Quantitative Doppler measures in coiled vessels: Investigation on excised umbilical veins

Quantitative assessment of umbilical venous blood velocity with Doppler ult rasound (US) must cope with the coiled structure of the vein inside the cor d. Both an experimental and a theoretical approach showed remarkable variat ions in the insonation angle when the probe was moved along the vein, provi ded the inclination between the Doppler probe and the cord was kept constan t. Inaccurate signal processing, stochastic variability and flow disturbanc es could, however, mask the influence of the geometry. The above hypotheses were assessed by investigating five cords in vitro a few hours after deliv ery from normal pregnancies at term. The Doppler signal was sampled at diff erent sites along each cord and the mean Doppler shift estimated by FFT spe ctral analysis, both directly and through the noise rejection D'Alessio's a lgorithm, which proved effective in improving the Doppler shift estimate in condition of low signal-to-noise ratio (SNR), (C) 1999 World Federation fo r Ultrasound in Medicine & Biology.