Anatomically Constrained vs Unconstrained Dipole Fit in the Combination of MEG and MRI
The most common Solution approach to the inverse problem in neuromagnetism is the anatomically unconstrained current dipole fit with Simplex, Levenberg-Marquardt or a similar method. The result of this dipole fit is not correlated to the anatomy (anatomically unconstrained) and might yield unexpected dipole locations e.g. in the white matter or the liquor space. In contrast, the combination of MEG (magnetoencephalography) and MRI (magnetic resonance imaging) allows an anatomically constrained dipole fit. This was suggested e.g. by Wieringaet al. . Recently, Lütkenhöner et al.  proposed a dipole patch model, where a number of dipoles (a patch) are riding on the cortical surface. A simpler model is used in this work. The model consists of a single current dipole riding on a surface 1 mm below the cortical surface and is called anatomically constrained dipole fit. For all anatomically constrained dipole fits is valid that only dipole positions in the cortex and dipole directions perpendicular to the cortex surface are considered as valid source space.
KeywordsGray Matter Volume Source Space Volume Conductor Model Boundary Element Method Model Dipole Position
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