Abstract: Positron emission tomography (PET)/computed tomography (CT)inline scanner combined with high performance PET and CT have been introduced to clinical in recent years. The application of PET/CT in oncology are rapid increasing. The addition of CT to PET offers many advantages, including ob, taining a fast and relatively accurate transmission map, shortening the duration of the examination, adding precise anatomical information to PET imaging, and providing additional diagnostic information. However, using CT for attenuation correction can led to some artifacts:quantitative measurements may be altered, high density IV and oral metallic objects may produce artifacts, and the registration of PET and CT may occasionally suboptimal. In head and neck tumor PET/CT offers particular potential advantages as well as abdomen and pelvic tumor. Even in the thorax, which the physical movement may produce unsatisfactory results, offers some advantages also. Preliminary results of PET/CT over PET or CT in oncology are very encouraging. It is clear the PET/CT fusion technology has an more and more impact on both diagnostic and therapeutic aspects of patient management.