X-Rays

• What are the 4 elements of an X-ray tube

  • Filament
  • Metal target
  • Cathode and Anode
  • High emf supply
• What is the purpose of the cathode filament

  Heats up and emits electrons due to thermionic emission
• What is the purpose of the cathode and anode

  Electrons are accelerated through the large pd between the cathode and anode
• What is the purpose of the heavy metal target

  Electrons hit the metal target and their energy is converted into an x-ray photon
• What is the purpose of the high emf supply

  Supplies the emf so the electrons can be accelerated to high enough speeds by the pd
• What are the 4 attenuation mechanisms

  • Simple scattering
  • Photoelectric effect
  • Compton scattering
  • Pair production
• What is simple scattering(attenuation mechanism)

  A photon is absorbed and re-emitted by an orbital electron. The new photon goes in a new direction and has the same energy as the old one
• What is the photoelectric effect (attenuation mechanism)

  Photon is absorbed by an orbital electron. The photon's energy is transferred into the kinetic energy of the electron. The electron is ejected from the atom
• What is Compton scattering(attenuation mechanism)

  A photon interacts with an orbital electron. Some of the photon's energy is transferred into the kinetic energy of the electron and ejected from the atom. The rest is transferred into a lower-energy photon
• What is pair production (attenuation mechanism)

  Photon interacts with an atom. The photon disappears and produces an electron positron pair
• What is a collimated beam

  A beam that is parallel so there is no decrease in intensity due to the inverse square law
• I = I0e-μx

  I = Transmitted intensity

  I0 = Initial intensity

  μ = Attenuation coefficient

  x = Thickness of material
• The attenuation coefficient is a property of a material. The higher the value the better the material is at absorbing x-rays
• What is the first step of producing an x-ray image

  X-rays are produced by an x-ray tube. They are then collimated and directed towards the patient.
• What is the second step of producing an x-ray image

  The x-rays pass through the patient and the different materials within the body attenuate the x-rays different amounts
• What is the final step of producing an x-ray image

  A photographic plate or x-ray detectors measure the relative intensity of x-rays. The darker areas show where there is a greater intensity, lower attenuation coefficients, soft tissue. The light areas show a lower intensity, high attenuation coefficient, hard materials (bones, metal)
• Why are contrast media used

  X-rays can show a clear outline between bones and soft tissue but they struggle to make out the difference between different soft tissues (where the attenuation coefficient is similar)
• What are contrast media

  Elements with large atomic numbers and therefore high attenuation coefficients (iodine and barium)
• How are contrast media used

  They are either injected or ingested by a patient into a particular soft tissue. Because of the higher attenuation coefficient this provides a sharper outline between the tissue of choice and the surrounding areas