An ultrasound scan is a medical test that uses high-frequency sound waves to capture live images from the inside of your body. It’s also known as sonography.

The technology is similar to that used by sonar and radar, which help the military detect planes and ships. An ultrasound allows your doctor to see problems with organs, vessels, and tissues without needing to make an incision.

Unlike other imaging techniques, ultrasound uses no radiation. For this reason, it’s the preferred method for viewing a developing fetus during pregnancy.

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Why an ultrasound is performed

Most people associate ultrasound scans with pregnancy. These scans can provide an expectant mother with the first view of her unborn child. However, the test has many other uses.

Your doctor may order an ultrasound if you’re having pain, swelling, or other symptoms that require an internal view of your organs. An ultrasound can provide a view of the:

• bladder

• brain (in infants)

• eyes

• gallbladder

• kidneys

• liver

• ovaries

• pancreas

• spleen

• thyroid

• testicles

• uterus

• blood vessels

An ultrasound is also a helpful way to guide surgeons’ movements during certain medical procedures, such as biopsies.

External ultrasound scan

An external ultrasound scan is most often used to examine your heart or an unborn baby in your womb.

It can also be used to examine the liver, kidneys and other organs in the tummy and pelvis, as well as other organs or tissues that can be assessed through the skin, such as muscles and joints.

A small handheld probe is placed on your skin and moved over the part of the body being examined.

A lubricating gel is put on your skin to allow the probe to move smoothly. This also ensures there's continuous contact between the probe and the skin.

You shouldn't feel anything other than the sensor and gel on your skin (which is often cold).

If you're having a scan of your womb or pelvic area, you may have a full bladder that causes you a little discomfort.

There will be a toilet nearby to empty your bladder once the scan is complete.

Internal or transvaginal ultrasound scan

An internal examination allows a doctor to look more closely inside the body at organs such as the prostate gland, ovaries or womb.

A "transvaginal" ultrasound means "through the vagina". During the procedure, you'll be asked to either lie on your back, or on your side with your knees drawn up towards your chest.

A small ultrasound probe with a sterile cover, not much wider than a finger, is then gently passed into the vagina or rectum and images are transmitted to a monitor.

Internal examinations may cause some discomfort, but don't usually cause any pain and shouldn't take very long.

Endoscopic ultrasound scan

During an endoscopic ultrasound scan, an endoscope is inserted into your body, usually through your mouth, to examine areas such as your stomach or gullet (oesophagus).

You'll usually be asked to lie on your side as the endoscope is carefully pushed down towards your stomach.

The endoscope has a light and an ultrasound device on the end. Once it's been inserted into the body, sound waves are used to create images in the same way as an external ultrasound.

You'll usually be given a sedative to keep you calm and local anaesthetic spray to numb your throat, as an endoscopic ultrasound scan can be uncomfortable and may make you feel sick. 

You may also be given a mouth guard to keep your mouth open and protect your teeth, in case you bite the endoscope.