Can a Spherical Model Substitute for a Realistic Head Model in Forward and Inverse MEG Simulations?
نویسنده
چکیده
Although the human head is not a sphere, models using spheres have been employed to simplify forward and inverse magnetoencephalographic (MEG) calculations. We compared the normal component of the magnetic field calculated at 61 detectors and the localization accuracy of 5 different spherical models to the results obtained using the finite element method (FEM) in a realistic head model. The spherical models used were an analytic equation for a single homogeneous sphere; a FEM single homogeneous sphere; concentric FEM spheres with skin, skull, and brain conductivity layers; concentric FEM spheres with skin, skull, CSF, gray, and white matter conductivity layers; and an overlapping sphere head model. No spherical model proved to be consistently the most accurate in determining forward magnetic field values or in localizing the 5 different dipoles used. Forward and inverse results for the spherical models tended to correspond more closely with the realistic model results for dipoles located near the surface of the head than for those deep inside the head. Large discrepancies in calculated magnetic field values and localization errors for some dipoles, however, limit at least these 5 spherical models as substitutes for the realistic head model in forward and inverse MEG calculations.
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