CT Scan (CAT)

A Computerized Axial Tomography Scan, also known as a CT scan or a Computerised Axial Tomography (CAT) scan, is a special type of imaging test that uses a computer to create detailed 3-dimensional images of organs, tissues, bones and blood vessels in the body. Some CT scans require a contrast medium. A substance used in some diagnostic procedures to help parts of the body show up better on x-rays or other imaging tests to show organs and abnormalities more clearly.

A CT scan can be done on almost any body part. It can show detailed views of many different types of tissue, such as the:

  • Brain
  • Airways
  • Lungs
  • Bones
  • Soft tissues
  • Blood vessels

The  video below demonstrates a CT scan for a child undergoing cancer treatment. This video was designed to educate parents and caregivers by showing actual patients receiving treatment.


Published on Sep 12, 2014

This video demonstrates a CT scan on a young patient. CT scans are used to create images of bones and soft tissues inside the body. For cancer patients, CT scans are often used to get images of the internal organs.

Performing the Procedure

CT scans are not invasive and are performed in the radiology department of a hospital. CT scans allow doctors to look not only at a person’s bones, but also at soft tissue and blood vessels. CT scans are often used for diagnosing cancer because doctors can see the exact size and location of a tumour inside the patient’s body.

Sometimes, CT scans are performed using contrast dye, to better examine a specific part of the body by making it appear opaque. When this is needed, the patient is given a thick, white liquid to drink before the test. Once enough time has passed for the contrast to reach the intestines, the CT scan can be performed. A CT scan does not hurt, but it may be uncomfortable or difficult for children to very lie still for a while.

Some CT scans take only a few moments, while others can take more than an hour. The length of time depends on what part of the body is being imaged. For very young children, mild sedation is often used to help them lie still.

Why a CT Scan is Done

A CT scan can help detect a wide range of abnormalities or disease in any part of the body. A CT scan may be done to:

  • Study the chest, abdomen or pelvis
  • Diagnose cancer; find out the size and location of tumours. Determine the stage (how far cancer has spread and if it is present in nearby organs and tissues), and guide the doctor during a needle aspiration or biopsy.
  • Help plan cancer treatment; find out if cancer treatment is working by comparing the size of the tumour before, during and after treatment, and check if cancer has come back (has recurred) after treatment

How a CT scan is done

CT scans are usually done as an outpatient procedure in the radiology department of a hospital or a specialsed CT centre. The test takes up to 1 hour, depending on the size of the area being scanned. If the person is sedated, the test may take longer (2–3 hours).

The person lies on a narrow table. Straps and pillows may be used to help the person stay in the correct position and hold still during the exam. The table slides into the CT scanner. The CT scanner looks like a large rectangular unit with a hole in its centre, like a giant doughnut or lifesaver.

The camera moves around in the scanner, taking many cross-sectional images or image slices. Computer software then stacks these image slices together to make a 3-dimensional image of the body. The person may be asked to hold their breath at times to ensure a clear image. Clicking or whirring noises may be heard during the scan. A moving light may be seen as the scanner takes images.

Special preparation may be needed, depending on the organ or structures being studied. Preparations may include:

  • Not eating or drinking anything for a certain number of hours before the test
  • Taking a laxative
  • Having an enema
  • Removing all metal objects, including glasses, braces or jewellery
  • Taking a contrast medium: Depending on the part of the body being scanned, a contrast medium may be given orally, intravenously (injected into a vein in the hand or arm); or by enema (a procedure used to inject a liquid into the colon and rectum through the anus)

Potential Side Effects

The amount of radiation used in a CT scan is higher than a regular x-ray. CT scans create low levels of ionizing radiation, which has the potential to cause cancer and other defects. However, the risk associated with any individual scan is small. CT scans and other x-rays are strictly monitored and controlled to make sure they use the least possible amount of radiation. The expected benefits of the x-rays must always outweigh any possible risk for the x-rays to be done.

About 5% of people react to the contrast medium. Symptoms may include: nausea; wheezing; shortness of breath; metallic or bitter taste in mouth; feeling flushed; itching or facial swelling

On rare occasions, the contrast medium may cause a severe allergic reaction.

Special Considerations for Children

Being prepared for a test or procedure can reduce anxiety, increase cooperation and help the child develop coping skills. Parents or caregivers can help prepare children by explaining to them what will happen, including what they will see, feel and hear during the test.

The child will probably be alone in the room, unless it is requested that someone be with the child. That person would need to wear a lead vest as protection against the x-rays.

The child needs to lie still on the table while the scanner takes images. Foam cushions and Velcro straps may be placed on the forehead and arms to prevent the child from moving. Children 4 months to 5 years old will usually need sedation or general anaesthesia so they will relax and lie still for the whole test.

If sedation or a general anaesthetic is used, children may not be allowed to eat or drink several hours before the test; have an IV put in; be on a heart monitor

Babies under 2 months old may be asleep for the test. Keep babies awake and do not feed them for 3 hours before the appointment. Bring a bottle (unless breast-feeding), security toy or blanket and pacifier if the child uses one. If babies are tired and feed just before the appointment, they will usually fall asleep for the scan.

If a contrast medium is used and given intravenously (into a vein), the child will feel a slight pin prick when the needle is inserted.

A CT scan does not hurt, but it may be uncomfortable to lie still for up to 1 hour.

The preparation you can provide for a CT scan depends on the age and experience of the child.