PETscanner

A PET scanner, or Positron Emission Tomography scanner, is a medical imaging device that produces three-dimensional images of metabolic or biochemical processes within the human body. It works by detecting pairs of gamma rays emitted indirectly by a positron-emitting radionuclide (a radiotracer) that is introduced into the body on a biologically active molecule. This radiotracer accumulates in specific organs or tissues depending on the molecule it is attached to. For example, a common radiotracer is fluorodeoxyglucose (FDG), a glucose analog that is taken up by cells with high metabolic activity, such as cancer cells.

When the unstable nucleus of the radiotracer decays, it emits a positron. This positron then travels a short distance and annihilates with an electron in the surrounding tissue. This annihilation event produces two photons of gamma radiation that travel in opposite directions. The PET scanner has a ring of detectors that surround the patient. When these detectors register a pair of gamma rays arriving simultaneously and in opposite directions, it indicates that an annihilation event has occurred along the line connecting the two detectors. By collecting data from many such events, the scanner can reconstruct a detailed map of where the radiotracer has accumulated in the body. This map reveals areas of increased or decreased metabolic activity, which can be indicative of various diseases such as cancer, heart disease, and neurological disorders. PET scans are often used in conjunction with other imaging modalities, like CT scans, to provide more comprehensive anatomical and functional information.