Abstracts

Visualization of time-frequency changes in EEG has traditionally been visualized using Fourier-based techniques (i.e. Short Time Fourier Transform, STFT). This approach is limited given its fixed-length analysis window and the non-stationary nature of EEG signals. The S Transform is a Fourier-based multi-resolution transform that has a variable length analysis window, thus circumventing the shortcomings of the STFT. In the present study, we introduce a novel application of the S Transform for visualization of normal and epileptiform EEG phenomena in humans. Selected recordings from five normal subjects and five patients with either focal or generalized epileptiform discharges were used. We identified a single channel that had a clear example of an electrographic feature of interest (e.g. alpha, mu, sleep spindles, eye blink, spike and wave, sharp wave) and applied the S Transform to it. The S Transform provided clear visualization of the frequency components, in time, of the electrographic events. Some of the spectral attributes of these events were not immediately apparent on conventional review of the EEG. The application of the S Transform to EEG is novel and can potentially be a useful tool for visualizing clinically relevant features in EEG.[figure1] (Supported by Canadian Institutes of Health Research and Alberta Heritage Foundation for Medical Research.)