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PET (Positron Emission Tomography) Scan

What is a PET scan?

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:

  • Detect tumors and monitor their growth
  • See where cancer has spread in the body
  • Find seizures in the brain
  • Measure blood flow through the heart and blood vessels
  • Check the function of organs, such as the heart or brain 

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. 

How to prepare for a PET scan

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.

  • For at least 4 hours before the PET scan, your child can only have water or sugar-free flavored water. The sugar in other foods and drinks can interfere with the test. If your child does not follow fasting guidelines, the scan may be delayed.
  • If your child is going to have general anesthesia or sedation, you will be given additional NPO instructions. 

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:

  • Is uncomfortable in small spaces
  • Has trouble staying still or has special behavior needs 
  • Might be pregnant
  • Has diabetes 

What to wear: Be sure your child dresses in loose, comfortable clothing. Avoid clothing and accessories that contain metal. These include:

  • Belts
  • Zippers
  • Snaps
  • Buttons
  • Hair accessories
  • Watch
  • Jewelry
  • A non-permanent retainer 
  • Glasses (especially for a head PET scan)

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.

PET Scans with Anesthesia

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. 

  • Sedation uses medicines that cause relaxation or sleepiness.
  • General anesthesia causes a complete loss of consciousness, like a deep sleep.

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.


What to expect during a PET scan

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. 

  • When it is time for the scan, a medical professional called a nuclear medicine technologist will take you and your child into a special area that houses the PET scanner. A child life specialist may also be there to help answer questions
  • A nurse or the technologist will check your child’s glucose (blood sugar) level. If it is good, they will inject a radioactive tracer into your child’s arm through an IV. A common tracer used in PET scans is FDG (fluorodeoxyglucose or Fludeoxyglucose F 18). 
  • You and your child will wait about 45 minutes for the tracer to move through your child’s body.
  • When it’s time for the scan, the technologist will position your child on the table.
  • The technologist may put towels, cushions, or safety belts around your child to keep them in the correct position. 
  • The technologist will move to a room close by during the test. They will be able to see, hear, and talk to your child during the scan. Each care center has different policies, but usually, a parent is allowed to be in that room with the technologist.

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.

After the PET 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:

  • Always wash your hands after changing your child’s diapers or handling body fluids.
  • Keep soiled diapers in a separate trash can for 2 days before placing them in the regular trash.
  • If you are pregnant, do not cuddle with your child for at least 24 hours after the scan. Also, your child should not touch infants or toddlers until the next day. 

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. 

Possible risks of PET scans

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:

  • High or low blood sugar: Signs and symptoms of this include dizziness, fast breathing, fast heartbeat, acting confused, sleepiness, weakness, headache flushing, peeing more, shaking, sweating, being more hungry or thirsty.
  • An allergic reaction: Signs and symptoms of this include problems breathing or swallowing, rash, hives, itching, red skin, wheezing, tightness in chest or throat, swelling in mouth, face, inside of nose, lips, tongue, or throat.

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.

Questions to ask your care team about PET scans

  • Why is the PET scan needed?
  • How will the results be used?
  • When does my child need to stop eating or drinking before the test?
  • What activities should my child avoid before the test?
  • How can I help my child stay still during the test?
  • Will my child get sedation medicines or general anesthesia?
  • What are the risks or side effects?
  • When and how will we get the results?
  • What precautions are needed after the test?

Key points about PET scans

  • A PET scan is an imaging test that uses a small amount of radioactive tracer to take pictures of cell activity and organ function in the body.
  • PET scans can be used to check for cancer, heart problems, brain disorders, and other health conditions.
  • Your child will have to stay very still for the scan so that the images will be clear.
  • Your care team will give instructions on how to prepare for the PET scan including fasting guidelines.
  • Follow your care team’s instructions for caring for your child after their scan until the radioactive tracer passes from their body.

Reviewed: January 2024