Positron Emission Tomography/Computed Tomography (PET/CT) is a diagnostic tool used mainly in oncology, neurology, cardiology, infection and inflammation, and in planning surgery and treatment. PET/CT combines two different techniques in one scanner, giving clinicians two sets of related information about the body – functional and structural – from one examination. The CT scanner takes a series of two-dimensional cross-section images (‘slices’) around an axis. Computer processing is then used to construct a three-dimensional image. PET works by detecting gamma rays given off by a radioactive tracer injected into the body.