Ultrasound scans are images of the internal organs created from sound waves. Here’s what to expect from the procedure.
Medically reviewed by Dr Louise Wiseman MBBS, BSc (Hons), DRCOG, MRCGP and Based on a text by Dr Carl J Brandt
Booked in for an ultrasound scan and not sure what to expect? Sometimes called a sonogram, an ultrasound scan is a procedure using high-frequency sound waves to create an image of part of the inside of the body.
We look at how ultrasound scans work, how they are carried out, what preparation is required and the best way to get your results:
What are ultrasound scans?
Ultrasound scans use sound waves to produce images of the internal organs, vessels and tissues. The images are produced when the sound waves are directed into the body then reflected back to a scanner that measures them.
How the sound waves are reflected back to the scanner depends upon the structure, which is being images and the pattern of reflection is specific to the structure.
Ultrasound scans use sound waves to produce images of the internal organs, vessels and tissues.
Sounds waves can even be used to assess moving structures, for example blood moving through a vessel can be looked at in this way. Sound waves are measured in frequencies, and different scanners produce sound waves of a specific frequency.
The type of scanner, and therefore the type of frequency, used depends upon the structure which is being imaged. For example, to look at the liver we would use a lower frequency sound wave than compared to imaging the blood vessels in the neck.
What are ultrasound scans used for?
Ultrasound scanning is a quicker and easier way to assess the organs, tissues and vessels when compared to other imaging methods such as CT and MRI for example, and is therefore frequently used to help monitor and diagnose conditions in many parts of the body. For example, the organs contained within the abdomen, such as the liver, gallbladder and spleen, are frequently assessed using ultrasound scanning.
Echocardiograms, are produced by ultrasound scanners used specifically to assess the heart. For example, they are often used to check how well your heart is functioning after a heart attack or to look the movement of the valves within the heart – including the kidneys, the liver and the heart (echocardiogram).
It’s often used to examine conditions affecting the organs in a woman’s pelvis – the uterus, cervix, vagina, Fallopian tubes and ovaries.
Ultrasound can also be used to guide medical procedures, such as needle biopsies. This is used when it is necessary to extract sample cells from an abnormal area, so that it can be sent to the laboratory for testing.
How does an ultrasound work?
The entire ultrasound scanner machine consists of: a control panel, a TV screen on which to look at the images and a probe, which contains the special crystals which produce the sound waves.
The ultrasound scanner probe looks like a small paint roller. It is the probe that is placed on the body in order to assess the underlying organs and tissues.
The ultrasound scanner probe looks like a small paint roller that is placed on the body to assess underlying organs and tissues.
Before the probe is placed on the body however, a special water-based gel is applied to the skin prior to starting the examination. This is because sound waves are unable to travel through air, and the use of this gel allows sound waves to travel from the probe, through the skin to the underlying structures.
The probe is then moved back and forth over the body, sending sound waves through the skin and muscles. These waves are reflected back from the organs, tissues and vessels. It is these reflected sound waves, or echoes, which are turned into an image that then appears on the TV screen.
The scan can also be copied onto paper or X-ray film, so that a permanent record can be kept of the scanned images. Moving scans can also be recorded and kept permanently.
How is an ultrasound scan performed?
The way the ultrasound scan is performed depends on the purpose of the examination. The scanner can be used externally on the skin, or through the natural openings of the body, such as the mouth or vagina. For example, if the kidneys or liver are being examined the patient will be told to lie on their back or side on an examination table.
The water-based gel described above is then spread over the skin, enabling the scan to define the organs as clearly as possible.
Where the probe is placed depends on the location of the organs. Therefore for the liver the probe would be placed just below the rib cage on the right, and for the kidneys to the sides of the tummy.
The heart lies just in front of the food tube or oesophagus and the ultrasound probe can be swallowed, still attached to the machine to gain a better image of the heart and its structures, including the valves opening and closing.
Because the echoes are continuously produced, and therefore the picture on the TV screen is being constantly updated, the scan can show real-time movement of the valves.
The person operating the ultrasound scanner can change the position of the probe in order to look at the organ being scanned from many different angles.
- Ultrasound scans for women’s pelvic organs
If a woman’s pelvic organs are under examination, a transvaginal scan provides a better picture. The patient will be asked to lie down on their back, with their knees bent and their feet in holders called stirrups.
The ultrasound probe is gently inserted into the vagina up to the cervix to get the best image. It should not cause more than a slight discomfort. In some cases, it may be necessary to perform a special kind of ultrasound scan called a sonohysterogram or hysterosonogram, which is performed to allow a clearer view of the uterus.
If this is to be performed, sterile water is placed into the uterus before carrying out the ultrasound scan. The water helps to detect any abnormalities, for example by outlining any abnormal masses within the uterus.
By outlining a mass in this way, the person operating the ultrasound scanner can get a more accurate measurement of the size of the mass, its morphology and how it relates to structures close by.
- Ultrasound scans during pregnancy
Ultrasound scanning of the baby during pregnancy usually takes place around the 9th to 13th week of pregnancy, and the number of scans that the expectant mother will eventually have will depend on the results of previous scans and other tests, such as blood tests for example, which determine whether a problem has been detected and requires following up.
The scan is usually performed with the ultrasound probe placed on the lower part of the mother’s tummy, but in some cases it may need to be done transvaginally, as described above.
The woman will often be asked to fill their bladder prior to the scan being carried out, by drinking 2 to 3 glasses of water about an hour before the scan. This is because a full bladder helps to get a better picture of the developing baby.
Ultrasound scans can take approximately 15 to 45 minutes, depending on the area of the body being scanned and the number of organs and structures which are being assessed.
Does an ultrasound scan hurt?
An ultrasound scan does not hurt but the gel used for the examination can feel a bit cold. Also, there may be some discomfort for the woman during pregnancy scans, since they will be asked to fill their bladder, and compression on this part of the body can be uncomfortable.
Transvaginal ultrasound scans can feel uncomfortable, but this should pass once the ultrasound probe is gently inserted within the vagina and therefore should only last a few seconds. It’s not possible to feel the sound waves when they pass from the ultrasound probe and down to the underlying organs and tissues.
Where are ultrasound scans performed?
The examination has traditionally taken place in hospital, with patients being referred by their GP or midwife.
However the accessibility and ease with which an ultrasound scan can be performed means that it is available in a small but growing number of doctors’ surgeries.
Who carries out the ultrasound scan?
Which professional will be performing your scan will depend on the type of scan that is being carried out.
Ultrasound scans were traditionally carried out by doctors, but now sonographers can also carry out these scans too.
For example, the majority of scans performed during pregnancy will be carried out by a sonographer, whereas needle biopsy procedures will usually be carried out by a doctor.
How to prepare for an ultrasound scan
For most ultrasound scans, no special preparation is required. You should continue with any of your usual medication. Wearing comfortable and loose fitting clothing is also advised. You may also be asked to remove any jewellery.
If the organs in the pelvis are being looked at, then you may be asked to drink several glasses of water.
In some cases, there may be some specific instructions, which will depend on the type of scan being carried out. For example, if the organs in the abdomen are being assessed, you may be asked to eat a lo-fibre diet for a day or so before the day of the test. This helps reduce the amount of ‘gas’ in the bowel, and so makes visualisation of organs much easier.
If the organs in the pelvis are being looked at, then you may be asked to drink several glasses of water just before the examination. This fills the bladder and aids visualisation of pelvic organs.
Ultrasound scan side-effects or complications
Because ultrasound scanning does not use any radiation, it is not dangerous, is completely painless and has no serious associated side-effects.
This is the reason that it is therefore routinely used during pregnancy, to monitor the growth of the unborn child and to look for any abnormalities.
Ultrasound scan results
The scan will be assessed by a radiologist, which is a doctor who has been specifically trained to supervise and interpret medical images.
Once they have done so, they will send the final report to either your GP or whichever healthcare provider originally referred you for the scan, who will then contact you to make arrangements to discuss the results given in the report.
In some cases, follow-up examinations may be necessary, and the reasons behind this will be explained when the results are discussed with you. For example, a follow-up examination may be required if there is a suspicious finding which warrants further investigation or if there’s a known abnormality that needs to be monitored over time.
Follow-up may also be necessary if the initial view was limited, and therefore additional images are required before a proper assessment can be made.
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