Unlike, bone scans, MRIs and CT scans, a PET scan, or Positron Emission Tomography, is an imaging test that aids visualization of how organs and tissues inside your body are actually functioning.
The PET scan often includes the injection of a small amount of a radioactive material linked to a glucose-based substance, called a radiotracer, into a vein of your arm. Your organs and tissues absorb the tracer. You will then lie down on an examination table that is moved into a doughnut-like shaped machine (that looks very much like a CT scanner). This machine detects and records the amount of energy given off by the tracer substance as the glucose is metabolized over time. Three-dimensional images reveal the degree to which the tracer is being metabolized, locating possible tumor activity where it may be taking place because tumor cells tend to metabolize glucose more quickly than nearby normal cells.
The doughnut-shaped PET scanner is usually open, and rarely induces claustrophobia. PET scans are not used often to visualize prostate cancer because prostate cancer cells tend not to metabolize glucose as aggressively as other types of cancer cells, thereby making the prostate cancer difficult to distinguish from normal cells.
Many modern machines combine a PET scan with a CT to get the best possible view (with minimal exposure to radiation) of your internal functioning.