 Positron emission tomography PET is a nuclear medicine procedure based on the measurement of positron emission from radiolabelled tracer molecules. These radiotracers allow biologic processes to be measured and whole body images to be obtained which demonstrates sites of radiotracer accumulation. The most common radiotracer in use today is 18F-fluorodeoxyglucose 18F-FDG which is a radiolabelled sugar glucose molecule. Imaging with 18F-FDG PET is used to determine sites of abnormal glucose metabolism and can be used to characterize and localize many types of tumours. 