Effects of sutures and fontanels on MEG and EEG source analysis in a realistic infant head model

Abstract

In infants, the fontanels and sutures as well as conductivity of the skull influence the volume currents accompanying primary currents generated by active neurons and thus the associated electroencephalography (EEG) and magnetoencephalography (MEG) signals. We used a finite element method (FEM) to construct a realistic model of the head of an infant based on MRI images. Using this model, we investigated the effects of the fontanels, sutures and skull conductivity on forward and inverse EEG and MEG source analysis. Simulation results show that MEG is better suited than EEG to study early brain development because it is much less sensitive than EEG to distortions of the volume current caused by the fontanels and sutures and to inaccurate estimates of skull conductivity. Best results will be achieved when MEG and EEG are used in combination.

Magnetoencephalography signals are influenced by skull defects

“…Specifically, the influence of a human skull defect on the MEG signals should be strongest if the source is central beneath the defect. A neonatal simulation study supports this finding (Lew et al, 2013). In the following, we evaluate the differences between our experiment and potential human recordings.…”

“…The qualitative observations should be transferable to burr holes in humans. This is supported by a neonatal simulation study (Lew et al, 2013) that showed that the MEG and EEG signals of sources beneath neonate thin sutures are influenced by these sutures. Larger skull defects should cause a wider spread of signal changes.…”

“…The neonatal simulation study of Lew et al (2013) found flux density map topography differences due to fontanels of up to RDM ⁄ 0.017-0.022. Considering (1) the very thin, higher conducting skull and comparatively lower conductivity of the defects (0.3 S/m) in their model and (2) that RDM ⁄ was evaluated including large field-map areas distant from the skull defect, their results concur with ours in that skull defects cause a measurable topography difference when the source is beneath the defect.…”

“…In a simulation study, Lew et al (2013) found that the MEG signal magnitude simulated with fontanels and sutures as natural skull defects can be measurably different to the MEG signal magnitude simulated for a closed skull. In agreement with the present results, the MEG signal amplitude change was strong when a tangential source was under a skull defect and weak otherwise.…”

Compensation of domain modelling errors in the inverse source problem of the Poisson equation: Application in electroencephalographic imaging

“…In EEG source problem, neural sources are reconstructed inside the brain based on electric potential measurements around the scalp, and it is well known that the inverse solution depends strongly on the accuracy of discretized head geometry [2,4,7,8,16,39,49,54] and the accuracy of electric conductivity modelling of different tissues [3,47,25,48,34,50,51]. The head features can be extracted, to some extent, by using multi-modal imaging (computed tomography / diffusion magnetic resonance imaging), for example.…”