The first human positron emission tomography (PET) scanner, an instrument which creates high resolution computerized images was built by Michael Phelps and Ed Hoffman. PET imaging is based on the detection of radiation that is released from chemicals introduced into the body. CT and MRI create good images of anatomical structures they do not provide information about the biological activity (i.e. cell growth) of the imaged area.
PET provides information about the biochemical activity of the observed structures. This allows for the discrimination between objects that are non-living such as a scar from growing cells such as those in a tumor.1