Modified Lock-In Detection for Extraction of Impressed EEG Signals in Low-Frequency Bounded-EIT Studies of the Human Head

In the paper we describe a method to extract the topography of an impressed current for our bounded electrical impedance tomography (bEIT) studies. The frequency of the impressed current is low (up to a few hundred Hz), and is buried in background EEG and other noise. For the development of the extraction method, special consideration is given to maximize the signal-to-noise ratio. The standard lock-in detection framework, with its remarkable sensitivity at the locked-in frequency, is modified to suit our acquisition and post-processing environment. Simulation results are provided to showcase the accuracy and robustness of the modification in extracting both the amplitude and phase offset of the impressed signal in the face of different types of noise.