STUDY OF FUNCTIONAL IMAGING OF THE BRAIN BASED ON A 3-D VECTOR MEASUREMENT OF A MAGNETOENCEPHALOGRAM.

脑磁图（MEG）测量垂直于头皮的磁场被广泛使用。当皮层的许多不同区域活跃时，存在分离在时间上重叠的多个源的问题。我们已经开发了一个三维（3D）的二阶梯度仪连接到三个超导量子干涉器件（SQUID）的MEG的矢量测量，可以同时检测垂直和切向头皮的磁场分量。为了评估多个源的辨别和分离，我们进行了MEG的混合听觉诱发场（AEF）和体感诱发场（SEF）在时间上重叠的3D矢量测量。垂直于头皮的磁场分布对估计源的位置和数量没有帮助，因为缺乏偶极子模式。但切向头皮的磁场分布可以提供有关约束条件的信息。我们估计多个来源的混合AEF和SEF从MEG数据的磁场切向头皮，使用逆计算算法开发。通过与受试者头部叠加源的磁共振成像（MRI）的比较，证实了该结果。我们得出结论，这种3D矢量磁场测量可以提供约束条件的信息。在计算多源反问题时，可以从切向磁场中得到。到目前为止，我们只使用垂直于头皮的磁场。

Magnetoencephalogram (MEG) measurement of the magnetic field perpendicular to the scalp is widely used. There are problems of separating multiple sources overlapping in time when many distinct areas of the cortex are active. We have developed a three dimensional (3D) second-order gradiometer connected to three superconducting quantum interference devices (SQUIDs) for vector measurement of the MEG that can detect magnetic-field components perpendicular and tangential to the scalp simultaneously. To asses discrimination and separation of multiple sources, we carried out a 3D vector measurement of the MEG with a mixed auditory evoked field (AEF) and a somatosensory evoked field (SEF) overlapping in time. The magnetic-field distribution perpendicular to the scalp was not helpful in estimating the location and number of sources, owing to the lack of a dipole pattern. But the magnetic-field distribution tangential to the scalp can provide information about constraint conditions. We estimated multiple sources of the mixed AEF and SEF from the MEG data of the magnetic-field tangential to the scalp, using a inverse calculation algorithm developed. The result was confirmed by comparison with magnetic resonance imaging (MRI) of a subject's head superimposed source.We conclude that this 3D vector magnetic-field measurement can provide information on constraint conditions. which can obtained from the tangential magnetic-field when we calculate the inverse problem with multiple sources. Up to the present time, we have used only the magnetic-field perpendicular to the scalp.