Abstract
A new 19 channel SQUID magnetometer system has been developed for research use in order to measure the neuromagnetic fields originating from cortices of human brain. This is the total hardware system consisting of 19 SQUID sensors with detecting coils, readout electronics, a liquid helium dewar, a gantry, and an electro-magnetically shielded room. The detecting coils cover an area of 15 cm radius circle. The dewar is newly designed for low consumption of liquid He, and we used fine stainless steel leads for low thermal conduction between the sensors and room temperature electronics. The system could work for a week with one time supply of liquid He.
The noise characteristics, including both time and frequency domain, of all channels were measured. The power spectrums of the noise field are under 10fT/_??_Hz at 30-100Hz and under 18fT/_??_Hz at 1-30Hz. Some other peaks such as 27, 30, 50, and 60Hz are observed at several channels, suggesting power line noise and vibrations of sensors. An alpha rhythm occurring from a subject's head was recorded with the amplitude of about 1 pTpp. From these results, the system has a sufficient ability to measure magnetic fields from human brain.
