A SQUID System for Measurement of Spinal Cord Evoked Field of Supine Subjects

An LTS SQUID biomagnetometer system was developed for the non-invasive diagnosis method of the spinal cord function for orthopedic and neurologic application. The developed biomagnetometer system is characterized by a uniquely shaped cryostat. It has a vertical cylinder-shaped main body and a protrusion from its side surface. An array of SQUID vector gradiometers with a 5 times 8 matrix-like arrangement for 90 mm times 140 mm observation area is installed in the protrusion. Supine subjects are able to fit their cervixes stably to the sensor array by putting them against the protrusion during the measurement. The sensors directed vertically upwards detect magnetic signals from the back of the cervix. An X-ray imaging apparatus is integrated to the SQUID system for the in-situ acquisition of the anatomical information that reveals the position of cervical vertebrae relative to the location of the sensor array. For the performance verification of the developed system, we examined the spinal cord evoked field measurement of a normal subject. We succeeded in observing the transition of the cervical magnetic field distribution induced by the electric pulse stimulation on the median nerve at the subject's wrist.