What is duplex ultrasound?
Duplex ultrasound combines Doppler flow information and conventional imaging information, sometimes called B-mode, to allow physicians to see the structure of your blood vessels. Duplex ultrasound shows how blood is flowing through your vessels and measures the speed of the flow of blood. It can also be useful to estimate the diameter of a blood vessel as well as the amount of obstruction, if any, in the blood vessel.
Conventional ultrasound uses painless sound waves higher than the human ear can detect that bounce off of blood vessels. A computer converts the sound waves into two-dimensional, black and white moving pictures called B-mode images.
Doppler ultrasound measures how sound waves reflect off of moving objects. A wand bounces short bursts of sound waves off of red blood cells and sends the information to a computer. Doppler ultrasound produces two-dimensional color images that show if blood flow is affected by problems in the blood vessels, such as cholesterol deposits.
When performing duplex ultrasound, your physician uses the two forms of ultrasound together. The conventional ultrasound shows the structure of your blood vessels and the Doppler ultrasound shows the movement of your red blood cells through the vessels. Duplex ultrasound produces images that can be color coded to show physicians where your blood flow is severely blocked as well as the speed and direction of blood flow.
Your physician may recommend a duplex ultrasound to help diagnose and examine conditions that affect the blood vessels. These conditions include:
You may have the test performed in an ultrasound lab. The lab may be part of the physician's office or it may be in a hospital. In some cases your vascular physician may perform the test. However, a specially trained vascular ultrasound technologist usually performs duplex ultrasound.
The test usually lasts about 30 minutes, does not require special medication and is associated with minimal discomfort.
How do I prepare?
For most types of duplex ultrasound not involving the abdomen, you will not have to follow any special instructions. Your physician or the center performing the test may have specific instructions for a particular type of duplex ultrasound. For instance, you may have to fast overnight before having an abdominal ultrasound. Ultrasound waves cannot break through gas in the bowels or air in the lungs.
What happens during a duplex ultrasound?
Before the test begins, your physician or the technician will ask you to lie on the table with your head slightly elevated. The technician will also ask you to lie still because any movement could change the image. The technician then spreads a special gel over the area that he or she will examine. The gel allows better transmission and reception of the ultrasound waves. The technician presses the ultrasound wand against your skin and moves it back and forth. The pressure may cause some mild discomfort, but most people usually do not find the test particularly painful. As the wand moves back and forth, it sends the information to the computer that produces the images the technician can view and record on a television-like screen. During the test, you may hear a whooshing sound, which is the sound that the ultrasound machine makes to represent your blood moving through your body.
What can I expect after a duplex ultrasound?
There are no special instructions for you to follow after the test. You may resume all of your pre-test activities. Since the test is usually painless, sedation is not routinely required.
Are there any complications?
Complications are very rare with ultrasound examinations.
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Reviewed January 2011