Ultrasound scan
What is an ultrasound scan?
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.
Read NHS 111 Wales information about ultrasound scansHow ultrasound scans work
A small device called an ultrasound probe is used. It gives off high-frequency sound waves.
You cannot hear these sound waves, but when they bounce off different parts of the body, they create echoes. These echoes are picked up by the probe and turned into a moving image.
The image is displayed on a monitor while the scan is carried out.
Preparing for an ultrasound scan
Before some types of ultrasound scan, you may be asked to follow certain instructions to help improve the quality of the images.
You may be asked to:
- drink water and not go to the toilet until after the scan, for example before a scan of your unborn baby or pelvic area
- avoid eating for several hours before the scan, for example before a scan of your digestive system, liver or gallbladder
- remove some clothing and wear a hospital gown, depending on the area being examined
If you need a sedative to help you relax, this may be given through a small tube into the back of your hand or arm. In some cases, you may also be given a contrast agent before the scan to make the images clearer.
What happens during an ultrasound scan?
Most ultrasound scans last between 15 and 45 minutes.
They usually take place in a hospital radiology department and are performed by a radiologist or a sonographer. They can also be carried out in community locations, such as GP practices, by healthcare professionals who have been specially trained in ultrasound.
The 3 main types of ultrasound scan are:
- external ultrasound scan: the probe is moved over the skin
- internal ultrasound scan: the probe is inserted into the body
- endoscopic ultrasound scan: the probe is attached to a long, thin, flexible tube called an endoscope and passed further into the body
External ultrasound scan
An external ultrasound scan is often used to examine the heart or an unborn baby in the 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.
A lubricating gel is put onto your skin to allow the probe to move smoothly and keep contact between the probe and skin.
You should not usually feel anything other than the probe and gel on your skin, although the gel can feel cold. If you are having a scan of your womb or pelvic area, you may have a full bladder that causes some discomfort. There will usually be a toilet nearby so you can empty your bladder after the scan.
Internal or transvaginal ultrasound scan
An internal scan allows a doctor or healthcare professional to look more closely inside the body at organs such as the prostate gland, ovaries or womb.
A transvaginal ultrasound means “through the vagina”.
You may be asked to 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 gently passed into the vagina or rectum. Images are then transmitted to a monitor.
Internal examinations may cause some discomfort, but they do not usually cause pain and should not take 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.
You will usually be asked to lie on your side while the endoscope is carefully passed down towards your stomach.
The endoscope has a light and an ultrasound device on the end. Once it has been inserted, sound waves are used to create images in the same way as an external ultrasound.
You may be given a sedative to help you stay calm and a local anaesthetic spray to numb your throat. 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.
NHS 111 Wales: local anaestheticAfter an ultrasound scan
In most cases, there are no after-effects and you can go home soon after the scan has finished.
If a sedative was not used, you can usually drive, eat, drink and return to your normal activities straight away.
If you had an endoscopic ultrasound and were given a sedative, you will usually be advised to stay in hospital for a few hours until the medicine starts to wear off.
You will need to arrange for someone to pick you up from hospital and stay with you for the next 24 hours. You should not drive, drink alcohol or operate machinery during this time.
You may be told the results of your scan soon after it has been carried out. In many cases, the images need to be reviewed and a report will be sent to the doctor who referred you. They will discuss the results with you later or at your next appointment.
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 CT scans, ultrasound scans do not involve exposure to radiation.
External and internal ultrasound scans do not usually have side effects and are generally painless, although you may feel some discomfort as the probe is pressed over your skin or inserted into your body.
If you are having an internal scan and you are allergic to latex, tell the sonographer or doctor carrying out the scan so they can use a latex-free probe cover.
Endoscopic ultrasounds can be more uncomfortable and may cause temporary side effects, such as a sore throat or bloating. There is also a small risk of more serious complications, such as internal bleeding.
NHS 111 Wales: CT scansFurther information
For more information about ultrasound scans, including preparing for a scan, what happens during the scan and possible risks, visit NHS 111 Wales.