Together is a new resource for anyone affected by pediatric cancer - patients and their parents, family members, and friends.Learn More
A PET (positron emission tomography) scan is an imaging test that takes pictures of the inside of the body. This scan gives information about the activity of cells and how organs and tissues work.
PET scans can be used to:
Watch this video to learn more about PET scans.
PET scans measure the level of glucose, or sugar, in cells. Active cells use more sugar for energy. Abnormal cells, like cancer cells, grow and divide quickly. They need more glucose than normal cells.
The scan uses a substance called a tracer. The tracer is a form of glucose with a small amount of radioactive material. The tracer lets off a small amount of energy (light) in areas where the cells are more active than normal. This light is captured in pictures taken by a special camera in the PET scan machine.
Each care center has its own procedures. Talk to your care team about what to expect and how to get ready for your appointment.
Eating and drinking before the scan: Your care team will give you fasting guidelines (sometimes called NPO) for what your child can eat or drink before the scan. The instructions may differ based on the type of test or your child’s medical needs.
Activity before the scan: Do not let your child exercise for several hours before the test because it can affect the PET scan results.
Talk to your child about lying still: It is important that your child knows what to expect and that they need to lie still during the test. If they move, the pictures will be blurry. A child life specialist or care team member may teach your child ways to relax, stay calm, and stay still (relaxation techniques).
Comfort items: Most centers will allow your child to bring a comfort item, such as a stuffed animal or a blanket. Ask your care team if your child can bring a comfort item to the appointment.
Checking in for your appointment: Be sure to arrive several minutes early. Check in at the registration desk with your child. Then you will wait until your child’s name is called.
Be sure to let the care team know if your child:
What to wear: Be sure your child dresses in loose, comfortable clothing. Avoid clothing and accessories that contain metal. These include:
In some cases, your child may need to change into a hospital gown. PET scanners must be kept cool, so the room may be chilly.
Your child must stay still during the PET scan so that images do not blur. In some cases, your child may get sedation medicines or general anesthesia for a PET scan.
Anesthesia is safe for most patients. But health care providers try to limit the use of general anesthesia in children. Talk to your care team about options for your child. There might be other ways to help your child stay still during imaging tests.
The PET machine is a big machine shaped like a donut. It has a special bed, called a table, in the middle. This table moves through the opening so that your child is in the right location for the scan.
The PET scan will not hurt, but some children may feel anxious or have trouble staying still for 30–45 minutes. It can help if you tell your child to pretend to be a statue. Or they can pretend to be asleep. Depending on your child’s age, the technologist may ask them to hold their breath for a moment. In some cases, your child may get general anesthesia or sedation medicine so they can sleep through the process.
What your child will see and hear during the PET scan
The table will move slowly into the scanner until your child is in the correct position. When the scan starts, your child will see the red lines of the camera. The PET scan machine will make noises, such as a “clunk,” when the scanner starts. It will make a “whir” or “whoosh” sound as the camera works.
The machine will turn around your child so it can take pictures from different angles. The camera will not touch your child. Your child will not feel anything during the scan. The table will slide through the large hole in the machine's center a few times during the test.
Your child may be able to listen to music or watch a movie during the scan.
When the scan is complete, the technologist will unfasten safety belts and disconnect the IV and remove towels or cushions if they were used. Then your child may get off the table and leave the area.
Your child can resume normal activities if they did not have general anesthesia or sedation. If your child did get these medicines, they will need to recover first.
Radiation safety after a PET scan
The level of radiation in a PET scan is very small. Only a small amount of radioactive tracer is used, and it does not stay in the body long. The tracer will also lose its radioactivity over time. It may also pass out of the body through urine or stool during the first few hours after the test.
Make sure your child drinks plenty of fluids to help flush out the radioactive material from their body.
Even though the amount of radioactivity is low, follow these precautions when caring for your child after the scan:
A doctor called a radiologist will study the images and prepare a report of the results for your child’s care team. The report may take a few days.
Your health care provider will discuss the results of the PET scan with you.
PET scans use a small amount of radiation. Your child’s care team will discuss the risks and benefits. Patients and families should talk to their care team if they have any concerns.
Pregnant women should not have direct contact with the patient for 12 hours after receiving the FDG tracer or until instructed by the nuclear medicine staff.
Side effects of the tracer
Though rare, some side effects of the FDG tracer used for a PET scan may be:
If you notice signs of high or low blood sugar, or an allergic reaction, get help right away.
If you have questions about PET scan side effects or safety, talk with your child’s care team. Learn more about imaging tests.
Reviewed: January 2024