<prompt> What is meant by PET scan?Positive Emission TomographyPositron Emission TomographyPositron Energy TomographyPositive Energy Tomography  <response>: SPECT single photon emission computed tomography PETpositron emission tomography PET is a functional imaging technique that is used to observe metabolic processes in the body as an aid to the diagnosis of disease. The system detects pairs of gamma rays emitted indirectly by a positron-emitting radionuclide tracer, which is introduced into the body on a biologically active moleculeThe common molecule used is fludeoxyglucose FDG, an analogue of glucoseRef: Grainger and Allison;s diagnostic radiology 6th edition, page 123 