Fractal Analysis of Umbilical Artery Doppler Signals from Normal Pregnant Subject Using Hurst Exponent

Doppler signals from the umbilical artery of 20 women with normal pregnancy between 18-20 weeks of gestation were recorded. As a new alternative technique to take the place of traditional short-time Fourier transform (STFT) method, the application of fractal analysis method to the umbilical artery Doppler signals is presented. Traditional Doppler indexes which are resistance index (RI), pulsality index (PI), systolic: diastolic ratio (S/D) indexes have been calculated from the maximum frequency envelope of Doppler sonograms and from the fractal dimension curve. Area under the curve from ROC curve for RI, PI and S/D indexes derived from maximum frequency waveform were calculated as 0.937, 0.959, 0.930 respectively and area under the curve for RI, PI and S/D indexes derived from fractal dimension curve were calculated as 0.939, 0.960, and 0.941 respectively. Furthermore, this result showed the Doppler indexes derived from fractal dimension curve are more sensitive than the Doppler indexes derived from maximum velocity curve.