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Positron Emission Tomography (PET) Scan

What is a PET Scan?

A PET (positron emission tomography) scan shows how organs and tissues work in the body.

What is a PET Scan Used for?

PET scans can help doctors diagnose and treat cancer.

They can see and track the activity of cancer and other cells. PET scans can measure:

  • Blood flow
  • Tumor growth rate
  • How chemotherapy drugs are working

What is a PET-CT scan?

Sometimes a PET scan is performed at the same time as a computed tomography (CT) scan. A PET-CT scan collects images from both PET and CT scans and combines them. 

A PET-CT scan gives doctors information about the function, size, shape, and location of cancer and the areas around it.

The CT scan is first. It creates anatomic pictures of the body’s organs and structures.

Then, the PET scan creates pictures showing metabolic or functional changes in tissues.

PET CT Scan of a pediatric non-Hodgkin lymphoma patient
PET CT Scan of the lateral plane of a pediatric non-Hodgkin lymphoma patient
PET CT Scan of the axial plane of a pediatric non-Hodgkin lymphoma patient

A PET-CT scan collects images from both PET and CT scans and combines them.

How Does a PET Scan Work?

PET scans can measure the level of glucose, or sugar, in cells.

Before the PET scan, your child will get an injection with a radioactive tracer. It's a form of glucose with a small amount of radioactive material attached.

Cancer cells may grow and divide quickly. So, they absorb much more glucose than normal cells. The radioactive material attached to the glucose molecule causes it to light up on the PET scan. 

Young male cancer patient receives radioactive tracer while in position for PET scan.

Patients are injected with a radioactive tracer, a form of glucose with a small amount of radioactive material attached.

What Can You and Your Child Expect During a PET Scan Appointment?

Every pediatric center is different, but here’s what you can generally expect.

  • You’ll check in at the registration desk and go to a waiting area. Then you and your child will be called back to the area with the PET scanner.
  •  A nurse or technologist will check your child’s glucose level. If it is good, the nurse or technologist will inject the radioactive tracer (called FDG).
  • You and your child will wait about 45 minutes for the tracer to move through the body.
  • The PET machine is large and round and has an opening in the center with a bed that slides through the opening. When it’s time for the scan, the technologist will help your child onto the bed. They will help them get into the right position. Then, they’ll go into an adjoining room where the technologist can see, hear, and talk to your child during the test.
  • The test will not hurt. But it may be uncomfortable for your child to lie still for 30-45 minutes. Your child may receive sedation medicine so they can sleep through the process. A child life specialist may work with your child on relaxation techniques, too.
Young male cancer patient is beginning PET scan, red lights visible on his face.

When the machine is turned on the patient will see the red laser lights of the scan, but will not feel them.

When the machine is turned on your child will see the red laser lights of the scan but will not feel them.

  • When the machine is turned on your child will see the red laser lights of the scan but won’t feel them. The PET scanner does not make a lot of noise. It will not touch your child. Your child may be able to listen to music or watch a movie during the scan.
  • The table will slide through the large hole in the center of the machine a few times during the test.
  • If no sedation was used, your child can usually return to normal activity right away. If sedation was needed, your child will need to go to recovery first and wait until the effects of the anesthesia have worn off.

What Should Your Child do Before a PET Scan?

Be sure to talk with your child’s care team. But these general tips can help.

  • To prepare for the test, your child should not have certain foods and drinks or exercise several hours before the test because it can affect the scan readings.
  • Your child should wear loose, comfortable clothes. PET scanners need to be kept cool, so the room may be chilly.
  • Arrive a few minutes before appointment time to allow time for check-in. 

Is a PET Scan Safe?

The level of radiation is very small. Your child’s care team will discuss the risks and benefits involved. Patients and families should talk to their care team if they have any concerns.

The radioactive material does not stay in the body long. Through the natural process of radioactive decay, it will lose its radioactivity over time. It may also pass out of the body through urine or stool during the first few hours following the test.

The medical team will likely tell you to be sure your child drinks plenty of water to help flush out the radioactive material.

Even though the amount of radioactivity is very low, you should 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.
  • Hold soiled diapers in a separate trash can for 2 days before placing them in the regular trash.
  • If you’re pregnant, don’t cuddle with your child for at least 24 hours after the scan. Also, your child should avoid direct contact with infants and toddlers until the next day.

How Will You Find Out the Test Results?

A physician who has specialized training in nuclear medicine will analyze the images. They will send a report to your child’s doctor. The doctor will go over the information during your child’s next appointment.


Reviewed: January 2022