THE SPECTRAL EXPANSION OF A HEAD MODEL IN ELECTRICAL-IMPEDANCE TOMOGRAPHY

This paper examines whether electrical impedance tomography (EIT) can provide information of use to magneto-encephalographic modelling (MEG). The EIT image domain is expanded in a complete set of orthogonal basis images, the number of which is given by the number of independent measurements (104 for 16 electrodes). They are ordered according to their sensitivity to data noise, with more centrally located features and higher spatial frequency components appearing towards the higher terms in the series, in the case of uniform resistivity distribution. This indicates that the resolution can be improved at the expense of degrading signal-to-noise in the reconstructed image. Applied to an approximate model of the head, the technique generates a set of basis images that emphasises central features of the head.