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. 2021 Apr 12:15:637274.
doi: 10.3389/fnins.2021.637274. eCollection 2021.

Removal of Electrocardiogram Artifacts From Local Field Potentials Recorded by Sensing-Enabled Neurostimulator

Yue Chen  1 , Bozhi Ma  1 , Hongwei Hao  1 , Luming Li  1   2   3   4
Affiliations

Removal of Electrocardiogram Artifacts From Local Field Potentials Recorded by Sensing-Enabled Neurostimulator

Yue Chen et al. Front Neurosci. .

Abstract

Sensing-enabled neurostimulators are an advanced technology for chronic observation of brain activities, and show great potential for closed-loop neuromodulation and as implantable brain-computer interfaces. However, local field potentials (LFPs) recorded by sensing-enabled neurostimulators can be contaminated by electrocardiogram (ECG) signals due to complex recording conditions and limited common-mode-rejection-ratio (CMRR). In this study, we propose a solution for removing such ECG artifacts from local field potentials (LFPs) recorded by a sensing-enabled neurostimulator. A synchronized monopolar channel was added as an ECG reference, and two pre-existing methods, i.e., template subtraction and adaptive filtering, were then applied. ECG artifacts were successfully removed and the performance of the method was insensitive to residual stimulation artifacts. This approach to removal of ECG artifacts broadens the range of applications of sensing-enabled neurostimulators.

Keywords: ECG; artifact; local field potential; removal; sensing-enabled neurostimulator.

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Conflict of interest statement

LL, HH, and BM serve on the scientific advisory board for Beijing Pins Medical Co., Ltd., and were listed as inventors in issued patents and patent applications on the deep brain stimulator used in this work. The remaining author declares that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Figures

FIGURE 1
FIGURE 1
Illustration of the sensing-enabled neurostimulator system.
FIGURE 2
FIGURE 2
Schematic of the recording module in the sensing-enabled neurostimulator. LFPs were recorded in the bipolar recording channel (between contacts 1 and 3). The ECG signals were recorded in the monopolar recording channel (between the titanium case and contact 4). The capacitors and resistors in each chain formed passive band-pass filters (0.3–250Hz) of the analog-front-end circuits. Monopolar stimulation was delivered between the titanium case and contact 2.
FIGURE 3
FIGURE 3
Illustration of the simulated recording setup. The titanium case and the DBS electrodes were fully immersed in the phantom that was filled with saline solution.Phantom size is expressed in centimeters. A 23Hz sinusoidal signal and a standard ECG waveform were delivered by two pairs of Ag/Cl disc-electrodes. The recordings were wirelessly transmitted toa computer.
FIGURE 4
FIGURE 4
Characteristics of the original recordings. (A) The top axis is the bipolar recording of the clean LFP (dark line) and the contaminated LFP (gray line). The bottom axis is the monopolar recording of theECG reference. The contaminated LFP and the ECG reference were synchronously recorded during stimulation (2.5 V, 150 Hz, 60μs). (B) The PSD of the clean LFP. (C) The PSD of the contaminated LFP.
FIGURE 5
FIGURE 5
Extraction of ECG spikes from monopolar recordings. (A) The averaged ECG spikes in DBS off and DBS on states. (B) The peak-to-peak values of the ECG spikes and DBS artifacts. The dots are mean values and the error bars are standard deviations.
FIGURE 6
FIGURE 6
The results of ECG artifact removal using template subtraction. (A) The results of ECG removal with the DBS off. The bipolar recordings before (contaminated, red line) and after (cleaned, gray line) ECG removal were plotted on the top axis. The monopolar recording of the ECG reference was plotted on the bottom axis. (B) The PSDs of the bipolar recording before and after ECG removal. The blue line is the PSD of the clean LFP. (C) The results of ECG removal fromthe recording with the DBS on. (D) The PSDs of the bipolar recordings before and after ECG removal.
FIGURE 7
FIGURE 7
The results of ECG artifact removal using adaptive filtering. (A) The results of ECG removal of the recording with the DBS off. The bipolar recordings before (contaminated, red line) and after (cleaned, gray line) ECG removal were plotted on the top axis. The monopolar recording of the ECG reference was plotted on the bottom axis. (B) The PSDs of the bipolar recording before and after ECG removal. The blue line is the PSD of the clean LFP. (C) The results of ECG removal from the recording with the DBS on. (D) The PSDs of the bipolar recordings before and after ECG removal.
FIGURE 8
FIGURE 8
ECG artifact removal without extra filtering of DBS artifacts. (A) The gray lines are the overlapped contaminated LFPs aligned according to the R-waves detected in the monopolar channel. The dashed red lines indicate the envelope of the ECG artifacts. The white line is the averaged waveform of the aligned recordings. (B) PSDs of the contaminated LFP and ECG-cleaned LFP. (C) The templates of the ECG artifacts in the contaminated LFPs with different DBS amplitudes.
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