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Medical Imaging

PET scanning

  • 3 things to know
  • Papers 1, 2 and 3

Overview

Recall questions on positron-electron annihilation, fluorine-18 tracers, 511 keV gamma photons, coincidence detection and lines of response, forming PET images, uses in cancer and neurology, and cyclotron supply.

What you need to know

Answer each one before you reveal it.

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Key term

Define the term 'line of response' in PET scanning, and explain how lines of response are used to form a three-dimensional image.

Key term

Why might a hospital with a PET scanner require an on-site cyclotron or rapid delivery service?

Key term

What type of decay does fluorine-18 undergo, and what is its approximate half-life?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    What are the products of positron-electron annihilation, and what are their properties?

    Model answer

    Two gamma photons of equal energy (511 keV each) that travel in opposite directions (180° apart).

  2. 2

    What type of decay does fluorine-18 undergo, and what is its approximate half-life?

    Model answer

    Fluorine-18 decays by positron emission with a half-life of approximately 110 minutes.

  3. 3

    In which imaging technique is fluorine-18 used as a tracer?

    Model answer

    PET (positron emission tomography) scanning.

  4. 4

    Into which compound is fluorine-18 incorporated for PET scanning, and why does this compound accumulate in certain tissues?

    Model answer

    Fluorine-18 is incorporated into fluorodeoxyglucose (FDG), which accumulates in tissues with high metabolic activity.

  5. 5

    What happens to a positron emitted from a tracer in PET scanning before detection occurs?

    Model answer

    The positron travels a short distance before encountering an electron, resulting in annihilation.

  6. 6

    State the equation used to calculate the energy of each annihilation gamma photon from the rest mass of an electron or positron.

    Model answer

    E = mₑc², where E is energy, mₑ is the rest mass of an electron (or positron), and c is the speed of light.

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