There are various types of Doppler ultrasound
A color Doppler visualizes the movement, speed, and direction of blood flow.
A duplex Doppler takes a standard image of a blood vessel and graphs the data.
A power Doppler is a new form of color Doppler that provides more detail, but it cannot show in which direction blood is flowing.
A spectral Doppler shows blood flow as graphed data, and it can show whether the blood flow is blocked.
A continuous wave will show a stream of soundwaves, which allows the ultrasound to more accurately measure blood moving at a faster speed.