Synthetic gradiometer systems for MEG

This paper will describe features and performance of low-Tc whole-cortex ME G systems which utilise synthetic gradiometers to achieve a high level of e nvironmental noise cancellation (MEG = magneto-encephalography). The near f ield MEG sensitivities achieved through use of synthetic gradiometers typic ally range from 3 to 7 fT/root Hz above 1 Hz in moderately shielded rooms a nd less than 10 fT/root Hz above a few Hz in open environments. This perfor mance has been observed for fixed vertical and also adjustable MEG systems which can tilt between vertical and horizontal orientations.