A 129-channel Vector Neuromagnetic Imaging System

We developed a 129-channel vector neuromagnetic imaging system detecting magnetic fields as a vector value. It is expected that further information can be obtained from vector neuromagnetic field than a conventional system. An axial vector first-order gradiometer was developed as a detection coil, which consists of three first-order differential coils wound on the surface of the same bobbin. These three coils are perpendicular to each other. In addition to a radial component of magnetic fields, two tangential components can be calculated from the measured field at each measuring point. The measuring area with a diameter of nearly 20 cm has 43 measuring points. The DC-SQUID which we developed, adopted a double-washer superconducting ring and employed week link Josephson junctions instead of the conventional tunnel junction. Therefore magnetic flux penetrating the SQUID ring is canceled. In addition, the feedback coil is directly connected with the input coil magnetically so that the current in the detection coil can be canceled by the feedback flux. Therefore a crosstalk between adjacent detection coils is negligible. The read-out electronics is based on the Direct Offset Integration Technique. The system noise in a magnetically shielded room is less than 10fT/Hz1/2 above 10Hz. We confirmed that this system could measure various evoked responses. In this report the features of this system and an application will be shown.