Ultrasound Imaging

Ultrasound Imaging, medical diagnostic technique in which very high frequency sound is directed into the body. The tissue interfaces reflect the sound, and the resulting pattern of sound reflection is processed by a computer to produce a photograph or a moving image on a television. Ultrasound can be used to examine many parts of the body, but its best known application is the examination of the fetus during pregnancy.

The sound waves used in the ultrasound beam are produced by a rapidly oscillating crystal, and are inaudible to humans. A device called a transducer is used to transmit the sound waves and receive the echoes. The transducer must be in close contact with the skin, and a jellylike substance is smeared on the skin to improve the transmission of sound.

Ultrasound can be used to examine the arterial system (see Artery), heart, pancreas, peritoneal cavity (see Peritoneum), urinary system, ovaries, venous system (see Vein), brain, and spinal cord. Fluid conducts the sound waves well, making ultrasound a useful technique for diagnosing cysts (which are filled with liquid), examining fluid-filled structures such as the bladder or biliary system, and viewing the fetus in the amniotic sac. Ultrasound also can measure bone mineral density to determine the risk of osteoporosis.

Ultrasound examination of the heart is known as echocardiography. Echocardiography is used to study congenital heart disease, coronary artery disease, tumors of the heart, and other cardiac disorders. Ultrasound can also be used to guide surgical procedures, for example, during the insertion of a biopsy needle into a particular area or the pregnancy diagnostic test called amniocentesis. Doppler ultrasound is used to measure the flow of a liquid, for example, blood flow.

During pregnancy, ultrasound is used to monitor the growth, development, and well-being of the fetus. Unlike X-ray examination, ultrasound is safe during pregnancy, with no risk to either the fetus or the mother. Ultrasound can also be used to check the baby's due date; the size of the fetus's head can be measured and this is used to estimate its age. If multiple births are suspected, ultrasound may be used in order to confirm the number of fetuses. Ultrasound can be used to detect some fetal abnormalities, such as spina bifida, short-limbed dwarfism, or severe congenital heart diseases; this early diagnosis allows appropriate treatment to be given during pregnancy and childbirth.