Semi-Blind Source Separation for fetal ECG extraction

In contrast, methods utilizing the Abdominal Electrocardiogram (AECG) have a greater prospect for long-term monitoring of FHR (e.g., 24 h) and fetal well-being using signal-processing techniques.
In fact, the fECG is an electrical signal that can be obtained noninvasively by applying multi-channel electrodes placed on the abdomen of a pregnant woman; therefore the three main characteristics that need to be obtained from the fECG extraction for useful diagnosis include:
- Fetal heart rate
- Waveform amplitudes

The detection of fECG signals with powerful and advanced methodologies is becoming a very important requirement in biomedical engineering with the increasing in fECG signal analysis in clinical diagnosis and biomedical applications.

The fECG contains potentially valuable information that could assist clinicians in making more appropriate and timely decisions during labor, but the fECG signal is vulnerable to noise, and difficulty of processing it accurately without significant distortion has impeded its use.

Unobtrusive, long-term and risk-free monitoring are obviously the major requirements for obtaining the fECG. However, there is not yet a good stated and reliable method for fECG extraction. The major disadvantages with this technique are that the acquisition of the fECG cannot be guaranteed and often has a very low SNR because of the interference caused by mECG.

In addition, at around the 28th to 32nd weeks of gestation, the amplitude of the fECG is markedly attenuated due to the electrically insulating effect of the vernix caseosa covering the fetus and the existence of preferred conduction pathways between the fetal heart and maternal abdomen around this time.

The Electromyography (EMG) signal due to an uncomfortable position of the patient or to the uterus contraction, together with motion artifact lead to difficulties in determining the FHR from the AECG signal.

To overcome the above problems, some multiple-lead algorithms use the thoracic mECG to cancel the abdominal mECG, though this is inconvenient for the patient during long-term monitoring. Hence, to make the AECG suitable for the detection of the fECG, the SNR must be enhanced. The decision was therefore made to base the investigation on the possibility of constructing an ambulatory FHR recorder around the acquisition of the abdominal fECG.