Design And Implementation Of Fetal ECG Signal Extraction System Based On Blind Source Separation

Fetal Electrocardiogram (FECG) is a kind of the physiological signals, which can most reflect the panorama of fetal heart activity. It provides an important method for maternal and fetal safety. The change in the shape of the FECG occurs much earlier and more sensitive than the fetal heart rate based on ultrasonic doppler electronic monitoring and cardiotocography (CTG), when the fetus is abnormal. It can timely detect fetal hypoxia, umbilical cord w fetal hypoxia and umbilical cord wrapped pregnancy or childbirth and other pathological conditions in order to take early measures to ensure fetal health and reduce perinatal morbidity and mortality.A noninvasive method to place the electrodes in the mother’s abdomen where close to the fetal heart, can be used to obtain the FECG with high signal noise ratio (SNR). However, the original ECG collected from the mother’s abdomen is inevitable aliased various kinds of interference and noise, such as power frequency interference and baseline drift, electromyographic (EMG) signal, Mother ECG (MECG), etc. These noises in addition to the ECG can be removed by used the traditional method. But the MECG is the largest amplitude noise, and FECG and MECG will be superimposed on each other in the time and frequency domain. So it is very difficult to extract the FECG from abdominal ECG. This paper will design and implement a system to extract FECG, which contains three main parts:the hardware system of the multi-channel signal acquisition, the system of FECG signal separation and the system to display.The hardware system of the multi-channel signal acquisition mainly includes four modules:a MECG signal module, an abdominal original ECG module, a fetal heart sound (FHR) signal module and an embedded control system module. As the function of the MECG channel and abdominal ECG channel is similar so some of the common features can be merger to implement. The circuits of those two parts include analog filter circuits and an analog to digital converter (ADC). They preprocess and digitalize the ECG signals. The FHR module is consist of a low pass filter, an amplifier circuit and an analog circuit after the processing. It uses ADC which highly integrated controller chip to digitalize fetal heart sound signal. The function of the embedded control system module is to respond the embedded control system module function is the response of the command from PC, then control of the peripheral chips. At last the digital signals of the ECG signals and the heart sound signal will be sent to the PC through a serial port. The hardware system of the multi-channel signal acquisition is the key to guarantee the system to obtain a clear signal.The system of FECG signal separation is to extract FECG from the abdomen based on the use of single-channel ECG oblique projection of the semi-blind separation method. This method requires the R wave position of the mother and fetus ECG signal.The display system is used ActiveX for data communication between PC and the embedded control system module and to display the original data received, MECG and FECG in graphical form.