Objective: Recently, the extended brain symmetry index (BSI) was introduced to assist the visual interpretation of the EEG, in particular to quantify both the spatial (left-right) and the temporal spectral characteristics. The BSI has found application in monitoring during carotid endarterectomy, acute stroke and focal seizure detection. Here, we present additional relevant characteristics and a slightly modified version of this index, simulating its behavior as may occur in various clinical conditions, with an emphasis on the detection of cerebral ischaemia.
Methods: The behavior of the revised and standard sBSI and tBSI is illustrated using random noise signals to simulate various changes in the EEG. The indices are evaluated as a function of spatial and temporal changes, and as a function of the number of channels.
Results: The r-sBSI and the r-tBSI are normalized in the range [0-1] with sensitivities of about 0.05 for a 10% difference in signal amplitude, either spatial or temporal. The baseline value of the sBSI shows a modest dependence on the number of channels used.
Conclusions: The revised BSI has an improved sensitivity (about two times) to detect interhemispheric asymmetry and diffuse changes. The modified expression of the tBSI is more compact and allows a more intuitive understanding than previously proposed.
Significance: qEEG assists in a more objective interpretation of the EEG, and is relevant in neuromonitoring.