Reference Layer Artefact Subtraction (RLAS): Electromagnetic Simulations
Reference Layer Artefact Subtraction (RLAS): Electromagnetic Simulations
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DOI：
10.1109/access.2019.2892766
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发表时间：
2019-01-01
期刊：
影响因子：
3.9
通讯作者：
Bowtell, Richard
中科院分区：
文献类型：
--
作者：
Chowdhury, Muhammad E. H.;Khandakar, Amith;Bowtell, Richard
脑电图-功能磁共振成像（EEG-fMRI）的应用受到并发功能磁共振成像（fMRI）期间脑电图记录产生的大伪电压的限制。因此，需要新的方法来减少人工制品的大小和可变性。其中一种方法是使用包含参考层（RL）的EEG帽，该参考层具有与生物组织相似的导电性，并且与头皮电隔离。RL带有一组次级电极和引线，它们精确地覆盖在头皮电极上，因此在静态和时变磁场存在的情况下，RL和头皮电极预计会感应到相似的电压。因此，RL伪影减法（RLAS），包括取两个电极的电压差，应该在不影响神经元电压的情况下减弱伪影。先前的实验工作已经证明了RLAS系统在去除不同类型的脑电信号伪影方面的潜力。然而，为了使RLAS系统获得最佳性能，验证RLAS的基本假设并基于电磁仿真对RLAS系统进行优化是非常重要的。本文采用电磁学建模方法，模拟了静态磁场和时变磁场梯度作用下半球形RL和球形体积导体（VC）的感应电压。通过评估RL和VC中产生的电压差异，随着RL几何形状的变化，测试了RLAS方法的有效性，并确定了最佳RL设计。所进行的模拟考虑了RLAS系统相对于梯度等心的真实旋转、移动、点头和晃动，从而深入了解了最佳RLAS设置以及改进RLAS系统EEG帽设计的潜力。
The utility of EEG-fMRI is limited by the large artefact voltages produced in EEG recordings made during concurrent fMRI. Novel approaches for reducing the magnitude and variability of the artefacts are, therefore, required. One such approach involves using an EEG cap incorporating a reference layer (RL), which has similar conductivity to biological tissue and is electrically isolated from the scalp. The RL carries a secondary set of electrodes and leads that precisely overlay on the scalp electrodes so that similar voltages are anticipated to induce at the RL and scalp electrodes in the presence of static and time-varying magnetic fields. RL artefact subtraction (RLAS), which involves taking the difference of the voltages at the two electrodes, should, therefore, attenuate artefacts while leaving neuronal voltages unaffected. Previous experimental work has demonstrated the potential of the RLAS system in removing different types of EEG artefact. However, to get the best performance from the RLAS system, it is important to verify the underlying assumptions of RLAS and to optimize the RLAS system based on electromagnetic simulations. In this paper, electromagnetic modeling was used to simulate the voltages induced in a hemispherical RL and a spherical volume conductor (VC) under the influence of a static magnetic field and time-varying magnetic field gradient. By evaluating the differences in the voltages produced in the RL and VC, as the RL geometry is varied, the efficacy of the RLAS approach is tested and an optimal RL design is identified. The simulations performed accounted for realistic rotations, shifts, nodding, and shaking of the RLAS system with respect to the gradient isocentre, thus giving insight into the optimum RLAS set-up and the potential for improved EEG cap design for an RLAS system.