PET stands for Positron Emission Tomography. CT (also known as a CAT scan) stands for Computerised Tomography.
The PET part of the scan measures cellular uptake of radioactive glucose. Abnormal cell uptake can be a sign of disease. The CT part of the scan shows the internal anatomy of the body.
Together, the PET CT examination gives valuable information on both the anatomy (structure) and metabolism (function) of tissues in the body.