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Definition Doppler ultrasonography is a non-invasive diagnostic procedure that changes sound waves into an image that can be viewed on a monitor. Purpose Doppler ultrasonography can detect the direction, velocity, and turbulence of blood flow. It is frequently used to detect problems with heart valves or to measure blood flow through the arteries. Specifically, it is useful in the work up of stroke patients, in assessing blood flow in the abdomen or legs, and in viewing the heart to monitor carotid artery diseases. Precautions The test is widely used because it is noninvasive, uses no x rays, and gives excellent images. It is harmless, painless, and widely available. Description Doppler ultrasonography makes use of two different principles. The ultrasound principle is this: when a high-frequency sound is produced and aimed at a target, it will be reflected by its target and the reflected sound can be detected back at its origin. In addition, it is known that certain crystals (called piezoelectric crystals) produce an electrical pulse when vibrated by a returning sound. The Doppler principle is simply that sound pitch increases as the source moves toward the listener and decreases as it moves away. Medical science utilizes these two principles in the following way. A transducer (sometimes called a probe) containing piezoelectric crystals sends a series of short sound pulses into the body and pauses between each pulse to listen for the returning sounds. The machine then determines the direction and depth of each returning sound and coverts this into a point of light on a television monitor. Thousands of these pulses are computed and displayed every second to produce an image of the organ being studied. The image allows the doctor to see the organ functioning in real time. The newest addition to this test is the addition of color. Adding color to the image shows the direction and rate of blood flow more clearly. During a Doppler ultrasonography procedure the technician will apply a gel to the skin, then place the transducer against the skin at various angles. The transducer sends the information it receives to a television monitor that shows a moving image of the organ being studied. The technician can save these images either on video tape, paper, or x-ray film for further study. Preparation There is no special preparation needed for this test. The ultrasound technician may apply a clear gel to the skin in order to help the transducer more freely over the body. Aftercare No aftercare is necessary. Normal results A Doppler ultrasonography test showing no restricted blood flow, is a normal finding. Abnormal results Disrupted or obstructed blood flow through the neck arteries may indicate the person is a risk of having a stroke. (Narrowed arterial flow in the legs does not necessarily indicate a risk of stroke.) - Doppler effect
- The principle that the sound of an object moving toward you has a higher pitch than the sound when it's moving away from you.
- Transducer
- The part of a machine that changes signals in one form into another form.
- Ultrasound
- Sound that is too high for the human ear to hear.
For Your Information Books - McGoon, Michael D., ed. Mayo Clinic Heart Book: The Ultimate Guide to Heart Health. New York: William Morrow and Co., Inc., 1993.
- Office Practice of Neurology. Ed. Martin Samuels and Steven Feske. New York: Churchill Livingstone, 1996.
- von Reutern, G. M., and H. J. von Budingen. Ultrasound Diagnosis of Cerebrovascular Disease. New York: Georg Thieme Verlag, 1993.
Source: Gale Encyclopedia of Medicine, Published December, 2002 by the Gale Group
The Essay Author is Dorothy Elinor Stonely.
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