Huang M X, Mosher J C, Leahy R M
Neuroimaging Center, New Mexico Regional Federal Medical Center, Albuquerque 87108, USA.
Phys Med Biol. 1999 Feb;44(2):423-40. doi: 10.1088/0031-9155/44/2/010.
The spherical head model has been used in magnetoencephalography (MEG) as a simple forward model for calculating the external magnetic fields resulting from neural activity. For more realistic head shapes, the boundary element method (BEM) or similar numerical methods are used, but at greatly increased computational cost. We introduce a sensor-weighted overlapping-sphere (OS) head model for rapid calculation of more realistic head shapes. The volume currents associated with primary neural activity are used to fit spherical head models for each individual MEG sensor such that the head is more realistically modelled as a set of overlapping spheres, rather than a single sphere. To assist in the evaluation of this OS model with BEM and other head models, we also introduce a novel comparison technique that is based on a generalized eigenvalue decomposition and accounts for the presence of noise in the MEG data. With this technique we can examine the worst possible errors for thousands of dipole locations in a realistic brain volume. We test the traditional single-sphere model, three-shell and single-shell BEM, and the new OS model. The results show that the OS model has accuracy similar to the BEM but is orders of magnitude faster to compute.
球形头部模型已在脑磁图（MEG）中用作简单的正向模型，用于计算神经活动产生的外部磁场。对于更逼真的头部形状，则使用边界元法（BEM）或类似的数值方法，但计算成本会大幅增加。我们引入了一种传感器加权重叠球（OS）头部模型，用于快速计算更逼真的头部形状。与初级神经活动相关的体电流用于为每个单独的MEG传感器拟合球形头部模型，从而将头部更逼真地建模为一组重叠球，而不是单个球体。为了协助使用BEM和其他头部模型评估此OS模型，我们还引入了一种基于广义特征值分解的新颖比较技术，该技术考虑了MEG数据中的噪声存在。通过这种技术，我们可以检查逼真脑体积中数千个偶极位置的最坏可能误差。我们测试了传统的单球模型、三壳和单壳BEM以及新的OS模型。结果表明，OS模型具有与BEM相似的精度，但计算速度要快几个数量级。
