How does ultrasound work?
Ultrasound travels freely through fluid and soft tissues. However, ultrasound is reflected back (it bounces back as 'echoes') when it hits a more solid (dense) surface. For example, the ultrasound will travel freely though blood in a heart chamber. But, when it hits a solid valve, a lot of the ultrasound echoes back. Another example is that when ultrasound travels though bile in a gallbladder it will echo back strongly if it hits a solid gallstone.
So, as ultrasound 'hits' different structures of different density in the body, it sends back echoes of varying strength.
What does an ultrasound scan involve?
You lie on a couch and an operator places a probe on your skin over the part of your body to be examined. The probe is a bit like a very thick blunt pen. Lubricating jelly is put on your skin so that the probe makes good contact with your body. The probe is connected by a wire to the ultrasound machine, which is linked to a monitor. Pulses of ultrasound are sent from the probe through the skin into your body. The ultrasound waves then echo ('bounce back') from the various structures in the body.
The echoes are detected by the probe and are sent down the wire to the ultrasound machine. They are displayed as a picture on the monitor. The picture is constantly updated so the scan can show movement as well as structure. For example, the valves of a heart opening and closing during a scan of the heart. The operator moves the probe around over the surface of the skin to get views from different angles.
The scan is painless and takes about 15 minutes, depending on which parts of the body are being examined. A record of the results of the test can be made as still pictures or as a video recording.
What is an ultrasound test used for?
It is used in many situations. The way the ultrasound bounces back from different tissues can help to determine the size, shape and consistency of organs, structures and abnormalities.