Garcés Pilar, López-Sanz David, Maestú Fernando, Pereda Ernesto
Laboratory of Cognitive and Computational Neuroscience (UCM-UPM), Centre for Biomedical Technology, 28223 Madrid, Spain.
Biomedical Research Networking Center in Bioengineering Biomaterials and Nanomedicine (CIBER-BBN), Av. Monforte de Lemos 3-5, 28029 Madrid, Spain.
Sensors (Basel). 2017 Dec 16;17(12):2926. doi: 10.3390/s17122926.
Modern Elekta Neuromag MEG devices include 102 sensor triplets containing one magnetometer and two planar gradiometers. The first processing step is often a signal space separation (SSS), which provides a powerful noise reduction. A question commonly raised by researchers and reviewers relates to which data should be employed in analyses: (1) magnetometers only, (2) gradiometers only, (3) magnetometers and gradiometers together. The MEG community is currently divided with regard to the proper answer.
First, we provide theoretical evidence that both gradiometers and magnetometers result from the backprojection of the same SSS components. Then, we compare resting state and task-related sensor and source estimations from magnetometers and gradiometers in real MEG recordings before and after SSS.
SSS introduced a strong increase in the similarity between source time series derived from magnetometers and gradiometers (r² = 0.3-0.8 before SSS and r² > 0.80 after SSS). After SSS, resting state power spectrum and functional connectivity, as well as visual evoked responses, derived from both magnetometers and gradiometers were highly similar (Intraclass Correlation Coefficient > 0.8, r² > 0.8).
After SSS, magnetometer and gradiometer data are estimated from a single set of SSS components (usually ≤ 80). Equivalent results can be obtained with both sensor types in typical MEG experiments.
现代的医科达神经磁图（MEG）设备包含102个传感器三元组，其中包括一个磁力计和两个平面梯度计。第一个处理步骤通常是信号空间分离（SSS），它能有效降低噪声。研究人员和审稿人常提出的一个问题是：分析中应使用哪些数据：（1）仅磁力计数据，（2）仅梯度计数据，（3）磁力计和梯度计数据一起使用。目前MEG领域对于正确答案存在分歧。
首先，我们提供理论证据，证明梯度计和磁力计均来自相同SSS分量的反投影。然后，我们比较了在SSS前后实际MEG记录中，磁力计和梯度计在静息状态以及与任务相关的传感器和源估计情况。
SSS使源自磁力计和梯度计的源时间序列之间的相似度大幅提高（SSS前r² = 0.3 - 0.8，SSS后r² > 0.80）。SSS后，源自磁力计和梯度计的静息状态功率谱、功能连接以及视觉诱发反应高度相似（组内相关系数> 0.8，r² > 0.8）。
经过SSS后，磁力计和梯度计数据是根据一组单一的SSS分量（通常≤ 80）估计得出的。在典型的MEG实验中，两种传感器类型均可获得等效结果。
