Extended Spatiotemporal Separation for noise reduction in magnetocardiography

Abstract

Magnetocardiography (MCG) is a fast and noninvasive method for diagnosing heart diseases but is very susceptible to external noise. MCG using optically pumped magnetometers (OPMs) has the advantages of not needing cooling and high time resolution. The Spatiotemporal Signal Space Separation method can effectively suppress noise outside the heart in the MCG. However, the number of MCG sensors is relatively small, and sensors are usually arranged flat, which limits the use of spatiotemporal signal space separation in MCG. Therefore, this paper proposed a new method called Extended Spatiotemporal Separation (ESTS) based on Signal Space Separation (SSS), which is suitable for smaller and flat-arranged channels. Besides, we proposed a real-time automatic ESTS method to remove destructive huge noise while ensuring less distortion. In addition, we conducted simulations and experimental verifications to prove the effectiveness of ESTS in MCG noise reduction. We compared it with ordinary SSS and standard denoising methods like Independent Component Analysis (ICA). The results show that when faced with a huge noise for MCG with few sensor channels, ESTS has a higher signal-to-noise ratio (SNR) and can better restore the waveforms. As a result, this paper provided new ideas for clinical real-time noise reduction of MCG and unshielded MCG measurement.