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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, such as the heart.
As sound waves are used rather than radiation, the procedure is safe. Ultrasound scans are commonly used during pregnancy to produce images of the baby in the womb.
Ultrasound scans can also be used to:
- detect heart problems
- examine other parts of the body such as the liver, kidneys and abdomen
- help guide a surgeon performing some types of biopsy
Read more information about when an ultrasound scan is used.
What happens during an ultrasound scan?
Most ultrasound scans don’t take long to perform, typically between 15 and 45 minutes. Your ultrasound scan will generally take place in an X-ray department in hospital and be performed either by a doctor, who will provide a diagnostic report, or by a sonographer.
A sonographer is a specialist trained in the use of ultrasound, who will provide a descriptive report for the doctor to make a diagnosis.
Preparing for an ultrasound scan
Before having some types of ultrasound scan, you may be asked to follow certain instructions before the procedure, such as:
- drink water and not go to the toilet until after the test – this is to fill your bladder and 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 abdomen to lower the amount of air and gas in your stomach or bowel and enable your gallbladder to be better assessed
Depending on the area of your body being examined, the hospital may also ask you to remove some clothing and wear a hospital gown.
You may choose to have a sedative, or it may be needed for some ultrasound procedures. If you have a sedative, you will need someone to take you home and stay with you for around 24 hours, until the effects wear off.
Types of ultrasound scan
There are different kinds of ultrasound scans depending on which part of the body is being scanned and why. The three main types are:
- external ultrasound
- internal ultrasound
- endoscopic ultrasound
An external ultrasound scan is most often used to examine your heart or an unborn baby in your womb. It is also used to examine the liver, kidneys and other organs in the abdomen and pelvis.
A small handheld device called a transducer 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 transducer to move smoothly. This also ensures there is continuous contact between the sensor and the skin. The transducer is connected to a computer and a monitor. Pulses of ultrasound are sent from a probe in the transducer, through your skin and into your body. They then bounce back from the structures of your body to be displayed as an image on the monitor.
As well as producing still pictures, an ultrasound scan shows movement that can be recorded onto video.
You should not feel anything other than the sensor and gel on your skin (which is often cold). If you are having a scan of your uterus, your full bladder may cause you a little discomfort. There will be a toilet nearby to empty your bladder once the scan is complete.
An internal examination allows a doctor to look more closely inside the body at organs such as the prostate gland, ovaries or womb.
You will be asked to either lie on your back, or on your side with your knees drawn up to your chest. An ultrasound probe is placed into the vagina or rectum and images are transmitted to a screen.
Internal examinations may cause some discomfort but do not usually cause any pain and shouldn't take very long.
Endoscopic ultrasound is where a long, thin, flexible tube (an endoscope) is inserted into your body, usually through your mouth, to examine areas such as your stomach, gullet (oesophagus) or the lymph nodes in your chest.
You will usually be asked to lie on your side and swallow the endoscope, which is then carefully pushed down towards your stomach.
The endoscope has a light and an ultrasound device on the end. Once it has been inserted into the body, ultrasound waves are used to create images in the same way as an external ultrasound.
You will usually be given painkillers and a sedative to keep you calm, as endoscopic ultrasound can be uncomfortable and can make you feel sick. You may also be given a mouth guard to protect your teeth in case you bite the endoscope.
Internal and endoscopic ultrasound is more effective than external ultrasound for examining some organs in close detail. However, because an object enters your body, there is more discomfort and a small risk of side effects, such as internal bleeding.
Read more information about an endoscopy.
Other types of scan
Ultrasound waves cannot pass through bone, air or gas. This means they are unable to produce clear and detailed images of some parts of the body, for example the brain, because it is surrounded by bone.
Other methods can be used to examine parts of your body not suitable for ultrasound scanning, such as: