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ABSTRACT: To examine whether the magnitude-squared coherence between uterine and umbilical blood flow velocity waveforms can, in conjunction with estimated fetal weight, uterine and umbilical pulsatility indices, fetal and maternal heart rates, diastolic notching and the amniotic fluid index, create a sensitive and specific model for the prediction of placental dysfunction. Binary logistic prediction models are created for preeclampsia, pregnancy induced hypertension and intrauterine growth restriction in a study group of 284 unselected midtrimester pregnancies. In each study group, the median value of derived parameters were compared with the uncomplicated pregnancy control group. The magnitude-squared coherence function between the uterine and umbilical flow velocity waveforms was found to be a statistically significant predictor of preeclampsia during the midtrimester of pregnancy. The magnitude-squared coherence did not improve the prediction of intrauterine growth restriction or pregnancy induced hypertension. The inclusion of magnitude-squared coherence as one of the prediction parameters may improve the early identification of pregnancies subsequently complicated by preeclampsia.
Ultrasound in Medicine & Biology 08/2007; 33(7):1057-63. · 2.29 Impact Factor
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ABSTRACT: The application of ultrasound in assessing the fetal cardiovascular system often requires the accurate estimation of maximum blood flow velocity waveforms using Doppler measurements. The modified geometric method estimates the maximum Doppler frequency as the frequency at which the vertical distance between the integrated spectrum and the reference line that connects the origin to the maximum value of the integrated spectrum is the largest. This paper presents a mathematical formulation for a class of maximum blood flow velocity estimation algorithms that includes the modified geometric method. The analysis provides a rationale for the continued use of the modified geometric method for estimating the maximum frequency envelopes of Doppler signals. This paper also contains experimental results demonstrating the superiority of the modified geometric method over a commonly used threshold crossing method.
IEEE Transactions on Biomedical Engineering 11/2004; 51(11):2085-8. · 2.28 Impact Factor
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ABSTRACT: This paper presents a new measure of heart rate variability (HRV) that can be estimated using Doppler ultrasound techniques and is robust to variations in the angle of incidence of the ultrasound beam and the measurement noise. This measure employs the multiple signal characterization (MUSIC) algorithm which is a high-resolution method for estimating the frequencies of sinusoidal signals embedded in white noise from short-duration measurements. We show that the product of the square-root of the estimated signal-to-noise ratio (SNR) and the mean-square error of the frequency estimates is independent of the noise level in the signal. Since varying angles of incidence effectively changes the input SNR, this measure of HRV is robust to the input noise as well as the angle of incidence. This paper includes the results of analyzing synthetic and real Doppler ultrasound data that demonstrates the usefulness of the new measure in HRV analysis.
IEEE Transactions on Biomedical Engineering 09/2003; 50(8):950-7. · 2.28 Impact Factor
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ABSTRACT: Many applications involving Doppler signals require the accurate estimation of the power-weighted mean frequency over short durations of the signal due to it's nonstationarity. This paper presents a novel algorithm for estimating mean frequencies using the eigenstructure of the covariance matrix of the Doppler data. Experimental results indicate that this method is superior to the competing non-parametric methods.
Acoustics, Speech, and Signal Processing (ICASSP), 2002 IEEE International Conference on; 06/2002 · 4.63 Impact Factor
