Background: Positron Emission Tomography (PET) is a specialized nuclear medicine procedure that uses positron emitting radiolabeled tracer molecules to measure biological activity. The most common of these tracers, 18F-2-fluoro-2-deoxyglucose (FGD), an analog of glucose, is used to determine abnormal glucose metabolism in tumours and other sites. FDG has general applications where abnormal glucose metabolism may be present such as differentiating tumour from scar tissue, evaluating the presence of tumour in light of rising tumour markers and normal morphological imaging, and assessing response to therapy.