Source modelling in magnetoencephalography (MEG) requires precise co-registration of the sensor array and the anatomical structure of the measured individual's head. In conventional MEG, the positions and orientations of the sensors relative to each other are fixed and known beforehand, requiring only localization of the head relative to the sensor array. Since the sensors in on-scalp MEG are positioned on the scalp, locations of the individual sensors depend on the subject's head shape and size. The positions and orientations of on-scalp sensors must therefore be measured at every recording. This can be achieved by inverting conventional head localization, localizing the sensors relative to the head - rather than the other way around. In this study we present a practical method for localizing sensors using magnetic dipole-like coils attached to the subject's head. We implement and evaluate the method in a set of on-scalp MEG recordings using a 7-channel on-scalp MEG system based on high critical temperature superconducting quantum interference devices (high-Tc SQUIDs). The method allows individually localizing the sensor positions, orientations, and responsivities with high accuracy using only a short averaging time (≤ 2 ​mm, < 3° and < 3%, respectively, with 1-s averaging), enabling continuous sensor localization. Calibrating and jointly localizing the sensor array can further improve the accuracy of position and orientation (< 1 ​mm and < 1°, respectively, with 1-s coil recordings). We demonstrate source localization of on-scalp recorded somatosensory evoked activity based on co-registration with our method. Equivalent current dipole fits of the evoked responses corresponded well (within 4.2 ​mm) with those based on a commercial, whole-head MEG system.

译文

脑磁图 (MEG) 中的源建模需要对传感器阵列和被测个体头部的解剖结构进行精确的配准。在传统的MEG中,传感器相对于彼此的位置和取向是固定的并且预先知道的,仅需要将头部相对于传感器阵列定位。由于头皮上的MEG中的传感器位于头皮上,因此各个传感器的位置取决于对象的头部形状和大小。因此,必须在每次记录时测量头皮上传感器的位置和方向。这可以通过反转传统的头部定位来实现,从而相对于头部定位传感器,而不是相反。在这项研究中,我们提出了一种实用的方法,该方法使用附着在受试者头部的类偶极子线圈来定位传感器。我们使用基于高临界温度超导量子干涉设备 (高Tc SQUIDs) 的7通道头皮上MEG系统在一组头皮上MEG记录中实施和评估该方法。该方法允许仅使用短平均时间 (分别 ≤ 2毫米、 <3 ° 和 <3%,具有1-s平均) 以高精度单独地定位传感器位置、取向和响应性,从而实现连续的传感器定位。校准和联合定位传感器阵列可以进一步提高位置和方向的精度 (分别为 <1毫米和 <1 °,具有1-s线圈记录)。我们基于与我们的方法的共同配准,证明了头皮上记录的体感诱发活动的源定位。诱发响应的等效电流偶极子拟合与基于商业全头MEG系统的等效电流偶极子拟合非常一致 (在4.2毫米内)。

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