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Positron Emission Tomography (PET)

This information will help you prepare for your PET scan.

A PET scan is an imaging procedure that is used to:

  • See how the tissues and organs in the 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 the 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.


Before your PET scan, you will be given a radioactive medication called a tracer through an intravenous (IV) line in your arm. The radioactive tracer is looked at with a special camera.

Fluorodeoxyglucose (FDG) is the tracer that is most often used. FDG and most other tracers used for PET scans don't stay in the body long.

Before Your PET Scan

  • Tell your doctor if you:
    • Are pregnant or think you may be pregnant
    • Are breastfeeding
    • Have diabetes. You will need to work with your doctor to determine the safest way for you to prepare for your scan
    • Feel nervous or anxious in small areas. Your doctor can give you medication to help you relax
  • In very rare cases, some patients receive anesthesia (medication to make you sleepy) during a PET scan. If your doctor told you that you would receive anesthesia while you have your PET scan, you will need someone 18 years or older to take you home afterward. If you are receiving anesthesia, you will also need to follow the additional instructions below:
    • Do not eat or drink anything after midnight the night before 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.
    • Leave all valuables, such as credit cards and jewelry, at home.
    • If you wear contact lenses, wear your glasses instead.
  • A staff member will call you before your scan to:
    • Confirm the time of your scan
    • Give you an estimate of how long your scan will take. This estimate may change on the day of your scan, depending on the type of scan you are having
    • Review the steps below

The Day of Your PET Scan

  • For 6 hours before you arrive for your scan:
    • Do not eat anything.
    • You may drink only water or coffee or tea without milk, cream, or sugar.
    • Do not chew gum or suck on hard candy, cough drops, or mints.
  • If you have diabetes, you may not be able to follow the guidelines above. Talk with the doctor who manages your diabetes about how to prepare for your scan.
  • If you take medications, take them with water only.
  • If you have a fever or chills, please tell us. Any shaking or movement during your scan will reduce the quality of the images.
  • Avoid strenuous activity, such as running, jogging, or cycling for 24 hours before your scan. These types of activities can reduce the quality of the images.
  • Bring your most recent CT and MRI scan results if they were not done at MSKCC, or if they are not yet in our system.

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.

When You Arrive for Your PET Scan

  • At the main hospital, register in Nuclear Medicine or in the Department of Radiation Oncology. At any other MSKCC location, register in the Radiology Department.
  • Once you are in the department:
    • You will be asked to fill out a brief questionnaire.
    • You will have a fingerstick blood test or blood will be drawn from your arm to measure your blood sugar level.
    • Your height and weight will be measured.
    • The tracer will be injected into your vein. Some patients will also have to drink contrast to help with the imaging.
  • 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. 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.

During Your PET Scan

When we are ready to do your scan, a technologist will bring you to the scanning room and will position you on the scanning table. It may feel cool in the room but blankets are available to keep you warm.

  • The table will move slowly through the scanning ring. It is similar to the large donut-shaped scanner used for CT scans.
  • 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.

After Your PET Scan

  • You may leave as soon as your scan is done, unless you have other tests or procedures scheduled.
  • You will get a card stating that you had a test done with a tracer. The card includes instructions specific to the type of tracer you had.
  • Drink a lot of water or other liquids to help remove the tracer from your body.
  • Go back to your usual diet right away, unless you are given other instructions.
  • Limit close contact with infants or pregnant women for 24 hours after your scan.
  • If you are breastfeeding, stop for 24 hours after your scan. You can manage your breastfeeding schedule with a breast pump during this 24-hour period, but throw away the milk you pumped during this time.
  • A doctor who specializes in PET will read your scan. The results are usually ready for your doctor in 2 business days.