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
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:
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.
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:
computerised tomography (CT) scans
magnetic resonance imaging (MRI) scans
When an ultrasound scan may be used
An ultrasound scan can be used in several different ways, such as monitoring an unborn baby, diagnosing a condition or guiding a surgeon during certain procedures.
Ultrasound scans are a routine procedure for pregnant women. They produce images of the unborn baby inside the womb and display them on a monitor.
Most women are offered at least two ultrasound scans during pregnancy:
the first scan (at around 8-14 weeks) can help to confirm the pregnancy and determine when the baby is due
the second scan (usually at around 18-21 weeks) checks for structural abnormalities, particularly in the baby's head or spine
However, an ultrasound scan can be done at any time during pregnancy and causes no harm to the baby.
Ultrasound scans can help diagnose problems in many parts of your body, including your:
For example, it can help to detect whether a lump in one of these organs is a tumour or a cyst.
Ultrasound may also be used to diagnose problems with your:
blood vessels (aneurysm)
joints, ligaments and tendons
The hip, spine and brain of newborn babies can be scanned for abnormalities, but by 18 months old the skull has fully grown and it is no longer possible to use ultrasound on the brain without surgery.
An ultrasound scan can be used to examine the size, shape and movement of your heart. For example, it can check that the structures of your heart, such as the valves and heart chambers, are working properly and your blood is flowing normally. This type of ultrasound scan is called an echocardiogram (ECG).
ECG can also be used to diagnose heart problems in babies, even before they are born. This is called foetal echocardiography, and is carried out during routine antenatal examinations.
Ultrasound can be used to guide doctors during certain procedures, such as a biopsy (where a tissue sample is taken for analysis). This is to make sure the surgeon is working in the right area and is often used when diagnosing breast cancer.