PET Scan Preparation: What to Do Before Your Exam
A PET scan shows how your body is functioning, not just how it looks — which is why its preparation is stricter than most imaging. Follow these rules closely and the scan gives its best answers.
Prepare for a PET scan by fasting (usually 6 hours, water only), avoiding sugar and strenuous exercise for 24 hours, and keeping blood sugar controlled if you have diabetes. You will receive a small radioactive tracer injection, rest quietly for 30–60 minutes while it circulates, then lie on a table for a 20–30 minute scan. The whole visit takes about 2–3 hours. Diabetic? Ask for special instructions about medications.
What is a PET scan and why is prep so strict?
PET (positron emission tomography) images metabolism — most commonly using FDG, a sugar-like molecule tagged with a tiny radioactive marker. Cells that burn sugar fast, like most cancers, grab more FDG and light up. That is exactly why your preparation matters: if your blood sugar is high or you have just eaten, your cells absorb the tracer unevenly and the images lose their meaning.
What should I do the day before a PET scan?
- No strenuous exercise for 24 hours — hard workouts pull tracer into muscles and muddy the images
- Eat normally but moderately, favoring low-carbohydrate choices; avoid sweets and alcohol
- Stay hydrated with water
- Confirm medications with the facility — most are fine, but diabetic drugs need a plan
What should I do on the day of the scan?
- Fast for about 6 hours — no food, no sugared drinks; plain water is encouraged
- No gum, candy, cough drops, or coffee with cream/sugar
- Take medications with small sips of water unless told otherwise
- Wear warm, metal-free clothing — PET/CT rooms are kept cool, and shivering creates muscle uptake
- Leave jewelry at home
What happens during the PET scan?
A technologist checks your blood sugar, places an IV, and injects the tracer — a brief pinprick, no sensation from the tracer itself. You then rest quietly in a recliner for 30–60 minutes while the tracer circulates: reading is fine, but no phone scrolling or walking around, because movement draws tracer into muscles. For the scan you lie on a table that slides through a donut-shaped opening while the detector rings collect data for 20–30 minutes. You can breathe normally; just stay still.
What should I do after a PET scan?
Drink plenty of water through the rest of the day — the tracer leaves your body in your urine, and most of its radioactivity is gone within hours. You can drive, resume normal activities, and eat as usual unless told otherwise. Brief precautions apply around pregnant women and small children for a few hours (the exact window comes from your facility), mainly by keeping a little extra distance.
If you have diabetes
Blood sugar control is central to a good PET scan — high glucose competes with the tracer. Ask the imaging team for diabetes-specific instructions before the day: they will likely adjust morning medication or insulin and schedule you early. Bring your glucose meter, and expect a blood sugar check on arrival.
Hydration Helper after your PET scan
Water helps flush the tracer efficiently. Enter your weight for a sensible daily target (no extra needed beyond this):
Educational tool only. Not medical advice. If you have heart failure, kidney disease, or a fluid restriction, follow your care team's instructions and your facility's discharge sheet.
PET prep questions?
Strict prep, big payoff. Ask our team anything before your scan day.
Contact SATMED HealthFrequently asked questions about PET scan preparation
Can I drink water before a PET scan?
Yes — plain water is encouraged right up to the scan, unless told otherwise. Sugared, caffeinated, and creamy drinks are off the table.
Why no exercise before a PET scan?
Working muscles absorb the sugar-like tracer, creating false "hot spots" that can look like disease. Take it easy for 24 hours before.
Does the tracer injection hurt?
Only the IV placement — a routine pinprick. The tracer itself has no sensation, taste, or smell.
Can I use my phone during the uptake hour?
Usually not — tapping and scrolling activate hand muscles. Most facilities ask you to rest quietly; bring a paper book instead.
How long does a PET scan take?
About 2–3 hours total: check-in, tracer injection, a 30–60 minute quiet uptake period, then a 20–30 minute scan.
Is the radiation from a PET scan dangerous?
The tracer dose is small and fades within hours to a day, cleared mostly through urine. The diagnostic information outweighs the small exposure.
How SATMED Health makes contrast imaging safer
If your exam includes contrast, the delivery equipment matters as much as the scanner. SATMED Health engineers the systems behind every injection.
Contrast injector systems built for controlled, consistent delivery — the right dose at the right moment, every time.
Learn more →Engineered syringes for smooth, low-pressure injections that reduce discomfort and protect the vessel at the IV site.
Learn more →Patient lines and accessories designed for safe, reliable contrast administration from injector to vein.
Learn more →Contrast management solutions that help departments prepare, verify, and track every dose before it reaches a patient.
Learn more →Keep reading
More free, clinician-reviewed guides from SATMED Health.
Sources
- RadiologyInfo.org (ACR · RSNA · ASRT). PET/CT. Reviewed June 15, 2026.
- RadiologyInfo.org (ACR · RSNA · ASRT). How to Read Your PET-CT Radiology Report.
- American College of Radiology. ACR Accredited Facilities Database.
Prepped right, a PET scan tells its story clearly
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Contact SATMED HealthMedical disclaimer: This article is for education only and is not medical advice, diagnosis, or treatment. Always follow the instructions of your imaging facility and your own physician. If you think you are having an emergency, call 911 (or your local emergency number) immediately.
Please note: SATMED Health is not a medical facility. Please contact your physician with specific medical questions or for a referral to a radiologist. To locate an accredited medical imaging provider in your community, search the ACR accredited facilities database. This website does not provide cost information; imaging costs vary by region.
