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What is positron emission tomography?

Positron emission tomography, also called a PET/CT scan, is a safe, effective and non-invasive diagnostic imaging technique that provides highly detailed images of the body.

A PET scan shows metabolic changes and physiologic uptake that may not be seen on MRI or CT scans alone.

Frequently asked questions

What is a PET/CT scan?

Positron emission tomography (PET) is a highly sensitive technology that uses a radioactive substance to show the chemical and functional changes within the body.

  • A PET/CT scan measures body functions such as blood flow, oxygen use, and sugar metabolism to help doctors evaluate how well your child's organs and tissues are functioning.
  • Images obtained from a PET/CT scan help doctors diagnose a problem, choose the best treatment, and/or see how well a treatment is working.
  • Physiologic uptake from the PET scan is digitally combined with anatomic information from the low-dose CT to provide a high quality diagnostic study, showing not only the presence of uptake but also its precise location.

The radiopharmaceutical used is designed to go to the part of the body that is being tested.

  • A common type of radiopharmaceutical, fluorine-18 FDG (fluorodeoxyglucose), acts almost exactly like sugar.
  • The body uses sugar for fuel, so the radioactive sugar goes to the parts of the body that are very active, such as the brain, the heart, and the muscles.
  • The PET/CT scanner can "read" any chemical changes within those areas.
When might a PET/CT scan be needed?

PET/CT scans can be a key to early diagnosis of cancer, as well as diseases of the brain and heart. They are performed to:

  • assess the effectiveness of a treatment plan
  • detect cancer or determine whether a cancer has spread in the body or returned after treatment
  • evaluate brain abnormalities, such as tumors, memory disorders, and seizures
  • evaluate central nervous system disorders
  • map normal human brain and heart function
How should I prepare my child for a PET/CT scan?

You will be given specific instructions when you make your child's appointment. It is very important that you follow all preparation instructions or the scan will be rescheduled. In general:

  • Your child should not have any candy, sugar, or gum for four hours prior to the appointment.
  • Your child should not ingest any form of caffeine (including soda, tea, and chocolate) for 12 hours prior to the scan. She should also, of course, not have any nicotine or alcohol.
  • Your child should avoid any exercise and strenuous physical activity for 24 hours prior to the appointment.
  • Your child should not have any solid food or fluids four hours prior to the scan.
  • Your child is allowed to drink plain water, but not flavored water.
  • You may give your child his or her normal medications on the morning of the scan.

In addition:

  • It is helpful to give your child a simple explanation as to why a PET/CT scan is needed and assure him or her that you will be with him or her for the entire time.
  • You may want to bring your child's favorite book, toy, or comforting object to use during waiting times.
  • We have various DVDs to choose from for your child to watch during the procedure or you can bring one from home.
  • If your child's doctor has given you a requisition for the exam, please bring it with you. If we have to call the doctor's office to get the requisition after you have arrived for the appointment, this will cause a delay in performing the scan.
  • If your child is scheduled for sedation or if you think sedation is necessary (to hold still) and a nuclear medicine staff member has not contacted you, please call us at 617-355-7010 for specific instructions.
What should I expect when I bring my child to the hospital for a PET/CT scan?

When you arrive, please go to the Nuclear Medicine check-in desk on the second floor of the main hospital. A clinical intake coordinator will check in your child and verify his or her registration information.

What happens during a PET/CT scan?

Obtaining a PET/CT scan involves three steps: injection of the radiopharmaceutical, an uptake period, and scanning by the PET/CT camera.

Injection of the radiopharmaceutical:

  • You will be greeted by one of our nuclear medicine technologists who will explain the scan in detail to you and your child.
  • Your child's sugar level will be checked.
  • A tiny amount of the radiopharmaceutical will be injected into one of your child's veins through a small intravenous catheter (IV).
  • Once the radiopharmaceutical reaches its destination, it will transmit signals (gamma rays) that can be detected from outside the body by the PET/CT scanner.

The uptake period:

  • After the injection, your child must wait for 60 minutes.
  • During this time, while the radiopharmaceutical is circulating within the body, the room is kept warm and the lights are dimmed to aid in the uptake of the tracer. It is important for your child to be very quiet — no talking, moving, or playing with electronic devices. These activities can alter the radiopharmaceutical distribution in the body and affect the image.
  • Often patients will watch a movie, or rest, during this uptake period.

The PET/CT scan:

  • After the waiting period, the technologist will ask your child to empty his bladder.
  • You and your child will be taken to the PET/CT suite. You are welcome to sit in the room with your child during imaging.
  • Your child will be asked to lie on the imaging table.
  • The table will slide into the scanner.
  • Your child must remain still while the images are taken. This is crucial, as any movement can lead to mis-registration between the low-dose CT and the PET scan.
  • The technologist will be watching the procedure through the window and by TV monitor.
  • While your child lies within the scanner, a computer will create images of the body.
  • If a diagnostic CT scan is clinically indicated and has been ordered by the prescribing physician, it will be performed either right before or after the PET scan.

Depending on the type of PET/CT scan, your child will be in the scanner from 30 to 45 minutes.

Will my child feel anything during a PET/CT scan?

Your child may experience some discomfort associated with the insertion of the intravenous needle. The needle used for the procedure is small. Once the radiopharmaceutical is injected, the needle is withdrawn and a bandage is placed over the site of the injection. If a diagnostic CT is indicated, your child may receive IV contrast, and we will keep the IV in place and remove at the completion of the study. If your child receives IV contrast during the CT scan, it will be normal for him/her to feel warm during the administration, however, that feeling will go away after the administration of IV contrast is complete. IV contrast is only given when the physician feels it will aid in the diagnostic quality and/or interpretation of the study.

The PET/CT scanner does not touch your child, nor will he or she feel anything from the scanner.

Is a PET/CT scan safe?

We are committed to ensuring that your child receives the smallest radiation dose needed to obtain the desired result.

  • Nuclear medicine has been used on babies and children for more than 40 years with no known adverse effects from the low doses employed.
  • The radiopharmaceutical and a low-dose attenuation CT present a very small amount of radiation exposure to your child, but we believe that the benefit to your child's health outweighs potential radiation risk.
What happens after the PET/CT scan?

Once the PET/CT scan is complete, the images will be evaluated for quality by a nuclear medicine physician. If the scan is adequate, your child will be free to leave and resume normal activity.

One of the Children's nuclear medicine physicians will review your child's images and create a report of the findings and diagnosis.

How do I learn the results of the PET/CT scan?

The nuclear medicine physician will provide a report to the doctor who ordered your child's PET/CT scan. Your child's doctor will then discuss the results with you.

How Boston Children's Hospital approaches a PET scan

Our Nuclear Medicine and Molecular Imaging staff are committed to providing a safe, comfortable, and child-friendly atmosphere with:

  • a new, state-of-the-art, hybrid PET/CT scanner which allows for shorter imaging times, and anatomic information from a low-dose CT done in conjunction with the PET scan.
  • specialized nuclear medicine physicians with expertise in interpreting PET/CT scans in children of all ages
  • certified nuclear medicine technologists with years of experience imaging children and teens
  • Child Life specialists to help families prior to and during exams
  • protocols that keep radiation exposure as low as reasonably achievable while assuring high image quality

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