Muluaka M, Uchikawa Y, Kotani M, Yamashita Y
Faculty of Science and Engineering, Tokyo Denki University, Saitama, Japan.
Front Med Biol Eng. 1997;8(1):35-45.
To determine the possibility of discriminating multi-sources in the brain by 3D vector magnetic field measurement of a magnetoencephalogram (MEG), measurements were made of magnetic fields produced by two current dipoles implanted in a spherical head model. The 3D vector magnetic field measurements were made by using a 3D second-order gradiometer connected to three rf-SQUIDs, which can detect magnetic field components perpendicular to and tangential to the scalp. The MEG distribution measuring the magnetic field perpendicular to the scalp was not helpful in estimating the location and number of sources because of the lack of a dipole pattern. By referring to the MEG distribution measuring the magnetic field distribution tangential to the scalp, however, two current sources could be clearly discriminated in a spherical head model. It was found that this MEG distribution measuring tangential to the scalp could provide information on new constraint conditions for the calculation of inverse problems with multi-sources. These results were also confirmed by measurement of the mixed somatosensory evoked fields elicited by simultaneous electric stimulation to the median nerve and the thumb.
为了通过脑磁图（MEG）的三维矢量磁场测量来确定在大脑中区分多源的可能性，对植入球形头部模型中的两个电流偶极产生的磁场进行了测量。三维矢量磁场测量是通过使用连接到三个射频超导量子干涉器件（rf-SQUID）的三维二阶梯度仪进行的，该梯度仪可以检测垂直于头皮和平行于头皮的磁场分量。由于缺乏偶极模式，测量垂直于头皮的磁场的脑磁图分布对于估计源的位置和数量没有帮助。然而，通过参考测量平行于头皮的磁场分布的脑磁图分布，可以在球形头部模型中清楚地区分两个电流源。发现这种测量平行于头皮的脑磁图分布可以为多源逆问题的计算提供关于新约束条件的信息。通过对同时电刺激正中神经和拇指所诱发的混合体感诱发电场的测量，也证实了这些结果。
