The Leeds Teaching Hospitals NHS Trust

Computerised Tomography (CT)

x ray scanner

What is a CT Scan?

 A computerised tomography (CT) scan uses X-Rays (radiation) and a computer to create detailed images of the inside of the body, within a single breath hold. A CT scanner is a ‘polo-mint’ shaped machine containing a bank of X-Ray tubes/detectors which spin around an axis in order to create 3D images through the body.

During a CT scan, you'll usually lie on your back on a flat bed. The bank of X-Ray tubes/detectors rotates around your body, and you will be moved continuously through this rotating beam. The detectors pick up the X-Ray signals and produce an image of the body on the computer. A CT scan can produce images of structures inside the body, including the internal organs, blood vessels, bones and tumours.

The scan is painless and will usually take between ten and twenty minutes depending on the part of your body being scanned.

 How do I prepare for the test?

You will be given an appointment letter; please read this letter carefully as it will tell you which hospital your CT scan has been booked at and the time of your appointment.

It is advisable to attend wearing comfortable clothing, you may be asked to remove clothing which has any metal e.g., zips, belts, braces, and underwired bras.

There is no need to stop taking any medication before the scan however you may wish to avoid eating 1hr prior to scanning as this can sometimes make you feel queasy when combined with the CT contrast media injection.

How is a CT performed?

A CT scan is performed by a Radiographer; Radiographers are specially trained Allied Healthcare Professionals who have completed a degree and have expertise in radiographic technique and radiation protection. It is the Radiographers job to ensure that all CT exposures are/have been justified, doses are as low as reasonably practicable and that images are diagnostic to answer the clinical question.

Before having a CT scan, you'll be asked about any previous scans, existing health conditions, whether you are taking any medication, and if you have any allergies. You may also be asked to remove some items of clothing or jewellery; including dentures of hearing aids, to ensure that these do not affect the images. The Radiographer will advise you which items to remove prior to your scan.

The Radiographer will operate the scanner from an adjoining room. While the scan is taking place, you'll be able to hear and speak to them through an intercom. While each scan is being taken, you'll need to lie very still and breathe normally. This ensures that the scan images aren't blurred. You may be asked to breathe in, breathe out, or hold your breath at certain points.

The X-ray unit inside the ring will rotate around you. Each time it goes round it creates a new X-ray scan. The bed will move forward slightly after each scan is completed. Depending on the area of your body being investigated, a CT scan may last up to 20 minutes. You should be able to go home soon after the scan has been completed.

All patients aged between 11-55 years will also be asked if there is any chance of pregnancy; this is a legal requirement, and the Radiographer may ask for further information about menstrual cycle or contraceptives. CT scans aren't recommended for pregnant individuals unless there's an urgent medical reason, as there's a small chance that the X-rays could harm the unborn child.

Tell the radiographer if you feel anxious or claustrophobic about having a CT scan. They'll be able to give you advice to help you feel calm.
Contract Medium

Your scan may require an injection or drink of CT contrast media. CT contrast media is a liquid that shows up clearly on the images of certain tissues or blood vessels. It helps distinguish blood vessels from other structures in your body.

Contrast medium can be given in different ways, depending on the part of your body being scanned. It can be swallowed in the form of a drink or can be injected into your bloodstream. If your scan requires this injection, then a cannula (small plastic tube) will be placed in your arm or hand by the Radiographic Assistant or Radiographer.

The CT contrast media injection can make you feel warm all over your body and give you a metallic taste. On rare occasion people may be allergic to the CT contrast media (please see statements above regarding contacting the department). Extravasation (leakage) of the contrast outside the vein may also occur in rare instances, causing localised pain or swelling around the injection site.

Radiology staff will check that it is safe to continue with the CT contrast injection before your scan.

If your kidney function is poor, contrast medium isn't usually given intravenously as it can depress kidney function further. If it is necessary to give the contrast media despite your kidney function, then you may be asked to drink several litres of water before and after your scan. In rare cases you may be admitted to a ward for some IV hydration.

Contrast medium is usually harmless and will pass out of your body in your urine. In rare cases, contrast medium can cause an allergic reaction.

Tell the Radiographer if you have had an allergic reaction to iodine or contrast medium in the past, or if you have any other allergies.

Are there any associated risks?

 CT scans are only used when the doctor responsible for your care decides there's a clear medical benefit.

Although CT scans are generally safe, they do expose you to slightly more radiation than other types of imaging tests. The amount of radiation you're exposed to can vary depending on the type of scan you have. In most cases, the benefits outweigh any potential risks because a CT scan can provide your doctor with much clearer images than those produced by a normal X-ray.

The risk of radiation from a CT can be described in relation to the level of background radiation we receive naturally every year. Background radiation is the radiation to which you are naturally exposed resulting from low levels of radiation in rocks, food and the atmosphere. The main risk from exposure to X-Rays (as used in CT) is the possibility that the patient may develop cancer at some time after the exposure – this may be a number of decades after the initial exposure.

The below table outlines some ‘average’ adult risks associated with common CT scans; this is a rough guide and individual risk assessments can be completed or discussed with Radiology and Medical Physics.

results table






CT scans aren't routinely recommended for pregnant individuals because there's a risk that the X-rays could harm the unborn baby. Children are also more at risk of developing a build-up of radiation than adults. A CT scan will therefore only be recommended if a child has a serious condition that puts them at greater risk.

If you are/could be pregnant or you have any concerns then please contact the Radiology Department to discuss further.

 Benefit versus risks

The benefits of having a CT scan to help diagnose a medical condition, or to check the symptoms of an existing condition, will usually greatly outweigh any potential risk. CT scans are quick and accurate, and often eliminate the need for invasive surgery.

However, if you don't have any symptoms, the benefits of having a CT scan may not outweigh the risks, particularly if it leads to further unnecessary testing and added anxiety.


CT scans are usually carried out on an outpatient basis, which means you'll be able to go home on the same day as the procedure. You should resume eating and drinking as normal following your scan; it is recommended that you drink plenty of fluids for the days following.

A Radiologist or Reporting-Radiographer will review your images and produce a report which is sent back to your referrer to share with you and action or continue any required treatment.

If you have not had any results after four weeks, please contact your referrer. Radiology cannot give any results out directly to patients.

Cancellations and DNAS

If you are unable to attend your appointment for any reason, then please contact the Radiology department as soon as possible so that we can rearrange this for you and prevent any wasted appointments which could have been offered to someone else.

Contacting the Department

 Appointment Enquiries & Bookings

0113 7334974

Leeds General Infirmary

CT Dept, B Floor, Jubilee Wing

Reception: 0113 39 (25621)

St James’s Hospital

CT Dept, Level 1, Bexley Wing

Reception: 0113 20 (63840)

Useful Links

 Radiology patient information leaflets

Giving Feedback

We are always interested in collecting feedback on your experience so that we can continue to learn and improve our service. This feedback can also be used to celebrate staff achievements and examples of excellent care.