Brookes Matthew J, Vrba Jiri, Robinson Stephen E, Stevenson Claire M, Peters Andrew M, Barnes Gareth R, Hillebrand Arjan, Morris Peter G
Sir Peter Mansfield Magnetic Resonance Centre, School of Physics and Astronomy, University of Nottingham, University Park, Nottingham, UK.
Neuroimage. 2008 Feb 15;39(4):1788-802. doi: 10.1016/j.neuroimage.2007.09.050. Epub 2007 Oct 10.
In recent years, the use of beamformers for source localisation has significantly improved the spatial accuracy of magnetoencephalography. In this paper, we examine techniques by which to optimise experimental design, and ensure that the application of beamformers yields accurate results. We show that variation in the experimental duration, or variation in the bandwidth of a signal of interest, can significantly affect the accuracy of a beamformer reconstruction of source power. Specifically, power will usually be underestimated if covariance windows are made too short, or bandwidths too narrow. The accuracy of spatial localisation may also be reduced. We conclude that for optimum accuracy, experimenters should aim to collect as much data as possible, and use a bandwidth spanning the entire frequency distribution of the signal of interest. This minimises distortion to reconstructed source images, time courses and power estimation. In the case where experimental duration is short, and small covariance windows are therefore used, we show that accurate power estimation can be achieved by matrix regularisation. However, large amounts of regularisation cause a loss in the spatial resolution of the MEG beamformer, hence regularisation should be used carefully, particularly if multiple sources in close proximity are expected.
近年来，用于源定位的波束形成器显著提高了脑磁图的空间精度。在本文中，我们研究了优化实验设计的技术，并确保波束形成器的应用能产生准确的结果。我们表明，实验持续时间的变化或感兴趣信号带宽的变化，会显著影响波束形成器对源功率重建的准确性。具体而言，如果协方差窗口设置过短或带宽过窄，功率通常会被低估。空间定位的准确性也可能降低。我们得出结论，为了获得最佳精度，实验者应尽可能多地收集数据，并使用跨越感兴趣信号整个频率分布的带宽。这将使重建的源图像、时间历程和功率估计的失真最小化。在实验持续时间较短且因此使用小协方差窗口的情况下，我们表明通过矩阵正则化可以实现准确的功率估计。然而，大量的正则化会导致脑磁图波束形成器的空间分辨率下降，因此应谨慎使用正则化，特别是在预期有多个紧邻源的情况下。
