What is a PET-MRI?

A PET-MRI is a powerful diagnostic imaging tool that combines the metabolic information provided by positron emission tomography (PET) with the detailed, high-resolution images produced by magnetic resonance imaging (MRI).

Merging the two technologies into a combined PET-MRI scanner enables doctors to make precise and accurate diagnoses with a single test.

Benefits of combined scanning for children

A single, combined test is especially beneficial to children who need both a PET scan and an MRI, or a PET scan and a CT scan. By cutting out the CT, children are exposed to less overall radiation and are sedated just once, making the entire experience easier on your child.

CHOP was the first facility on the east coast to offer a pediatric PET-MRI.

Why your child may need a PET-MRI

A combined PET-MRI scan can be used to help diagnose certain cancers and to determine whether the cancer has spread.

PET scans measure metabolism. Because cancer cells have a higher metabolism rate than other cells, the test can be particularly effective in locating cancer cells and tracking the spread of these cells. MRI provides clear, high-resolution images. When used together, PET-MRI combines the high quality images of MRI with the metabolic details collected by PET to pinpoint the exact location of tumors. This capability makes it ideal for staging of tumors and pre-surgical planning.

The PET-MRI can also be used to diagnose neurological disorders such as epilepsy.

What should you do prior to the exam?

Your medical team will give you specific instructions about your child’s test.

General preparations:

  • Avoid exercise or strenuous activity for 24 hours prior to the appointment, 48 hours if you exercise regularly.
  • Starting four hours before your appointment, your child should not have anything to eat or drink other than plain water.
  • Avoid jewelry and metal (zippers, snaps, hair accessories). All jewelry and hair accessories will be removed, no matter what part of the body is being scanned, because of the MRI magnet.
  • If you have copies of your child’s previous imaging studies from another institution, please bring them as well as your child’s medication history.
  • If your child has an allergy to medication or MR contrast agents, this information should be provided when scheduling the study.
  • If you need to cancel or reschedule, please notify us 24 hours ahead of time.


During the PET-MRI scan, it’s important for your child to stay very still. If you’re concerned your child might not be able to hold still or stay calm during the procedure, sedation may be required. Please be sure to discuss this with your clinical team in advance. Sedation must be scheduled before the day of your child’s appointment to make the necessary arrangements.

If your child is scheduled to be sedated, our nursing staff will call the evening before your scheduled appointment to review sedation requirements.

Find additional instructions related specifically to PET scans.

Note: If your child is not sedated, one parent or caregiver will be allowed to accompany their child into the exam room. Other arrangements should be made for siblings.

Women who are pregnant or may be pregnant will be asked to leave the exam room during the procedure. Please make sure that there is someone else available to accompany your child during the exam, if needed.

What should you expect during the exam?

Your scheduled arrival time will be two hours prior to when your child’s exam will take place. During this time, we’ll get you checked in and complete all of your paperwork and pre-test work-ups.

  • A technologist will give you and your child a detailed explanation of the test.
  • We will place an IV (this is how we administer the radiopharmaceutical and sedation medicine if needed).
  • We will prepare your child for sedation if it has been determined it will be needed. Typically, sedation or anesthesia is required for all children under 8 and many under 10 years of age.
  • About one hour after your arrival, your child will receive a radiopharmaceutical injection. Its emissions are what is measured by the PET scanner. We’ll wait about one hour to give the radiopharmaceutical time to be absorbed and distributed throughout the body.
  • During this time, we would like your child to relax and be still. If your child’s head and neck area will be evaluated, your child should avoid talking or chewing immediately before and after the injection.
  • After the waiting period is over, your child will have the chance to empty their bladder before going to the exam room to start the scan.
  • A technologist will get your child set up for the scan, which will include placement of a device that holds the head and covers the body, called a coil.
  • The exam will take approximately one and a half to two hours. A full body scan will take the longest, while a more limited area will take less time.
  • Your child can listen to music from the start of the exam. Once any imaging of the head is complete, they can also watch a movie. This typically is not an option until about a half hour or 45 minutes in to the exam.

The PET-MRI scanner includes a 3 Tesla (T) MRI machine. A customized PET detector that is attached to the MRI unit.

If you’d like, our child life specialists will help you prepare and support your child during the procedure. We can also arrange to have a child life specialist at your child's appointment to explain the procedure in developmentally appropriate ways and to help your child better cope with the stress of the hospital experience. Ask your team when you make your appointment if you’d like us to arrange for a child life specialist.

What should you do after the exam?

Please keep your child well hydrated after the exam and make frequent bathroom trips for a few hours after the test. This will help your child pass the radiopharmaceutical. Within 24 hours all of the radioactivity will be gone.

If your child received sedation, follow any instructions given by the sedation nurses upon completion of this procedure. Sedated patients will be taken back to the Sedation Center for recovery.

Test results

The images from your child's exam are interpreted by the next day and a report sent to your physician's office.

Your physician may call us at 215-590-2584 with questions about the report.