Epileptic Source Localization from MEG data: Local maxima of 2DII current density solutions compared to ECD locations of spike events

摘要

The Equivalent Current Dipole (ECD) technique is limited, to imaging sources for brief time windows when source amplitude is high and other activity low. Two Dimensional Inverse Imaging (2DII) [1] is a current density technique capable of imaging multiple source activity, and allowing the study of source activity time evolution. One would expect that 2DII solutions would contain ECD results as a subset in which the ECD locations correspond to local maxima of 2DII source solutions. Using a 148 channel MEG. interictal spikes were acquired from eight patients with complex partial seizures. Dipole selection criteria were; correlation coefficient >0.95, goodness of fit >0.95, Q>400nAm, RMS>800fT, and confidence region <1mm{sup}3. 2DII current density source solutions were generated for seven to fifteen spike events per patient. The distance between 2DII maximum and corresponding ECD peaks was used to quantify solution difference between the two imaging techniques. The average difference between 2DII and ECD source locations for individual spike events across all patients was 1.0cm. This study demonstrates that 2DII imaging is useful in verifying ECD results with the added ability to study the interaction of an epileptic focus with other brain structures. The advantage of ECD is rapid calculation and quantification of final results with minimum number of parameters, (location, amplitude, quality of fit). The 2DII technique allows the observation of the dynamics of individual spike events and, when combined with the ECD technique, the correspondence of source location serves as a crosscheck on the validity of the results of each technique.