An ultrasound scan, sometimes called a sonogram, is a procedure that uses high-frequency sound waves to create an image of part of the inside of the body. An ultrasound scan can be used to monitor an unborn baby, diagnose a condition, or guide a surgeon during certain procedures.

How ultrasound scans work

A small device called an ultrasound probe is used, which gives off high-frequency sound waves. These sound waves bounce off different parts of the body and create "echoes" that are picked up by the probe and turned into a moving image. This image is displayed on a monitor while the scan is carried out.

Preparing for an ultrasound scan

Before having some types of ultrasound scan, you may be asked to follow certain instructions to help improve the quality of the images produced. For example, you may be advised to:

  • drink water and not go to the toilet until after the scan this may be needed before a scan of your unborn baby or your pelvic area


  • avoid eating for several hours before the scan this may be needed before a scan of your digestive system, including the liver and gallbladder


Depending on the area of your body being examined, the hospital may ask you to remove some clothing and wear a hospital gown.


What happens during an ultrasound scan

Most ultrasound scans last around 15 minutes. They usually take place in a hospital radiology department and are performed either by a radiologist or a sonographer. They can also be carried out in community locations or outpatient/ ward areas by other healthcare professionals.

There are different techniques as described below.

  • External ultrasound scan 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 onto your skin, and moved over the part of the body being examined.


  • Internal or transvaginal ultrasound scan allows a doctor to look more closely inside the body at organs such as the prostate gland, ovaries or womb. 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.


  • Endoscopic ultrasound scan is undertaken with the help of an endoscope inserted into your body, usually through your mouth, to examine areas such as your stomach or gullet (oesophagus).


After an ultrasound scan

In most cases, there are no after-effects and you can go home soon after the scan is finished. If a sedative wasn't used, you can drive, eat, drink and return to your other normal activities straight away.

If you had an endoscopic ultrasound and were given a sedative to help you relax, you'll usually be advised to stay in hospital for a few hours, until the medication starts to wear off. You'll need to arrange for someone to pick you up from the hospital and stay with you for the next 24 hours. You shouldn't drive, drink alcohol or operate machinery during this time.

Are there any risks or side effects?

There are no known risks from the sound waves used in an ultrasound scan. Unlike some other scans, such as computerised tomography (CT) scans, ultrasound scans don't involve exposure to radiation.

External and internal ultrasound scans don't have any side effects and are generally painless, although you may experience some discomfort as the probe is pressed over your skin or inserted into your body.

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Leicester Bowel Clinic