A quantitative comparison of traditional reading of the EEG and interpretation of computer-extracted features in patients with supratentorial brain lesions.

The EEGs of adult patients with suspected supratentorial brain lesions were recorded on paper and on magnetic tape, using a small computer. The spectra of 16 channels were computed on a 40 sec sample. For each channel, a ratio of the type (delta + theta)/(alpha + beta) was computed and displayed on the computer terminal, a measure of the asymmetry in slow wave activity between homologous areas of the head was also displayed. This display is called a canonogram. It is believed to be a meaningful representation of the important characteristics of the EEG in the presence of supratentorial lesions. In order to assess the clinical value of the canonogram, the presumed localization of the lesion obtained from the interpretation of the traditional EEG and from that of the canonogram were compared to the known location of the lesion is a group of 87 subjects. The comparison was made quantitative by the use of a structured report encoding the traditional interpretation and that of the canonogram as well as the reference data (unequivocal surgical, radiological and clinical localizing evidence). The results varied among the anatomical regions: whereas in the frontal and occipital regions the EEG was slightly more accurate than the canonogram, both methods were similar in the temporal areas and the canonogram seemed more accurate in the centro-parietal regions. An attempt was made to interpret these differences. Furthermore, three readers read the cononograms and gave very consistent interpretations. These results show the reliability and value of this simple computer display for the particular type of EEG studied.