A bi-planar coil system for nulling background magnetic fields in scalp mounted magnetoencephalography.
A bi-planar coil system for nulling background magnetic fields in scalp mounted magnetoencephalography.
复制标题
在头皮安装的磁刻摄影术中用于无效背景磁场的双平面线圈系统。
DOI：
10.1016/j.neuroimage.2018.07.028
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发表时间：
2018-11-01
期刊：
影响因子：
5.7
通讯作者：
Bowtell R
中科院分区：
文献类型：
--
作者：
Holmes N;Leggett J;Boto E;Roberts G;Hill RM;Tierney TM;Shah V;Barnes GR;Brookes MJ;Bowtell R
小型商用光泵磁力仪（OPM）可用于构建一种可穿戴的脑磁图（MEG）系统，该系统允许在记录过程中头部大幅移动。然而，这些传感器的动态范围较小，这意味着在典型的磁屏蔽室（MSR）内剩余静磁场中的移动可能会使传感器输出饱和，导致数据无法使用。通过使用一组电磁线圈来减弱空间变化的剩余磁场，可以缓解这一问题。在此，设计并构建了一种双平面线圈阵列，它能产生一个开放且可进入的扫描环境。这些线圈是使用一种先前用于磁共振成像（MRI）中梯度线圈设计的谐波最小化方法设计的。构建了六个线圈来抵消\(B_x\)、\(B_y\)和\(B_z\)以及三个主要的场梯度\(G_x\)、\(G_y\)和\(G_z\)。这些线圈在\(40×40×40\)立方厘米的体积内产生均匀（在\(\pm5\%\)范围内）的场或场梯度。这个体积足以在基本和自然运动过程中容纳安装在3D打印扫描架中的一组OPM。利用参考传感器测量对线圈进行自动控制，可以将静磁场的最大分量\(B_z\)从\(21.8\pm0.2\)纳特降低到\(0.47\pm0.08\)纳特。最大梯度\(G_z\)从\(7.4\)纳特/米降低到\(0.55\)纳特/米。高精度光学跟踪使得涉及可控和可测量头部运动的实验得以进行，结果表明，当应用场归零技术时，在该场中扫描架旋转\(\pm34°\)以及OPM平移\(\pm9.7\)厘米，在OPM阵列上仅产生\(1\)纳特的磁场变化。通过对与测量运动参数相关的场变化进行线性回归，这种变化可进一步降低到\(0.04\)纳特。为了在实际的MEG实验中证明双平面线圈场抵消系统的有效性，研究了一种新的视网膜拓扑结构测量方法，其中刺激保持固定，受试者的头部运动将视觉呈现转移到视野的左下或右下象限。左右视野刺激在对侧半球产生了预期的反应。这个简单的演示表明，双平面线圈系统允许在不受约束的受试者身上进行准确的OPM - MEG记录。
描述了用于磁场归零的双平面线圈的设计和使用。
磁场归零允许在头皮MEG记录过程中受试者大幅移动。
光学跟踪表明在这些运动过程中可以获取高质量数据。
展示了一种受试者移动头部的视网膜拓扑结构的新测量方法。
Small, commercially-available Optically Pumped Magnetometers (OPMs) can be used to construct a wearable Magnetoencephalography (MEG) system that allows large head movements to be made during recording. The small dynamic range of these sensors however means that movement in the residual static magnetic field found inside typical Magnetically Shielded Rooms (MSRs) can saturate the sensor outputs, rendering the data unusable. This problem can be ameliorated by using a set of electromagnetic coils to attenuate the spatially-varying remnant field. Here, an array of bi-planar coils, which produce an open and accessible scanning environment, was designed and constructed. The coils were designed using a harmonic minimisation method previously used for gradient coil design in Magnetic Resonance Imaging (MRI). Six coils were constructed to null , and as well as the three dominant field gradients , and . The coils produce homogeneous (within ±5%) fields or field gradients over a volume of 40 × 40 × 40 cm3. This volume is sufficient to contain an array of OPMs, mounted in a 3D-printed scanner-cast, during basic and natural movements. Automated control of the coils using reference sensor measurements allows reduction of the largest component of the static field () from 21.8 ± 0.2 nT to 0.47 ± 0.08 nT. The largest gradient () was reduced from 7.4 nT/m to 0.55 nT/m. High precision optical tracking allowed experiments involving controlled and measured head movements, which revealed that a rotation of the scanner-cast by ±34° and translation of ±9.7 cm of the OPMs in this field generated only a 1 nT magnetic field variation across the OPM array, when field nulling was applied. This variation could be further reduced to 0.04 nT by linear regression of field variations that were correlated with the measured motion parameters. To demonstrate the effectiveness of the bi-planar coil field cancellation system in a real MEG experiment, a novel measurement of retinotopy was investigated, where the stimulus remains fixed and head movements made by the subject shift the visual presentation to the lower left or right quadrants of the field of view. Left and right visual field stimulation produced the expected responses in the opposing hemisphere. This simple demonstration shows that the bi-planar coil system allows accurate OPM-MEG recordings to be made on an unrestrained subject. The design and use of bi-planar coils for magnetic field nulling is described. Field nulling allows large subject movements during onscalp MEG recordings. Optical tracking shows high quality data can be acquired during these movements. A novel measurement of retinotopy where the subject moves their head is shown.
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影响因子：
3.7
作者：
Boto E;Bowtell R;Krüger P;Fromhold TM;Morris PG;Meyer SS;Barnes GR;Brookes MJ
通讯作者：
Brookes MJ
影响因子：
3.5
作者：
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通讯作者：
Weisend M
影响因子：
5.7
作者：
Iivanainen J;Stenroos M;Parkkonen L
通讯作者：
Parkkonen L
影响因子：
44.1
作者：
HAMALAINEN, M;HARI, R;LOUNASMAA, OV
通讯作者：
LOUNASMAA, OV
影响因子：
3.7
作者：
Engel, SA;Glover, GH;Wandell, BA
通讯作者：
Wandell, BA