FDG PET-CT for Cancer

FDG PET-CT exams use a radioactive tracer called fluorodeoxyglucose (FDG) and an imaging machine to find cancer in your body. If you've been scheduled for a FDG PET-CT,  you doctor may want to:

  • find cancer cells.
  • plan your cancer treatment.
  • check to see whether your cancer treatment is working.

FDG PET-CT scans look at your body’s use of sugar. This is because cancer cells take in sugar faster than normal tissue. Because you can get sugar from your food and drink, it is very important to follow the preparation instructions.


A radiotracer is a radioactive medication that is injected into your body through an intravenous (IV) line. A PET scanner then detects cells in your body that absorb the radiotracer, which gives doctors information about where cancer is and how it is responding to treatment. Your PET-CT will use FDG as the radiotracer. The radiotracer decays naturally over the course of a day. It leaves your body mainly through your urine.

Oral Contrast

You may be asked to drink oral contrast before your exam. Oral contrast is a type of dye that highlights the ripples and folds of the colon, for a better picture of your colon. You will be asked if you are allergic to iodinated contrast (contrast with iodine) when you check in for your appointment. If you are allergic to iodinated contrast, you may be given barium to drink. Both types of contrast work the same way and are safe if you have diabetes. You’ll start drinking the oral contrast 45 to 60 minutes before your PET-CT. This will give the contrast solution time to move through your body.

How to Prepare For Your Exam

Avoid Exercise

Avoid strenous activity for 24 hours before your exam, such as running or cycling. Muscles use a large amount of sugar when you exercise, which may lower the image quality and cause inacccurate results.

Stay Warm

Be sure to stay warm before your exam. If you get cold, a type of fat known as "brown fat" becomes active, which can make it hard to read your PET-CT scan. In the winter, wear hats, scarves, gloves, and extra layers. In the summer, avoid turning on your air conditioner very high. You should not feel cold or have cold hands or feet. Bring a sweater to your appointment.

Food Restrictions

Your last meal before your scan should include high-protein foods and plenty of water. Avoid carbohydrates and foods with sugar, which may affect the results of your scan.

  • Please follow a low-carb, high-fat, high-protein (ketogenic) diet for 48 hours prior to your appointment to avoid high blood sugar. (no bread, pasta, sugar, etc.)
  • Do not eat or drink anything other than water for six hours before your appointment. No smoothies or liquid meals (Ensure, Boost, etc).
  • Do not chew gum or suck on hard candy, mints, or cough drops on the day of your exam.
  • Drink between 32 and 64 ounces of water two hours before your appointment.
  • If you take medications, take them with water only.

On the Day of Your FDG PET-CT Exam

You will have a CT scan at the same time as your PET scan. A CT scan is a fast series of X-ray pictures. The CT pictures are combined with your PET scan to create pictures of your soft tissues and bones.

  • Check in for your appointment on the Connect patient portal. You may also check in when you arrive at the imaging center. 
  • Wear loose, comfortable clothing your appointment. Do not wear clothes that contain metal, such as hooks, buckles, or wires.
  • When you arrive for your appointment, a healthcare provider will explain the procedure and answer your questions.
  • A healthcare provider will prick your finger or draw blood from your arm to measure your blood sugar level. If your level is 200 mg/dL or above, your procedure will be rescheduled.
  • You will be given a radiotracer called FDG through an intravenous (IV) line in your arm. You will then be asked to wait in the room for about 60 minutes.
  • You may need to drink a contrast dye for your scan. You will start drinking the oral contrast 45 to 60 minutes before your scan.
  • Please relax and limit your movement during this time and stay warm. You can sleep, bring music to listen to, or watch videos on your personal device.
  • If you are receiving a brain scan, you will not be able to watch videos or listen to music. These activities stimulate certain areas of your brain and may interfere with the results of your scan.
  • Next we will ask you to lie on a narrow, padded table that slides into the scanner. The technologist will leave the room, but they will be able to see, hear, and speak with you at all times.
  • During the scan you will need to lie very still because movement can affect the results of the PET-CT scan.
  • Depending on your height, the scan itself will take between 20 and 40 minutes. The entire process will take about two hours.

After Your FDG PET-CT Exam

Most people can return to their normal activities immediately after a PET-CT scan.

  • A very small amount of radioactive sugar will remain in your body, so be sure to drink plenty of water to help flush it out your system.
  • If you are 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.


Doctors have used nuclear medicine procedures to diagnose disease for more than 50 years, and there are no known long-term adverse effects of these procedures. The doses of radiotracer used in a PET scan are small, so your radiation exposure is very low compared with the potential benefits. Rarely, the radiotracer causes an allergic reaction.


A board-certified doctor will review and compare your PET-CT scan with your other imaging tests and write up a detailed report explaining their findings. We will share the results with the doctor who requested the exam. Your doctor will then discuss the results with you.

How to Access Your Images

You can view, download, or share your exams through your Connect patient portal

Once you are logged in, select “View Radiology Images” from the menu. A new web browser window will open to display a list of your exams.

Questions About Your Exam?

If you have questions or concerns before your FDG PET-CT exam, you may contact us directly at: 212-342-2899.