Bispectral Analysis of Scalp Electroencephalograms: Quadratic Phasecoupling Phenomenon in Detecting Brain Tumor

Abstract

Since the power spectral analysis of a non-Gaussian process generated by a nonlinear mechanism e.g., EEG, does not provide much information on the underlying nonlinear dynamics due to the lack of phase information, the higher-order statistics such as the bispectra are used to better understand the underlying nonlinear dynamics e.g., the quadratic phase coupling phenomena. The quadratic phase couplings have been observed in the EEG by the researchers over a decade for many diagnostic applications such as epilepsy, sleep, mental states. This study discusses the use of bispectral analysis of the EEG recorded from the posterior region of the head of the brain tumor patient in quantifying the quadratic phase couplings to indicate the presence of the tumor. The Bicoherence Index (BCI) or simply the Bicoherence (BIC) has been used for the purpose. Self-couplings (around 27-52%) in the [8-13] Hz (alpha) band and phase couplings (around 23-42%) in the [1-8] Hz (delta-theta) band have been observed for the normal subjects while only self-couplings (around <6.5% and around 40-53%) have been seen in both bands for the brain tumor patients. Significant lowering of coupling strengths (from 38.15% (±12.76%) to 3.51% (±3.28%)) in the alpha band and mild increase of them (from 32.76% (±18.73%) to 45.49% (±17.49%)) in the delta band have been observed for the brain tumor patients. The Power Ratio Index (PRI) based on the power spectrum is only statistically inferior (p>0.05) to the BIC in discriminating the brain tumor case from the normal one.