Discrimination of Multi-Sources Using a Three-Dimensional Magnetoencephalogram Measurement.
Koichiro KOBAYASHI, K. Enomoto, Y. Uchikawa, M. Kotani · Journal of the Magnetics Society of Japan · 1994
We developed a 3-D second-order gradiometer connected to three rf-SQUIDs, which can simultaneously detect field components perpendicular and tangential to the scalp. To assess a 3-D second-order gradiometer for experimental use, we used data from somatosensory evoked fields (SEFs) elicited by simultaneous electrical stimulation of the median nerve in the right wrist and the right thumb. The magnetic field distribution perpendicular to the scalp was not helpful for estimating the location and number of sources owing to the lack of a dipole pattern. By referring to fields tangential to the scalp, however, we were able to clearly discriminate the two sources of excitation of the median nerve and the thumb. It was found that this gradiometer is a powerful device for use in separating a source from multi-sources located close together in the cortex. This can provide information on the new constrained conditions for calculation of the inverse problem with multiple sources, which we found difficult when we used data on the perpendicular magnetic field.