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GCSE Physics · key term
A three-dimensional imaging technique that detects pairs of gamma-ray photons produced following positron emission.
Used by Edexcel
Specification 6.34P, 6.35P · Paper 1
Revise: Medical DiagnosisPET stands for positron emission tomography. A PET radiopharmaceutical contains a radionuclide that undergoes positron emission. A positron has the same mass as an electron but the opposite charge.
A medical imaging technique that detects radiation resulting from positron-emitting radiotracers inside the body.
For a PET question, describe the complete chain: positron–electron annihilation produces two gamma rays travelling in opposite directions; radiation detectors detect the gamma rays; a computer uses detections from many events to locate the source and construct an image.
Do not say that the PET scanner detects positrons. The positrons travel only a short distance in tissue; the scanner detects the gamma rays produced after annihilation.
Do not say that a PET isotope suddenly disappears after one half-life. Half remains undecayed after each half-life.
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