Doppler ultrasound is a special ultrasound technique that evaluates blood velocity as it flows through a blood vessel, including the body's major arteries and veins in the abdomen, arms, legs and neck.
There are three types of Doppler ultrasound:
- Colour Doppler uses a computer to convert Doppler measurements into an array of colours to visualize the speed and direction of blood flow through a blood vessel.
- Power Doppler is a newer technique that is more sensitive than colour Doppler and capable of providing greater detail of blood flow, especially when blood flow is little or minimal. Power Doppler, however, does not help the radiologist determine the direction of blood flow, which may be important in some situations.
- Spectral Doppler. Instead of displaying Doppler measurements visually, Spectral Doppler displays blood flow measurements graphically, in terms of the distance travelled per unit of time.
Doppler is used to identify:
- blockages to blood flow (such as clots).
- narrowing of vessels (which may be caused by plaque).
- tumors and congenital malformation.