What it is
An scan (also called sonography or USG) uses sound waves too high for us to hear to make pictures of the inside of the body. A small handheld probe sends the sound waves in and picks up the echoes, and a computer turns them into a moving picture on a screen. It shows soft parts such as the liver, kidneys, womb and blood vessels, and a baby in the womb. Unlike an X-ray or a , it does not use radiation.
Why it is done
A doctor may ask for an to find the cause of pain or a lump, to check an organ or follow a condition such as a thyroid problem, or to guide a needle during a . Tummy scans are often used for gallstones, kidney stones, appendicitis and liver problems. A Doppler scan, which shows how blood flows, can look for blood clots in the legs and for narrowed or blocked blood vessels. In pregnancy, scans check how a baby is growing.
What it helps with
How to prepare
You will be told what to do, because it depends on the area being scanned.
Do
- If asked, drink the water you are told to and hold on to your urine so the bladder is full
- If asked to fast for a tummy scan, keep to the hours you were given
- Wear clothes that are easy to move aside, and take off jewellery in the area
- Before an internal scan, tell the team if you have a latex allergy
Do not
- Do not pass urine before a scan that needs a full bladder; if you cannot hold on, tell the team
- Do not stop any medicine unless the doctor tells you to
What happens
An external scan, over the skin, goes like this:
- You lie down and move your clothing aside, or change into a gown.
- The person doing the scan puts clear gel on your skin. It may feel cool.
- They move the probe over the area, pressing gently. You may be asked to change position or to hold your breath for a moment.
- The pictures appear on a screen. The gel is wiped off and you get dressed.
For an internal scan, such as a pelvic scan, a probe in a cover is placed inside the vagina or back passage. You can ask to put it in yourself, and to stop at any time.
Afterwards
For a standard scan there is usually nothing to recover from. The report goes to the doctor who asked for the scan. You may be told the result at the end of the visit, or it may take a few weeks. If you have heard nothing after a few weeks, contact that doctor.
Risks and side effects
uses sound waves, not radiation, and has not been linked to harm when trained people use it properly. It can affect fluids and tissues in some situations, so it is used when it gives useful medical information, not for keepsake pictures.
An external scan is not usually painful, though pressing on a sore area, such as a swollen joint, can hurt. An internal probe can be uncomfortable, so tell the person, who can help. Tell the team about a latex allergy before an internal scan.
Results and what comes next
Your doctor explains the report and may arrange another appointment. What cannot show: sound waves do not pass well through bone or air, so it is not good for looking at bones or the lungs.
A or an may be used when more detail is needed, and an X-ray is better for bones and the chest.
Questions to ask your doctor
Tick the ones you want answered and take them with you.
Common questions
Is an ultrasound scan safe?
Ultrasound uses sound waves and no radiation. It has not been linked to harm when trained people use it properly. It is still done only when there is a medical reason, not for keepsake pictures.
Does an ultrasound scan hurt?
An external scan is not usually painful, and the gel may feel cool. Pressing on a sore area can hurt, and an internal scan can be uncomfortable. You are in control and can ask the person to stop at any time.
Why was I asked to drink water and not pass urine?
Some scans, such as one of the urinary tract, need a full bladder to see the area properly. Follow what the team tells you, and let them know if you cannot hold on.
Is an ultrasound the same as an X-ray or a CT scan?
No. Ultrasound uses sound waves, while X-rays and CT scans use radiation. Ultrasound is the usual way to look at a baby in the womb and is good for soft parts, while an X-ray is better for bones and the chest.