A velocity evaluation phantom for colour and pulsed Doppler instruments.

We describe a phantom designed to evaluate the velocity measurements made with colour and pulsed Doppler instruments. Using a belt to translate a large volume of semi-rigid material through the entire Doppler sample volume eliminates many of the problems associated with flow and string phantoms. A servo-motor with feedback circuitry ensures accurate control of the belt velocity with an uncertainty in the mean velocity of 0.14%. The phantom provides velocities with typical variations of 0.07 cm/s. We have demonstrated the usefulness of this phantom by evaluating the linearity and accuracy of three pulsed Doppler instruments over belt velocities ranging from 0 to 80 cm/s. In addition, the measurements show the effects of the wall filter at low belt velocities. Using this phantom, we have quantified the accuracy, linearity and precision of the velocity measurements made by three colour Doppler instruments. The results also show regions where the colour instruments are aliased and where the wall filter dominates.