The Summit Doppler Vista AVS Advanced Vascular System for the Best Diagnosis!

While B-mode ultrasound can show images from within the body, the movement of blood and its speed cannot be measured with it alone.

Doppler ultrasound can detect and measure the movement of red blood cells as they cause a change in pitch of the reflected sound waves (called the Doppler effect). There would be no phase shift (rate of change in pitch) if the blood wasn't moving.

How Doppler Ultrasound is Performed
Ultrasound technicians trained in ultrasound imaging (sonographers) place a probe (transducer) over the area of the body being diagnosed. First an image of the region of interest is acquired. Then the vessel is located and the transducer is angled so that the best Doppler shift can be obtained. The best location would be to be able to look directly into the vessel (much like looking into a tunnel). Because of how the vessels are located in the body this is of course often not possible. Thus maneuvering the probe or steering the ultrasound/Doppler beam will make this plausible.

Acquired Doppler information can be heard, shown on a chart (much like and EKG) or in colored blood streaming through the vessel.

Types of Doppler Ultrasound
Commonly, two types of Doppler transducers are used Continuous Wave Doppler and Pulsed Wave Doppler.

Continuous Wave Doppler ultrasound transducers use two crystals, one to send and one to receive echoes. The transmitter emits a continuous sinusoidal wave so a receiver can detect the phase shift. An audible sound is recorded and analyzed. CW Doppler provides high sensitivity to low velocities and detection of high velocities without aliasing. However, CW Doppler cannot distinguish between the sending and receiving signals or extraneous echoes. CW Doppler ultrasound does not produce images like Pulsed Wave Doppler does.

Pulsed-Wave Doppler Ultrasound is combined B-mode to produce images of a certain structure. PW uses a pulsed echo system, the PW transducer both sends and receives the signal. It sends in short bursts, on and off, so it can receive when it is not sending.