CT scan

Computerised tomography (CT) is a type of scan that uses multiple X-ray images to show detailed two and three-dimensional views of the inside of your body. It’s suitable for every part of the body, including:

• Blood vessels
• Bones
• Brain
• Internal organs

CT scans can help diagnose and monitor many different medical conditions including bone fractures, injuries to internal organs, inflammation, disease, and cancer.

It is sometimes called a CAT scan. They are carried out in a hospital by a person specially trained in performing imaging tests (a radiographer).

Your doctor may recommend a CT scan for many different reasons, including:

• To assess internal injuries or internal bleeding eg damage to your kidneys, spleen or liver, or damage to any part of your skeleton, including the small bones in your hands and feet
• To diagnose conditions — this includes:
• Cancer — CT scans are often used to diagnose liver, lung and pancreatic cancer; CT scans also help locate a tumour, and assess its size and whether it has affected nearby tissues
• Circulatory problems, bleeding and blood clots
• Damaged joints and bones — this includes bone diseases and assessing bone density
• Diseases of internal organs, such as your heart, lungs or liver, or muscle disorders
• Infections
• Stroke
• To diagnose swelling and inflammation
• To guide tests and treatments eg to provide an accurate image of a cancerous tumour, which can be used to target treatments such as radiotherapy, or to help doctors to take tissue samples (biopsies) for testing
• To monitor the progress of treatment eg to see how much a cancerous tumour has shrunk after chemotherapy

Any area or internal organ of your body can be scanned, but common areas for CT scans are:

• Abdomen and chest
• Head and shoulders
• Heart
• Knees
• Pelvis
• Spine

To avoid unnecessary imaging and any associated anxiety, you will usually only be referred for a CT scan if you have symptoms.

A CT scanner has a large ring that rotates around your body and sends X-ray beams from different angles into the area that’s being scanned. This is different to an X-ray machine, which sends X-ray beams in one direction.

When X-rays pass through your body, they’re absorbed differently by each type of tissue or organ, showing up as shaded areas from black to white. These cross-sectional views are then combined by a computer to create a more detailed image than a standard X-ray. A CT scan can reveal different types of tissue within an organ and can be used to create 3D images too.

For some types of CT scan you’ll need to have a contrast agent (a special dye), which shows up certain tissues in more detail.

A CT scan uses X-rays, a type of ionising radiation, while an MRI scan uses radio waves and strong magnets.

An MRI scan can capture images of your tendons and ligaments, while a CT scan cannot. MRI scans are very good at capturing images of your brain (eg to detect a brain tumour) and spinal cord. CT scans are good at capturing images of your chest cavity and lungs, and detecting internal bleeding (eg in the brain), broken bones (eg broken spinal bones) and cancer.

CT scans are also quicker for detecting injuries to organs and are, therefore, often the preferred imaging test following trauma.

A CT scan takes between 10 to 15 minutes. But it can take up to an hour depending on the part of your body being scanned and the number of images needed. You’ll be able to go home shortly afterwards.

You may need to avoid eating for several hours before your CT scan — your care team will advise you about this before you come in for your scan. If you have allergies, kidney problems, or take diabetes medication, you should inform your care team as this may affect whether or not a contrast agent can be safely used during your CT scan.

If you are pregnant, you may not be able to have a CT scan as it uses low levels of ionising radiation, which although generally considered safe for most adults, may harm developing babies.

When preparing to attend your scan, wear loose, comfortable clothing without any metal attachments (eg zips, buckles or metal buttons) and do not wear any jewellery. Depending on which part of the body is being scanned, any metal items may need to be removed before the scan.

You may be given a contrast agent before your scan, either as a drink, an injection into a vein or as an enema passed into your back passage (rectum). Contrast agent injections are given to image blood vessels.

If you feel anxious about having a CT scan, tell your radiographer. They will advise you on how to remain calm.

If you are having a contrast agent, you may need to fast for four to six hours before your CT scan.

Before your CT scan, you may be asked to change into a hospital gown and may be asked to remove any metal objects (eg dentures, jewellery and glasses). You will then usually lie down on a table that passes into the CT scanner. Your radiographer will operate the CT scanner from another room but will still be able to see you and communicate with you via an intercom.

As the table gradually slides into the CT scanner, the X-ray machine will rotate around you, capturing images of the inside of your body. Your CT scan may take from 10 minutes to 15 minutes, but for a CT scan with oral contrast, it could take up to 1 hour.

During your CT scan, you must lie still to prevent the images from becoming blurry. At points, your radiographer may ask you to hold your breath so that your chest doesn't move.

Standard CT scans, where no contrast agent is used, do not cause any side effects and you can return to your usual activities immediately afterwards.

If you have a contrast agent, you may need to wait for up to 20 to 30 minutes before leaving the department, in case you develop a rare reaction to the contrast agent. In most cases, the contrast agent doesn't cause any reaction and it will pass out of your body in your urine.

Results are always returned to your referrer - this can be a GP, an organisation (such as the MoD) or a private consultant/GP. You should arrange a follow up appointment with your referrer to receive the results of imaging examinations.

The results of imaging examinations often only form a part of the investigations and treatments requested or carried out by consultants, so should not be read in isolation. Your referrer will have a holistic view of your medical history, so can advise on the outcome of a radiology report alongside all other tests results and previous or current medical conditions. Your radiographer will let you know when you can expect your results.

Depending on what’s seen on your scan, your doctor may recommend further tests or if a diagnosis is clear, they may recommend specific treatments.

A CT scan is painless and modern scanners are designed to use as little X-ray radiation as possible. Depending on how much of your body is scanned, the amount of radiation is the same as the background radiation you’d naturally be exposed to over a few days, months or years.

X-rays aren't usually recommended for pregnant women as although the levels of ionising radiation are considered safe for adults, they aren’t safe for developing babies. If you are pregnant or suspect you may be pregnant, tell your doctor — they may recommend a different imaging test that doesn’t use ionising radiation eg an MRI scan.

During a CT scan, the ring through which you’re passed doesn’t cover your entire body so you’re less likely to feel claustrophobic. Our experienced team will help you to relax and ensure you’re as comfortable as possible.

Very rarely, the special contrast agent causes a reaction such as sickness or a rash, but this is usually mild. The contrast agent often contains iodine, so if you have previously had a reaction to iodine, tell your care team. If you still need to have a contrast agent, your doctor may recommend taking allergy medication or steroids to counteract any allergic reaction or side effects.

At Spire Healthcare, we’re careful to weigh up the benefits and risks of any CT scan and discuss it with you if you have any concerns.

Why would a doctor order a CT scan of the chest?

Your doctor may order a chest CT scan if you have symptoms of chest pain or breathlessness, and/or to check for signs of bleeding, blockages, infection or tumours.

What are the disadvantages of a CT scan?

A CT scan uses a very low level of ionising radiation and so is not suitable for pregnant women. It also can’t capture images of your ligaments or tendons, as an MRI scan can, and is not as good at detecting brain abnormalities (such as brain tumours) as an MRI scan. In some cases, you may need to have a contrast agent for your CT scan, which in rare cases, can cause side effects.

Can a CT scan tell if a tumour is benign?

CT scans can’t usually tell if a tumour is benign. However, it can determine the exact location and size of the tumour, as well as whether it is affecting surrounding tissues.

Can I wear a bra during a CT scan?

You can wear a bra during a CT scan but it should not be an underwire bra as the metal of the underwire can interfere with the CT scan images.

Why do you have to drink water before a CT scan?

You may be given a drink called a Gastrografin or water before a CT scan if your doctor needs clearer images of your gullet and stomach. The drink contains iodine, a type of contrast agent that helps make certain tissues appear clearer on a CT scan.