The PET Scanner

• What does PET stand for in medical imaging?

  Positron Emission Tomography
• What is the primary purpose of a PET scan?

  To image tissues by measuring metabolic activity
• What type of radioactive tracer is used in PET scanning?

  Beta-plus emitting radioactive tracer
• What is produced when a positron annihilates with an electron?

  Gamma photons

  
• How are gamma photons detected in PET scanning?

  Using a ring of gamma cameras
• What happens to the positrons emitted from the F-18 nuclei during a PET scan?

  They annihilate with electrons in the patient
• What is the significance of the delay time between gamma-ray photons?

  It determines the location of annihilation
• What is ignored during the detection of gamma photons?

  Photons not arriving within a nanosecond
• What is the role of the computer in PET scanning?

  To build up an image from signals
• What happens to the positron after it is emitted from the tracer?

  It travels less than a millimeter before annihilating
• What is conserved during the annihilation of a positron and an electron?

  Mass, energy, and momentum
• What is the energy of each gamma-ray photon produced in annihilation?

  512 keV

  
• What equation relates the energy of a photon to its frequency?

  E = hf
• What does the variable 'h' represent in the energy equation?

  Planck's constant
• How is the energy of each photon calculated from the total energy?

  By dividing the total energy by two
• If the total energy released is $1.64 \times 10^{-13} \text{ J}$, what is the energy of one photon?


  $8.2 \times 10^{-14} \text{ J}$
• How do you convert energy from joules to electronvolts?

  Divide by $1.6 \times 10^{-19} \text{ J/eV}$
• What is the relationship between the energy of the photons and their frequency?

  Higher energy means higher frequency
• What is the frequency of the gamma rays if their energy is $8.2 \times 10^{-14} \text{ J}$?


  $1.2 \times 10^{20} \text{ Hz}$
• What are the steps involved in PET scanning?

  1. Patient injected with F-18 isotope
  2. Body part surrounded by gamma cameras
  3. Positrons annihilate with electrons
  4. Two gamma photons produced
  5. Delay time used to locate annihilation
  6. Signals processed to create an image