Functional magnetic resonance imaging (fMRI) of the spinal cord (spinal fMRI) is an adaptation of the fMRI method that has been developed for use in the brain. Although the basic principles underlying the methods are the same, spinal fMRI requires a number of specific adaptations to accommodate the periodic motion of the
spinal cord
The spinal cord is a long, thin, tubular structure made up of nervous tissue, which extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column (backbone). The backbone encloses the central canal of the spin ...
, the small cross-sectional dimensions (roughly 8 mm × 15 mm at the largest region) and length (~45 cm in adult humans) of the spinal cord, and the fact that the magnetic field that is used for
MRI varies with position in the spinal cord because of
magnetic susceptibility
In electromagnetism, the magnetic susceptibility (Latin: , "receptive"; denoted ) is a measure of how much a material will become magnetized in an applied magnetic field. It is the ratio of magnetization (magnetic moment per unit volume) to the ap ...
differences between bone and tissues.
Spinal fMRI has been used to produce maps of neuronal activity at most levels of the spinal cord in response to various stimuli, such as touch, vibration, and thermal changes, and with motor tasks.
Research applications of spinal fMRI to date include studies of normal sensory and motor function,
and studies of the effects of trauma
and
multiple sclerosis on the spinal cord.
Two different data acquisition methods have been applied, one based on the established BOLD (
blood-oxygen-level dependent
Blood-oxygen-level-dependent imaging, or BOLD-contrast imaging, is a method used in functional magnetic resonance imaging (fMRI) to observe different areas of the brain or other organs, which are found to be active at any given time.
Theory
Ne ...
) fMRI methods used in the brain, and the other based on SEEP (
signal enhancement by extravascular water protons
Signal enhancement by extravascular water protons, or SEEP, is a contrast mechanism for functional magnetic resonance imaging (fMRI), which is an alternative to the more commonly employed BOLD ( blood-oxygen-level dependent) contrast. This mechan ...
) contrast with essentially proton-density weighted spin-echo imaging (see
MRI). The majority of the studies published to date are based on the SEEP contrast method. Methods demonstrated to overcome the challenges listed above include using a recording of the heart-beat to account for the related time course of spinal cord motion, acquiring image data with relatively high (~ 1–2 mm) spatial resolution to detect fine structural details, and acquiring images in thin contiguous sagittal slices to span a large extent of the spinal cord. Methods based on BOLD contrast have employed parallel imaging techniques to accelerate data acquisition, and imaging slices transverse to the spinal cord, in order to reduce the effects of spatial magnetic field distortions.
Methods based on SEEP contrast have been developed specifically because they have low sensitivity to magnetic field distortions while maintaining sensitivity to changes in neuronal activity.
References
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Neuroimaging