text: Positron emission tomography (PET) is a functional imaging technique that uses radioactive substances known as radiotracers to visualize and measure changes in metabolic processes, and in other physiological activities including blood flow, regional chemical composition, and absorption. Different tracers are used for various imaging purposes, depending on the target process within the body.
  For example:
  * Fluorodeoxyglucose ([F]FDG or FDG) is commonly used to detect cancer;
  * [[Sodium fluoride#Medical imaging|[F]Sodium fluoride]] (NaF) is widely used for detecting bone formation;
  * Oxygen-15 (O) is sometimes used to measure blood flow.
  PET is a common imaging technique, a medical scintillography technique used in nuclear medicine. A radiopharmaceutical – a radioisotope attached to a drug – is injected into the body as a tracer. When the radiopharmaceutical undergoes beta plus decay, a positron is emitted, and when the positron interacts with an ordinary electron, the two particles annihilate and two gamma rays are emitted in opposite directions. These gamma rays are detected by two gamma cameras to form a three-dimensional image.
  PET scanners can incorporate a computed tomography scanner (CT) and are known as PET-CT scanners. PET scan images can be reconstructed using a CT scan performed using one scanner during the same session.
  One of the disadvantages of a PET scanner is its high initial cost and ongoing operating costs.