Abstracts

Advanced digital technology significantly improved accuracy of EEG feature analysis, but detection of interictal focal epileptiform transients (IFET) with clinical relevance continues to depend on human visual analysis. Particularly problematic has been the difficult-to-define spatiotemporal IFET profile that experienced interpreters find no difficulty in recognizing and applying to polygraphic EEG analysis. EEG geometry was examined in IFET polygraphic derivations from randomly chosen clinical cases. The primary objective was to delineate the time-series characteristics of well-formed IFET. The secondary objective was to demonstrte polygraphic variations that indicate subtle variation in IFET source location within an area of unit interelectrode distance. During 2004 a total of 53 standard EEG cases revealed a varying number of IFET. A representative IFET chosen from each case was reformatted in common average reference derivations. One derivation with the largest IFET deflection was chosen, approximating its source to a 10-20 scalp electrode. The 53 representative IFET were reviewed for waveform criteria culled from the literature, and ranked in a descending order by evaluating the degree of fit, when polygraphically superimposed. Well-formed IFET were then reformatted in serial bipolar derivations for detailed examination of the IFET peak and phase relationship. The first 5 ranked IFET referred to common average reference are summarized in Figure. [figure1] A well-formed IFET consists of 3 major peaks with different waveform. The third (blunt) peak varied most, and attenuated in lesser-ranked IFET. When displayed in a chain of 5 serial bipolar derivations, phase relationship surrounding the IFET peak differed among cases. This finding was confirmed by examining multiple IFET within each case Digital technology enables the viewer to reformat EEG data off-line and improve EEG feature extraction. The notion of well-formed IFET is elementary, but robust, because it allows to supplement voltage criteria with additional clinically relevant geomatric paramaters, and can improve automated IFET screening and source modeling. Demonstration of phase relationship surrounding the IFET peak specific to each case confirmed the feasibility of demonstrating subtle variation in location of an equivalent current dipole relative to head-surface electrodes. This method is easy to apply in clinical settings and can expand the scope of EEG analysis in space domain.