A Doppler ultrasound test uses reflected sound waves to see how blood flows through a blood vessel. It helps doctors evaluate blood flow through major arteries and veins, such as those of the arms, legs, and neck. It can show blocked or reduced flow of blood through narrow areas 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 pictures of a stroke and an embolus . During pregnancy, Doppler ultrasound may be used to look at blood flow in an unborn baby ( fetus ) to check the health of the fetus.
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 a picture of a Doppler ultrasound .
The four basic types of Doppler ultrasound are:
Why It Is Done
Doppler ultrasound is done to:
A transcranial Doppler (TCD) ultrasound may be used in children with sickle cell disease to evaluate their risk of stroke. In adults, TCD can be used to evaluate blood flow in the brain.
How To Prepare
You may need to stop using products that contain nicotine (cigarettes, chewing tobacco) for 30 minutes to 2 hours before the test. Nicotine causes blood vessels to constrict and may give false results.
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) who is supervised by a radiologist. 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.
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.
Arteries in the arms and legs
This test is often performed on both arms or both legs. Even if the suspected blood flow problem is in only one limb, both may be tested for comparison. If your arms are being tested, they will be tested first while you are lying down and then again while you are sitting.
Depending on which blood vessels are being tested, a blood pressure cuff may be wrapped around one or both limbs so that the blood pressure can be taken at several different places. When testing the legs, a blood pressure cuff may be wrapped first around the calf and then around the thigh. The test may be done at several locations on your leg. When testing the arms, the pressure cuff may be wrapped first around the forearm and then around the upper arm.
Testing may be done before and after exercise, if you are healthy enough.
Veins in the arms and legs
For this test, you will be asked to lie down and breathe normally. You must lie very still. Any changes in blood flow that occur as a response to your breathing patterns are noted.
The test may be repeated while the examiner presses on the veins close to the surface of your skin to help detect a clot in the vein (called a compression maneuver). The examiner may do this with your legs or arms in different positions to ensure that the blood supply is not blocked in these positions. The examiner may also squeeze your calf or forearm to help blood move more quickly through the veins (called an augmentation maneuver). This is done to evaluate blood flow toward your heart.
While your legs are being tested, you may also be asked to try to breathe out strongly with your nose pinched and your mouth closed (called a Valsalva maneuver ). This maneuver usually causes a sudden change in blood flow through the veins.
Arteries in the neck
You will be asked to lie down with a pillow underneath your head for support. The test is performed on both sides of your neck, and then the results are compared to standard values to determine the amount of blockage or narrowing of the arteries.
For a transcranial ultrasound, the transducer is passed lightly over the skin at the base or side of your skull.
The transducer is moved back and forth on your belly until the doctor finds the blood vessel that needs to be studied. After the doctor has found the blood vessel, it may take some time to check the blood flow.
How It Feels
There is normally no discomfort involved with having a Doppler ultrasound test. The gel may feel cold when it is put on your skin unless it is first warmed to body temperature. If your blood pressure is taken during the test, you will feel pressure when the blood pressure cuff is inflated.
There are no known risks linked with a Doppler ultrasound test. This test will not harm a developing baby ( fetus ).
A Doppler ultrasound test uses reflected sound waves to see how blood flows through a blood vessel.
What Affects the Test
Reasons you may not be able to have the test or why the results may not be helpful include:
What To Think About
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