The localization of energized coils using MEG sensors: theory and applications

An algorithm is described that localizes a set of simultaneously energized coils using MEG detectors. The algorithm is based on a mathematical model which describes the coils as stationary magnetic dipoles, of which the source time functions are known. It is assumed that the source time functions are orthogonal. It is shown how this a priori knowledge can be used to improve the efficiency of the algorithm. Furthermore, a method is presented to detect bad channels, automatically. The method is useful for continuous or intermittent head position registration during long MEG sessions, to registrate MR and MEG data, and to localize EEG electrodes attached to the head, when EEG and MEG are recorded simultaneously. Experimental data shows that the localization error can smaller than 2 mm.