Fetal ECG Extraction using ICA of Multi-Channel Maternal ECG Suppression
Date Issued
2009
Date
2009
Author(s)
Hsu, Chao-Yang
Abstract
Electrocardiography (ECG or EKG) is the important and general non-invasive method for heart diagnosis. The recording of the electrical activity from cutaneous electrodes provides observation of abnormal heart function. Likewise, the recording of the electrical activity from cutaneous electrodes of the pregnant woman can use for observation of fetal heart function, called fetal ECG (FECG). As same as standard ECG, the fetal ECG also represents other biomedical information, such as the observation of fetal autonomic nervous system (ANS) by successive changes of fetal hart rate variability (HRV). Different from this, the observation of fetal ECG has difficulty in practice. Because fetus is stored inside maternal body, there are two natural identical signal sources exist simultaneously, such as maternal and fetal heart in recording signal from skin electrodes. Especially the signal strength of maternal ECG is much large then fetal ECG is increase the difficulty of signal processing. Furthermore, compare with weak fetal ECG, it is very evident that the interference generated by other physiologic phenomenon or measuring noise influence the signal of fetal ECG. The research of this thesis focuses on the signal obtainment of fetal ECG. The objective of this thesis is to propose new algorithm architecture for proper fetal ECG extraction without thoracic electrode, based on few abdominal electrodes only. The processing result can be used for further analysis of fetal medical information. The proposed algorithm integrates several processing by various perspectives, including frequency domain, time domain, spatial domain and statistic domain. The first band-pass filter preliminary removes other interference and noise based on signal composite differences of frequency component. Next, the maternal ECG is represented as a summation of sequential PQRST complexes. The maternal ECG reconstructed by positioning template of PQRST complex on each fiducial point in time. Based on this approach, the output of band-pass filter is subtracted to the estimated maternal ECG for maternal ECG elimination. Due to time-dependent of real heart beat, even neighboring PQRST complex is hardly identical. Therefore the direct subtraction method does not remove maternal ECG entirely. Afterward, the further elimination of residual maternal ECG and other noises achieves by using a kind of independent component analysis (ICA) method, call projection pursuit (PP). It extracts fetal ECG based on statistical characterization of source signal. The experimental signals download from “Non-Invasive Fetal Electrocardiogram Database” of “PhysioBank”, a publish database in internet. Those signals had measured by Ph.D. Marocelino Martinez Sober and Jorge Granado Marco in the University of Valencia, Spain. The experimental results demonstrate proposed algorithm achieves fetal ECG extraction from four recording of abdominal electrodes only. Meanwhile, the discussion of how several design parameters, such as the cut-off frequency of band-pass filter, the length and position of template of maternal PQRST complex, the processing window of projection pursuit impact the fetal ECG extraction is described in this thesis. In conclusion, corresponding experimental results prove the template based maternal ECG subtraction method and ICA based projection pursuit method can be integrated together by following a proper sequence and adjustment, the proposed algorithm succeeds fetal ECG extraction effectively and accurately.
Subjects
fetal electrocardiogram
signal processing
template PQRST complex
independent component analysis
projection pursuit
Type
thesis
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