+44 (0)800 6 34 34 35

  • Chelsea-Orthopaedics-banner-01-Waiting-Room
  • Chelsea-Orthopaedics-banner-02-Fast-Care
  • Chelsea-Orthopaedics-banner-04-Quality-Care
  • Chelsea-Orthopaedics-banner-03-Team
  • Chelsea-Orthopaedics-banner-05-Appointments
  • Chelsea-Orthopaedics-banner-06-Lister-Hospital

What is a CT scan?

A CT scan, is carried out by using a special x-ray machine which produces an image of a cross-section, or slice of the body. The scanner consists of a ‘doughnut’-shaped structure, through which you pass on a couch.

A narrow fan-shaped beam of x-rays is produced from inside the doughnut, and rotates in a complete circle around you. The x-rays pass through your body and are detected by electronic sensors on the other side of the doughnut, the information passes to a computer which then produces a picture of the internal structure of the body. The pictures are displayed on a TV screen and can be examined by the radiologist.

A scan of the whole body can be completed in less than a minute.

Who will be doing the CT scan?

A radiographer who is highly trained to carry out x-rays and other imaging procedures and a radiologist who is a doctor specially trained to interpret the images and carry out more complex examinations.

Are there any risks?

CT scanning involves x-rays. Female patients who are or might be pregnant must inform a member of staff in advance. The amount of radiation used is more than an ordinary x-ray of the chest or body and is equal to the natural radiation we receive from the atmosphere over a period of approximately three years.

Many CT examinations involve you having a contrast medium injected into a vein in order to increase the amount of information obtained from the scan. The injection usually cases nothing more than a warm feeling passing around your body.

Despite these slight risks, your doctors believes it is advisable that you should have this examination, and do bear in mind there are greater risks from missing a serious disorder by not having it.

What happens during the CT scan?

You will be taken into the special x-ray room and made comfortable lying on the couch. Straps and pillows may be used to help maintain the correct position and to hold still during the exam. You may be given an injection of a contract medium into a vein in your arm. The couch will be moved slowly to position the part of your body under investigation within the ‘doughnut’.

The radiographers will retire to the control room but you will be able to talk to them via an intercom, and they will be watching you all the time. When you enter the CT scanner special lights may be used to ensure that you are properly positioned. With modern CT scanners, you will only hear slight buzzing, clicking and whirring sounds as the CT scanners revolves during the course of the procedures.

During the scan, you may be asked to hold your breath or not swallow while each image is being produced. However, if you feel any discomfort or apprehension, please mention it immediately to the radiographer.

Will it be uncomfortable?

No. You will not feel any pain, although you might feel a slight discomfort arising from having to lie still, and of having a full bladder or rectum.

How long will it take?

If you are given fluid to drink on arrival, you might have to wait an hour before entering the scanning room. The scanning process will then take about 20 minutes.

Are there any side-effects?

Not usually, although you might need to visit the toilet again. You can drive home afterwards and may return to work as necessary. If you have had a contrast injection, you should wait at least one hour before driving.

Can you eat and drink afterwards?



A CT scan involves exposure to radiation in the form of X-rays. In excessive amounts, X-ray radiation can increase your risk of getting cancer. However, the amount of radiation you are exposed to during a CT scan is safe and is not enough to cause any harm.

If you have a CT scan to diagnose a condition or to check symptoms of a known medical condition, the benefits of this will outweigh any potential risk. In this situation, CT scans are quick and accurate, and often eliminate the need for invasive surgery.

However, if you are asymptomatic (have no symptoms), the risk of having a CT scan increases, especially as it may lead to further unnecessary testing and added anxiety.

CT scans are not 100% accurate. There is a chance that the test may be wrong, causing you to be needlessly alarmed or falsely reassured. Around 1 in 20 abnormal cases may be missed from a highly sensitive CT scan.

The Department of Health asked a group of experts to investigate the risk of CT scans in healthy people, such as those who decide to pay for a CT scan as part of a private health assessment.

The Committee on Medical Aspects of Radiation in the Environment (COMARE) made a number of recommendations on the use of CT scans for screening. Read the full COMARE report (PDF).

The possible benefits and risks of having a CT scan should always be weighed up before you choose to have one. It is recommended that you only have a scan on the basis of a medical referral.

Pregnant women and children

Pregnant women should not have CT scans as there is a small risk that X-rays may cause an abnormality to the unborn child. Tell your doctor if you think there is a chance that you may be pregnant before having a scan.

Children are more at risk from a build-up of radiation doses than adults and should only have a CT scan if it is justified by a serious condition that puts them at a higher risk.


In rare cases, the contrast medium used before CT scans can cause an allergic reaction. Tell the radiologist if you have had an allergic reaction to iodine or a contrast dye in the past, or if you have any other allergies.

problem area

Select the part of the body you wish to read about.

Spine and Coccyx
Hip and Pelvis
Foot and Ankle


Text Size: