Accurate localization of brain activity recorded by magnetoencephalography (MEG) requires that the forward problem, i.e. the magnetic field caused by a dipolar source current in a homogeneous volume conductor, be solved precisely. We have used the Galerkin method with piecewise linear basis functions in the boundary element method to improve the solution of… (More)
Sources of brain activity, e.g. epileptic foci, can be localized with Magnetoencephalography (MEG) measurements by recording the magnetic field outside the head. For a successful surgery a very high localization accuracy is needed. The most often used conductor model in the source localization is an analytic sphere, which is not always adequate, and thus a… (More)
We describe the iterative solution of dense linear systems arising from a surface integral equation of electromagnetic scattering. The complex symmetric version of QMR has been used as an iterative solver together with a sparse approximate inverse preconditioner. The preconditioner is computed using the topological information from the computational mesh.… (More)
The volume integral equation of electromagnetic scattering can be used to compute the scattering by inhomogeneous or anisotropic scatterers. In this paper we compute the spectrum of the scattering integral operator for a sphere and the eigenvalues of the coeecient matrices that arise from the discretization of the integral equation. For the case of a… (More)
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Sources of brain activity, e.g., epileptic foci can be localized by measuring the magnetic eld outside the head (MEG) or by recording the electric potential on the scalp (EEG). For a successful surgery a very high localization accuracy is needed. The most often used conductor model in the source localization is an analytic sphere, which is not always… (More)
Magnetoencephalography (MEG) is a noninvasive technique for studying neuronal activity in the living human brain. Weak magnetic elds caused by the activity are measured from outside the head. Based on these measurements the source of the activity is located with the help of a mathematical model. A part of the localization is the repeated computation of the… (More)
We studied the source localization accuracy in MEG with single-surface brain-shaped conductor models. The Galerkin method with linear basis functions was used as a discretization method. To Þnd a dipolar source, a variant of the Newton method was used for solving nonlinear least-squares problems. Reference magnetic Þelds were computed using a very large… (More)