Doppler ultrasonography

Doppler Ultrasonography 

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.

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.

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.)

Resources

Books

Samuels, Martin, and Steven Feske, editors. Office Practice of Neurology. New York: Churchill Livingstone, 1996.

Key terms

Doppler 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.

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ultrasonography /ul·tra·so·nog·ra·phy/ (-sŏ-nog´rah-fe) the imaging of deep structures of the body by recording the echoes of pulses of ultrasonic waves directed into the tissues and reflected by tissue planes where there is a change in density. Diagnostic ultrasonography uses 1–10 megahertz waves.ultrasonograph´ic

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Doppler ultrasonography  that in which the shifts in frequency between emitted ultrasonic waves and their echoes are used to measure the velocities of moving objects, based on the principle of the Doppler effect. The waves may be continuous or pulsed; the technique is frequently used to examine cardiovascular blood flow (Doppler echocardiography).

gray-scale ultrasonography  a B-scan technique in which the strength of echoes is indicated by a proportional brightness of the displayed dots.

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Doppler ultrasonography

n.

Ultrasonography applying the Doppler effect, in which frequency-shifted ultrasound reflections produced by moving targets in the bloodstream, usually red blood cells, are used to determine the direction and velocity of blood flow.

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Doppler ultrasonography

Etymology: Christian J. Doppler

a technique used in ultrasound imaging to monitor moving substances or structures, such as flowing blood or a beating heart. The frequency of ultrasonic waves reflected by a moving surface is slightly different from that of the incident waves. The detected frequency shift yields information about the moving surface. The technique can be used to locate vessel obstructions, observe fetal heart sounds, localize the placenta, and image heart functions. Also called Doppler scanning.

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ultrasonography

an imaging technique in which deep structures of the body are visualized by recording the reflections (echoes) of ultrasonic waves directed into the tissues.

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, 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 piezoelectric crystal called a transducer. As the beam strikes an interface or boundary between tissues of varying acoustic impedance (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) 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. It is a fast, relatively safe, and reliable technique for diagnosing pregnancy, and for detecting some typical fetal anomalies.

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A-mode ultrasonography

(amplitude modulation) that in which on the cathode-ray tube (CRT) display one axis represents the time required for the return of the echo and the other corresponds to the strength of the echo, as in echoencephalography.

B-mode ultrasonography

(brightness modulation) 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

see doppler ultrasound.

endoscopic ultrasonography

a high resolution ultrasound transducer, mounted on a flexible endoscope, can be used to gain images from within a hollow organ, such as the gastrointestinal tract. This overcomes some of the problems ingesta and fecal material cause in other methods of ultrasound examination.

gray-scale ultrasonography

B-mode ultrasonography in which the strength of echoes is indicated by a proportional brightness of the displayed dots.

M-mode ultrasonography

(motion mode) a type of B-mode ultrasonography in which spots on the CRT display produce a tracing of the motion of echogenic objects. Used in echocardiography.

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, thus giving a true display of motion, such as that of the heart.