X-ray, computed tomography (CT) and magnetic resonance imaging (MRI) are all techniques which produce pictures of the inside of your body that can be used by hospital doctors to assist in the diagnosis of a medical condition. The equipment is operated by healthcare professionals known as radiographers who are specially trained to operate these machines and produce high quality images of internal organs and structures.
The images which are produced are looked at by radiologists, who specialise in diagnosing illness by reviewing these images.1 If you have an X-ray, CT or MRI scan, the results of these tests may not always be available immediately; once the images have been analysed, the radiologist will write a report and send it to your doctor. This usually takes 2-3 weeks but will vary depending on the hospital you visit.
An X-ray is usually a quick and painless procedure commonly used to produce images of the inside of the body. It's a very effective way of looking at the bones and can be used to help detect a range of conditions. X-rays are usually carried out in hospital X-ray departments by trained specialists called radiographers, although they can also be done by other healthcare professionals, such as dentists.2
X-rays are a type of radiation that can pass through the body. They can't be seen by the naked eye and you can't feel them.2
As they pass through the body, the energy from X-rays is absorbed at different rates by different parts of the body. A detector on the other side of the body picks up the X-rays after they've passed through and turns them into an image. Dense parts of your body that X-rays find it more difficult to pass through, such as bone, show up as clear white areas on the image. Softer parts that X-rays can pass through more easily, such as your heart and lungs, show up as darker areas.2
You don't usually need to do anything special to prepare for an X-ray. You can eat and drink as normal beforehand and can continue taking your usual medications. However, you may need to stop taking certain medications and avoid eating and drinking for a few hours if you're having an X-ray that uses a contrast agent. For all X-rays, you should let the hospital know if you're pregnant. X-rays aren't usually recommended for pregnant women unless it's an emergency. It's a good idea to wear loose comfortable clothes, as you may be able to wear these during the X-ray. Try to avoid wearing jewellery and clothes containing metal (such as zips), as these will need to be removed.2
During an X-ray, you'll usually be asked to lie on a table or stand against a flat surface so that the part of your body being examined can be positioned in the right place. The X-ray machine, which looks like a tube containing a large light bulb, will be carefully aimed at the part of the body being examined by the radiographer. They will operate the machine from behind a screen or from the next room. The X-ray will last for a fraction of a second. You won't feel anything while it's carried out. While the X-ray is being taken, you'll need to keep still so the image produced isn't blurred. More than one X-ray may be taken from different angles to provide as much information as possible. The procedure will usually only take a few minutes.2
For more information on this topic, please visit https://www.nhs.uk/conditions/x-ray
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. An ultrasound scan can be used to monitor an unborn baby, diagnose a condition, or guide a surgeon during certain procedures.5
A small device called an ultrasound probe is used, which gives off high-frequency sound waves. You can't hear these sound waves, but when they bounce off different parts of the body, they create "echoes" that are picked up by the probe and turned into a moving image. This image is displayed on a monitor while the scan is carried out.5
Before having some types of ultrasound scan, you may be asked to follow certain instructions to help improve the quality of the images produced.
For example, you may be advised to:
- drink water and not go to the toilet until after the scan – this may be needed before a scan of your unborn baby or your pelvic area.
- avoid eating or drinking for several hours before the scan – this may be needed before a scan of your digestive system, including the liver and gallbladder.
Before having some types of ultrasound scan, you may be asked to follow certain instructions to help improve the quality of the images produced. Depending on the area of your body being examined, the hospital may ask you to remove some clothing and wear a hospital gown. If you need a sedative to help you relax, this will be given through a small tube into the back of your hand or into your arm.5
In some cases, you may also be given an injection of contrast agent before the scan, as this can make the image clearer.5 Adverse reactions ranging from mild to severe do occur with contrast agents but severe reactions are very uncommon. The most common side effects (seen in up to 1 in 100 patients) are headache, nausea (feeling sick) and reactions at the injection site. There is a very small risk that the area where the cannula was inserted may bleed following the injection.8
Most ultrasound scans last between 15 and 45 minutes. They usually take place in a hospital radiology department and are performed either by a radiologist or a sonographer. They can also be carried out in community locations such as GP practices, and may be performed by other healthcare professionals, such as midwives or physiotherapists who have been specially trained in ultrasound.5
For more information on this topic, please visit https://www.nhs.uk/conditions/ultrasound-scan/
Computed Tomography (CT)
A CT scan (which is sometimes called a CAT scan) uses X-rays and a computer to create detailed, cross-sectional images of the inside of the body focusing on things like internal organs, blood vessels, bones and tumours. CT scans are also often used to look inside the body before procedures take place, such as radiotherapy treatment or a biopsy (where a small sample of tissue is taken to be examined under a microscope).3
Before having the scan, you may be given a special dye called a contrast to help improve the quality of the images. This may be swallowed in the form of a drink, passed into your bottom (enema), or injected into a blood vessel.
During a CT scan, you will normally lie on your back on a flat bed. The CT scanner consists of an X-ray machine in the shape of a ring that moves around your body; you will usually be moved through the ring whilst lying flat on the bed. The scan is painless and will usually take between 10 and 20 minutes, depending on the part of your body being scanned.3 The radiographer controls the scanner using a computer which is in a different room, usually separated by a large window. You will be able to talk to the radiographer through an intercom and they will be able to see you on a television monitor throughout the scan.
CT scans are generally considered safe3 : however, there is a small risk you could have an allergic reaction to the contrast dye used, and you'll be exposed to X-ray radiation.
CT scans are not routinely recommended for pregnant women because there is a risk that the X-rays could harm the unborn baby.3
For more information on this topic, please visit https://www.nhs.uk/conditions/ct-scan/
Magnetic Resonance Imaging (MRI)
An MRI scanner uses strong magnetic fields and radio waves to produce detailed, cross-sectional images of the inside of the body. The scanner is a large tube that contains powerful magnets. It can be used to examine almost any part of the body, such as the brain and spinal cord, bones and joints, heart and blood vessels and internal organs to look for any changes or abnormalities.4 The results of the MRI can be used to help diagnose medical conditions, plan future treatments and assess how effective previous treatments have been.
During an MRI scan you will lie on a flat bed which is moved into the scanner. Depending on the part of your body being scanned, you will enter the scanner either head or feet first. It is important that you keep as still as possible during your MRI scan to allow the images to be clear for the radiologist to review. The scan will last between 15 and 90 minutes, depending on the size of the area being scanned and the number of images being taken.4
The radiographer controls the scanner using a computer which is in a different room. You will be able to talk to the radiographer through an intercom and they will be able to see you on a television monitor throughout the scan. At certain times during the scan, the scanner will make loud tapping noises; this is the electric current in the scanner coils being turned on and off. You will be given earplugs or headphones to wear for your comfort.4
There is no evidence to suggest that the magnetic fields and radio waves used during MRI scans pose a risk to the human body.4
For more information on this topic, please visit https://www.nhs.uk/conditions/mri-scan/
Contrast Agents for X-Ray, Ultrasound, CT and MRI
Contrast agents (otherwise known as contrast media or dyes) are chemical substances used within X-ray, CT and MRI to improve the quality of the images. Using contrast agents can help differentiate between structures in the body and its fluids, and also help to distinguish between similar looking organs.6 This allows the radiologist to more accurately report on any abnormality or disease present. The contrast agents temporarily enhance the images of the internal areas of your body that are being examined, and are later excreted through your urine or bowel movements.6
Common methods of contrast agents administration
Swallowed (given orally) – you may find the taste mildly unpleasant; however, most patients can easily tolerate it.6
Given via an injection:
- Intravenously (into a vein) or intra-arterially (into an artery), the needle may cause you some discomfort when it is inserted, and once it is removed, you may experience some bruising6
- Intra-articularly (into a joint)7
- Intrathecally (into areas such as the brain or spinal cord)
- Rectally (administered by the enema)3
Adverse reactions ranging from mild to severe do occur with contrast agents but severe reactions are very uncommon. Because contrast materials carry a slight risk of causing an allergic reaction or adverse reaction, you should tell your doctor about:
- Allergies to contrast materials, food, drugs, dyes, preservatives, or animals
- Medications you are taking, including herbal supplements
- Recent illnesses, surgeries, or other medical conditions
- History of asthma and hay fever
- History of heart disease, diabetes, kidney disease, thyroid problems or sickle cell anemia
- You will be given specific instructions on how to prepare for your exam.
- https://www.healthcareers.nhs.uk/explore-roles/clinical-radiology accessed March 2020
- http://www.nhs.uk/conditions/x-ray/Pages/Introduction.aspx accessed March 2020
- http://www.nhs.uk/Conditions/ct-scan/Pages/Introduction.aspx accessed March 2020
- http://www.nhs.uk/conditions/mri-scan/pages/introduction.aspx accessed March 2020
- https://www.nhs.uk/conditions/ultrasound-scan/ accessed March 2020
- http://www.radiologyinfo.org/en/safety/index.cfm?pg=sfty_contrast accessed March 2020
- https://www.insideradiology.com.au/iodine-containing-contrast-medium/ accessed March 2020
- https://www.radiologyinfo.org/en/info.cfm?pg=safety-contrast accessed March 2020