A PET scan uses a small amount of radioactive tracer that is detected by a scanner to show how active tissues are, helping to find cancer or brain and heart problems.
How it works
A PET (positron emission tomography) scan uses a small amount of radioactive tracer, often FDG (a form of glucose), injected into the body. Active cells, like cancer cells, absorb more glucose. The scanner detects gamma rays from the tracer and builds a 3D picture.
Uses
Detect and stage cancer, check heart function, evaluate brain disorders (Alzheimer’s, epilepsy).
Procedure
- Fast for 4 to 6 hours.
- Injection and a wait of about an hour.
- Scan takes 20 to 45 minutes.
Radiation
About 7 mSv, similar to 2 years of natural background radiation.
Combined
PET/CT merges anatomy and function.
Safety
Tell your doctor if pregnant or diabetic.
Tracer
The scan uses a radioactive tracer, most commonly fluorodeoxyglucose (FDG), a sugar molecule attached to fluorine-18. Cells that use more energy, such as many cancer cells, take up more of the tracer.
Detection
As fluorine-18 decays, it releases positrons that meet electrons and produce two gamma rays moving in opposite directions. Rings of detectors record these and a computer builds a 3D image.
Preparation
- Fast for about 4 to 6 hours, though water is usually fine.
- Avoid strenuous exercise for 24 hours.
- People with diabetes need special instructions for blood sugar before the scan, as high glucose reduces FDG uptake.
- Tell the team about pregnancy, breastfeeding, allergies and medicines.
During the scan
After injection, you rest for 45 to 60 minutes while the tracer spreads. The scan itself takes 20 to 30 minutes, and the whole visit can take 2 to 3 hours.
Uses
- Finding and staging cancer and checking treatment response.
- Examining heart muscle for viability.
- Evaluating brain disorders like Alzheimer’s disease, epilepsy and some tumors.
PET/CT and PET/MRI
Combined scanners join metabolic data with detailed anatomy, giving more accurate location of problems.
Radiation exposure
A typical PET/CT delivers roughly 7 to 25 millisieverts, depending on protocol. The tracer decays quickly, with a half life of about 110 minutes, and leaves the body in a day or so.
After the scan
Drink fluids to flush the tracer. Avoid close contact with pregnant women and infants for several hours if advised.
Radiotracer and imaging process
A PET (positron emission tomography) scan uses a small amount of a radioactive tracer, most often fluorodeoxyglucose (FDG), a form of glucose tagged with fluorine-18, which has a half life of about 110 minutes. Active cells such as cancer cells take up more glucose, so they appear bright. The tracer is injected into a vein, and you rest for about 60 minutes while it distributes, then lie on a table that slides through a ring shaped scanner for about 20 to 30 minutes. Preparation usually includes fasting for 4 to 6 hours, avoiding strenuous exercise the day before and managing blood sugar, since high glucose lowers accuracy.
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Uses and safety
PET is used to stage and monitor cancer, check heart tissue viability and evaluate brain conditions such as Alzheimer disease and epilepsy. Most scanners are combined PET/CT or PET/MRI, which merge function and anatomy. The effective radiation dose of an FDG PET scan is about 7 millisieverts, and a CT adds more, compared with about 3 millisieverts of natural background radiation per year in the US. The tracer leaves the body through urine and decay, so drinking fluids helps. Tell the team if you are pregnant or breastfeeding, and avoid close contact with infants and pregnant women for several hours if advised.
Based on data from the American College of Radiology and the National Cancer Institute
