Taulu S, Simola J
Elekta Neuromag Oy, Helsinki, Finland.
Phys Med Biol. 2006 Apr 7;51(7):1759-68. doi: 10.1088/0031-9155/51/7/008. Epub 2006 Mar 16.
Limitations of traditional magnetoencephalography (MEG) exclude some important patient groups from MEG examinations, such as epilepsy patients with a vagus nerve stimulator, patients with magnetic particles on the head or having magnetic dental materials that cause severe movement-related artefact signals. Conventional interference rejection methods are not able to remove the artefacts originating this close to the MEG sensor array. For example, the reference array method is unable to suppress interference generated by sources closer to the sensors than the reference array, about 20-40 cm. The spatiotemporal signal space separation method proposed in this paper recognizes and removes both external interference and the artefacts produced by these nearby sources, even on the scalp. First, the basic separation into brain-related and external interference signals is accomplished with signal space separation based on sensor geometry and Maxwell's equations only. After this, the artefacts from nearby sources are extracted by a simple statistical analysis in the time domain, and projected out. Practical examples with artificial current dipoles and interference sources as well as data from real patients demonstrate that the method removes the artefacts without altering the field patterns of the brain signals.
传统脑磁图（MEG）的局限性使得一些重要患者群体无法进行MEG检查，例如带有迷走神经刺激器的癫痫患者、头部有磁性颗粒或有导致严重运动相关伪迹信号的磁性牙科材料的患者。传统的干扰抑制方法无法去除源自如此靠近MEG传感器阵列的伪迹。例如，参考阵列方法无法抑制比参考阵列（约20 - 40厘米）更靠近传感器的源所产生的干扰。本文提出的时空信号空间分离方法能够识别并去除外部干扰以及这些附近源产生的伪迹，即使是头皮上的伪迹。首先，仅基于传感器几何结构和麦克斯韦方程，通过信号空间分离完成与大脑相关信号和外部干扰信号的基本分离。在此之后，通过时域中的简单统计分析提取来自附近源的伪迹，并将其投影出去。使用人工电流偶极子和干扰源的实际示例以及来自真实患者的数据表明，该方法在不改变脑信号场模式的情况下去除了伪迹。
