A Combined Independent Source Separation and Quality Index Optimization Method for Fetal ECG Extraction from Abdominal Maternal Leads

Figures

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  Figure 1. Block-diagram of the three methods compared in this study: ICAQIO-based, QIO-based and ICA-based. The pre-processing and the fQRS detection steps are common to the three algorithms.

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  Figure 2. 5 s interval of the four selected channels of the FECGSYNDB after pre-processing. Selected record: dipole model = 2, simulation = 1, case = 3, SNR = 0 dB.

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  Figure 3. Components resulting from ICA application to the signals in Figure 2. Intensity values are expressed in arbitrary units (au).

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  Figure 4. Application of maternal ECG canceling. Top: ECG after the application of ICA (ic3 in Figure 2); middle: estimated mECG (emECG) obtained by SVD; bottom: residual fECG signal resulting from by the two previous signals subtraction. Intensity values are expressed in arbitrary units (au).

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  Figure 5. Residual signals (res1, res2, res3, res4) obtained after maternal ECG canceling from the four selected channels.

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  Figure 6. The fQRS-enhanced signal obtained by fQI optimization from the residual signals of Figure 5. Compared to the signal in Figure 4 (bottom) it can be observed that some QRSs (i.e., 161.4 s) are enhanced and the noise amplitude around the QRSs is lower. Arbitrary units are used for the ordinate axis because the optimization of fQI includes signals normalization.

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  Figure 7. Fetal RR series estimation after the application of the ICAQIO-based method. mRR: maternal RR series obtained by the reference maternal channels (magenta); rfRR: reference fetal RR series (blue); efRR: estimated (red) fetal RR series obtained by the application of the two-pass fetal QRS detection procedure.

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  Figure 8. Application of the ICAQIO-based algorithm to the record “a75” of the PhysioNet CinC 2013 Database.

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  Figure 9. Fetal RR series estimation after the application of the ICA-based method. mRR: maternal RR series obtained by the reference maternal channels (magenta); rfRR: reference fetal RR series (blue); efRR: estimated (red) fetal RR series obtained by the application of the two-pass fetal QRS detection procedure.

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  Figure 10. Comparison of F1 results for the three tested algorithms, ICAQIO-based, QIO-based and ICA-based, all the selected cases. Dots represent mean values, crosses represent extreme values. Samples tested: 1750 synthetic signals; 0 and 3 dB SNR levels; 10 different heart dipole models; 5 simulations.

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  Figure 11. F1 histograms for the three tested algorithms, ICAQIO-based, QIO-based and ICA-based, for case 3 (uterine contraction). Samples tested: 1750 synthetic signals; 0 and 3 dB SNR levels; 10 different heart dipole models; 5 simulations.

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  Figure 12. F1 histograms for the three tested algorithms, ICAQIO-based, QIO-based and ICA-based, for case 4 (maternal and fetal ectopic beats + noise). Samples tested: 1750 synthetic signals; 0 and 3 dB SNR levels; 10 different heart dipole models; 5 simulations.