The influence of ventricles and lesions on MEG and EEG is studied. The ventricles have an intricate shape and are filled with cerebrospinal fluid. Lesions can have various shapes and their conductivity is unknown. A realistically shaped three-compartment model is used, describing the scalp, skull and brain, which includes the realistically shaped ventricles or a spherical lesion. The potential is computed by means of the finite-element method, and the magnetic field by applying the law of Biot-Savart (Broek, S.P.v.d., Zhou, H. and Peters, M.J. 1996, computation of neuromagnetic fields using finite-element method and Biot-Savart law, Med. Biol. Eng. Comput., 34,21-26). An influence of the ventricles on the potential is only noticeable for dipoles that are within a few centimetres of a ventricle and on the relatively weak potentials on the opposite side of the head. The 'radial' component of the magnetic field generated by superficial dipoles is not influenced by the ventricles in a healthy subject. The influence on the other components, and on the field generated by dipoles near the ventricles can be large. A lesion has a large effect on the potential for sources near the lesion. The effects on the MEG are smaller, but noticeable. Care should be taken in explaining abnormalities in EEGs and MEGs, as it is possible that they are caused by the presence of an inhomogeneity.
|Publication status||Published - 8 Mar 1997|
|Event||8th International ISBET Congress 1997: with The KEY Foundation Symposium “Brain Fields in Psychiatry” - Zurich, Switzerland|
Duration: 6 Mar 1997 → 8 Mar 1997
Conference number: 8