9702 · 24.3
PET scanning flashcards
Revision flashcards for Cambridge 9702 PET scanning (syllabus 24.3). Flip, recall, then mark a real past-paper question.
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What does PET stand for?
Positron Emission Tomography.
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What type of particle is emitted by the radionuclide in PET scanning?
Positrons (β⁺ particles).
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What primary physiological process does PET scanning measure or map?
Metabolic activity (e.g., glucose consumption).
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What event in PET scanning directly produces the gamma rays that are detected?
The annihilation of a positron with an electron.
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In what spatial relationship are the two gamma rays produced during an annihilation event?
They are emitted in exactly opposite directions (180 degrees apart).
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Where does the injected tracer accumulate within the body?
In regions exhibiting high metabolic activity, such as tumours or active brain areas.
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Name one advantage of PET scanning.
It provides functional information about metabolic activity, not just structure. Also, gamma rays can penetrate dense tissue like the skull.
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Name one disadvantage of PET scanning.
Patient exposure to ionizing radiation, long scan duration, or high equipment cost.
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How does the computer reconstruct images in PET scanning?
By processing the timing and location data of millions of detected gamma ray pairs (coincidence detection).
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What is the role of the 'tracer' in PET scanning?
It is a biologically active molecule tagged with a positron-emitting radionuclide, which delivers the radionuclide to specific areas of the body.
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What is the approximate energy of each gamma photon produced during positron-electron annihilation in a PET scan?
Approximately 0.511 MeV.
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What fundamental physics principle explains the creation of energy from mass in a PET scan?
Einstein's mass-energy equivalence principle, E=mc².
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Name a common radionuclide used in PET tracers and its typical half-life.
Fluorine-18 (¹⁸F), with a half-life of approximately 110 minutes.
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Why is it important for radionuclides in PET tracers to have a short half-life?
To minimise the patient's exposure to ionising radiation and ensure the radioactive material decays quickly after the scan.
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What is 'coincidence detection' in a PET scanner?
The process where the detector ring identifies two gamma photons arriving at opposite sides at the same time, indicating they came from a single annihilation event.