DOPPLER ULTRASOUND

A Doppler ultrasound test uses reflected sound waves to evaluate blood as it flows through a blood vessel. It helps doctors evaluate blood flow through the major arteries and veins of the arms, legs, and neck. It can show blocked or reduced blood flow through narrowing in the major arteries of the neck that could cause a stroke. It also can reveal blood clots in leg veins (deep vein thrombosis, or DVT) that could break loose and block blood flow to the lungs (pulmonary embolism). See an illustration of a stroke or an embolus.
During Doppler ultrasound, a handheld instrument (transducer) is passed lightly over the skin above a blood vessel. The transducer sends and receives sound waves that are amplified through a microphone. The sound waves bounce off solid objects, including blood cells. The movement of blood cells causes a change in pitch of the reflected sound waves (called the Doppler effect). If there is no blood flow, the pitch does not change. Information from the reflected sound waves can be processed by a computer to provide graphs or pictures that represent the flow of blood through the blood vessels. These graphs or pictures can be saved for future review or evaluation. See an illustration of a Doppler ultrasound.

The four types of Doppler ultrasound are:

1. “Bedside” or continuous wave Doppler. This type uses the change in pitch of the sound waves to provide information about blood flow through a blood vessel. The doctor listens to the sounds produced by the transducer to evaluate the blood flow through an area that may be blocked or narrowed. This type of ultrasound can be done at the bedside in the hospital to provide a rapid estimate of the extent of blood vessel damage or disease.
2. Duplex Doppler. Duplex Doppler ultrasound uses standard ultrasound methods to produce a picture of a blood vessel and surrounding organs. In addition, a computer converts the Doppler sounds into a graph that provides information about the speed and direction of blood flow through the blood vessel being evaluated.
3. Color Doppler. Color Doppler uses standard ultrasound methods to produce a picture of a blood vessel. In addition, a computer converts the Doppler sounds into colors that are overlaid on the image of the blood vessel and that represent the speed and direction of blood flow through the vessel.
4. Power Doppler. Power Doppler is a newer ultrasound technique that is up to five times more sensitive in detecting blood flow than color Doppler. Power Doppler can obtain some images that are difficult or impossible to obtain using standard color Doppler. However, power Doppler is most commonly used to evaluate blood flow through vessels within solid organs. Blood flow in individual blood vessels is most commonly evaluated by combining color Doppler with duplex Doppler. Together, they are able to provide better information on the direction and speed of blood flow than when these techniques are used individually.

How It Is Done

This test is done by a doctor who specializes in performing and interpreting imaging tests (radiologist) or by an ultrasound technologist (sonographer). It is done in an ultrasound room in a hospital or doctor's office.
You will need to remove any jewelry that might interfere with the Doppler ultrasound scan. You may need to take off all or most of your clothes, depending on which area is being examined (you may be allowed to keep on your underwear if it does not interfere with the test). You will be given a cloth or paper covering to use during the test.
For abdominal scans, you will lie on your back.
For chest scans, you will lie on your back with your neck slightly extended.
For head and neck scans, your head may be turned to one side.
For an arm or leg scan, your head is slightly raised and the exposed arm or leg is turned slightly outward. Occasionally for a leg scan, you may be asked to lie on your stomach.
Gel is applied to the skin to promote the passage of the sound waves. The transducer is placed in the gel and moved along the skin. You need to lie very still during the procedure. You may hear sounds that represent the flow of blood through the blood vessels.
The test usually takes 30 to 60 minutes.