Effects of the local skull and spongiosum conductivities on realistic head modeling

Abstract

In the most head modeling, the skull tissues are considered either homogeneous, inhomogeneous or anisotropic conductive medium due to its anatomical structure. The skull consists of two dense, poorly conducting compact bone separated by a spongiosum region containing blood. The spongiosum tissues are sandwiched by compact tissues. The major part of the skull remains the spongiosum tissues. The structure of the compact and spongiosum tissue layers is not identical which makes the coarse anatomical structure and conductivity variations. The conductivity of the spongiosum tissue changes with changing the thickness of the skull and the internal blood vessels. Accounting the skull thickness, considering the variable spongiosum conductivity, we consider local conductivity for the skull. We develop a realistic head model assigning the local skull conductivity (LSC), inhomogeneous anisotropic conductivity and perform forward computation to show the effects of the skull conductivity on EEG. Our simulated results show that 3% ± 1% average relative distance measurement (RDM) and 0.998 ± 0.02 magnification (MAG) values are obtained from LSC model. We also find 2% ± 0.3% RDM and no MAG errors for inhomogeneous anisotropic model. We then vary the conductivity of the spongiosum from -2 to +2 times the reported conductivity and compute EEGs. We find the maximum 4% RDM and 1.004 MAG values by varying the spongiosum conductivity.