Department of Epileptology, Tohoku University Graduate School of Medicine, Sendai, Japan.
Clin Neurophysiol. 2013 Jul;124(7):1283-9. doi: 10.1016/j.clinph.2013.04.004. Epub 2013 May 9.
Localization accuracy in magnetoencephalography (MEG) recordings is highly dependent on signal to noise ratio, which is difficult to control.
We have post-processed our data in order to reduce noise to a level permitting adequate source localization with equivalent current dipole methods. In 30 consecutive epilepsy patients, MEG was recorded using a whole-head MEG system consisting of 204 planar gradiometer and 102 magnetometers, with simultaneous EEG. Data were reviewed to identify interictal spikes. The initial analysis was done after employing a spatiotemporal signal space separation (tSSS) method. A total of 18 dipole clusters in 15 patients were reanalyzed without tSSS, to compare the number, goodness of fit, and locations of acceptable dipoles before and after processing.
In 8 of 18 clusters, although acceptable dipole clusters were captured before processing, there was a clear improvement of all parameters with tSSS. In another 5 clusters, all from patients with vagus nerve stimulators, there were few or no acceptable dipoles before processing, but sufficient dipole clusters were obtained with tSSS.
In contrast to volunteer research subjects, clinical patients cannot be expected to cooperate as fully, and their MEG data are likely to include more interference. This study demonstrates that processing the MEG data with a method to eliminate artifact arising from outside the brain significantly improves the data.
In some cases, this improvement can mean the difference between satisfactory dipole fits vs no possible localization.
脑磁图（MEG）记录中的定位精度高度依赖于信噪比，而信噪比很难控制。
为了将噪声降低到足以用等效电流偶极子方法进行适当源定位的水平，我们已经对数据进行了后处理。在 30 例连续癫痫患者中，使用由 204 个平面梯度计和 102 个磁强计组成的全头 MEG 系统，同时记录脑电图（EEG），对 MEG 进行记录。为了识别发作间期棘波，对数据进行了回顾。初始分析是在采用时空信号空间分离（tSSS）方法之后进行的。在没有 tSSS 的情况下，对 15 例患者中的 18 个偶极子簇进行了总共 18 次重新分析，以比较处理前后可接受偶极子的数量、拟合优度和位置。
在 18 个偶极子簇中的 8 个中，尽管在处理之前已经捕获了可接受的偶极子簇，但 tSSS 仍明显改善了所有参数。在另外 5 个偶极子簇中，所有偶极子簇均来自植入迷走神经刺激器的患者，在处理之前，几乎没有或没有可接受的偶极子，但使用 tSSS 获得了足够的偶极子簇。
与志愿研究对象不同，临床患者不能期望完全合作，并且他们的 MEG 数据可能包含更多干扰。本研究表明，使用消除源自大脑外部的伪影的方法处理 MEG 数据可以显著改善数据。
在某些情况下，这种改进可能意味着令人满意的偶极子拟合与无法进行定位之间的区别。
