Ogura Y, Sekihara K
Central Research Laboratory, Hitachi, Ltd., Tokyo, Japan.
IEEE Trans Biomed Eng. 1993 Sep;40(9):919-24. doi: 10.1109/10.245613.
The relationship between dipole parameter estimation errors and measurement conditions in magnetoencephalography is determined by computer simulation. The model uses a single current dipole in a spherical homogeneous medium. Dipole parameters are estimated using a moving dipole procedure. Signal-to-noise ratio (SNR) is defined as the square-root of the ratio of the average signal power to the average noise power over all measurement points. At SNR > 20, accurate estimation can be carried out independently of dipole depth and coil size. At SNR < 20, dipole depth influences estimation error. When the dipole is located near the center of the sphere, the measurement region should include both extrema of the magnetic field to minimize estimation error. However, when the dipole is not so deep, the position of the measurement region does not influence estimation error. When SNR < 4, estimation error increases as coil size increases. Coil size minimizing estimation error is determined by the ratio of environmental magnetic field noise to electrical noise. For a constant size of measurement region, increasing the number of measurement points decreases estimation error to a certain level. This error level depends on SNR. The number of measurement points required to minimize estimation error also depends on SNR.
通过计算机模拟确定了脑磁图中偶极子参数估计误差与测量条件之间的关系。该模型在球形均匀介质中使用单个电流偶极子。使用移动偶极子程序估计偶极子参数。信噪比（SNR）定义为所有测量点上平均信号功率与平均噪声功率之比的平方根。在SNR>20时，可以独立于偶极子深度和线圈尺寸进行准确估计。在SNR<20时，偶极子深度会影响估计误差。当偶极子位于球体中心附近时，测量区域应包括磁场的两个极值，以最小化估计误差。然而，当偶极子不太深时，测量区域的位置不会影响估计误差。当SNR<4时，估计误差随着线圈尺寸的增加而增加。使估计误差最小化的线圈尺寸由环境磁场噪声与电噪声的比率决定。对于恒定大小的测量区域，增加测量点的数量会将估计误差降低到一定水平。该误差水平取决于SNR。使估计误差最小化所需的测量点数量也取决于SNR。
