Decreasing motion artifacts in calcium-dependent fluorescence transients from the perfused mouse heart using frequency filtering

Abstract

A strategy has been developed for the removal of motion artifact and noise in calcium-dependent fluorescence transients from the perfused mouse heart using frequency filtering. An analytical model indicates that the spectral removal of motion artifacts is independent of the phase shift of the motion waveform in the frequency domain, and thus to the time shift (or delay) of motion in the time domain. This is based on the "shift theorem" of Fourier analysis, which avoids erroneous correction of motion artifact when using the motion signal obtained using reflectance from the heart. Several major steps are adopted to implement this model for elimination of motion as well as detection noise from the fluorescence transient signals from the calcium-sensitive probe Rhod-2. These include (1) extracting the fluorescence calcium transient signal from the raw data by using power spectrum density (PSD) in the frequency domain by subtracting the motion recorded using the reflectance of excitation light, (2) digitally filtering out the random noise using multiple bandpass filters centralized at harmonic frequencies of the transients, and (3) extracting high frequency noise with a Gaussian Kernel filter method. The processed signal of transients acquired with excessive motion artifact is comparable to transients acquired with minimal motion obtained by immobilizing the heart against the detection window, demonstrating the usefulness of this technique. Published by Elsevier Ltd.

Interpolated template subtraction method for stimulation artifact removal

“…There are already many methods to remove artifacts in various cases, such as blind source separation (BSS) 1 and independent component analysis (ICA) 2 for EEG signal and frequency filter for calcium signal. 3 However, given that we may apply the methods to flexible systems, we only consider the time-domain methods. There are two practical methods to effectively eliminate stimulation artifacts in the time domain.…”