Doppler Ultrasound

	Test Overview
	Why It Is Done
	How To Prepare
	How It Is Done
	How It Feels
	Risks
	Results
	What Affects the Test
	What To Think About
	References
	Credits
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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 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 an illustration of a Doppler ultrasound.

The four types of Doppler ultrasound are:

• “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 with a portable machine to provide a rapid estimate of the extent of blood vessel damage or disease.
• Duplex Doppler. Duplex Doppler ultrasound uses standard ultrasound methods to produce a picture of a blood vessel and the 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.
• 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.
• Power Doppler. Power Doppler is a newer ultrasound technique that is up to 5 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.

Doppler ultrasound is done to:

• Detect blood clots and blocked or narrowed blood vessels in almost any part of the body, especially in the neck, arms, and legs. Blocked or narrowed arteries of the neck can cause dizziness, loss of vision, paralysis, weakness, numbness, or other symptoms of a stroke. Blood clots in the deep veins of the leg can cause leg pain and swelling and can increase a person's risk of pulmonary embolism.
• Evaluate leg pain that may be caused by intermittent claudication, a condition caused by atherosclerosis of the lower extremities.
• Evaluate blood flow after a stroke or other condition that might be caused by a problem with blood flow. Evaluation of a stroke can be done through a technique called transcranial Doppler (TCD) ultrasound.
• Evaluate for abnormal veins causing varicose veins or other problems.
• Map veins that may be used for blood vessel grafts. It also can evaluate the condition of grafts used to bypass blockage in an arm or leg.
• Determine the amount of blood flow to a transplanted kidney or liver.
• Monitor the flow of blood following blood vessel surgery.
• Determine the presence, amount, and location of arterial plaque. Plaque in the carotid arteries can reduce blood flow to the brain and may increase the risk of stroke.
• Guide treatment such as laser or radiofrequency ablation of abnormal veins.
• Look at blood flow through the middle cerebral artery (MCA) of a fetus to monitor fetal health. This may be done when Rh sensitization has occurred and the health of the fetus needs to be followed to help guide treatment decisions.

A transcranial Doppler ultrasound (TCD) may be used in children with sickle cell disease to evaluate their risk of stroke. In adults, it can be used to evaluate blood flow and vessel spasms in the brain.

You may be asked to avoid 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.

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.

• 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.

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.

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 Valsalva's 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.

Transcranial ultrasound

For a transcranial ultrasound, the transducer is passed lightly over the skin at the base or side of your skull.

There is normally no discomfort involved with having a Doppler ultrasound test. The gel may feel cold when it is applied to 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 cuffs are inflated.

There are no known risks associated with a Doppler ultrasound test.

A Doppler ultrasound test uses reflected sound waves to evaluate blood as it flows through a blood vessel.

Factors that can interfere with your test and the accuracy of the results include:

• Bones above the area being studied or gas in the intestines.
• The inability to remain still during the test.
• Extreme obesity.
• Irregular heart rhythms (arrhythmias) or heart disease, which may cause changes in blood flow patterns even though the blood vessels are not abnormal.
• Having a cold arm or leg. Blood flow through that limb may be slowed.
• Having an open wound in the area that needs to be viewed.

• Producing accurate test results with Doppler ultrasound requires a skilled examiner. The scans are usually read within a short period of time in case repeat tests are needed.
• Because Doppler ultrasound requires a person to hold very still, some children may need to be sedated so that their movements do not interfere with the results.
• Angiography and venography are X-ray tests that require the injection of contrast material. In many cases, Doppler ultrasound may be done instead of angiography or venography, since it is faster, less expensive, and noninvasive. If results from a Doppler ultrasound are inconclusive, an angiography or venography test may be done. Angiography is usually more accurate than Doppler ultrasound and is considered the most definitive test for evaluating blood flow through an artery. Magnetic resonance angiography (MRA) and computed tomography (CT) angiography may be done instead of conventional angiography because these tests are less invasive and easier to perform than conventional angiography. In some cases, venography may be needed to confirm a suspected vein problem. For more information, see the medical tests Angiogram, Venogram, and Magnetic Resonance Angiogram (MRA).
• A Doppler ultrasound may be used to evaluate many body organs. It can also be used safely during pregnancy.

Other Works Consulted

• Chernecky CC, Berger BJ, eds. (2004). Laboratory Tests and Diagnostic Procedures, 4th ed. Philadelphia: Saunders.

• Fischbach FT, Dunning MB III, eds. (2004). Manual of Laboratory and Diagnostic Tests, 7th ed. Philadelphia: Lippincott Williams and Wilkins.

• Pagana KD, Pagana TJ (2006). Mosby’s Manual of Diagnostic and Laboratory Tests, 3rd ed. St. Louis: Mosby.

• Roman AS, Pernoll ML (2007). Rh isoimmunization and other blood group incompatibilities section of Late pregnancy complications. In AH DeCherney et al., eds., Current Diagnosis and Treatment Obstetrics and Gynecology, pp. 282–287. New York: McGraw-Hill.