A Positron Emission Tomography - Computed Tomography (PET-CT scan) combines a CT scan and a PET scan into one to give detailed information about the cancer in question.

A CT scan takes pictures from all around the body and uses a computer to put them together. There is detailed information about CT scans in our section about cancer tests. A PET scan uses a very small amount of an injected radioactive drug to show where cells are active in the body.

PET-CT has revolutionised medical diagnosis in many fields, by adding precision of anatomic localisation to functional imaging, which was previously lacking from pure PET imaging. For example, in 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 centres have been gradually abandoning conventional PET devices and substituting them with PET-CTs. Although the combined/hybrid device is considerably more expensive, it has the advantage of providing both functions as stand-alone examinations, being, in fact, two devices in one.