Operation of a hybrid 28-channel neuromagnetometer

A 28-channel system for neuromagnetic measurements is operative at CNR-IESS in Roma. The instrument uses 28 Nb/PbAuIn dc-SQUID sensors coupled with a flux transformer configuration. The detection coils are arranged on concentric circumferences. In the internal circles are arranged 16 axial first-order gradiometers whereas the external circle is made by 12 first-order planar gradiometers. The vertical gradiometers show a white noise level of ? 5fT/?Hz while the planar ones have a noise ? 6fT/cm?Hz, with a 1/f corner at a few Hz. The evoked potentials of normal subjects and patients affected by various kind of vascular disturbances has been studied. The system has succeeded in 'one shot' localization of some cortical activity. The instrument has also been used to record the spontaneous brain activity in patients affected by focal epilepsy.