A magnetoencaphalogram (MEG) detects the neuromagnetic brain signals of a subject by bringing a set of magnetic sensors, preferably SQUIDs (superconducting quantum interference device), close to the scalp of the subject. The adverse effect of environmental magnetic noise is reduced by using a second set of magnetic sensors which are placed near the subject. The system includes a bandpass filter, to divide the signals from the various sensors into predetermined frequency bands, and a computer to provide a least squares noise component estimate of the noise from each brain wave sensor and to calculate therefrom a filtered brain wave signal having reduced noise.
Low noise magnetoencephalogram system and method