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Ultrasound scanning is also known as sonography or ultrasonography; a diagnostic screening technique that uses high-frequency sound waves transmitted from a wand-like instrument called a transducer into the body to create images of internal anatomical structures. The sound waves are reflected back as an echo that a computer translates into an image of the body area being examined.
Why It Is Performed
Because ultrasound scanning does not involve exposure to ionizing radiation (as X rays do), it is a safe screening tool for many areas of the body. The technique can be safely used during pregnancy to assess the position, size, and gestational age of the fetus and the location of the placenta. Ultrasound scans can also reveal multiple pregnancies. In children, the procedure may be used to examine organs and structures including the kidneys, the liver and spleen, the female pelvis, and the hips. Diagnostic screening of adults with ultrasound may be performed on these organs and structures as well as on the gallbladder, thyroid, parathyroid, ovaries, uterus, breasts, testicles and prostate. The arteries and veins also can be evaluated by ultrasound scanning. Conditions leading to stroke, such as narrowing of the carotid arteries, can be detected by this technique. Ultrasound scanning can serve as a guide for minimally invasive outpatient procedures including the insertion of small catheters to drain infections and thin-needle biopsies of tumors.
How It Works
The sound waves used in ultrasound scanning are a higher frequency, or pitch, than can be heard by the human ear. When these sound waves are transmitted into the body by a transducer resting on a person's skin, they pass through tissue and are reflected back off internal structures, creating an echo. The echoes are received by the transducer and converted by an electronic instrument into electrical impulses, which are translated by a computer into a moving image that is produced on a monitor. The continuously changing images are recorded on videotape or film to be analyzed.
Solid-mass structures give off stronger ultrasound echoes and produce a
brighter image on the monitor than fluid-filled areas. This allows abnormal
growths in the body to be distinguished from normal tissue.
How It Is Performed
Ultrasound scanning is usually performed on an outpatient basis by a health care professional called a sonographer. If the scan is being performed on a woman who is in the early stages of pregnancy, she will be asked to drink several glasses of water about an hour before the scan. She also will be asked to refrain from urinating because a full urinary bladder allows for clearer visualization of the uterus and fetus.
For all ultrasound scanning, the person lies on an examining table, and a special water-soluble gel is applied to the skin area to be examined. The gel may feel cool to the skin. The transducer is placed on the skin, positioned over the internal organ or structure that will be scanned, and gently pressed against the area that has been lubricated with gel. For certain examinations, a wandlike transducer may be inserted into the vagina or rectum. For example, in early pregnancy, insertion of the transducer into the vagina allows a closer view of the uterus and fetus. A rectal probe is helpful for assessing a man's prostate gland. Ultrasound scanning is generally considered painless and does not require special care after the procedure.