Value of the spectral broadening index in continuous wave Doppler measurements

In an experimental study the value of the spectral broadening index (SBI) in continuous-wave (CW) Doppler measurements has been evaluated. The minimum SBI-value per heart beat (i.e. during systole) was calculated from intraoperatively obtained near-field and far-field Doppler spectra of the infrarenal aorta of 10 dogs. Near-field Doppler spectra show the same shape as far-field Doppler spectra but have a significantly different SBI. The minimum SBI of CW Doppler only contains useful information if the Doppler measurements are performed in the far field using a wide ultrasound beam (low emitting frequency). In that case the velocity profile in the blood vessel can be deduced from the SBI. The SBI depends strongly on the distance between the main axis of the ultrasound beam and the centre of the insonated blood vessel. A proper centring of the ultrasound beam corresponds with SBI-curves during the heart cycle which shown minimal spectral broadening. A real-time display of the SBI-curve on the spectrum analyser provides the means of securing optimal CW Doppler spectra by minimising the SBI-curve during acquisition.