord was investigated, and the response pattern was compared with that obtained by fist clenching.

METHODS: A dynamic cardiac-gated T2*-weighted imaging sequence was used to quantify cervical spinal cord activation under two paradigms with different numbers of subjects. Seven subjects underwent electrical median nerve stimulation at the elbow sufficient to elicit a maximal compound muscle action potential in the flexor carpi radialis muscle. Eleven subjects performed self-paced fist clenching. Cord activation was measured in the sagittal and transverse imaging planes.

RESULTS: In the sagittal view, five of seven subjects had an fMR imaging response in the lower cervical spinal cord upon median nerve stimulation, whereas seven of 11 subjects showed activation with the fist-clenching task. Within the cord, the measured fMR imaging response level was approximately 8–15% with respect to the baseline signal level. In the transverse imaging plane, significant fMR imaging responses could be measured in only two of six and six of nine subjects with median nerve stimulation or fist clenching, respectively. A consistent cross-sectional localization of the activity measured in the spinal cord was not detected, either in terms of the right and left sides or in terms of the posterior and anterior directions.

CONCLUSION: In the sagittal plane, median nerve stimulation at the elbow can evoke an fMR imaging response in the lower cervical spinal cord. The activation pattern was comparable with that obtained by fist clenching. The localization of the segmental fMR imaging activation (C4 through T1) is consistent with the known functional neuroanatomy for both paradigms. In the transverse plane, reliable fMR imaging responses were obtained much less frequently, and assignment of distinct areas of the spinal cord to the stimulation methods used was not possible.