Study of conducting volume boundary influence on source localization using a realistic MEG phantom

In order to gauge the applicability of a source reconstruction technique in MEG it is necessary to assess the overall accuracy and precision of the method. Computer simulation is useful in this regard, but it is inherently limited in the extent that it can model factors such as sensor performance and environmental noise accurately. We have designed a realistically shaped physical phantom with moveable dipole sources to examine the influence of the conductor boundary used in forward model generation on localization accuracy. The scalp and inner skull surfaces were compared using single sphere and overlapping-sphere models in both dipole fitting and event-related beamforming (ERB) techniques. Over all source locations and methods, the mean localization error when using the inner skull boundary was significantly lower than when using the scalp surface (scalp/inner skull = 9.08 mm/6.76 mm P < 0.0002). As expected, the difference was largest in inferior regions where the curvature of the skull diverges greatly from that of the outer scalp.