Estimation of Epileptic Source Location by Means of the Dipole Tracing Method

偶极子跟踪系统(简称DT)是我们在这十年中发展起来的，旨在根据头皮电位来估计作为时间函数的人类大脑中活跃神经元的位置。该方法基于具有均匀电导率的逼真头部模型。这种方法固有的困难在于去除头骨的影响，头骨的电导率低至脑组织的1/80。瑞典乌普萨拉大学医院的实验结果是，估计的当前偶极子向头骨中心有系统地移动了30%，并且这个数字得到了大多数成功的使用。然而，当头部距离球体很远时，很难找到矫正的中心，而且当大脑中的电源在空间中分离时，我们在颅骨矫正方面也有困难。我们获得了一种可自动使用…的颅骨矫正术的新思路更多关于计算机工作的内容。基本思路如下。将观察到的由皮质表面上已知位置的人工电偶极子产生的头皮电位与没有颅骨的头皮电位进行比较。它们之间的线性变换应该是数值推导出来的。如果找到这个变换矩阵的算法，就能自动得到偶极子的正确位置。具体的数学过程正在调查中。两个偶极子同时出现的情况下的头骨矫正尚不清楚。乌普萨拉小组有自己的数据采集系统，该系统与我们的兼容，并定期向我们发送数据磁带，供我们制作数据库，用于头骨矫正和追踪癫痫发作期间的异常电活动。当单个字母出现在右侧视野时，第一个偶极子出现在初级视觉皮质，然后移动到左侧视觉关联区、左角回和左侧颞枕叶下部皮质。我们的结果部分与PET数据相吻合。另一方面，当字母出现在左侧视野时，右侧视觉关联区中的偶极子移动到左侧半球，并遵循如上所述的相同路径。较少

The Dipole Tracing (abbreviated as DT) system which we have developed in these ten years is aimed at estimating locations, as a function of time, of active neurons in the human brain in terms of the scalp potentials. This method is based on a realistic head model with uniform electric conductivity. Difficulty inherent in this method is in removal of the effect of skull which has electric conductivity as low as 1/80 times that of the brain tissue. A systematic displacement of the estimated current dipoles towards the center of the skull by 30% was observed as a result of the experiment at University Hospital, Uppsala, Sweden, and this number was used mostly successfully. However, when the head is very remote from a sphere, it is difficult to find the center for the correction, and moreover when electric sources in the brain are separated in space we also have a difficulty in the skull correction. We have obtained a new idea for skull correction technique which can be used automatically … More on computer work. The basic idea is the following. The observed scalp potentials generated by an artificial current dipole on the cortical surface at a know position are compared with scalp potentials which would be obtained without the skull. A linear transformation between these should be numerically derived. If algorithm of finding this transformation matrix is found, the correct position of a dipole is automatically obtained. The detail mathematical processes are under investigation. The skull correction in case of two simultaneous dipoles is not clear as yet. The Uppsala group has their own data acquisition system which is compatible to ours and are sending us data magnetic tape routinely for us to make a data base for the skull correction and tracing abnormal electric activity during seizure.Cognition processes of single letters and characters were examined with the DT system. When a single letter was presented on the right visual field, the first dipole appeared in the primary visual cortex and then moved to the left visual association area, left angular gyrus, and to left inferior temporo-occipital cortex. Part of our result agrees with PET data. When, on the other hand, a letter was presented on the left visual field, a dipole in the right visual association area moved to the left hemisphere and followed the same path as described above. Less