Modelling of electrical impedance epigastrography signals to investigate the efficacy of a motion artifact rejection algorithm

Abstract

Electrical Impedance Epigastrography (EIE) is a non-invasive method that allows the assessment of gastric emptying rates without using ionizing radiation. This method works by applying an alternating current with a frequency of 32 kHz, which can be varied by the operator from 1 to 4 mA, through electrodes over the epigastric region, and measuring the potential difference between them. The post acquisition analysis relies on the Short-Time Fourier Transform (STFT) to extract the gastric motility component of the signal (centre frequency of 0.05 Hz with a bandwidth of 0.02 Hz). Motion artifacts that occur during the test have been found to produce positive and negative spikes. Software was produced to model the EIE signals and apply simulated motion artifacts of known amplitude at specific points in the signal. The signals were labelled pseudo EIE signals. Due to the large frequency range of a delta function, the spikes produced false positives in the frequency domain, suggesting the presence of gastric contractility when there was none, or exaggerating the magnitude of real events in both real and pseudo EIE signals. A motion artifact rejection algorithm (MARA) was developed for removing the artifacts in the time domain, before processing by the STFT. The efficacy of the algorithm was tested on the pseudo EIE signals by comparing the power density calculated by the STFT before and after the simulation of artifacts and after the application of the algorithm.