We proposed a composite superconducting quantum interference devices (SQUIDs) gradiometer with an axial-type gradiometric pick-up coil and two planar-type gradiometric pick-up coils. Three gradiometers are built into a single module in orthogonal position to each other and the pick-up coils of two planar-type gradiometers are concentric. Therefore, the sensor can detect magnetic fields elicited by action currents in a living body as a quasi three-dimensional vector at a specific point. The outward form of the sensors is identical to our conventional axial-type gradiometric SQUID magnetometer. Therefore, the new sensor can be mounted on our conventional sensor array without large modification. We applied the new sensors to the SQUID magnetometer system for the spinal cord evoked magnetic fields and successfully measured the magnetic fields from the spinal cords from small animals.

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The intraoperative transcranial electrical stimulation-motor evoked potential was detectable in all cases in which the preoperative transcranial magnetic stimulation-motor evoked potential was elicited by a lower intensity than 50% of the maximum output of the stimulator. Therefore, simultaneous use of other methods of monitoring should be considered in such cases that need higher output. However, the Japanese Orthopedic Association score or central motor conduction times were not useful criteria. CONCLUSIONS.: The threshold intensity of the preoperative transcranial magnetic stimulation-motor evoked potential was helpful in predicting elicitation of the intraoperative transcranial electrical stimulation-motor evoked potential.