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. 2014:2014:784862.
doi: 10.1155/2014/784862. Epub 2014 Jan 29.

New estimators and guidelines for better use of fetal heart rate estimators with Doppler ultrasound devices

Iulian Voicu  1 , Sébastien Ménigot  1 , Denis Kouamé  2 , Jean-Marc Girault  1
Affiliations

New estimators and guidelines for better use of fetal heart rate estimators with Doppler ultrasound devices

Iulian Voicu et al. Comput Math Methods Med. 2014.

Abstract

Characterizing fetal wellbeing with a Doppler ultrasound device requires computation of a score based on fetal parameters. In order to analyze the parameters derived from the fetal heart rate correctly, an accuracy of 0.25 beats per minute is needed. Simultaneously with the lowest false negative rate and the highest sensitivity, we investigated whether various Doppler techniques ensure this accuracy. We found that the accuracy was ensured if directional Doppler signals and autocorrelation estimation were used. Our best estimator provided sensitivity of 95.5%, corresponding to an improvement of 14% compared to the standard estimator.

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Figures

Figure 1
Figure 1
A real Doppler signal (PRF = 1 kHz) of 1000 ms, recorded with the second transducer in the fourth-channel: (a) Doppler signal (dashed line) and its envelope (solid line); (b) the envelopes of directional signals corresponding to ultrasound scatters approaching to the transducer (solid line) and moving away from the transducer (dash-dot line), respectively.
Figure 2
Figure 2
Envelope of a real directional Doppler signal of 2000 ms. The parameters defining the synthetic signal are the amplitudes and durations of peaks, the lag, and the differences in amplitude of two consecutive peaks over time.
Figure 3
Figure 3
General diagram of the Doppler data processing acquired using one transducer and one channel. x F and x B represent the envelopes of the directional signals, and x e represents the envelope of the nondirectional signal. I 1, I 2 are the two autocorrelation estimators.
Figure 4
Figure 4
Duration of the analyzing window W required to reach an error of at least 0.25 bpm with the autocorrelation estimator (I 1) and a SNR > 0.6 dB.
Figure 5
Figure 5
Duration of the analyzing window W required to reach an error of at least 0.25 bpm with the autocorrelation estimator (I 2) and with a SNR > 0.6 dB.
Figure 6
Figure 6
True positive rates for I 1 and I 2 with SNR > 0.6 dB, W = 4096, and an error of estimation of 0.25 bpm. (a) True positive rate for I 1. (b) True positive rate for I 2.
Figure 7
Figure 7
False negative rates for I 1 and I 2 with SNR > 0.6 dB, W = 4096. Accuracy of 25 bpm was obtained only for I 1 whatever the frequency, whereas for I 2 accuracy was obtained for only 100, 150, 200, 220, and 240 bpm. (a) False negative rate for I 1. (b) False negative rate for I 2.
Figure 8
Figure 8
FHR error of estimation (bpm) when the false negative rate was zero, when the SNR ∈ (0 dB, 2 dB), and when the signals tested were x F, x B, and x e.
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References

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