Accuracy of EEG dipole source localization using implanted sources in the human brain

Objectives: The location of electrical sources in the brain can be estimate d by calculating inverse solutions in which the location, amplitude and ori entation of the electrical sources are fitted to the scalp EEG. To assess l ocalization accuracy of the moving dipole inverse solution algorithm (ISA), we studied two patients who had depth electrodes implanted for presurgical planning of epilepsy surgery. Methods: Artificial dipoles were created by connecting a single sine wave p ulse generator to different pairs of electrodes in multiple orientations an d depths. Surface EEG recordings of the resulting pulses were evaluated wit h the ISA using a 4 shell spherical head model and plotted on the subjects' MRI. Dipole localization errors were evaluated with respect to the number of averaged pulses, different electrode montages and different dipole locat ions and orientations. Results: Dipoles located at 40-57 mm from the scalp surface had localizatio n errors that were greater than those located at 62-85 mm. Localization acc uracy improved with increasing numbers of pulses and recording electrodes. Results with a standard 10-20 array of 21 electrodes showed an average loca lization error of 17 mm, whereas 41 electrodes improved this to 13 mm. Mean angular errors were 31 and 30 degrees, respectively. Conclusions: The ISA was able to differentiate between tangential and radia l dipoles. We conclude that our implementation of the ISA is a useful and s ound method for localizing electrical activity in the brain. (C) 1999 Elsev ier Science Ireland Ltd. All rights reserved.