An ultrasound scan is a painless test that uses sound waves to create images of organs and structures inside your body. It is a very commonly used test. As it uses sound waves and not radiation, it is thought to be harmless. Doppler and duplex scans are used to visualise blood or fluids flowing through the body.
Note: the information below is a general guide only. The arrangements, and the way tests are performed, may vary between different hospitals. Always follow the instructions given by your doctor or local hospital.
What is ultrasound?
Ultrasound is a high-frequency sound that you cannot hear, but it can be emitted and detected by special machines.
How does ultrasound work?
Ultrasound travels freely through fluid and soft tissues. However, ultrasound is reflected back (it bounces back as 'echoes') when it hits a more solid (dense) surface. For example, the ultrasound will travel freely though blood in a heart chamber. But, when it hits a solid valve, a lot of the ultrasound echoes back. Another example is that when ultrasound travels though bile in a gallbladder it will echo back strongly if it hits a solid gallstone.
So, as ultrasound 'hits' different structures of different density in the body, it sends back echoes of varying strength.
What does an ultrasound scan involve?
You lie on a couch and an operator places a probe on your skin over the part of your body to be examined. The probe is a bit like a very thick blunt pen. Lubricating jelly is put on your skin so that the probe makes good contact with your body. The probe is connected by a wire to the ultrasound machine, which is linked to a monitor. Pulses of ultrasound are sent from the probe through the skin into your body. The ultrasound waves then echo ('bounce back') from the various structures in the body.
The echoes are detected by the probe and are sent down the wire to the ultrasound machine. They are displayed as a picture on the monitor. The picture is constantly updated so the scan can show movement as well as structure. For example, the valves of a heart opening and closing during a scan of the heart. The operator moves the probe around over the surface of the skin to get views from different angles.
The scan is painless and takes about 15-45 minutes, depending on which parts of the body are being examined. A record of the results of the test can be made as still pictures or as a video recording.
What is an ultrasound test used for?
It is used in many situations. The way the ultrasound bounces back from different tissues can help to determine the size, shape and consistency of organs, structures and abnormalities. So, it can:
- Help to monitor the growth of an unborn child, and check for abnormalities. An ultrasound scan is routine for pregnant women.
- Detect abnormalities of heart structures such as the heart valves. (An ultrasound scan of the heart is called an echocardiogram.)
- Help to diagnose problems of the liver, gallbladder (such as gallstones), pancreas, thyroid gland, lymph nodes, ovaries, testes, kidneys, bladder and breast. For example, it can help to determine if an abnormal lump in one of these organs is a solid tumour or a fluid-filled cyst.
- Detect abnormal widening of blood vessels (aneurysms).
Some specialist ultrasound techniques
In some situations, a clearer picture can be obtained from a probe that is within the body. So a small probe, still attached by a wire to the ultrasound machine, can be:
- Swallowed into the gullet. This is sometimes used to get clearer images of the heart, which lies just in front of the gullet.
- Placed in the vagina or rectum to get clearer images of the pelvic and reproductive organs.
- Used to help guide a surgeon during an operation, in order to look deeper into structures.
The above are not exhaustive lists, and ultrasound scanning has various other uses.
What is a Doppler ultrasound scan?
A Doppler ultrasound records sound waves reflecting off moving objects, such as blood cells, to measure their speed and other aspects of how they flow through the body.
How does Doppler ultrasound work?
If the structure is moving then the echo comes back at a slightly different frequency (called the Doppler effect). This difference in frequency can be used to measure the speed of movement. Blood moving in an artery or vein causes small echoes and these are used to measure the speed of movement of the blood cells. The sound waves may be amplified though speakers. This allows the practitioner to listen to the flow of blood cells to determine whether or not there is normal flow (for example, listening to the flow of blood through the heart of a baby during a routine antenatal check-up, or damaged veins or arteries following an injury). The sound waves may also be converted to colour pictures on a screen so that flow can be seen through the arteries or veins (colour Doppler), or on a graph showing changes in velocity.
What is Doppler ultrasound used for:
- To listen to the heartbeat of an unborn baby (fetus) during pregnancy.
- To examine blood flow in arteries or veins in your arms or legs to see if you might have:
What does a Doppler ultrasound involve?
During pregnancy, the Doppler ultrasound is very similar to an ultrasound scan. A probe covered with gel is put on your skin over the pregnant womb (uterus). This is connected to a speaker and the practitioner simply listens to the flow of blood through the fetus's heart.
During a Doppler ultrasound of the arms and legs, blood pressure cuffs are placed along the thigh, calf, or ankle, or to different points along the arm. A paste is applied to the skin over the arteries being examined. Images are created as the probe is moved over each area.
What is a duplex ultrasound?
Duplex ultrasound is a special technique which combines traditional ultrasound with Doppler ultrasound. Images of the solid object being examined - for example, the artery and the blood flowing through it - are displayed on a screen or monitor. The object is usually grey and the blood flow is usually in colour (colour Doppler).
What is duplex ultrasound used for?
Duplex ultrasound is most commonly used to evaluate the blood flow in various arteries and veins in the body. The scan can help diagnose the following conditions:
- Widening of the main artery in the tummy (abdominal aneurysm).
- Blockage to an artery (an arterial occlusion).
- Blood clot.
- Blockage to the arteries in the neck (carotid occlusive disease).
- Renal duplex examines the kidneys and their blood vessels.
- Varicose veins.
- Venous insufficiency (a condition where veins have a problem sending blood back to the heart).
What does a duplex ultrasound involve?
This test is very similar to an ultrasound scan. A probe covered with gel is placed over the area to be examined. Images of the solid organ and the blood flowing through it are then seen on a monitor
What should I do to prepare for these tests?
Usually there is no special preparation needed. Continue to take your usual medication. You should eat and drink normally before and after the test unless otherwise instructed. For example:
- If certain parts of the tummy (abdomen) are being examined, you may be asked to eat a low-fibre diet for a day or so before the test (to minimise 'gas' in your gut).
- You may be asked not to eat for several hours before a scan of the abdomen.
- For a scan of the lower bowel, you may be given an enema to clear the bowel.
- To scan the bladder or pelvis, you may be asked to drink some fluid before the test so that you have a full bladder.
You will be told what you need to do before any particular scan.
Are there any side-effects or complications from ultrasound, Doppler or duplex scans?
These scans are painless and safe. Unlike X-rays and other imaging tests, they do not use radiation. They have not been found to cause any problems or complications.
Dr Rachel Hoad-Robson
Dr Michelle Williams
Prof Cathy Jackson