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Ultrasound

How Does An Ultrasound Work?

Last modified: 
26/04/2012 - 09:45

Contributing Author: Guy Slowik FRCS

Ultrasound imaging uses the principles of sonar developed for ships at sea. As sound passes through the body it produces echoes, which can identify distance, size and shape of objects inside.

  • During the ultrasound examination, a machine called a transducer is used to view the target organ and produce pictures for study. The transducer emits sound and detects the returning echoes when it is placed on or over the body part being studied.
  • When the emitted sound encounters a border between two tissues that conduct sound differently, some of the sound waves bounce back to the transducer, creating an echo.
  • The echoes are analyzed by a computer in the ultrasound machine and transformed into moving pictures of the organ or tissue being examined.
  • Ultrasound waves pass easily through fluids and soft tissues, making the procedure especially useful for examining fluid-filled organs such as the uterus in pregnancy, as well as the gallbladder, and soft organs like the liver.
  • Ultrasound waves are unable to penetrate bone or gas, so ultrasound is of limited use for examining regions surrounded by bone, or areas that contain gas or air. Even so, ultrasound has been used to examine most parts of the body.

Nice To Know:

What are the benefits and limitations of ultrasound?

  • Ultrasound is a noninvasive imaging technique. It is a painless procedure.
  • Ultrasound is widely available, low cost and easy to use.
  • Because it does not use radiation, the side effects of radiation are not an issue. So, ultrasound is the preferred technique for monitoring pregnant women and their unborn children.
  • Real-time images are generated by ultrasound, so it is a good tool for guiding invasive procedures like needle biopsies.
  • Ultrasound can display the movement and actual function of the body's organs and blood vessels.
  • There are no known harmful effects of standard ultrasound imaging.
  • The main limitation of ultrasound imaging is that it does not reflect clearly from bone or air. Therefore, other imaging techniques are preferred for areas such as the lungs and the bones.
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From Andrew Maynard - Chair of the University of Michigan Department of Environmental Health Sciences, with help from David Faulkner - 2013 Master of Public Health graduate.