CT scan
Published by Bupa's health information team, July 2009.
This factsheet is for people who are considering having a CT scan that has been recommended by their doctor. Your care will be adapted to meet your individual needs and may differ from what is described here.
- About CT scanning
- What are the alternatives to a CT scan?
- Preparing for your CT scan
- About the procedure
- What to expect afterwards
- What are the risks?
- Questions and answers
- Related topics
- Further information
- Sources
About CT scanning
Computerised tomography (CT) is a test that uses X-ray equipment and computer software to create pictures of the inside of your body.
The CT scanner is a ring-shaped machine. Inside the ring is an X-ray tube that produces a fan-shaped beam of X-rays. The tube rotates around your body as you lie flat, creating individual pictures that are cross-sections - slices - through your body.
The images from CT are black, white and grey, as with plain X-rays, but the computer joins the slices together to give three-dimensional views. This means that a CT scan allows doctors to see the height, width and depth of something inside the body.
The images are usually kept in a digital format and shown on a computer screen. Older systems may produce films.
The amount of time you spend in the scanner and the preparations made beforehand vary depending on which part of your body is being scanned and which conditions your doctors are aiming to diagnose. Most machines now use a technology called 'multislice' scanning, and can carry out detailed scans in a matter of seconds.
CT scans are used to diagnose and monitor many health conditions including cancer. They can also be used to provide views of your body so that another procedure or treatment can take place, for example, taking a biopsy (small sample of tissue).
What are the alternatives to a CT scan?
Alternative imaging procedures include ultrasound and magnetic resonance imaging (MRI). There may be other ways of looking inside the body, such as an endoscopy or surgery. Your doctor will explain the benefits and risks of having a CT scan and discuss with you which procedure is most suitable for you.
Preparing for your CT scan
If you usually take medication, continue to take this as usual unless your doctor specifically tells you not to.
Please read your appointment letter for instructions on how to prepare for your CT scan. You may be asked not to eat or drink for a few hours beforehand. If you have any concerns, please contact your doctor.
What to expect at the hospital
A radiographer (a health professional trained to perform imaging procedures) will operate the scanning equipment. You must tell your radiographer about any medicines you're taking and if you have any allergies, glaucoma or heart disease.
If you're a woman of childbearing age, you will be asked if you're pregnant. This test isn't recommended for pregnant women, unless there is an urgent medical reason. For example, if there is a risk that you may have a blood clot on your lung, you may need to have a CT scan to diagnose this. Please tell your radiographer if you could be pregnant.
Contrast medium
Depending on the part of your body being examined, a dye (contrast medium) may be used to make some tissues show up more clearly. This is harmless to your body and you will pass it out in your urine. However, rarely, you may be allergic to the dye that is used so your radiographer will ask you if you have previously had an allergic reaction to this. He or she may also ask if you get asthma or have an allergy to shellfish because these may make it a little more likely that you will have side-effects from the dye.
The dye is injected into a vein usually in your hand or arm.
If you're having a scan of your stomach or bowels, you may be given a special drink before the scan. This allows your bowels to show up more clearly. For some scans of the colon and rectum, dye and/or air may be inserted into your back passage.
Your radiographer will explain what is involved with the examination and ensure that you're happy to proceed.
About the procedure
The time in the scanner takes from 10 to 45 minutes depending on what type of scan you're having. If an additional procedure or treatment is planned, it may take longer.
You will be asked to remove your clothing and put on a gown. For head scans you may be asked to remove contact lenses, dentures, hair clips and hearing aids. For other scans you may be asked to take off your jewellery and wristwatch.
The scanner is a large, ring-shaped machine with a hole in the centre. Only the part of your body inside the ring can be scanned. You will be asked to lie on a table that can slide in or out of the ring.
Your radiographer will position the table so that the part of your body to be scanned is in the centre of the scanner. The table will move backwards or forwards slowly. The X-ray unit inside the ring will rotate around you as the table moves - this creates a new scan each time it goes round. You may be asked to inhale, exhale or hold your breath at certain points during the scan. For the rest of the time, it's important to lie very still.
Your radiographer will operate the scanner from a control room behind a window. He or she will be able to see, hear and speak to you during the procedure.
If you get claustrophobic, it's a good idea to mention this to your doctor or radiographer beforehand.
CT scan
What to expect afterwards
When the scan is complete, the table is moved back out of the scanner and you will be helped down. When you feel ready, you can go home.
If you had a contrast injection, wait an hour before driving. Try to keep well hydrated for the next 24 hours. An extra glass of water every hour may be helpful.
If you're breastfeeding, it's recommended that you wait 24 hours after having a contrast injection before you breastfeed. You may need to express and discard your milk for 24 hours. Please ask your doctor or radiographer for advice.
Results
A radiologist, a doctor who specialises in using imaging methods to diagnose medical conditions, will look at the images. A report will be sent to the doctor who requested your test - this can take several days.
If you haven't been told the results of your scan within two weeks, contact the doctor who requested your test.
What are the risks?
CT scans are commonly performed and generally safe. In order to make an informed decision and give your consent, you need to be aware of the possible side-effects and the risk of complications for this procedure.
You will be exposed to X-ray radiation. In excessive amounts this can increase your risk of getting cancer. However, having a CT scan isn't considered dangerous and any risk is generally heavily outweighed by the advantages of having the scan. Your doctor will be able to explain this to you in greater detail.
If you are pregnant
Pregnant women are advised not to have CT scans as there is a risk the radiation may cause some damage to the unborn child. If you could be pregnant, please tell your doctor or radiographer.
Side-effects
These are the unwanted but mostly temporary effects of a successful procedure. The contrast injection, if you have one, may give you a warm or flushed feeling, or make you feel that you want to pass urine. These side-effects should last only a minute or two.
Complications
Complications are when problems occur during or after the procedure. Most people aren't affected.
In rare cases, it's possible to have an allergic reaction to the contrast injection. If you have any itching or difficulty breathing, tell your radiographer immediately. Medicines are available to treat any allergic reaction.
Related topics
Further information
- The Royal College of Radiologists
www.rcr.ac.uk - Brain and Spine Foundation
0808 808 1000
www.brainandspine.org.uk
Sources
- Garvey C, Hanlon R. Computed tomography in clinical practice. BMJ 2002; 324:1077
- Personal communication. Dr Philip Taylor, FY1 doctor, East and North Hertfordshire NHS Trust, March 2009
- Frank JW. Introduction to imaging: ionising radiation. Student BMJ 2003; 11:358-61
- Royal College of Obstetrics and Gynaecology. Thromboembolic disease in pregnancy and the puerperium: acute management. Green top guide 28. February 2007
- Ultravist Summary of Product Characteristics. electronic Medicines Compendium. www.emc.medicines.org.uk, accessed 26 February 2009
- CT scan. A guide for patients and carers. The Brain and Spine Foundation. www.brainandspine.org.uk, accessed 25 February 2009
This information was published by Bupa's health information team and is based on reputable sources of medical evidence. It has been peer reviewed by Bupa doctors. The content is intended for general information only and does not replace the need for personal advice from a qualified health professional.
Publication date: July 2009
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