Computed Tomography device is a medical imaging device which combines in a single gantry system both positron emission tomography (PET) and an x-ray computed tomography & images acquired from both devices can be taken sequentially, in the same session from the patient & combined into a single superposed image. Thus, functional imaging obtained by PET, which depicts the spatial distribution of metabolic or biochemical activity in the body can be more precisely aligned or correlated with anatomic imaging obtained by CT scanning. Two- and three-dimensional image reconstruction may be rendered as a function of a common software and control system. PET-CT has revolutionized many fields of medical diagnosis, by adding precision of anatomic localization to functional imaging, which was previously lacking from pure PET imaging. Oncology, surgical planning, radiation therapy and cancer staging have been changing rapidly under the influence of PET-CT availability, to the extent that many diagnostic imaging procedures and centers have been gradually abandoning conventional PET devices and substituting them by PET-CTs. Although the combined device is considerably more expensive, it has the advantage of providing both functions as stand-alone examinations, being, in fact, two devices in one.