Nolte G, Curio G
Department of Neurology, Freie Universitat Berlin, Germany.
IEEE Trans Biomed Eng. 1999 Apr;46(4):400-8. doi: 10.1109/10.752937.
The consequences of artifact suppression by means of signal-space projection on dipole localization accuracy for magnetoencephalography measurements are studied. Approximate analytical formulas, equivalent to the Cramer-Rao bound, are presented and verified by Monte Carlo simulations which relate the increase of localization error for individual coordinates to the similarity of the artifact field and respective (contravariant) quadrupole fields obtained by differentiating the dipole field with respect to its origin. The expressions simplify significantly for dipoles placed below the center of the measuring system giving rise to highly symmetric field patterns. Formulas are presented both for single- and for multiple-artifact rejection. As illustrative examples artifact fields are constructed which a) lead to highly decreasing signal-to-noise ratio and goodness-of-fit (GOF), while the localization error is unaffected for all coordinates and b) lead to an increase of localization error while the SNR and the GOF stays constant. Finally, the rich structure of localization error increase is demonstrated for a class of artifact fields originating from artifact current dipoles.
研究了通过信号空间投影抑制伪迹对脑磁图测量中偶极子定位精度的影响。给出了与克拉美罗界等效的近似解析公式，并通过蒙特卡罗模拟进行了验证，该模拟将单个坐标的定位误差增加与伪迹场和通过对偶极场相对于其原点求导得到的相应（逆变）四极场的相似性联系起来。对于放置在测量系统中心下方的偶极子，表达式显著简化，从而产生高度对称的场模式。给出了单伪迹和多伪迹抑制的公式。作为示例，构建了伪迹场，其中a）导致信噪比和拟合优度（GOF）大幅下降，而所有坐标的定位误差不受影响；b）导致定位误差增加，而信噪比和GOF保持不变。最后，展示了一类源自伪迹电流偶极子的伪迹场的定位误差增加的丰富结构。
