Comparison of three-shell and simplified volume conductor models in magnetoencephalography
Comparison of three-shell and simplified volume conductor models in magnetoencephalography
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DOI：
10.1016/j.neuroimage.2014.01.006
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发表时间：
2014-07-01
期刊：
影响因子：
5.7
通讯作者：
Haueisen, Jens
中科院分区：
文献类型：
--
作者：
Stenroos, Matti;Hunold, Alexander;Haueisen, Jens
实验MEG源成像研究通常采用球对称头部模型或根据颅骨内表面形状的单壳边界元（BEM）模型进行。这些简化模型背后的概念和比较导致了对颅骨和头皮在脑磁图中的作用的误解。在这项工作中，我们评估了由于不同的头骨/头皮近似以及由于模型几何形状的差异和误差而导致的前向模型误差。我们使用一组t1加权磁共振扫描和三个常用工具箱建立了志愿者的五个解剖模型。其中3个模型代表了实验MEG中的典型模型，1个是人工构建的，1个在颅底存在较大的分割误差。对于这些解剖模型，我们使用四种简化方法和三壳BEM方法建立了正演模型，这是以往研究中使用的参考方法。我们的参考模型还包含颅骨精细结构（海绵状骨）。我们计算了左半球皮质受限源的信号地形，并使用相对误差和相关指标比较了地形。结果表明，海绵骨对脑磁图形貌的影响很小，因此三壳模型的颅骨近似是合理的。三壳模型表现最好，其次是修正球和单壳模型，而局部球和单球模型明显较差。三壳模型对引入的分割误差的鲁棒性最强。与之前的说法相反，现实形状模型和基于球体的模型在计算时间上没有显著差异，构建三壳模型和简化模型的人工工作量是相当的。因此，我们推荐实际形状的三壳模型用于实验MEG工作。在这种情况下，这是不可能的，我们建议一个现实形状的修正球体或单壳模型。(C) 2014爱思唯尔公司版权所有。
Experimental MEG source imaging studies have typically been carried out with either a spherically symmetric head model or a single-shell boundary-element (BEM) model that is shaped according to the inner skull surface. The concepts and comparisons behind these simplified models have led to misunderstandings regarding the role of skull and scalp in MEG. In this work, we assess the forward-model errors due to different skull/scalp approximations and due to differences and errors in model geometries.We built five anatomical models of a volunteer using a set of T1-weighted MR scans and three common tool-boxes. Three of the models represented typical models in experimental MEG, one was manually constructed, and one contained a major segmentation error at the skull base. For these anatomical models, we built forward models using four simplified approaches and a three-shell BEM approach that has been used as reference in previous studies. Our reference model contained in addition the skull fine-structure (spongy bone).We computed signal topographies for cortically constrained sources in the left hemisphere and compared the topographies using relative error and correlation metrics. The results show that the spongy bone has a minimal effect on MEG topographies, and thus the skull approximation of the three-shell model is justified. The three-shell model performed best, followed by the corrected-sphere and single-shell models, whereas the local-spheres and single-sphere models were clearly worse. The three-shell model was the most robust against the introduced segmentation error. In contrast to earlier claims, there was no noteworthy difference in the computation times between the realistically-shaped and sphere-based models, and the manual effort of building a three-shell model and a simplified model is comparable. We thus recommend the realistically-shaped three-shell model for experimental MEG work. In cases where this is not possible, we recommend a realistically-shaped corrected-sphere or single-shell model. (C) 2014 Elsevier Inc. All rights reserved.