30-Second Summary
A PET scan is a type of nuclear scan that shows areas in the body where cells take up glucose (sugar).
Cancer cells often take up more glucose than healthy cells, so they can stand out on a PET scan.
Before the scan, you receive an injection of a radioactive tracer, then lie on a table that moves through the scanner.
Combined PET/CT pairs PET's activity information with CT's detailed anatomy in a single procedure.
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The simple version
A PET scan — positron emission tomography — is a type of nuclear scan. It makes detailed 3-D pictures of areas inside your body where cells take up glucose, a sugar. Because cancer cells often take up more glucose than healthy cells, those areas can show up on the scan, helping doctors find cancer in the body.
What to expect
Before the scan, you receive an injection of a tracer. The most common one is FDG, a radioactive form of glucose. During the scan, you lie still on a table that moves back and forth through the scanner while it makes the pictures.
Combined PET/CT
PET is frequently paired with CT in a single PET/CT procedure. The CT is done first to create detailed "anatomic" pictures of the organs and structures in your body. The PET then adds "functional" information — showing where cells are more active — because cancer cells often use energy differently from normal cells.
Combining the two can provide a more complete picture of a tumor's location and whether it is growing or spreading than either test alone. According to NCI, PET/CT may improve the ability to diagnose cancer, determine how far a tumor has spread, plan treatment, and monitor how well treatment is working — and it may reduce the number of additional imaging tests a person needs.
How PET fits with other tests
Like all imaging, a PET or PET/CT scan is one part of the overall picture. Its results are read alongside lab tests and, in most cases, a biopsy. Your doctor decides when PET is the right tool and explains what the findings mean for your care.
Words to know
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Common questions
▸What is a PET scan?
A PET scan is a type of nuclear scan that makes detailed 3-D pictures of areas inside your body where glucose (a sugar) is taken up. Because cancer cells often take up more glucose than healthy cells, the pictures can help find cancer in the body.
▸What happens during a PET scan?
Before the scan, you receive an injection of a tracer — often a radioactive form of the sugar glucose, called FDG. During the scan, you lie still on a table that moves back and forth through a scanner while it makes the pictures.
▸What is a combined PET/CT scan?
A PET/CT combines two imaging methods in one procedure. The CT is done first to create detailed pictures of the organs and structures in your body, and the PET shows areas where cells are more active. Cancer cells often behave differently from normal cells, so combining the two can give a more complete picture.
▸Why would I have a PET/CT instead of just one scan?
Combining CT and PET may show a tumor's location and its growth or spread more completely than either test alone. NCI notes it may improve the ability to diagnose cancer, determine how far a tumor has spread, plan treatment, and monitor response — and it may reduce the number of additional tests needed.
▸Does a PET scan involve radiation?
Yes. A PET scan uses a small amount of radioactive tracer, and a combined PET/CT also includes the CT's X-ray radiation. The amounts are carefully controlled. Your doctor can explain the benefits and any risks for your situation.
Questions for your care team
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