Merck Manual

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Mustafa A. Mafraji

, MD, Rush University Medical Center

Reviewed/Revised Nov 2023
Topic Resources

Ultrasonography is a type of medical imaging that uses high-frequency sound (ultrasound) waves to produce images of internal organs and other tissues.

During an ultrasound, a device called a transducer converts electrical current into sound waves, which are sent into the body’s tissues. Sound waves bounce off structures in the body and are reflected back to the transducer, which converts the waves into electrical signals. A computer converts the pattern of electrical signals into an image, which is displayed on a monitor and recorded as a digital computer image. No x-rays are used, so there is no radiation exposure during ultrasonography.

Procedure for Ultrasonography

If certain parts of the abdomen are being examined during an ultrasound, people may be asked to refrain from eating and drinking for several hours before the test. Normal gas build up in the intestines from eating or drinking can sometimes make ultrasound images difficult to obtain. In other instances, such as an ultrasound of female reproductive organs, women may be asked to drink a large amount of fluid to fill their bladder.

Usually, the examiner places thick gel on the skin over the area to be examined to ensure good sound transmission. A handheld transducer is placed on the skin and moved over the area to be evaluated.

To evaluate some body parts, the examiner inserts the transducer into the body—for example, into the vagina to better image the uterus and ovaries or into the anus to image the prostate gland.

The examiner sometimes attaches the transducer to a viewing tube called an endoscope and passes it into the body. This procedure is called endoscopic ultrasonography. The endoscope can be passed down the throat to view the heart (transesophageal echocardiography Echocardiography and Other Ultrasound Procedures Ultrasonography is a type of medical imaging that uses high-frequency (ultrasound) waves to produce a moving image of internal organs and other tissues. Echocardiography is ultrasonography of... read more Echocardiography and Other Ultrasound Procedures ) or through the stomach to view the liver and other nearby organs.

After the test, most people can resume their usual activities immediately.

Did You Know

  • Ultrasonography and magnetic resonance imaging (MRI) do not use x-rays.

Uses of Ultrasonography

Ultrasound images are acquired rapidly enough to show the motion of organs and structures in the body in real time (as in a movie). For example, the motion of the beating heart can be seen, even in a fetus.

Ultrasonography is effectively used to check for growths and foreign objects that are close to the body’s surface, such as those in the thyroid gland, breasts, testes, and limbs, as well as some lymph nodes.

Ultrasonography is effectively used to image internal organs in the abdomen, pelvis, and chest. However, because sound waves are blocked by gas (for example, in the lungs or intestine) and by bone, ultrasonography of internal organs requires special skills. People who have been specifically trained to do ultrasound examinations are called sonographers.

Ultrasonography is commonly used to evaluate the following:

Ultrasonography can also be used to guide doctors when they remove a sample of tissue for a biopsy. Ultrasonography can show the position of the biopsy instrument, as well as the area to be biopsied (such as a mass). Thus, doctors can see where to insert the instrument and can guide it directly to its target.

Variations of Ultrasonography

Ultrasound information can be displayed in several ways:

  • A-mode: As spikes on a graph (used to scan the eye)

  • B-mode: As a 2-dimensional anatomic images (used during pregnancy to evaluate the developing fetus or to evaluate internal organs)

  • M-mode: As waves displayed continuously to show moving structures (used to evaluate the fetus's heartbeat or to evaluate heart valve disorders)

B-mode ultrasonography is most commonly done.

Doppler ultrasonography

Doppler ultrasonography uses changes that occur in the frequency of sound waves when they are reflected from a moving object (called the Doppler effect). In medical imaging, the moving objects are red blood cells in the blood. Thus, Doppler ultrasonography can be used to evaluate

  • Whether blood is flowing through blood vessels

  • How fast it flows

  • Which direction it flows in

Doppler ultrasonography is used

  • To evaluate how well the heart is functioning (as part of echocardiography)

  • To detect blocked blood vessels, especially in leg veins, as in deep vein thrombosis, when veins are blocked by a blood clot

  • To detect narrowed arteries, especially the carotid arteries in the neck, which carry blood to the brain

Spectral Doppler ultrasonography

Spectral Doppler ultrasonography shows blood flow information as a graph. It can be used to assess how much of a blood vessel is blocked.

Duplex Doppler ultrasonography

Duplex Doppler ultrasonography combines spectral and B-mode ultrasonography.

Color Doppler ultrasonography

For color Doppler ultrasonography, color is superimposed on the shades-of-gray image of blood flow produced by Doppler ultrasonography. The color indicates direction of blood flow. Red may be used to indicate flow toward the transducer, and blue may be used to indicate flow away from the transducer. The brightness of the color indicates how fast the blood is flowing.

Transthoracic Echocardiography

Disadvantages of Ultrasonography

If the examiner inserts the transducer into the body for the ultrasonography, insertion of the transducer may cause some discomfort. Rarely, when a transducer is inserted, tissue is damaged, causing bleeding or infection.

Bone or gas can block ultrasonography. Thus, using ultrasonography to obtain images of certain structures (those behind bone or gas) is difficult.

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