Influence of unfused cranial bones on magnetoencephalography signals in human infants

Objective: To clarify the effects of unfused cranial bones on magnetoencephalography (MEG) signals during early development. Methods: In a simulation study, we compared the MEG signals over a spherical head model with a circular hole mimicking the anterior fontanel to those over the same head model without the fontanel for different head and fontanel sizes with varying skull thickness and conductivity. Results: The fontanel had small effects according to three indices. The sum of differences in signal over a sensor array due to a fontanel, for example, was < 6% of the sum without the fontanel. However, the fontanel effects were extensive for dipole sources deep in the brain or outside the fontanel for larger fontanels. The effects were comparable in magnitude for tangential and radial sources. Skull thickness significantly increased the effect, while skull conductivity had minor effects. Conclusion: MEG signal is weakly affected by a fontanel. However, the effects can be extensive and significant for radial sources, thicker skull and large fontanels. The fontanel effects can be intuitively explained by the concept of secondary sources at the fontanel wall. Significance: The minor influence of unfused cranial bones simplifies MEG analysis, but it should be considered for quantitative analysis. (C) 2021 International Federation of Clinical Neurophysiology. Published by Elsevier B.V. All rights reserved.