Positron Emission Tomography, is a type of nuclear medicine imaging. PET scan may detect the early onset of disease by identifying changes at the cellular level before other imaging tests can. PET uses a small amount of radioactive material that can be detected on the PET scanner. The most commonly used radiotracer is F-18 fluorodeoxyglucose, or FDG, a molecule similar to glucose. Cancer cells are more metabolically active and may absorb glucose at a higher rate. This higher rate can be seen on PET scans.