d) PET scan

• describe the structure of a PET scanner

• patient lies on their back on a horizontal table that slides through a vertical ring

• the ring contains gamma detectors connected to a computer

• explain the PET scanning process

• FDG emits positrons

  • they annihilate with electrons in the body

  • they emits two gamma photons travelling in opposite directions

• the point of annihilation can be determined

  • from the difference in arrival times of the photons to the opposite gamma detectors

  • and their speed

• gamma photons hit the scintillator

  • they produce thousands of visible light photons

• visible light photons travel through the light guide into the photomultiplier tubes

• one photon is converted into a voltage signal

• voltage signals generate an image depending on the concentration of the tracer

• state how the PET scanning process creates gamma images

• multiple gamma images in different angles are combined into a 3D image

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