Algorithm for local filtering of low frequency and large amplitude noise in electroencephalograms data
Purpose. One of the problems in operation of electroencephalograms (EEG) data is the existence of “noise” in these data. The noise is connected both to a behavior of the patient, and to external influences. The purpose of this study is creation of an algorithm for filtering of low frequency and large amplitude noise arising from different sources in EEG data. At the same time one of requirements to the algorithm is elimination of the phase distortion in a wave. Methods. The algorithm is based on the Fourier analysis of data and can be applied locally in the set time interval. In the developed algorithm the approach to division of high-frequency and low-frequency fluctuations which is widely applied in the theory of turbulence is used. The algorithm is analog of the method of the sliding average. However it has a number of fundamental differences. The algorithm includes an averaging interval assessment procedure proceeding from the spectral analysis of data, and also criterion according to which the decision on removal of a low-frequency component of data (noise) in the set point is made. Results. Numerical experiments with real data of electroencephalograms are made. EEG registered on the basis of scientific research institute of physiology and fundamental medicine with the help of 128 channel encephalograph of Brain Products, Germany with bandpass range of 0.1-100 Hz, the frequency of digitization of a signal of 1000 Hz. Electrodes (126 EEG + VEOG) settled down according to the international diagram of 10-10 % with the reviewer Cz and a grounding electrode of AFz. Numerical experiments with real data of electroencephalograms (selection from 85 EEG) showed that the algorithm allows to adjust EEG data, cleaning low frequency noise and slightly changing wave phase. Conclusions. In this work the algorithm of a filtration of low-frequency noise in EEG data is proposed. Distinctive property of the offered algorithm is lack of distortion of a phase of a wave (within computational error of the method).