To put it plainly, a Radiopharmaceutical, or Tracer, is a radionuclide (, or radioisotope) attached to a substance that will target a specfic part of a patient's body - for example, cancerous cells have an uncontrolled cell division, so take up more glucose to fuel the divisions. Therefore glucose would be a suitable substance to attach a radioactive marker to if you were looking for cancerous tissue.
Once ingested or injected into the patient's body (and after a suitable time period so the radiopharmaceutical has `zoned in` on the targeted tissue or area), the patient is screened using a Gamma Camera.
A diagram showing a Gamma Camera taking in Gamma radiation, γ.
The γ-radiation emitted from the patient is projected in every direction. The Collimator, shown on the diagram, ensures only the γ-radiation travelling at the right plane enters the camera. The collimator is usually made from lead to stop other planes of radiation entering.
The Scintillator, shown in the diagram as the crystal, only detects photons travelling along the axis of the collimator, so any radiation at a slight angle is cut out. The γ-photons that are dead on strike the crystal, and electrons are emitted on the other side (the Photoelectric effect). The electron travels up the photomultiplier tube, and impacts involving the dynode release more electrons. Soon there is a huge number of electrons and an electrical pulse is noticeable.
Those pulses from the photomultiplier tubes are processed electronically by an attached computer and reassembled to produce an image.
