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DictionarySeeultrasonographyDoppler ultrasonography
Doppler Ultrasonography DefinitionDoppler ultrasonography is a non-invasive diagnostic procedure that changes sound waves into an image that can be viewed on a monitor.PurposeDoppler 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.PrecautionsThe test is widely used because it is noninvasive, uses no x rays, and gives excellent images. It is harmless, painless, and widely available.DescriptionDoppler 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. Doppler ultrasonography can detect the direction, velocity, and turbulence of blood flow. Because it is non-invasive and uses no x rays, doppler ultrasonography is widely used for numerous diagnostic procedures. (Illustration by Electronic Illustrators Group.)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.PreparationThere 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.AftercareNo aftercare is necessary.Normal resultsA Doppler ultrasonography test showing no restricted blood flow is a normal finding.Abnormal resultsDisrupted 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.)ResourcesBooksSamuels, Martin, and Steven Feske, editors. Office Practice of Neurology. New York: Churchill Livingstone, 1996.Key termsDoppler effect — The principle that the sound of an object moving toward you has a higher pitch than the sound when it is 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.ultrasonography [ul″trah-sŏ-nog´rah-fe] a radiologic technique in which deep structures of the body are visualized by recording the reflections (echoes) of ultrasonic waves directed into the tissues. adj., adj ultrasonograph´ic.in the nursing interventions classification, a intervention" >nursing intervention defined as performance of ultrasound exams to determine ovarian, uterine, or fetal status. Frequencies in the range of 1 million to 10 million hertz are used in diagnostic ultrasonography. The lower frequencies provide a greater depth of penetration and are used to examine abdominal organs; those in the upper range provide less penetration and are used predominantly to examine more superficial structures such as the eye.
The basic principle of ultrasonography is the same as that of depth-sounding in oceanographic studies of the ocean floor. The ultrasonic waves are confined to a narrow beam that may be transmitted through or refracted, absorbed, or reflected by the medium toward which they are directed, depending on the nature of the surface they strike.
In diagnostic ultrasonography the ultrasonic waves are produced by electrically stimulating a crystal called a transducer. As the beam strikes an interface or boundary between tissues of varying density (e.g., muscle and blood) some of the sound waves are reflected back to the transducer as echoes. The echoes are then converted into electrical impulses that are displayed on an oscilloscope, presenting a “picture” of the tissues under examination.
Ultrasonography can be utilized in examination of the heart (echocardiography), in location of aneurysms of the aorta and other abnormalities of the major blood vessels, and in identifying size and structural changes in organs in the abdominopelvic cavity. It is, therefore, of value in identifying and distinguishing cancers and benign cysts. The technique also may be used to evaluate tumors and foreign bodies of the eye, and to demonstrate retinal detachment. Ultrasonography is not, however, of much value in examination of the lungs because ultrasound waves do not pass through structures that contain air.
A particularly important use of ultrasonography is in the field of obstetrics and gynecology, where ionizing radiation is to be avoided whenever possible. The technique can evaluate fetal size and maturity and fetal and placental position. It is a fast, relatively safe, and reliable technique for diagnosing multiple pregnancies. Uterine tumors and other pelvic masses, including abscesses, can be identified by ultrasonography.A-mode ultrasonography that in which on the cathode-ray tube display one axis represents the time required for the return of the echo and the other corresponds to the strength of the echo.B-mode ultrasonography that in which the position of a spot on the CRT display corresponds to the time elapsed (and thus to the position of the echogenic surface) and the brightness of the spot to the strength of the echo; movement of the transducer produces a sweep of the ultrasound beam and a tomographic scan of a cross section of the body.Doppler ultrasonography that in which measurement and a visual record are made of the shift in frequency of a continuous ultrasonic wave proportional to the blood-flow velocity in underlying vessels; used in diagnosis of extracranial occlusive vascular disease. It is also used in detection of the fetal heart beat or of the velocity of movement of a structure, such as the beating heart. Normal versus abnormal Doppler arterial waveform patterns. A, Normal waveform with triphasic pattern of sharp upstroke and downstroke and good amplitude: (1) systolic component, (2) diastolic component, and (3) elastic wall rebound. B, Abnormal waveform with monophasic pattern of low amplitude and flat waves. This pattern indicates severe arterial obstruction. From Malarkey and McMorrow, 2000.gray-scale ultrasonography B-mode ultrasonography in which the strength of echoes is indicated by a proportional brightness of the displayed dots.real-time ultrasonography B-mode ultrasonography using an array of detectors so that scans can be made electronically at a rate of 30 frames a second.Dopp·ler ul·tra·so·nog·ra·phy (dop'lĕr), application of the Doppler effect in ultrasound to detect movement of scatterers (usually red blood cells) by the analysis of the change in frequency of the returning echoes.In many settings, ultrasound has supplanted x-radiography as the imaging method of choice, because it poses no known risk to patients, is noninvasive, and is of moderate cost. Doppler-created ultrasound makes possible real-time viewing of tissues, blood flow, and organs that cannot be observed by any other method. It is particularly valuable in cardiology and obstetrics. Dopp·ler ul·tra·son·og·ra·phy (dop'lĕr ŭl'tra-sŏ-nog'ră-fē) Application of the Doppler effect in ultrasound to detect movement of scatterers (usually red blood cells) by the analysis of the change in frequency of the returning echoes.  DOPPLER ULTRASONOGRAPHY: Doppler probe used on (A) dorsal pedis and (B) posterior tibial arteriesDoppler ultrasonographyThe shift in frequency produced when an ultrasound wave is echoed from something in motion. The use of the Doppler effect permits measuring the velocity of that which is being studied, e.g., blood flow in a vessel. See: illustrationSee also: ultrasonographyDoppler, Christian J., Austrian mathematician and physicist in U.S., 1803-1853. Doppler bidirectional testDoppler echocardiography - use of Doppler ultrasonography techniques to augment two-dimensional echocardiography by allowing velocities to be registered within the echocardiographic image. Synonym(s): duplex echocardiographyDoppler effect - a change in frequency is observed when the sound and observer are in relative motion away from or toward each other. Synonym(s): Doppler phenomenon; Doppler principleDoppler flow testDoppler measurementDoppler phenomenon - Synonym(s): Doppler effectDoppler principle - Synonym(s): Doppler effectDoppler probeDoppler pulse evaluationDoppler scopeDoppler shift - the magnitude of the frequency change in hertz when sound and observer are in relative motion away from or toward each other.Doppler ultrasonography - application of the Doppler effect in ultrasound to detect movement of scatterers (usually red blood cells) by the analysis of the change in frequency of the returning echoes.Doppler ultrasound flowmeterDoppler ultrasound segmental blood pressure testing |