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Medical Physics

Imaging techniques

  • 5 things to know
  • Paper 3, section B

Overview

The tracers used in nuclear medicine, what makes a good one, and the technetium generator.

What you need to know

Answer each one before you reveal it.

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Numbers

Why is technetium-99m suited to imaging, and what is its half-life?

Numbers

What radiation does iodine-131 emit, and what is its half-life?

Numbers

What are the half-life and gamma energies of indium-111, and what is it used for?

Numbers

What makes a good medical tracer, and how is technetium-99m produced?

Numbers

Why is a generator used on site rather than delivering technetium-99m directly?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    How does a gamma-emitting tracer allow imaging of internal body structures?

    Model answer

    The tracer accumulates in specific organs or tissues, emitting gamma radiation that can be detected from outside the body to form an image of internal structures or physiological processes.

  2. 2

    What type of radiation does technetium-99m emit, and what is its energy?

    Model answer

    Technetium-99m emits gamma radiation with an energy of 140 keV.

  3. 3

    What does 'metastable' mean in the context of technetium-99m?

    Model answer

    It refers to an excited nuclear isomer that decays by emitting gamma radiation to reach a lower energy state, rather than undergoing alpha or beta decay.

  4. 4

    State the half-life of technetium-99m.

    Model answer

    6 hours.

  5. 5

    Why does technetium-99m minimise radiation dose to the patient compared to isotopes that emit alpha or beta radiation?

    Model answer

    Technetium-99m emits only gamma radiation (no alpha or beta particles); gamma rays are weakly ionising, so little energy is deposited in tissues, while most escape the body for external detection.

  6. 6

    How can technetium-99m be made to target specific organs for imaging?

    Model answer

    It can be chemically labelled with compounds that have affinity for specific organs, such as phosphate compounds for bone imaging.

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