Abstracts

In past decades, epilepsy surgery has been recognized increasingly as a viable treatment for patients with medically refractory seizures. However, the large gap between number of potential surgical candidates and number of patients being treated with surgery still exists due to the lengthy, complex, and expensive procedure of current practice of using invasive procedures to identify epileptic foci responsible for the seizures. If epileptic foci can be identified noninvasively, numerous epilepsy patients undergoing surgical treatment will benefit significantly from the noninvasive surgical planning. The aim of present study is to evaluate a novel noninvasive electrophysiological cortical imaging technique (He et al., IEEE-TBME, 46:1264-1268, 1999) to image and localize ictal activities from scalp EEG. All patients are pediatric patients with intractable partial epilepsy in the Pediatric Epilepsy Center at the University of Chicago. For each patient, multiple habitual seizures were visually identified according to the IFSECN criteria. Seizure activities with sudden propagation to whole brain were excluded from further analysis. For ictal EEG recordings with sustained rhythmic focal morphology, time-frequency analysis has been applied as preprocessing. Spatial-temporal evolution of ictal discharges were examined using wavelet analysis to obtain a time-varying energy distribution in each frequency band. The dominant frequency is determined with highest energy concentration, at which the phase encoding is used for multi-channel EEG around seizure onset to generate a scalp potential map representing the major ictal activity. The cortical imaging algorithm (He et al., 1999) was then applied to reconstruct the cortical potential distribution from the phase encoded scalp potential map. Since pediatric patients usually have seizure originating from neocortex, the estimated cortical potential generated by different underlying sources are less likely to overlap so that it can be used to observe the source activity with much less deviation as compared to that from a deeper source. Five pediatric epilepsy patients by various causes were studied, who are either seizure free or having substantial seizure reduction after neurosurgical resections. For all patients, the cortical imaging analysis has been able to successfully reveal underlying epileptogenic cortical zones at different lobes (temporal or extra-temporal, one or two epileptogenic foci for each patient), which are consistent with clinical findings and confirmed by neurosurgical resections and outcomes. Cortical imaging can reliably localize cortical activity in regions displaying epileptiform activity; these regions were confirmed by successful surgical resection. Cortical imaging may become a useful alternative for noninvasive pre-surgical and surgical planning in pediatric epilepsy patients. (Supported by NIH EB 00178 and NSF BES-0411898.)