What to Know About PET Scan Prep

PET scans provide your healthcare team with valuable information about the biochemical or metabolic function of your organs and tissues. This article will help you thoroughly prepare for a PET scan, explaining what to do before, during and after your scan to relieve any anxiety you might have about the procedure.

 

What is a PET scan?

Positron emission tomography, or PET scan, is an internal imaging technique that falls under the umbrella of nuclear medicine. An X-ray points a radioactive beam at the outside of the body. In a PET scan, a radioactive sugar substance is injected into the body instead. Then the PET scanning machine detects and captures images and information revealed by the cellular uptake of the radiotracer.

Doctors order PET scans to identify and monitor the treatment of diseases such as brain disorders, heart disease and cancer. A PET scan picks up what is metabolically active. Although they are used to assess, diagnose and monitor several conditions, PET scans are the standard of care in cancer treatment because they can identify if the cancer has spread to different parts of the body.

The radioactive chemical, a type of glucose, gathers in cells that use a lot of energy including cancer cells. Those areas show up as bright spots in colorful PET scan images.

Sometimes a PET scan is combined with a computed tomography (CT) scan for a more complete view. A CT scan uses multiple X-rays to create detailed cross-sectional images. PET-CT scans use the same preparation protocols as regular PET scans.

 

 

Preparing for your PET scan

When you understand what your PET scan procedure involves, you’ll find the entire process more seamless and worry-free.

What to do before a PET scan?

When your appointment is booked:

• It’s vital to inform the imaging clinic or hospital if you have diabetes and take insulin or if you are pregnant or breastfeeding. In any circumstance, you will be sent instructions. Follow them carefully and contact your clinic if you have any questions.
  Even if neither of the above applies to you, ask if there are any specific fasting and or other preparation instructions. Depending on the part of your body being scanned, there may be.

The day before your appointment:

• Avoid alcohol, tobacco and caffeine for 24 hours before your PET scan. The goal with a PET scan is to limit outside factors in order to better examine the radioactive uptake, which highlights any areas showing extra metabolic activity.
• Avoid strenuous exercise the day before your PET scan. You want to suppress any activity that could artificially affect the level of uptake. The heart and brain are active organs – it is entirely normal for them to demonstrate uptake. But recently exercised muscles might also show uptake, which would skew the results of your PET scan.

The day of your appointment:

• Don’t eat or drink anything at all for 4-6 hours before your PET scan appointment.
• Wear comfortable clothing without belts, buttons or metal (including zippers). Remove any jewelry before your scan.
• Arrive on time for your appointment and bring your requisition with you. If you’re in Canada, bring your health card: if you’re in the U.S., bring your insurance card.

What to do during a PET scan

What to expect during the procedure:

• A drug called fluorodeoxyglucose (FDG) will be issued, usually by injection. FDG, a type of radioactive glucose, is the most commonly used radioactive tracer.
• It takes about an hour for the radiotracer to make it through your system. Allergic reactions are potentially possible but extremely uncommon. But you’ll be monitored throughout the procedure anyway, just in case.

What happens during a PET scan:

• Depending on what part of your body is being scanned, you may be asked to change into a hospital gown.
• In the scanning room, you’ll lie on an exam table that will slide into a giant donut-shaped scanner. The cameras will record positron emissions as you move through the array, then compile them into colorful PET scan images.
• You must remain very still during the scan, and you might be asked to hold your breath during certain portions.
• The length of the scan will vary. A PET-CT scan can take 15 to 30 minutes, sometimes 45 minutes, depending on what part of the body is being scanned. Complex full-body PET scans can take two hours or even longer.

What you can do as a patient:

• Be sure to let the radiologist know if you have anxiety or claustrophobia. If you need one, you can be given a mild sedative to help you relax.
• Go over the possible risks of radiation with the radiologist, if that concerns you. The levels of radiation are higher with PET scans than with a traditional CT scan. First, because the imaging plane is larger, and second because a PET scan involves internally ingesting a radiotracer.

What to do after a PET scan?

For the most part, you can resume daily activities as normal after a PET scan, though if you had a sedative before the procedure, you’ll need someone to drive you home afterwards. Each hospital usually also has their own institution-specific guidelines for patients to follow after PET scans.

After the procedure:

• Patients should avoid close contact with babies, young children and pregnant women for the first 24-48 hours after having a PET scan. As the radiotracer is gradually eliminated, you will excrete the radiation in your sweat and urine.
• Drink plenty of liquids to flush the radiotracer from your system. If possible, use a separate toilet and bedroom than other family members for 24-48 hours.
• Book a follow-up appointment with your referring physician to review your PET scan results when they are ready

 

Accessing and reviewing your PET scan results

If you’ve had a PET or PET-CT scan, you’ll likely be eager to review and understand your results. For regular, non-emergency scans, the hospital or imaging clinic will release the results to your referring physician after several days. Your doctor will then book a follow-up appointment with you to discuss your results.

With PocketHealth, you get secure, early access to your PET imaging and report, often as soon as they’re released by the radiologist. You can review your report in advance of your follow-up appointment with Report Reader, which will give you easy to understand definitions of complex medical terms. MyCare Navigator will provide you with a customized list of questions to ask at your follow-up appointment and other personalized insights based on your report.

PocketHealth gives you the information and understanding you need to have a more informed discussion with your doctor at your follow-up appointment. Before that conversation, it may help to familiarize yourself with some of the terminology commonly found in a PET scan report:

• SUV (Standard Uptake Value): This number, also called a dose uptake, is a ratio which defines the activity of the radiotracer captured in a given area at a specific point in time. An increase in the SUV over time might indicate new or aggressive cancer growth.
• FDG uptake: This value explains how much of the radiotracer was “taken up” or used by cells. Areas that demonstrate abnormal uptake may need to be investigated more closely.
• Deauville score: A visual representation of FDG uptake, the score ranges from 1 to 5. The lower the score, the better.

Learning about their condition and educating themselves about PET scans can be empowering for patients, and often helps relieve anxiety about the process. But it’s okay to rely on the experts in your medical team. It’s important to remember that there’s a community of specialists working on your behalf to help guide you to the next step and ensure you have the best care.

 

 

Prepared and proactive

Properly preparing for your PET scan reduces the chances of being recalled for a second scan. No one wants to waste their own time or the hospital’s on unnecessary procedures, especially when it can be prevented with careful preparation.

More importantly, being prepared can help patients feel more in control of their health, especially at a time when they may be feeling stressed. The more information you have, the better equipped you are to take the next steps in your health journey.

Updated: May 12, 2025