Lütkenhöner B
Institute for Experimental Audiology, University of Münster, Germany.
IEEE Trans Biomed Eng. 1996 Nov;43(11):1049-61. doi: 10.1109/10.541247.
The goal of the study was to explore the most fundamental aspects of a magnetoencephalography (MEG)-based dipole source analysis. For that purpose, a MEG measurement with an ideal magnetometer system (providing the radial component of the magnetic field as a continuous function) is considered. The analytical formulas derived for the variances and covariances of the parameter estimation errors, validated by means of Monte Carlo simulations, allow quantitative predictions in terms of dipole depth, radius and span of the magnetometer system, signal-to-noise (SNR) ratio, and other parameters. A negative correlation exists between radial coordinate and longitudinal component of the moment (perpendicular to radial direction, same plane as actual dipole moment and center of sphere), whereas the other parameters are independent. The standard deviations of the five dipole parameters show fundamental differences with respect to their asymptotic behavior for deep dipoles: If the root mean square (rms) value of the magnetic field is kept constant (moment with depth-dependent amplitude), the error for the transverse coordinate (perpendicular to radial and longitudinal coordinate) is proportional to the distance R between dipole and center of sphere, the errors for the other dipole coordinates, and the relative error for the transverse component of the dipole moment are constant, and the relative error for the longitudinal component of the dipole moment follows a 1/R law.
本研究的目的是探索基于脑磁图（MEG）的偶极子源分析最基本的方面。为此，考虑使用理想磁力计系统进行MEG测量（将磁场的径向分量作为连续函数提供）。通过蒙特卡罗模拟验证的参数估计误差的方差和协方差推导的解析公式，允许根据偶极子深度、磁力计系统半径和跨度、信噪比（SNR）以及其他参数进行定量预测。径向坐标与矩的纵向分量（垂直于径向方向，与实际偶极矩和球心在同一平面）之间存在负相关，而其他参数是独立的。对于深偶极子，五个偶极子参数的标准差在其渐近行为方面表现出根本差异：如果磁场的均方根（rms）值保持恒定（矩具有与深度相关的幅度），横向坐标（垂直于径向和纵向坐标）的误差与偶极子与球心之间的距离R成正比，其他偶极子坐标的误差以及偶极矩横向分量的相对误差是恒定的，偶极矩纵向分量的相对误差遵循1/R规律。
