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CT scan


What is a CT scan?

A CT (computed tomography) scan is a way for doctors to see inside the body. It uses a computer and advanced X-ray equipment to take pictures of the body from many different angles. A CT scan is sometimes called a “CAT scan.”  

The images can be made even clearer and show more detail by using contrast agents. These agents may be swallowed as a liquid or injected into a vein.

Why does my child need a CT scan?

A CT scan gives your child’s doctor more information than a regular X-ray. Doctors use CT scans to view, monitor, or diagnose:

  • Muscle and bone disorders, such as tumors and fractures;
  • Diseases such as cancer and heart disease;
  • Tumors, infections, or blood clots; and
  • Injuries inside the body.

CT scans can also be used to guide procedures such as surgery, biopsy, and radiation therapy.

If your child has a CT scan at St. Jude, the doctor or nurse will tell you why it is being done.

How should I prepare my child for the scan?

Dressing your child for a CT scan

Dress your child in loose, comfortable clothing without metal snaps or zippers. Metal shows up on CT scans, so it can get in the way of what your doctor needs to see. Other items to avoid are:

  • A watch, jewelry, or hair clips with metal, and
  • Glasses, if your child has a head CT scan.

Important things to tell us ahead of time

Please tell us before the scan if your child:

  • Is allergic to contrast dye or iodine,
  • Might be pregnant,
  • Gets upset in small spaces or has special behavior needs, or
  • Has diabetes or kidney problems or takes diabetes medicine with Metformin.

What is contrast dye, and why does my child need it?

Contrast dye is a colored liquid that makes CT scans even clearer. This gives the doctor even more information about your child.

Some CT scans use contrast dye, but not all do. If your child needs contrast dye, your St. Jude team will tell you ahead of time.

How is contrast dye given?

Contrast dye is given 2 different ways:

  • Through a needle that goes into a vein (IV), or
  • In a liquid your child drinks.

The dye might smell or taste funny or make your child feel warm when it goes into the vein.

Helping your child hold still

A CT scan takes 10 to 30 minutes. Your child needs to lie completely still or the pictures will be blurry. It can help if your child pretends to sleep or be a statue.

If your child is younger than 5, she might need medicine to help her lie still. If she is a baby, we might ask you to feed her just before the scan. This can help a baby sleep through it. If you think your child might have trouble staying still, talk to the St. Jude staff.

What happens during a CT scan?

The scanner looks like a giant donut with a bed in the middle. Your child lies on this bed for the scan. The St. Jude staff might use pillows or a safety strap to help your child lie completely still.

Your child will hear some sounds during the CT scan. For example, there might be a “clunk” sound when the scanner starts and a “whir” or “whoosh” sound when the camera moves around your child’s body.

Does a CT scan hurt?

No. Nothing touches your child during a CT scan, and taking pictures does not hurt. If your child gets contrast dye through an IV, putting in the IV needle might hurt a little. The St. Jude staff can put a numbing medicine on your child’s skin before placing the IV.

Are CT scans safe for my child?

CT scans use a small amount of radiation, but this is adjusted for your child’s size. To learn more, talk to your child’s doctor or nurse.

Will someone be with my child during the CT scan?

A St. Jude team member is in the next room during your child’s scan. The team member watches through glass and controls the scanner. Someone is always watching your child, and can hear and talk to her through a speaker. A parent can be in the room during the child’s scan as long as the parent wears a lead apron. (If pregnant, the parent will have to remain in the waiting room.)

When will I get the results?

It can take one (1) to several days to get CT scan results. Ask your child’s doctor when to expect them.


If you have questions about CT scans, you can ask your child’s doctor, nurse, or radiation technologist.

This document is not intended to take the place of the care and attention of your personal physician or other professional medical services. Our aim is to promote active participation in your care and treatment by providing information and education. Questions about individual health concerns or specific treatment options should be discussed with your physician.

St. Jude complies with health care-related federal civil rights laws and does not discriminate on the basis of race, color, national origin, age, disability, or sex.

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