INTRACRANIAL EEG ELECTRODES - LOCALIZATION BY MEANS OF 3-DIMENSIONAL RECONSTRUCTION OF MAGNETIC-RESONANCE-IMAGING DATA FOR USE IN CHARACTERIZATION OF EPILEPTIC FOCI BEFORE SURGERY

Subdural strip electrodes or intracerebral electrodes are required in order to precisely localize epileptic foci, which is mandatory for epi lepsy surgery. The subdural electrodes are inserted via a borehole and thus precise positioning cannot be directly monitored. Therefore, the location of the electrodes in relation to the gyri and sulci has to b e determined by imaging techniques. In this study, a three-dimensional magnetic resonance imaging (3D MRI) technique was used for visualizat ion of intracranial EEG electrodes. A 3D gradient echo sequence with t hin slices of 1 mm is required for the assessment of the gyral anatomy of the brain surface. Using a short repetition time of 30 ms good ima ge quality within an acceptable acquisition time of about 15 min was p ossible. Postprocessing with 3D surface reconstruction was performed u sing a Sun workstation. Three-dimensional reconstruction allows a more precise delineation of the localization of the EEG electrodes and the simultaneous display of the adjacent brain structures. Misplacement o f intracranial electrodes is readily detected. 3D MRI with 3D surface reconstruction proved superior to 2D imaging and CT for the assessment of EEG electrode localization.