Electromagnetic source characterisation requires accurate volume conductor models representing head geometry and the electrical conductivity field. Head tissue conductivity is often assumed from previous literature, however, despite extensive research, measurements are inconsistent. A meta-analysis of reported human head electrical conductivity values was therefore conducted to determine significant variation and subsequent influential factors. Of 3121 identified publications spanning three databases, 56 papers were included in data extraction. Conductivity values were categorised according to tissue type, and recorded alongside methodology, measurement condition, current frequency, tissue temperature, participant pathology and age. We found variation in electrical conductivity of the whole-skull, the spongiform layer of the skull, isotropic, perpendicularly- and parallelly-oriented white matter (WM) and the brain-to-skull-conductivity ratio (BSCR) could be significantly attributed to a combination of differences in methodology and demographics. This large variation should be acknowledged, and care should be taken when creating volume conductor models, ideally constructing them on an individual basis, rather than assuming them from the literature. When personalised models are unavailable, it is suggested weighted average means from the current meta-analysis are used. Assigning conductivity as: 0.41 S/m for the scalp, 0.02 S/m for the whole skull, or when better modelled as a three-layer skull 0.048 S/m for the spongiform layer, 0.007 S/m for the inner compact and 0.005 S/m for the outer compact, as well as 1.71 S/m for the CSF, 0.47 S/m for the grey matter, 0.22 S/m for WM and 50.4 for the BSCR.
展开▼
机译:电磁源表征需要精确的体积导体模型,这些模型代表磁头的几何形状和电导率场。头组织电导率通常是根据以前的文献得出的,但是,尽管进行了广泛的研究,但测量结果却不一致。因此,对报告的人头电导率值进行了荟萃分析,以确定显着的变化和随后的影响因素。在跨越三个数据库的3121种确定的出版物中,有56篇论文被包括在数据提取中。根据组织类型对电导率值进行分类,并与方法,测量条件,当前频率,组织温度,参与者病理学和年龄一起记录下来。我们发现,整个头骨的电导率,头骨的海绵状层,各向同性,垂直和平行取向的白质(WM)以及脑与头骨的电导率之比(BSCR)的变化可归因于方法和人口统计学差异的结合。应该承认这种较大的变化,并且在创建体积导体模型时应格外小心,理想情况下应基于个体构造它们,而不是从文献中假设它们。当没有个性化模型时,建议使用当前荟萃分析的加权平均数。将电导率指定为:头皮为0.41 S / m,整个颅骨为0.02 S / m,或者更好地建模为三层颅骨的海绵状层为0.048 S / m,内部实体为0.007 S / m,0.005外部压块的S / m,CSF为1.71 S / m,灰质为0.47 S / m,WM为0.22 S / m,BSCR为50.4。
展开▼