Implementation of spectral width Doppler in pulsatile flow measurements

In this paper, we present an automatic beam-vector (Doppler) angle and flow velocity measurement method and implement it in pulsatile flow measurement s using a clinical Doppler ultrasound system. In current clinical Doppler u ltrasound flow velocity measurements, the axis of the blood vessel needs to be set manually on the B-scan image to enable the estimation of the beam-v ector angle and the beam-vector angle corrected flow velocity (the actual f low velocity). In this study, an annular array transducer was used to gener ate a conical-shaped and symmetrically focused ultrasound beam to measure t he flow velocity vectors parallel and perpendicular to the ultrasound beam axis. The beam-vector angle and flow velocity is calculated from the mode f requency (f(d)) and the maximum Doppler frequency (f(max)) of the Doppler s pectrum. We develop a spectrum normalization algorithm to enable the Dopple r spectrum averaging using the spectra obtained within a single cardiac cyc le. The Doppler spectrum averaging process reduces the noise level in the D oppler spectrum and also enables the calculation of the beam-vector angle a nd flow velocity for pulsatile flows to be measured. We have verified the m easurement method in vivo over a wide range of angles, from 52 degrees to 8 0 degrees, and the standard deviations of the measured beam-vector angles a nd flow velocities in the carotid artery are lower than 2.2 degrees and 12 cm/s (about 13.3%), respectively. (C) 1999 World Federation for Ultrasound in Medicine & Biology.