Operation of a hybrid 28-channel neuromagnetometer

A 28-channel system for neuromagnetic measurements operative at CNR-IESS (Instituto di Elettronica dello Stato Solido) is described. The instrument uses 28 Nb/PbAuIn DC-SQUID (superconducting quantum interference device) sensors coupled with a flux transformer configuration. The detection coils are arranged on concentric circumferences. Sixteen axial first-order gradiometers are arranged in the internal circles, while the external circle consists of 12 first-order planar gradiometers. The vertical gradiometers show a white noise level of approximately=5 fT/ square root Hz, while the planar ones have a noise approximately=6 fT/cm square root Hz, with a 1/f corner at a few hertz. The evoked potentials of normal subjects and patients affected by various kinds of vascular disturbances have been studied. The system has succeeded at 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.<
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