Sekihara Kensuke, Nagarajan Srikantan S, Poeppel David, Marantz Alec
Department of Electronic Systems and Engineering, Tokyo Metropolitan Institute of Technology, Asahigaoka 6-6, Hino, Tokyo 191-0065, Japan.
IEEE Trans Biomed Eng. 2004 Jan;51(1):90-9. doi: 10.1109/TBME.2003.820329.
The influence of external interference on neuromagnetic source reconstruction by adaptive beamformer techniques was investigated. In our analysis, we assume that the interference has the following two properties: First, it is additive and uncorrelated with brain activity. Second, its temporal behavior can be characterized by a few distinct activities, and as a result, the spatio-temporal matrix of the interference has a few distinctly large singular values. Namely, the interference can be modeled as a low-rank signal. Under these assumptions, our analysis shows that the adaptive beamformer techniques are insensitive to interference when its spatial singular vectors are so different from a lead field vector of a brain source that the generalized cosine between these two vectors is much smaller than unity. Four types of numerical examples verifying this conclusion are presented.
研究了外部干扰对自适应波束形成技术进行神经磁源重建的影响。在我们的分析中，我们假设干扰具有以下两个特性：第一，它是加性的且与脑活动不相关。第二，其时间行为可以由少数几种不同的活动来表征，因此，干扰的时空矩阵具有少数几个明显较大的奇异值。也就是说，干扰可以建模为低秩信号。在这些假设下，我们的分析表明，当干扰的空间奇异向量与脑源的导联场向量差异很大，以至于这两个向量之间的广义余弦远小于1时，自适应波束形成技术对干扰不敏感。给出了验证这一结论的四类数值示例。
