Estimation errors of single dipole model applied to twin dipole activity : Computer simulation study
Estimation errors of single dipole model applied to twin dipole activity : Computer simulation study
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单偶极子模型应用于双偶极子活动的估计误差：计算机模拟研究
DOI：
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发表时间：
2001
期刊：
影响因子：
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通讯作者：
H. Sekine
中科院分区：
文献类型：
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作者：
T. Imada;T. Mashiko;H. Sekine
尽管脑磁逆问题本身是不适定的，并且在原理上可能有无穷多个解，但已经提出了各种方法来求解脑磁逆问题。其中，最简单的方法是球形头模型中的单偶极子，这在许多论文中已经被实际使用，以获得由感觉和认知任务激活的偶极子。然而，如果大脑中的活动位置的数量多于一个，例如两个位置接近的偶极子，则这种最简单的单偶极子解决方案会带来位置和力矩的误差。当两个偶极子的距离较小时，当偶极子电流方向平行或反平行时，以及当偶极子电流强度相等时，该误差似乎较大。Lütkenhöner讨论了两个偶极子的可分性[1]。在他的论文中，通过模拟由具有各种关系（包括距离和力矩）的两个偶极子产生的磁场中单个偶极子的定位，他展示了引入多个偶极子解的必要性方面的两个偶极子的可分性。在他的模拟中，他使用了296通道平面型全头部虚拟测量系统的所有通道，从两个偶极子产生的磁场中定位单个偶极子。然而，如果我们使用检测由两个偶极子产生的磁场的全头部测量系统的几个局部通道来定位单个偶极子，则我们能够在某些条件下定位两个分离的偶极子，即当两个偶极子具有距离和力矩的某些关系时。这是经常观察到定位听觉N100m偶极子在左，右半球。此外，在大多数使用部分头部测量系统的实验中，使用多个局部选择的通道的这种定位。那些使用部分磁头测量系统来记录磁场的人在将通道阵列放置在磁头的某个部分上进行测量时，隐含地选择了局部通道。当通过单个偶极子方法定位多个偶极子活动时，这种局部通道选择方法比全通道选择方法具有优势。如图1所示，我们可以通过选择接收来自第一偶极子的较强磁信号和来自第二偶极子的较弱信号的局部通道来获得第一偶极子的更精确的定位。
Various methods have been proposed to solve magnetoencephalographic inverse problems although the problem itself is ill-posed and in principle infinite number of solutions are possible. Among them, the simplest method is the single dipole in a spherical head model, which has been practically used in a lot of papers to get the dipoles activated by the sensory and cognitive tasks. However, if the number of active locations in the brain is more than one, for example two closely located dipoles, this simplest single dipole solution brings an error in location and moment. This error seems to be larger when the distance of the two dipoles is smaller, when the dipole current orientations are parallel or antiparallel, and when the dipole current strengths are equal. Lütkenhöner discussed the separability of two dipoles [1]. In his paper, by simulating localization of a single dipole from the magnetic fields produced by two dipoles with various relationships including the distances and moments, he showed the separability of two dipoles in terms of necessity of introducing multiple dipole solution. In his simulation, he employed all channels of the 296-channel planar type whole-head virtual measurement system to localize a single dipole from the magnetic fields produced by two dipoles. However, if we localize a single dipole using several local channels of a whole-head measurement system that detected the magnetic fields produced by two dipoles, we are able to localize two separated dipoles under some conditions, namely when the two dipoles have some relationships of distance and moment. This is often observed when localizing the auditory N100m dipoles in the left and right hemispheres. Moreover, this localization with several locally selected channels is employed in most of experiments using a partial-head measurement system. Those who are using the partial-head measurement system to record the magnetic fields are implicitly selecting the local channels when they place the channel array over some part of the head for the measurement. When localizing multiple dipole activity by a single dipole method, this local-channel selection method has an advantage over the all-channel selection method. We can get more precise localization of the first dipole by selecting local channels that receive stronger magnetic signals from the first dipole and weaker signals from the second dipole as shown in Fig. 1.