11 Channel magnetometer for biomagnetic measurements in unshielded environments

The authors describe a novel 11-channel magnetometer designed for operation in unshielded environments. The planar geometry of the system is particularly suitable for recording biomagnetic signals over a flat surface, as required for cardiac and gastrointestinal applications. The specific configuration of the sensor array also makes it possible to use the system for reliable and fast cardiac clinical measurements. Ambient noise rejection was achieved by the use of second-order gradiometers, optimized by means of additional fine balancing, whereas a sensitivity of less than 10 fT/Hz/sup 1/2/ was obtained by low-noise DC-SQUIDs (superconducting quantum interference devices), using Nb/Nb/sub 2/O/sub 5//PbAuIn technology for the Josephson junctions. The system is presently utilized for a systematic investigation of the localization properties of cardiac sources from data obtained during single-shot measurements, which are believed to be suitable for clinical studies.The results of localization are compared with anatomical information from magnetic resonance imaging data.