Bardouille Timothy, Smith Vanessa, Vajda Elias, Leslie Carson Drake, Holmes Niall
Department of Physics and Atmospheric Science, Dalhousie University, Halifax, NS B3H 4R2, Canada.
Sir Peter Mansfield Imaging Centre, School of Physics and Astronomy, University of Nottingham, University Park, Nottingham NG7 2RD, UK.
Sensors (Basel). 2024 May 29;24(11):3503. doi: 10.3390/s24113503.
Magnetoencephalography (MEG) non-invasively provides important information about human brain electrophysiology. The growing use of optically pumped magnetometers (OPM) for MEG, as opposed to fixed arrays of cryogenic sensors, has opened the door for innovation in system design and use cases. For example, cryogenic MEG systems are housed in large, shielded rooms to provide sufficient space for the system dewar. Here, we investigate the performance of OPM recordings inside of a cylindrical shield with a 1 × 2 m footprint. The efficacy of shielding was measured in terms of field attenuation and isotropy, and the value of post hoc noise reduction algorithms was also investigated. Localization accuracy was quantified for 104 OPM sensors mounted on a fixed helmet array based on simulations and recordings from a bespoke current dipole phantom. Passive shielding attenuated the vector field magnitude to 50.0 nT at direct current (DC), to 16.7 pT/√Hz at power line, and to 71 fT/√Hz (median) in the 10-200 Hz range. Post hoc noise reduction provided an additional 5-15 dB attenuation. Substantial field isotropy remained in the volume encompassing the sensor array. The consistency of the isotropy over months suggests that a field nulling solution could be readily applied. A current dipole phantom generating source activity at an appropriate magnitude for the human brain generated field fluctuations on the order of 0.5-1 pT. Phantom signals were localized with 3 mm localization accuracy, and no significant bias in localization was observed, which is in line with performance for cryogenic and OPM MEG systems. This validation of the performance of a small footprint MEG system opens the door for lower-cost MEG installations in terms of raw materials and facility space, as well as mobile imaging systems (e.g., truck-based). Such implementations are relevant for global adoption of MEG outside of highly resourced research and clinical institutions.
脑磁图（MEG）能够非侵入性地提供有关人类脑电生理学的重要信息。与固定阵列的低温传感器不同，光泵磁力仪（OPM）在MEG中的使用日益增加，这为系统设计和用例的创新打开了大门。例如，低温MEG系统安置在大型屏蔽室内，以便为系统杜瓦瓶提供足够空间。在此，我们研究了在占地面积为1×2米的圆柱形屏蔽体内进行OPM记录的性能。从场衰减和各向同性方面测量了屏蔽效果，还研究了事后降噪算法的价值。基于定制电流偶极体模体的模拟和记录，对安装在固定头盔阵列上的104个OPM传感器的定位精度进行了量化。被动屏蔽将直流（DC）时的矢量场幅度衰减至50.0 nT，电力线频率时衰减至16.7 pT/√Hz，在10 - 200 Hz范围内衰减至71 fT/√Hz（中位数）。事后降噪提供了额外5 - 15 dB的衰减。在包含传感器阵列的体积内仍保持相当程度的场各向同性。数月来各向同性的一致性表明可以很容易地应用场归零解决方案。一个电流偶极体模体产生的源活动幅度适合人类大脑，产生的场波动约为0.5 - 1 pT。模体信号的定位精度为3毫米，未观察到明显的定位偏差，这与低温和OPM MEG系统的性能一致。这种对小尺寸MEG系统性能的验证，在原材料和设施空间方面为低成本MEG装置以及移动成像系统（例如基于卡车的）打开了大门。此类应用对于在资源丰富的研究和临床机构之外全球采用MEG具有重要意义。
