About Your PET-MRI

Time to Read: About 7 minutes

This information will help you get ready for your magnetic resonance imaging (MRI) with positron emission tomography (PET) scan.

A PET scan is an imaging test used to:

  • See how the tissues and organs in your body are working.
  • Find and diagnose many disorders, such as cancer.
  • Plan radiation therapy.
  • See how treatment is working.
  • Study your body’s use of glucose (a type of sugar). This is because cancerous cells take in glucose faster than normal tissue.

An MRI is a test that uses strong magnetic fields to produce pictures of the inside of your body. It’s used to see the type, size, and location of tumors. It’s also used to check your response to certain treatments.

An PET-MRI scan is the combination of these 2 tests that helps your doctor get a better look at the inside of your body to help your doctor plan your care.

If you have any of the devices listed below, call 646-227-2323. It may not be safe for you to have an MRI.
  • Pacemaker
  • Automatic implantable cardioverter-defibrillator (AICD)
  • Breast tissue expander
  • Aneurysm clip
If an MRI isn’t safe for you, your doctor will order a different test. If you have any other questions about your MRI, call your doctor’s office.
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Before Your PET-MRI

Getting ready for your PET-MRI

  • If you have a medical implant or device, ask the doctor who put it in for the exact name and manufacturer. If you don’t have this information before your scan, you may not be able to have it that day.
  • During your scan you’ll be lying in one position for about 1 hour. If you think you’ll be uncomfortable lying still or if you’re afraid of being in a narrow or small space, talk with your doctor or nurse ahead of time. They may prescribe medication to help you feel more comfortable.
  • If you wear a medication patch on your skin, you may need to remove it before your scan. This is because metal in the patch may heat up during your MRI and cause burns. Make sure you have an extra medication patch with you to apply after your MRI.

Diabetes care

If you have diabetes, talk to your doctor who ordered your test to see how you should manage your medication before your PET-MRI.

Remove Devices From Your Skin

Talk with the healthcare provider who manages your diabetes care before your appointment if you wear:

  • A continuous glucose monitor (CGM).
  • An insulin pump.

The manufacturer recommends you remove these devices from your skin before your scan or procedure. Your healthcare provider will tell you how to manage your glucose while your device is off. They can also help you schedule your appointment closer to the date you need to change your device.

Make sure you have an extra device with you to put on after your scan or procedure.

Practice relaxation exercises

The MRI machine makes loud noises during the scan. This video shows relaxation exercises you can practice before your MRI. You can do these exercises during your scan to feel more comfortable.

Injections before your PET-MRI

You may need to have contrast dye or glucagon on the day of your PET-MRI to help us get a clearer image. Your doctor or nurse will tell you if you’ll get these.


You may need to have contrast during your scan. Contrast is a special dye used to make it easier for your doctor to see differences in your internal organs.

There are different types of contrast used for imaging studies. The contrast used for PET-MRIs is a gadolinium contrast. MRI contrast is given through an intravenous (IV) catheter (thin, flexible tube) in your arm or central venous catheter (CVC).

Reactions to contrast

Some people may have an allergic reaction to contrast. Be sure to tell your doctor or nurse about any allergies you have or if you’ve had a reaction to gadolinium contrast (MRI contrast) in the past. If your doctor feels that they need to give you medication(s) to reduce your risk of having a reaction, you’ll get a resource called Preventing An Allergic Reaction to Contrast Dye.


Before your PET-MRI, you’ll get a radioactive medication with glucose (sugar) called a tracer through an intravenous (IV) line in your arm. This is done to show differences between healthy tissue and diseased tissue. Your PET-MRI will use fluorodeoxyglucose (FDG) as the tracer. FDG is taken up by your cells and doesn’t stay in your body long.

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The Day Before Your PET-MRI

Avoid doing demanding exercises

For 24 hours before your scan, avoid doing demanding exercises and repetitive muscle motion such as running, jogging, or cycling. These activities can reduce the quality of the images that we get from your scan.

Stay warm

It’s important that you stay warm the day before and the day of your scan. If you get cold, a special type of fat becomes active. This can make it hard for your radiologist to read your PET-CT. Staying warm will keep the fat from becoming active and make the pictures from your scan more clear.

Follow these instructions:

  • Avoid areas where you may become chilled.
  • Keep your hands and feet warm at all times.
  • In the winter, dress extra warmly. Wear hats, scarves, gloves, and extra layers.
  • In the summer, avoid turning on your air conditioner to very high.
  • Bring a sweater to your appointment.
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For People Getting Anesthesia

If your healthcare provider told you that you’d get anesthesia (medication to make you sleepy) while you have your PET-MRI, you must follow the additional instructions below.

Before your PET-MRI

Arrange for someone to take you home

You must have a responsible care partner take you home after your procedure. A responsible care partner is someone who can help you get home safely and report concerns to your healthcare providers, if needed. Make sure to plan this before the day of your procedure.

If you don’t have a responsible care partner to take you home, call one of the agencies below. They’ll send someone to go home with you. There’s usually a charge for this service, and you’ll need to provide transportation. It’s OK to use a taxi or car service, but you must still have a responsible care partner with you.

Agencies in New York:

Agencies in New Jersey:

Instructions for eating and drinking before your procedure

12 ounces of water
  • Do not eat anything after midnight the night before your procedure. This includes hard candy and gum.
  • Between midnight and up until 2 hours before your scheduled arrival time, you may drink a total of 12 ounces of water (see figure).
  • Starting 2 hours before your scheduled arrival time, do not eat or drink anything. This includes water.
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The Day of Your PET-MRI

If you aren’t getting anesthesia, you must follow the instructions below. You may not be able to have your PET-MRI done if you don’t follow these instructions before your procedure.

For 6 hours before you arrive for your scan:

  • Don’t eat anything.
  • Don’t chew gum or suck on hard candy, mints, or cough drops.
  • Drink only water.
  • If you take medications, take them with water only.

Things to remember

  • Remove all jewelry, including jewelry in body piercings.
  • Refer to the printed reminder you received from your doctor’s office for the time and location of your MRI.
  • If you wear a medication patch on your skin, bring an extra one with you.
  • If your doctor prescribed medication to help you relax, take it 30 to 60 minutes before your scan.

What to expect when you arrive

You’ll change into a hospital gown before going into the scanning area. For safety reasons, you’ll place your clothing, credit cards, and any objects (such as your phone, jewelry, coins, and glasses), in a locker. This is because objects with even a small amount of metal can fly into the magnet, and the magnet can damage mobile phones and credit cards.

Once you’re in the department:

  • You’ll fill out a brief questionnaire.
  • Your finger will be pricked or blood will be drawn from your arm to measure your blood glucose level.
    • Your blood sugar level needs to be between 70 milligrams/deciliter (mg/dL) and 199 mg/dL.
    • If your level is 200 mg/dL or above, you may need to get insulin, or your procedure may need to be rescheduled. Your nurse will speak with you about this.
    • If your blood sugar level is below 70, you may need to be rescheduled.
    • The tracer will be injected into your vein.
    • You’ll wait at least 60 minutes (usually 60 to 90 minutes) for your body to absorb the tracer. How long this takes will depend on the area of your body being scanned.
    • Try to relax and limit your movement during this time. Ask for a blanket if you feel cold while you are waiting. You can sleep, read, listen to music, or watch videos in the area provided for you.
    • If you’re having a brain PET-MRI, don’t read or listen to music. These activities stimulate certain areas of your brain and may interfere with the results of your scan.
    • You’ll be asked to urinate (pee) just before your scan.
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During Your PET-MRI

When it’s time for your scan, your technologist will bring you to the scanning room and help you onto the scanning table. The MRI machine is a large, donut-shaped magnet. It makes a loud tapping noise during the scan. Your technologist will offer you earplugs or earphones to listen to music.

Once you’re on the scanning table, your technologist will slide it into the magnetic part of the machine and begin the scan. You’ll be able to speak with your technologist during the entire scan.

It’s important to lie still and breathe normally during the scan. You may want to do your relaxation exercises during your MRI.

Your scan will take 30 to 60 minutes.

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After Your PET-MRI

  • You may leave as soon as your scan is done, unless you have other tests or procedures scheduled.
  • If you received anesthesia, you’ll be taken to the Post-Anesthesia Care Unit (PACU) after your scan. You’ll stay there until you’re fully awake.
  • You’ll have radioactive material in your body for about 12 hours.
  • You’ll get a wallet card stating that you had a test done with a radioactive tracer. Keep this card with you because some security equipment that may detect radioactivity.
  • Limit close contact with infants or pregnant women for 12 hours after your scan.
  • If you’re breastfeeding, stop for 12 hours after your scan. During this time, you can continue to pump milk and either throw it away or store it for 12 hours. After 24 hours, you can feed it to your baby. You can restart breastfeeding 12 hours after your scan.
  • Drink a lot of water or other liquids to help remove the tracer from your body.
  • You can resume your usual diet right away, unless you’re given other instructions.
  • Your radiologist will send a report of your scan to your doctor. Your doctor will use the results of your scan to help plan your care.
If you have any questions or concerns, call the Molecular Imaging and Therapy Service (MITS), which is sometimes called the Nuclear Medicine service, at 212-639-6652. You can reach a staff member Monday through Friday from to If you’re a patient at MSK and you need to reach a provider after , during the weekend, or on a holiday, call 212-639-2000.
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