Three-shell head model constructed from scalp geometry for electroencephalogram dipole localization.

One of the most sophisticated methods of dipole localization from (electroencephalograms) is based on a multi-compartment head model, which consists of the scalp, skull, cerebrospinal fluid (CSF) and brain cortex. The CSF layer in normal subjects is thin and can be ignored in dipole localization to good approximation. This multi-shell model is called the SSB (scalp-skull-brain) head model. The SSB head model is constructed from magnetic resonance imaging (MRI) or X-ray computed tomography slices of the head. These image slices, however, are not easy to obtain. The present paper presents a simple method for constructing the SSB head model only from the geometrical shape of the scalp, which is easily measured with a three-dimensional digitizer. We have derived a relationship between the head structure and the geometry of the head from statistical analysis of MRI slices of 12 normal subjects. The average estimation errors of the outer and inner boundaries of the skull were 1.2 and 2.2 mm, respectively. The head model thus estimated is called the sSSB (statistical SSB) model.