The short answer
A PET scan is a nuclear scan that makes detailed pictures of areas where cells take up glucose (sugar). Because cancer cells often take up more glucose, this can help find cancer. Before the scan, you get an injection of radioactive glucose. During the scan you lie still while a table moves through a scanner. PET is often combined with CT for more detailed pictures.
A PET scan makes detailed 3-D pictures of areas in the body where glucose (sugar) is taken up.
Cancer cells often take up more glucose than healthy cells, which is why PET scans can help find cancer.
Before the scan, you receive an injection of a tracer called radioactive glucose.
During the scan, you lie still on a table that moves back and forth through the scanner.
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The full explanation.
The short version
A PET scan works differently from an x-ray or an MRI. Knowing that difference can make the appointment feel less mysterious. A PET scan is a type of nuclear scan. It makes detailed 3-D pictures of places in the body where glucose, or sugar, is taken up. Cancer cells often take up more glucose than healthy cells do, so those pictures can help your care team find cancer.
Before the scan
Before your PET scan, you get an injection of a tracer called radioactive glucose. The tracer travels through your bloodstream. Cells around your body take it up to different degrees. Cells that use more energy, including many cancer cells, tend to take up more of it. That is what lets the scan highlight them.
Your care team will tell you if there is anything to do beforehand, such as timing around meals. What you eat can change how your body uses glucose.
During the scan
Once the tracer has had time to travel through your body, you lie still on a table. The table moves back and forth through the scanner. The machine detects where the tracer has gathered and builds detailed pictures from that. Staying still helps the scanner capture clear images.
PET combined with CT
PET scans are often combined with CT scans, done at the same time on one machine. This pairing is called PET/CT. The CT part adds detailed pictures of structure. The PET part shows where glucose is taken up. Together they tell your care team more than either scan would alone.
About the radioactive tracer
It is natural to wonder about the radioactive material used in the scan. The tracer loses its radioactivity over time. It may also leave your body in urine or stool as your body processes it. If you want to know about precautions, such as being around other people right afterward, ask your care team. They can give you guidance for your own procedure.
After the scan
Once your scan is finished, you can usually go back to your normal activities. Your care team will say if anything is different for you. A radiologist reviews the results and sends them to your doctor, who will go over what they mean for your care.
Questions for your team
Before your appointment, ask how the tracer will be given. Ask how long you should expect to be there. Ask whether your scan will be a PET scan alone or a combined PET/CT. Having a sense of the timeline in advance makes the day easier to plan around.
Words to know
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Common questions
What is a PET scan looking for?
A PET scan makes detailed 3-D pictures of areas in the body where glucose, or sugar, is taken up. Because cancer cells often take up more glucose than healthy cells do, these pictures can help find cancer.
What happens before the scan?
Before a PET scan, you receive an injection of a tracer called radioactive glucose. This tracer travels through your body so the scanner can detect where it collects.
What happens during the scan?
You lie still on a table that moves back and forth through the scanner while it takes pictures of where the tracer has gathered in your body.
Will I be radioactive after a PET scan?
The radioactive material used in a PET scan loses its radioactivity over time and may leave your body through urine or stool. Ask your care team about anything specific you should know for your situation.
What is a PET/CT scan?
PET is often combined with CT, done at the same time using one machine, which gives more detailed pictures than either scan alone.
Questions to ask your doctor
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Your next step
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Last updated: 2026-08-10Next planned review: 2027-07-14
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How this page was created
Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes. We do not employ clinicians and do not intend to — our work is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
Editorial status: Source checked — This page was written with AI assistance and checked line by line against the sources listed on it. That confirms the sources support what the page says. It is not a medical review, and it does not confirm the page is complete or right for your situation.
Human medical review: not completed. Pages here are not signed off by a clinician before they publish. That is not an oversight we are quietly working around: we restate published guidance and cite it, so the authority belongs to the source rather than to us, and every page names where its claims come from — you can verify us instead of trusting us. Where a volunteer clinician has reviewed a page, their name and credentials appear on it; where no name appears, no clinician has checked it. We are glad to have reviewers and are recruiting them, and we do not hold pages back waiting for one. Use this site to understand your situation and to ask better questions of the people treating you.
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