Measuring MEG closer to the brain: Performance of on-scalp sensor arrays.
Measuring MEG closer to the brain: Performance of on-scalp sensor arrays.
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DOI：
10.1016/j.neuroimage.2016.12.048
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发表时间：
2017-02-15
期刊：
影响因子：
5.7
通讯作者：
Parkkonen L
中科院分区：
文献类型：
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作者：
Iivanainen J;Stenroos M;Parkkonen L
光泵磁强计(OPM)最近达到了脑磁图(MEG)所需的灵敏度水平。OPM不需要低温，因此可以放置在距头皮几毫米范围内的阵列中，以适应个人头部的大小和形状，从而减少从皮质源到传感器的距离。在这里，我们量化了假想的头皮OPM阵列与306通道最先进的SQUID阵列(102个磁力计和204个平面梯度计)相比在记录脑磁图方面的改进。我们模拟了测量磁场的法向(nOPM；102个传感器)、切向(tOPM；204个传感器)或所有分量(aOPM；306个传感器)的OPM阵列。我们基于10个成人头部的磁共振图像建立了正演模型；我们采用三室边界元模型，电流偶极子均匀地分布在大脑皮层地幔上。与SQUID磁强计相比，nOPM和tOPM产生的信号功率分别高出7.5和5.3倍，而源偶极子场型之间的相关性分别降低了2.8和3.6倍。NOPM、tOPM和SQUID梯度计的场-模式关联值相似。体积电流使nOPM、tOPM和SQUID磁强计的初级电流信号分别平均减少10%、72%和15%。OPM阵列的信息容量明显高于SQUID阵列。与nOPM和tOPM阵列相比，SQUID阵列的偶极子定位精度相似，而基于最小范数的点扩展函数的平均扩展分别是nOPM和tOPM阵列的2.4倍和2.5倍。
Optically-pumped magnetometers (OPMs) have recently reached sensitivity levels required for magnetoencephalography (MEG). OPMs do not need cryogenics and can thus be placed within millimetres from the scalp into an array that adapts to the invidual head size and shape, thereby reducing the distance from cortical sources to the sensors. Here, we quantified the improvement in recording MEG with hypothetical on-scalp OPM arrays compared to a 306-channel state-of-the-art SQUID array (102 magnetometers and 204 planar gradiometers). We simulated OPM arrays that measured either normal (nOPM; 102 sensors), tangential (tOPM; 204 sensors), or all components (aOPM; 306 sensors) of the magnetic field. We built forward models based on magnetic resonance images of 10 adult heads; we employed a three-compartment boundary element model and distributed current dipoles evenly across the cortical mantle. Compared to the SQUID magnetometers, nOPM and tOPM yielded 7.5 and 5.3 times higher signal power, while the correlations between the field patterns of source dipoles were reduced by factors of 2.8 and 3.6, respectively. Values of the field-pattern correlations were similar across nOPM, tOPM and SQUID gradiometers. Volume currents reduced the signals of primary currents on average by 10%, 72% and 15% in nOPM, tOPM and SQUID magnetometers, respectively. The information capacities of the OPM arrays were clearly higher than that of the SQUID array. The dipole-localization accuracies of the arrays were similar while the minimum-norm-based point-spread functions were on average 2.4 and 2.5 times more spread for the SQUID array compared to nOPM and tOPM arrays, respectively.