Multichannel SQUID Biomagnetic Systems

The field of biomagnetism advanced considerably since the first recordings of magnetic fields of the human heart in 1963 and of the human brain in 1968. Since the introduction of whole-cortex magnetoencephalography (MEG) systems in 1992, the number of installed channels has dramatically increased, and the magnetic evaluation of the human brain has been gradually finding its place in clinical work. MEG is presently the most important biomagnetic application, and sophisticated MEG systems with large numbers of channels have been developed commercially. The MEG systems must meet certain specifications on noise, dynamic range, slew rate and linearity because they are exposed to environmental noise even when they are operated within shielded rooms. The systems are designed to meet these specifications through optimized design of SQUID flux transformers, SQUID control electronics and data acquisition, and development of various synthetic noise cancellation techniques. The interpretation of the resulting magnetic data is enhanced by combining the MEG results with information from electroencephalography (EEG) and other imaging modalities. In addition, an engineering effort is devoted to the development of various items of MEG peripheral equipment (stimulators, patient support, head positioning, etc.).