Meneghini Fabio, Vatta Federica, Esposito Fabrizio, Mininel Stefano, Di Salle Francesco
DEEI, University of Trieste, Via A. Valerio 10,Trieste, Italy.
Biomed Tech (Berl). 2010 Jun;55(3):133-46. doi: 10.1515/BMT.2010.010.
In electroencephalography (EEG) a valid conductor model of the head (forward model) is necessary for predicting measurable scalp voltages from intra-cranial current distributions. All inverse models, capable of inferring the spatial distribution of the neural sources generating measurable electrical and magnetic signals outside the brain are normally formulated in terms of a pre-estimated forward model, which implies considering one (or more) current dipole(s) inside the head and computing the electrical potentials generated at the electrode sites on the scalp surface. Therefore, the accuracy of the forward model strongly affects the reliability of the source reconstruction process independently of the specific inverse model. So far, it is as yet unclear which brain regions are more sensitive to the choice of different model geometry, from both quantitative and qualitative points of view. In this paper, we compare the finite difference method-based realistic model with the four-layers sensor-fitted spherical model using simulated cortical sources in the MNI152 standard space. We focused on the investigation of the spatial variation of the lead fields produced by simulated cortical sources which were placed on the reconstructed mesh of the neocortex along the surface electrodes of a 62-channel configuration. This comparison is carried out by evaluating a point spread function all over the brain cortex, with the aim of finding the lead fields mismatch between realistic and spherical geometry. Realistic geometry turns out to be a relevant factor of improvement which is particularly important when considering sources placed in the temporal or in the occipital cortex. In these situations, using a realistic head model will allow a better spatial discrimination of neural sources when compared to the spherical model.
在脑电图（EEG）中，为了从颅内电流分布预测可测量的头皮电压，头部的有效导体模型（正向模型）是必要的。所有能够推断产生大脑外部可测量电信号和磁信号的神经源空间分布的逆向模型，通常都是根据预先估计的正向模型来制定的，这意味着要考虑头部内部的一个（或多个）电流偶极，并计算头皮表面电极部位产生的电势。因此，无论具体的逆向模型如何，正向模型的准确性都会强烈影响源重建过程的可靠性。到目前为止，从定量和定性的角度来看，尚不清楚哪些脑区对不同模型几何形状的选择更为敏感。在本文中，我们在MNI152标准空间中使用模拟皮质源，将基于有限差分法的真实模型与四层传感器拟合球面模型进行了比较。我们重点研究了沿着62通道配置的表面电极，放置在新皮质重建网格上的模拟皮质源所产生的导联场的空间变化。通过评估整个大脑皮质的点扩散函数来进行这种比较，目的是找出真实几何形状和球面几何形状之间的导联场不匹配情况。结果表明，真实几何形状是一个重要改进因素，在考虑位于颞叶或枕叶皮质的源时尤为重要。在这些情况下，与球面模型相比，使用真实头部模型将能更好地对神经源进行空间分辨。
