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, and understanding that difference can make the appointment feel less mysterious. A PET scan is a type of nuclear scan that 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 your care team find cancer.
Before the scan
Before your PET scan, you will receive an injection of a tracer called radioactive glucose. This tracer travels through your bloodstream, and cells throughout your body take it up to different degrees. Cells that use more energy — including many cancer cells — tend to take up more of the tracer, which is what allows the scan to highlight them.
Your care team will let you know if there is anything specific to do beforehand, such as timing around meals, since what you eat can affect how your body uses glucose.
During the scan
Once enough time has passed for the tracer to travel through your body, you lie still on a table that moves back and forth through the scanner. The machine detects where the tracer has gathered and builds detailed pictures from that information. Staying still during this part helps the scanner capture clear images.
PET combined with CT
PET scans are often combined with CT scans, done at the same time using one machine. This combination, sometimes called PET/CT, gives your care team more detailed pictures than either scan would provide on its own, since the CT portion adds detailed structural images alongside the PET information about glucose uptake.
About the radioactive tracer
It is natural to wonder about the radioactive material used in the scan. The tracer loses its radioactivity over time, and it may leave your body through urine or stool as your body processes it naturally. If you have questions about precautions for your specific situation, such as being around others right after your scan, ask your care team — they can give you guidance based on your particular procedure.
After the scan
Once your scan is finished, you can typically resume your normal activities unless your care team gives you other instructions. Results are usually reviewed by a radiologist and shared with your doctor, who will go over what they mean for your care.
Questions for your team
Before your appointment, it can help to ask how the tracer will be given, how long you should expect to be there, and 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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