Positron Emission Tomography (PET) Scan With FDG Tracer

This information will help you prepare for your positron emission tomography (PET) scan with FDG tracer at Memorial Sloan Kettering (MSK).

A PET scan is an imaging procedure that is 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.

Most PET scans are done to study your body’s use of glucose (a type of sugar). This is because cancerous cells take in glucose faster than normal tissue. Often, a PET scan is done at the same time as a computed tomography (CT) scan. Because you can get glucose from food and drink sources, it is important that you follow the dietary guidelines listed in the “The Day of Your PET Scan” section.


Before your PET scan, you will be given a radioactive medication with glucose (sugar) called a tracer through an intravenous (IV) line in your arm. Your PET scan will use fluorodeoxyglucose (FDG) as the tracer. FDG is taken up by your cells and does not stay in the body long.

During your PET scan, a special camera is used to find the areas where the tracer has settled.  This allows your doctor to see which areas and cells are the most active.

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You may need to drink contrast for your scan. You’ll be asked if you are allergic to iodine, aspartame (Equal®), or saccharin (Sweet’N Low®) when you check in for your appointment. Depending on whether you have these allergies, we will give you one of the oral contrast solutions listed below. Both work the same way, are used for the same purpose, and are safe even if you have diabetes.

  • Iodine mixed with Crystal Light®, which contains aspartame.
  • Diluted barium sweetened with saccharin. Diluted barium does not have iodine.

You will start drinking the oral contrast 45 to 60 minutes before your scan. This will allow time for the solution to move into your bowels (intestines).

If you need to have intravenous (IV) contrast, the contrast material will be injected into your vein. IV contrast can be given to most people without any problems, but there are some risks.

Most reactions are similar to an allergic reaction, so be sure to tell your doctor or nurse about any allergies you have or if you’ve had a reaction to IV contrast in the past.

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Computed Tomography (CT) Scan

You may also have a computed tomography (CT) scan done at the same time as a PET scan. CT scans take a fast series of x-ray pictures. The x-ray pictures are combined to create pictures of the soft tissues and bones in the area that was scanned. If you are having a CT scan, you may need to drink contrast beforehand. This is the same contrast that you would drink for your PET scan with the FDG tracer.

If you are also having a CT scan done, ask your nurse for the resource Computed Tomography (CT) Scan.

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Before Your PET Scan

1 week before your PET scan

  • Tell your doctor if you:
    • Are pregnant or think you may be pregnant.
    • Are breastfeeding.

Arrange for someone to take you home, if you are getting anesthesia

In very rare cases, some people receive anesthesia (medication to make you sleepy) during a PET scan. If your doctor told you that you will receive anesthesia while you have your PET scan, you will need someone 18 years or older to take you home afterward. If you don’t have someone to do this, call one of the agencies below. They will provide someone to accompany you home; however, there is usually a charge for this service and you will also need to provide transportation.

In New York:

  • Partners in Care: 888-735-8913
  • Prime Care: 212-944-0244

In New York or New Jersey:

  • Caring People: 877-227-4649

1 day before your PET scan

Avoid strenuous and repetitive activity

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

Stay warm

It is important that you stay warm the day before and the day of your scan. This prevents a special type of fat from becoming active, which can make it hard for your radiologist to read your PET scan.  Follow these instructions:

  • Stay warm and avoid situations where you may become chilled.
  • 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. You should not feel cold, or have cold hands or feet. Bring a sweater to areas that are cool.

If you are receiving anesthesia

If you are having anesthesia before your scan, do not eat or drink anything after midnight the night before your PET scan. This includes water, gum, and hard candy.

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The Day of Your PET Scan

If you are not receiving anesthesia

  • For 6 hours before you arrive for your scan:
    • Do not eat anything.
    • Do not chew gum or suck on hard candy, mints, or cough drops.
    • You may drink only water.
    • If you take medications, take them with water only.
    • If you have diabetes, take your usual morning dose of insulin and eat a light meal 4 hours before your arrival time.

If you are receiving anesthesia

If you are having anesthesia before your scan, do not eat or drink anything the morning of your PET scan. This includes water, gum, and hard candy. If you take medications the morning of your PET scan, take them with only a few sips of water only.

It’s important for you to follow the instructions above. We may not be able to perform your PET scan if they are not followed.

Things to remember

If you are having anesthesia

  • Leave all valuables, such as credit cards and jewelry, at home.
  • If you wear contact lenses, wear your glasses instead. If you don’t have glasses, please bring a case for your contacts.
  • Do not apply cream or petroleum jelly (Vaseline®). You can use deodorant and light moisturizers.
  • Wear comfortable clothing that does not have any metal.
  • Remove all jewelry, including jewelry in body piercings.

What to bring

  • A sweater with you to wear while you wait for your scan.

Where to go

Check your appointment print reminder for where your PET scan will be.

  • If it is at the main building of MSK, please arrive at 1250 First Avenue between East 67th and East 68th Streets. Take the short flight of stairs on your left to the 2nd floor. If you are unable to take the stairs, tell the security guard at the desk, and he or she will help you take the elevator. Check in at the reception desk in Nuclear Medicine.
  • If your appointment is at any of the other MSK locations, check in at their Department of Radiology.

What to expect

  • Once you are in the department:
    • You will be asked to fill out a brief questionnaire.
    • Your finger will be pricked or blood will be drawn from your arm to measure your blood sugar level. Your blood sugar level needs to be between 60 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.
    • Your height and weight will be measured.
    • The tracer will be injected into your vein. You may be given contrast to drink at this time.
  • You will 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.
  • Please relax and limit your movement during this time and stay warm. 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. However, if you are receiving a brain PET scan, do not read or listen to music. These activities stimulate certain areas of your brain and may interfere with the results of your scan.
  • You will be asked to urinate just before your scan.
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During Your PET Scan

When we are ready to do your scan, your technologist will bring you to the scanning room and will position you on the scanning table. The PET machine looks like a large doughnut, with a hole in the middle. This is the scanning ring.

Once you are on the scanning table, the table will move slowly through the scanning ring.  You must lie very still in the scanning ring until your scan is done. This can take 30 to 45 minutes, depending on the type of scan you are having.

Some people may also have a CT scan done at the same. CT scans will be done with the same machine in the same room.

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After Your PET Scan

  • You may leave as soon as your scan is done, unless you have other tests or procedures scheduled.
  • You will have radioactive material in your body for about 12 hours.
    • You will get a card stating that you had a test done with a radioactive tracer. Please keep this card with you as there is some security equipment that may detect radioactivity.
    • Limit close contact with infants or pregnant women for 12 hours after your scan.
    • If you are breastfeeding, stop for 12 hours after your scan. You can pump your milk, but throw away the milk you pumped during this time.
  • 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 are given other instructions.
  • A radiologist will read your scan. The results are usually ready for your doctor in 2 business days.
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