A 30-channel SQUID vector biomagnetometer system optimized for reclining subjects

We propose an LTS-SQUID biomagnetometer system equipped with vector magnetometers for the purpose of measuring the evoked magnetic field from the spinal cord. In case of measurement around the neck, the number of sensors to be arranged is inevitably limited by the small observation area. To acquire more information on the magnetic field distribution in a limited area, we introduced a vector magnetometer, which has an axial-type gradiometric pick-up coil and two planar-type gradiometric pick-up coils located orthogonal to each other, which detects not only the magnetic field component radial to the body but also the tangential components. The cryostat was designed to put the SQUID sensors close to the back or back of the neck of the subject sitting in a reclining position, so that the subject can relax and hold the position throughout a long-time measurement. The fluctuation caused by the subject´s movement can be suppressed. We installed 10 vector magnetometers arranged in a zigzag pattern in the cryostat and successfully detected the biomagnetic signals from the neck of the subject.