Depth normalization in MEG/EEG current density imaging

Abstract

We analyze the minimum norm solution of the biomagnetic inverse problem. It is shown that the bias of this technique, i.e. the tendency to reconstruct superficial currents, can be reduced by the use of an appropriate weighting, which depends the used norm. The weighting factors are calculated by a singular value decomposition of the lead field matrix for each location and a noise regularization technique. With this weighting, the ability to reconstruct deep sources is maintained over the whole volume of sensitivity. The extend of this volume depends on the measurement setup and the noise level.