d) PET scan

d) positron emission tomography (PET scanner); annihilation of positron-electron pairs; formation of image

d) diagnosis using PET scanning

the structure of a PET scanner

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

• the ring contains gamma detectors connected to a computer

the PET scanning process

• the 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 oppositely placed gamma detectors

  • and their speed

• the gamma photons hit the scintillator and produce visible light photons

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

• one photon is converted into a voltage signal

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

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