The Delineation of Fiducial Points for Non-Contact Radar Seismocardiogram Signals Without Concurrent ECG

• Published in: IEEE journal of biomedical and health informatics Vol. 25; no. 4; pp. 1031 - 1040
• Main Authors: Xia, Zongyang, Shandhi, Md. Mobashir Hasan, Li, Yinghao, Inan, Omer T., Zhang, Ying
• Format: Journal Article
• Language: English
• Published: United States IEEE 01.04.2021; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Aorta; Aortic valve; aortic valve open; Bandpass filters; Biomedical materials; Delineation; Doppler radar; EKG; Electrocardiography; Fiducial point; Fourier analysis; Fourier transforms; Heart; Heart beat; Heart valves; Informatics; Intervals; microwave; Microwave theory and techniques; non-contact; Radar; Radar detection; Reference signals; Segmentation; seismocardiogram (SCG); Ventricle; Waveforms
• ISSN: 2168-2194; 2168-2208; 2168-2208
• DOI: 10.1109/JBHI.2020.3009997

Objective: Non-contact sensing of seismocardiogram (SCG) signals through a microwave Doppler radar is promising for biomedical applications. However, the delineation of fiducial points for radar SCG still relies on concurrent ECG which requires a contact sensor and limits the complete non-contact detection of SCG. Methods: Instead of ECG, a new reference signal, the radar displacement signal of heartbeat (RDH), was derived through the complex Fourier transform and the band pass filtering of the radar signal. The RDH signal was used to locate each cardiac cycle and mask the systolic profile, which was further used to detect an important fiducial point, aortic valve opening (AO). The beat-to-beat interval was estimated from AO-AO interval and compared with the gold standard, ECG R-to-R interval. Results: For the 22 subjects in the study, the evaluation of the AOs detected by RDH (AO RDH ) shows the average detection ratio can reach 90%, indicating a high ratio of the AO RDH that are exactly the same as AO detected using the ECG R-wave (AO ECG ). Additionally, the left ventricular ejection time (LVET) values estimated from the ensemble averaged radar waveform through AO RDH segmentation are within 2 ms of those through AO ECG segmentation, for all the detected subjects. Further analysis demonstrates that the beat-to-beat intervals calculated from AO RDH have an average root-mean-square-deviation (RMSD) of 53.73 ms when compared with ECG R-to-R intervals, and have an average RMSD of 23.47 ms after removing the beats in which AO cannot be identified. Conclusions: Radar signal RDH can be used as a reference signal to delineate fiducial points for non-contact radar SCG signals. Significance: This study can be applied to develop complete non-contact sensing of SCG and monitoring of vital signs, where contact-based SCG is not feasible.