Synthetic gradiometer systems for MEG

This paper will describe features and performance of low-T/sub c/ whole-cortex MEG systems which utilise synthetic gradiometers to achieve a high level of environmental noise cancellation. The near field MEG sensitivities achieved through use of synthetic gradiometers typically range from 3 to 7 fT//spl radic/Hz above 1 Hz in moderately shielded rooms and less than 10 fT//spl radic/Hz above a few Hz in open environments. This performance has been observed for fixed vertical and also adjustable MEG systems which can tilt between vertical and horizontal orientations.