Exploring the origins of EEG motion artefacts during simultaneous fMRI acquisition: Implications for motion artefact correction.
Exploring the origins of EEG motion artefacts during simultaneous fMRI acquisition: Implications for motion artefact correction.
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DOI：
10.1016/j.neuroimage.2018.02.034
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发表时间：
2018-06
期刊：
影响因子：
5.7
通讯作者：
Mullinger KJ
中科院分区：
文献类型：
--
作者：
Spencer GS;Smith JA;Chowdhury MEH;Bowtell R;Mullinger KJ
当受试者的头部相对于磁场旋转时，在与fMRI同时收集的EEG数据内诱发运动伪影（MA）。这些伪影的影响通常已经通过去除在EEG迹线中出现大伪影电压期间的数据周期而得到改善。然而，即使当与其他标准后处理方法相结合时，该策略也不会去除可以支配感兴趣的神经元信号的较小MA。因此，正在开发许多方法，通过测量参考信号，然后在伪影校正中使用这些信号来对MA进行校正。这些方法通常假设头部和EEG帽，加上任何附接的传感器，形成可以由六个运动参数的标准集合表征的刚体。在这里，我们调查的头部/EEG帽系统的运动，以提供更好的理解MA。我们专注于参考层伪影减法（RLAS）方法，因为这允许测量用于测量大脑活动的每个电极的单独参考信号。通过对幻影和受试者的一系列实验，我们发现EEG帽相对于幻影和前额皮肤的运动相对较小，并且这种非刚体运动似乎不会引起头皮和参考信号之间的伪影的相当大的差异。然而，观察到这些信号的幅度的差异，这可能是由于与脑信号相比测量参考信号的系统的几何形状的差异。此外，我们发现，有非刚体运动的头骨和皮肤产生额外的MA组件的摇头，这是不存在的点头。这导致在头皮和参考层上测量的MA的幅度和时间分布的大的差异，降低了基于参考信号的MA校正的功效。总之，我们的数据表明，使用任何基于参考的系统的MA校正的功效对于不同类型的头部运动可能是不同的，其中摇头是最难校正的。这提供了新的信息，通知硬件和后处理方法的发展，以消除MA从EEG数据同时获得的fMRI数据。
Motion artefacts (MAs) are induced within EEG data collected simultaneously with fMRI when the subject's head rotates relative to the magnetic field. The effects of these artefacts have generally been ameliorated by removing periods of data during which large artefact voltages appear in the EEG traces. However, even when combined with other standard post-processing methods, this strategy does not remove smaller MAs which can dominate the neuronal signals of interest. A number of methods are therefore being developed to characterise the MA by measuring reference signals and then using these in artefact correction. These methods generally assume that the head and EEG cap, plus any attached sensors, form a rigid body which can be characterised by a standard set of six motion parameters. Here we investigate the motion of the head/EEG cap system to provide a better understanding of MAs. We focus on the reference layer artefact subtraction (RLAS) approach, as this allows measurement of a separate reference signal for each electrode that is being used to measure brain activity. Through a series of experiments on phantoms and subjects, we find that movement of the EEG cap relative to the phantom and skin on the forehead is relatively small and that this non-rigid body movement does not appear to cause considerable discrepancy in artefacts between the scalp and reference signals. However, differences in the amplitude of these signals is observed which may be due to differences in geometry of the system from which the reference signals are measured compared with the brain signals. In addition, we find that there is non-rigid body movement of the skull and skin which produces an additional MA component for a head shake, which is not present for a head nod. This results in a large discrepancy in the amplitude and temporal profile of the MA measured on the scalp and reference layer, reducing the efficacy of MA correction based on the reference signals. Together our data suggest that the efficacy of the correction of MA using any reference-based system is likely to differ for different types of head movement with head shake being the hardest to correct. This provides new information to inform the development of hardware and post-processing methods for removing MAs from EEG data acquired simultaneously with fMRI data.
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