Venous Doppler Ultrasound

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Venous Doppler Ultrasound

Definition

Venous Doppler ultrasound, also called sonography and ultrasonography, is a noninvasive, painless procedure used to evaluate blood flow in major veins in the arms and legs. It uses high frequency sound waves that are above the level of human hearing (ultra sound). In Doppler ultrasound, these sound waves are transmitted through the body and are echoed back to produce images of blood flow in body tissues and organs.

Purpose

Venous Doppler ultrasound is used to assess the direction, velocity, and turbulence of blood flow through major veins in the patient's arms, legs, and neck. A Doppler study of blood flow can be used to diagnose many conditions, such as blood clots, incompetent valves in leg veins, which cause fluid to accumulate (venous insufficiency) or deep vein thrombosis. A blood clot forms when blood changes from a flowing liquid into a solid mass. A clot located in the heart or a blood vessel is a called a thrombus. Clots are usually found in veins. These clots can cause thrombosis, which is the obstruction of blood flow through the blood vessel. Deep vein thrombosis is a condition caused when a clot develops in the large vein. This condition usually occurs in the legs and arms.

The Doppler exam is also used to diagnose varicose veins. Varicose leg vein symptoms include swelling of the legs, twisted or enlarged leg veins, and leg discomfort. The test is also used to map a patient's veins. This provides information about portions of damaged veins that may need to be removed. Doppler ultrasound can be used to evaluate and diagnose tumors with vascular involvement and aids in the placement of a catheter, a narrow tube placed in a blood vessel. Venous Doppler ultrasound is done as an alternative to venography, which is an invasive procedures with greater risks to the patient than Doppler ultrasound. Diagnostic Doppler ultrasound can also be performed on arteries (see arterial Doppler ultrasound).

Precautions

Venous Doppler ultrasonography is harmless, as it uses no ionizing (x-ray) radiation, and there are no known harmful effects. It is a safe procedure for pregnant women and does not affect cardiac pacemakers, metal implants or metal fragments lodged in the body.

Although the ultrasound test is not painful, the transducer is pressed on the skin and may cause discomfort in a patient already experiencing pain from conditions such as swollen limbs.

Cigarette smoking may alter the results of the test, as nicotine can cause arteries in the extremities to constrict.

Description

Ultrasound is the medical use of sound waves with frequencies too high to be heard by humans. Ultrasound waves used for medical imaging are usually in the range of 2 to 10 megahertz (MHz). During this procedure, an instrument called a transducer converts electrical signals into ultrasound waves, directs the high-frequency sound waves to the vein being tested, and then converts the returning ultrasound waves that bounce off the body tissue back into electrical signals. These electrical signals can be converted into images by a computer. Computer images may be preserved as recorded movement or as still pictures.

Doppler ultrasound takes advantage of the Doppler effect, a physics principle that states that relative to an observer, the frequency of any sound or light wave will vary as the source of the wave approaches or moves away. For example, the pitch of a siren changes as a police car moves toward, past, and then away from the listener. When used to evaluate blood flow, sound waves increase in frequency when they echo from red blood cells moving toward the transducer and decrease in frequency when they move away from the transducer. The change in frequency is related to the velocity of the moving red blood cells and can be measured to determine the velocity of the blood flow. Flowing blood also makes a sound that can be heard with Doppler ultrasound.

Doppler ultrasound tests usually take between 30 and 60 minutes. Exam length is based on factors such as the location of the area to be scanned and the difficulty in obtaining images. The procedure begins with the patient being positioned for the scan. The patient may recline or stand. The health professional applies a water-soluble gel to the skin over the area to be scanned. The health care worker then places the transducer on the area covered by gel and moves the device on the skin.

Diagnostic information from the transducer is relayed in several ways:

Continuous-wave Doppler is the simplest mode. Information is received from all of the moving reflectors in the path of the beam.
In pulsed-wave Doppler, the transducer sends a series of short sound pulses into the body, with pauses between each pulse to allow for the detection of the returning sounds that are echoing back from the red blood cells. Pulsed-wave Doppler allows the operator to select a specific area of interest for flow analysis.
The duplex Doppler ultrasound scan is also known as 2-D or two-dimensional ultrasound. The duplex procedure uses two types of ultrasound at the same time. Information from the scan is relayed to a computer, which creates an image of blood vessels and organs. The images change continuously and may be filmed or taped. The computer also transforms the reflected sound into a graph that charts information about the direction and velocity of blood flow.
The color Doppler ultrasound produces a two-dimensional image of a blood vessel. The test also transforms reflected sound into colors that are displayed on the a computer monitor. These colors indicate the velocity and direction of blood flow. For example, red and blue indicate that the flow is away from the transducer, while blue and green indicate that the blood is flowing towards the transducer. The colors can be superimposed on the image of the blood vessel.
The power Doppler ultrasound scan is more sensitive than the color Doppler ultrasound. The sensitivity of this scan allows evaluation of areas that are unscannable by other ultrasound methods. The power Doppler scan is useful in examining small blood vessels.

The fee for venous Doppler ultrasound tests varies. Cost factors include the type of tests needed and the areas to be scanned. Medical insurance usually covers a portion of the test cost.

Preparation

Patients are advised to dress comfortably for the venous Doppler ultrasound test. Clothing, jewelry, and other items must be removed from the area to be scanned. The health care provider should be informed of any medications that the patient is taking, especially blood pressure and vascular medications that could interfere with interpretation of results. If a scan of the abdomen is planned, the patient may be instructed to fast six or more hours before the test.

Aftercare

No aftercare is required.

Complications

As of late 2005, there were no known complications related to the venous Doppler ultrasound test.

Results

Normal results for venous Doppler ultrasound show healthy vessels and unobstructed blood flow. Abnormal results revealed by Doppler ultrasound include the presence of blood clots in veins, closed veins, deep vein thrombosis and arterial conditions including arteriosclerosis, and arterial occlusion.

Health care team roles

A venous Doppler ultrasound examination may be performed by a physician, radiologist, or technologist. The radiologist is a physician and can interpret the test results. The primary-care physician usually discusses test results with the patient and if needed will prescribe treatment for conditions revealed by the test.

The technologist is an allied health professional with special training to perform ultrasound tests (a sonographer). Education for technologists and sonographers ranges from one to four years of training. The length of the program depends on factors such as whether the person is earning a degree or a professional certificate and what other ultrasound tests they are learning to perform.

Patient education consists of informing the patient about the test procedure. This can be done in advance by providing the patient with printed material about the venous Doppler ultrasound exam.

KEY TERMS

Artery— A blood vessel that carries blood away from the heart to the rest of the body.

Blood clot— A solid substance that develops in arteries or veins that can block the flow of blood and have serious health effects.

Blood vessel— A tube in which blood circulates. Arteries, arterioles capillaries, venules, and veins are blood vessels.

Varicose vein— An enlarged, twisted vein usually located in the leg.

Vein— A blood vessel that carries blood from a part of the body back toward the heart.

Resources

BOOKS

Evans, David and W. Norman McDicken. Doppler Ultrasound: Physics, Instrumentation and Signal Processing. Hoboken, NJ: John Wiley & Sons, 2000.

Kremkau, Frederick, James Eckenhoff, and Leroy Vandam. Diagnostic Ultrasound: Principles and Instruments. Philadelphia: Elsevier Health Sciences, 2005.

Ridgway, Donald P. Introduction to Vascular Scanning: A Guide for the Complete Beginner. Pasadena, CA: Davies Publishing, Inc., 2004.