FDG is used because it is taken up by many types of tumors and produces images of good contrast. PET has been found to assist in diagnosis, staging, monitoring therapy response and assessing recurrence in patients with different tumors, PET using F-18-FDG is more accurate than CT or other conventional imaging modalities for diagnosis of previously unknown recurrent or metastatic malignant foci, focal colonic F-18-FDG uptake has a high 70-80% probability of showing corresponding abnormal histopathological Finding.