PET scans

• PET is a medical imaging technique that uses radioactive isotopes to visualise organ function and diagnose medical conditions. 
• The radioisotope used in PET is usually fluorine-18, which decays by emitting positrons (anti-electrons).
• When the positron meets an electron it annihilates both particles into two gamma rays travelling at right angles to one another.
• • Radioactive isotopes, known as a tracers, are injected into the patient's bloodstream.
  • The tracers spread throughout the body and emits gamma radiation. Most of the tracers will go to the sites in the body that are most metabolically active (as they will have the best blood supply).  
  • The patient will lie in a PET scanner which will detect where the gamma radiation is being emitted from.
  • By seeing where most of the gamma radiation is being emitted from, the doctors can see where the tracers are concentrated, and use this to diagnose medical conditions. 
• The radioactive isotopes used in the tracers have short half-lives (to minimise harm to the patient).

  This means that they have to be made near the hospital as otherwise they would decay before they can be used.