PET/CT is superior to PET and CT alone, and/or magnetic resonance imaging (MRI), in the diagnosis and treatment of various primary or metastatic cancers. Dual modality PET/CT scanning provides accurately fused morphologic (CT) and functional (PET) data sets. A very small tumor is well detected by PET but can be missed by CT. On the other hand, a large tumor with minimal functional deviations may be seen on a CT image, but may not be detected by PET. In both situations, PET/CT would localize the tumor accurately. Thus, PET/CT is a more accurate test than either of its individual components. PET/CT has advantages over other imaging methods; it can differentiate benign from malignant lesions, staging and restaging tumors, detect functional changes before there is any change in clinical or radiological size of a mass, better in identifying cancer that has spread, making up treatment plan and monitoring tumor response, distinguish viable metabolically active tissue from scars, and it is indicated for restaging in patients with suspected recurrent and metastatic disease.