Computed tomography (CT)

What we do

CT is a special X-ray examination that is used to examine any area of the body. The scanner itself looks like a square doughnut. Unlike other X-ray examinations, the machine rotates around you collecting information that is then processed by a computer. The result is a series of pictures that show cross-sections of your body.

Your appointment

You will be asked to lie on a table that moves through the centre of the scanner—you are not enclosed. To prevent blurred or unreadable images you must keep still and will usually we asked to hold your breath for a few seconds at various stages of the scan. The CT examination causes no pain or any kind of bodily sensation.

All the information regarding your CT scan appointment is detailed in your appointment letter including whether or not you need to eat before you arrive for your scan. The CT scan will last between 5 and 20 minutes depending on the area of the body being scanned.

You may drink fluids such as water, tea and coffee and you should take all medications as normal. If you are having your abdomen or pelvis scanned you may on arrival be asked to drink a quantity of water to outline your stomach and intestines more clearly. Drinking the water will take between 30 and 60 minutes depending on the type of CT examination you are having.


Will I need an injection?

It may be necessary for you to have a contrast injection (X-ray dye) to give a clearer picture for the radiologist to interpret. This usually involves putting a small needle into a vein in your elbow or hand through which the dye is injected. When the dye is being injected you may experience a warm flush all over your body; you may get a metallic taste in your mouth; you may feel slightly sick; and sometime people feel as if they are going to the toilet - you will NOT be, it is just a trick of the dye. Any such feelings will only last a few minutes and then pass. Many people feel nothing at all.

Are there any risks with the dye injection?

Yes, but they are very rare. Millions of X-ray dye injections for medical imaging examinations are performed in the UK and worldwide each year. Mild reactions such as nausea, vomiting and skin hives occur in 1–3% of patients. Severe reactions are very rare occurring in 1 out of 6,250 examinations. Fatal reactions may occur in 1 out of 100,000 patients. If you experience a delayed skin rash please contact us for advice.

Can I have a CT scan if I am pregnant?

Pregnant women should not have a CT examination or any X-ray examination. CT examinations are only performed on pregnant women in specific circumstances. If you are pregnant or think you might be pregnant, please inform the radiographer before you have your scan as there is a risk to the unborn fetus.

Can I breastfeed after an injection?

Typically patients are advised to wait for 24–48 hours after receiving a CT contrast injection before breastfeeding again.

Can I bring someone into the scan room with me?

No—CT uses X-rays and only the person being scanned should be in the scanner room during the examination.

Are there any risks with this scan?

CT scanning uses X-rays to create the pictures. We are all exposed to background radiation each day of our lives. This comes from the ground and building materials, the air that we breathe, the food we eat and cosmic rays from outer space. Each medical X-ray or nuclear medicine examination gives us a small, additional dose. The level of dose varies with the type of examination, ranging from the equivalent of a few days of natural background radiation to a few years. Low doses do not cause any immediate harmful effects but it is possible that there is a very slight increase in the chance of cancer occurring many years or even decades later. However we all have a 1 in 3 chance of getting cancer even if we never have an X-ray.


Chelsea and Westminster Hospital

When you enter the front door of the hospital, take the escalator or lift to the 1st Floor. Walk to the back of the building following the signs for the X-ray Department. Once inside the X-ray Department follow the signs to the CT/MRI/Ultrasound reception desk. You are advised not to take valuables with you when you attend your scan as the hospital cannot be responsible for them.


T: 020 3315 2059 (Mon–Fri, 9am–5pm)

It is very important that you let us know as soon as possible if you cannot make the appointment.


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