SEFs from the Human Spinal Cord using a Novel Second Order Planar Gradiometer
Somatosensory evoked fields (SEF) elicited by electrical and mechanical  Stimuli have been recorded from the cortex using SQUID gradiometers of various designs, and the SI and SII sources localised (2]. In clinical practice the equivalent evoked potential (EP) study would always be combined with recordings of the afferent pathway in the peripheral nerve and spinal cord. These spinal evoked potentials are complex recordings of afferent volleys . SEF recordings of these locations have been limited due to a) the lack of devices with appropriate geometry for all locations b) the depth and orientation of the sources c) the need for highly screened environments (particularly for spinal cord measurements) d) the need for clinically unacceptable numbers of stimulus averages to achieve acceptable signal/noise ratios. To date for recordings of evoked magnetic fields from the spinal cord the most successful has been the use of a magnetometer in a highly shielded room and up to 8000 averages .
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