An ultrasound scan is a painless test that uses sound waves to create images of organs and structures inside your body. It is a very commonly used test and as it uses sound waves and not radiation, it is thought to be harmless.

What is ultrasound?

Ultrasound is a high frequency sound that you cannot hear, but it can be emitted and detected by special machines.

How does ultrasound work?

Ultrasound travels freely through fluid and soft tissues but 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: 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 in the body of different density, 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 it is a bit like a very thick blunt pen. Lubricating jelly is put on your skin so the probe makes good contact with your body. The probe is connected by a wire to the ultrasound machine and 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 skin surface to get views from different angles.

The scan is painless and takes about 15-45 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. So, it can:

• help to monitor the growth of an unborn child, and check for abnormalities. An ultrasound scan is routine for pregnant women.
• detect abnormalities of heart structures such as the heart valves. (An ultrasound scan of the heart is called an echocardiogram.)
• help to diagnose problems of the liver, gallbladder (such as gallstones), pancreas, thyroid gland, lymph nodes, ovaries, testes, kidneys, bladder and breast. For example, it can help to determine if an abnormal lump in one of these organs is a solid tumour or fluid-filled cyst.
• detect abnormal widening of blood vessels (aneurysms).

Some specialist ultrasound techniques
In some situations, a clearer picture can be obtained from a probe that is within the body. So a small probe, still attached by a wire to the ultrasound machine, can be:

• swallowed into the gullet. This is sometimes used to get clearer images of the heart which lies just in front of the gullet.
• placed in the vagina or rectum to get clearer images of the pelvic and reproductive organs.
• used during an operation to look deeper into structures to help guide a surgeon.

The above are not exhaustive lists, and ultrasound scanning has various other uses.

What should I do to prepare for the test?

Usually there is no special preparation needed. Continue to take your usual medication. You should eat and drink normally before and after the test unless otherwise instructed. For example:

• If certain parts of the abdomen are being examined, you may be asked to eat a low fibre diet for a day or so before the test (to minimise 'gas' in your gut).
• You may be asked not to eat for several hours before a scan of the abdomen.
• For a scan of the lower bowel you may be given an enema to clear the bowel.
• To scan the bladder or pelvis you may need to have a full bladder.

You will be told what you need to do before any particular scan.

Are there any side-effects or complications from ultrasound?

Ultrasound scans are painless and safe. Unlike x-rays and other imaging tests, ultrasound does not use radiation. It has has not been found to cause any problems or complications.

© EMIS and PIP 2006   Updated: February 2006

The authors and editors of this article are employed to create accurate and up to date content reflecting reliable research evidence, guidance and best clinical practice. They are free from any commercial conflicts of interest. Find out more about updating.

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