Having a CT Scan

A CT scan is an imaging investigation using X-rays. It is a performed on a specialised scanner which gives very detailed cross sectional images of the body. This helps us to look at your body more accurately than is possible using ordinary X-rays.

The scanner consists of a ‘doughnut-shaped’ structure, or gantry, about two feet thick with a hole in its centre, through which you pass while lying on a couch. The image on page 3 displays a Siemens CT scanner, similar to that at NHNN.

The CT scan enables diagnosis and follow-up of many disorders, diseases and injuries affecting the body's tissues and internal organs. Your doctor will have explained to you why you need to have a CT scan.

All treatments and procedures have risks and we will talk to you individually about the risks of a CT scan.

Problems that may happen straight away

Many CT examinations involve having a contrast agent (X-ray dye) injected. There is a small risk of a reaction to the contrast but before we proceed we ask you a number of safety questions in order to identify whether you are at risk of an adverse event occurring. Please let us know if you are sensitive to iodine or if you have had any previous problems with contrast agents. Our ‘Contrast Agents for X-ray, Fluoroscopy, CT and Angiography

Examinations: An Information Guide’ leaflet can provide you with further information.

Radiation Risk

Like all X-ray machines, a CT scanner produces X-rays which can potentially be harmful and may cause some cancers to develop in the future. Modern CT equipment and techniques are designed to keep the radiation exposure as low as possible whilst producing some exceptionally clear images of your body. In addition, your doctor will have made a judgement about your risk and benefit before agreeing to the scan (including the risk to your health of not having the scan). The dose of radiation for each procedure can be compared to the amount of background radiation that you will receive just by living in the UK. The amount you receive will depend on the type of scan you are having. For example, a CT scan of the head will be the same as receiving an additional 6 months of natural background radiation.

Patients of child bearing capacity between the ages of 12 and 55 years are required by law to be asked about possible pregnancy when undergoing examinations involving X-ray. Patients who either are, or think they may be pregnant must inform the Neuroradiology department as soon as possible. In some urgent cases the scan may still go ahead but with additional precautions in place.

If you do not wish to have a CT scan, this is your choice and you will not be treated any differently and this will not influence any other aspect of your care. It may mean, however, that your doctor or Clinical Nurse Specialist cannot be as certain or specific about any future treatment or diagnosis.

Other scans available include MRI or ultrasound, but these may be not suitable depending on the area of the body to be scanned. Some patients are unable to have MRI scans if they have pacemakers, or some other types of metallic or electronic implants. For your visit, the doctors have decided the CT is the most suitable scan and will give them the most useful information for diagnosis and treatment.

We advise you wear comfortable clothing to your appointment and where possible avoid wearing jewellery or clothing with metallic detailing. You will be sent specific preparation instructions (if any are required) with your appointment letter. For some scans patients are asked not to eat anything for a few hours before the scan. This is because an injection of contrast agent (X-ray dye) will be given during the scan.

You may eat and drink normally before a scan, unless advised otherwise. If you take any medication, please continue to take this as normal.

If you are diabetic, it is advisable to bring some food with you to have after the scan. You do not need to stop taking any of your medication either before or after the scan.

We want to involve you in all the decisions about your care and treatment, and some of the examinations or procedures being carried out will require you to sign a consent form. This confirms that you agree to have the procedure and understand what it involves. The Consultant, who refers you for this type of examination or procedure involving a CT scan, will explain the risks, benefits and any alternative tests. If you are unsure about any aspect of your CT scan, please do not hesitate to speak to either your doctor, or the radiographer carrying out the CT scan.

Depending on the area of your body being scanned, it may be necessary for you to drink some water prior to your scan. The staff will explain how and when to drink the water.

For some scans you may be asked to change into a gown, again, depending on the area of the body to be scanned. This will require you to undress down to your underwear, and put on a gown. Necklaces/chains will need to be removed, as will any bras with wires. You may bring your own gown if you wish, as long as the garment has no metallic zips, buttons or hooks.

You may also need an injection of contrast agent for the scan. This is a special X-ray dye which shows up the blood vessels

and organs on the scan. If required for the scan, one of the members of staff will insert a cannula in a vein in your arm prior to the scan, and ask you some questions regarding allergies and other relevant medical history.

You will lie on a bed and pass through the scanner several times. You may be asked to breathe in and hold your breath. The breath holds are not long, often only for a few seconds at a time.

If needed, the contrast will be connected to your cannula and injected during the course of the scan. This can make you feel warm, give a metallic taste in the mouth and may give a sensation like you are going to the toilet. These are only sensations, and won’t last very long. The CT scan usually takes around 10 minutes with you in the room.

One of the radiographers will help you off the bed, and you can leave straight away.

If you had an injection of contrast media for the scan, you will be asked to remain in the department for up to 30 minutes after the injection. This is a precautionary step taken to ensure your safety in the event of a contrast reaction. The cannula will be removed from your arm before you leave. You will feel no lasting effects from the contrast. We advise you keep well hydrated for 24 hours following your injection.

Your scan will be reported by a radiologist (a doctor specialising in reading scans and X-ray images) and the report will be sent back to the doctor who referred you for the scan. This can take up to two weeks.

There are a variety of websites on the internet with information for patients having a CT scan. These include:

• All About Having A CT Scan - Macmillan Cancer Support
• Radiologyinfo.org
• X-rays How safe are they?
• Patient's information and guide to CT scanning

UCL Hospitals cannot accept responsibility for information provided by other organisations.

Lysholm Department of Neuroradiology,
National Hospital of Neurology and Neurosurgery,
Queen Square,
London,
WC1N 3BG

Email: uclh.enquiry.nhnmrapp@nhs.net
Neuroradiology Appointment Booking Team (to change or cancel an appointment): 020 344 83440
Hospital Transport Services: 020 3456 67010
Switchboard: 020 345 67890 / 0845 155 5000
Extension: 83440 / 83103
Fax: 020 344 84723
Website: www.uclh.nhs.uk

The CT scanner at The National Hospital for Neurology and Neurosurgery is based in the Lysholm Department of Neuroradiology, which is on the lower ground floor of Chandler Wing.