Positron emission tomography (PET)

What is a PET 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.

• Chemical and functional changes cannot be seen by other imaging methods, such as magnetic resonance imaging (MRI) or computed tomography (CT).
• A PET 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 scan help doctors diagnose a problem, choose the best treatment and/or see how well a treatment is working.
• PET scans can be particularly useful when they are digitally combined with the images generated from MRI or CT.

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 scanner can "read" any chemical changes within those areas.

When might a PET scan be needed?

PET 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
• determine blood flow to the heart muscle
• 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 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), 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 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 videos or DVDs to choose from for your child to watch during the procedure or you can bring one from home.
• If MR and/or CT scans have been done at a facility other than Boston Children's Hospital, please bring those images with you. The nuclear medicine physician will compare the MR and CT scan to the PET scan.
• 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 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 scan?

Obtaining a PET scan involves three steps: injection of the radiopharmaceutical, a waiting period, and scanning by the PET 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 scanner.

The waiting period:

• After the injection, your child must wait for 60 minutes.
• During this time, while the radiopharmaceutical is circulating within the body, it is extremely 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.
• The lights in the room will be dim to help your child relax.

The PET 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 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.
• 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.

Depending on the type of PET scan, your child will be in the scanner from one to two hours.

A PET scan picture:

Will my child feel anything during a PET 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 gauze bandage with adhesive tape is placed over the site of the injection. The area where the injection was given may be a little sore.

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

Is a PET 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 contains a tiny amount of radioactive molecules, but we believe that the benefit to your child's health outweighs potential radiation risk.
• The camera used to obtain the images does not produce any radiation.

What happens after the PET scan?

Once the PET 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 scan?

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