Positron emission tomography (PET) is an imaging technique for the human body that uses an isotope of carbon (carbon – 11) as a radioactive tracer to measure changes in blood flow in the brain. Carbon – 11 can be introduced into the body by inhaling carbon monoxide. This is taken up by red blood cells in the normal way and transported around the body.
When carbon – 11 decays, it does so by positron emission. The positron annihilates with an electron and two gamma rays are produced, travelling in opposite directions. These gamma rays can be picked up by detectors that surround the patient, and the position at which the x – rays are produced calculated.
PET scans are much used in brain research. Brain activity is matched with specific tasks to pin down the areas of the brain associated with specific functions. A pet scan image of the brain is shown below, showing the effect of a dose of cocaine.