Brain positron emission tomography

Brain positron emission tomography is a form of positron emission tomography (PET) that is used to measure brain metabolism and the distribution of exogenous radiolabeled chemical agents throughout the brain. PET measures emissions from radioactively labeled metabolically active chemicals that have been injected into the bloodstream. The emission data from brain PET are computer-processed to produce multi-dimensional images of the distribution of the chemicals throughout the brain. The positron emitting radioisotopes used are usually produced by a cyclotron, and chemicals are labeled with these radioactive atoms. The radioisotopes used in clinics are normally 18F (fluoride), 11C (carbon) and 15O (oxygen). The labeled compound, called a radiotracer or radioligand, is injected into the bloodstream and eventually makes its way to the brain through blood circulation. Detectors in the PET scanner detect the radioactivity as the compound charges in various regions of the brain. A computer uses the data gathered by the detectors to create multi-dimensional (normally 3-dimensional volumetric or 4-dimensional time-varying) images that show the distribution of the radiotracer in the brain following the time. Especially useful are a wide array of ligands used to map different aspects of neurotransmitter activity, with by far the most commonly used PET tracer being a labeled form of glucose, such as fluorodeoxyglucose (18F). The greatest benefit of PET scanning is that different compounds can show flow and oxygen, and glucose metabolism in the tissues of the working brain. These measurements reflect the amount of brain activity in the various regions of the brain and allow to learn more about how the brain works. PET scans were superior to all other metabolic imaging methods in terms of resolution and speed of completion (as little as 30 seconds), when they first became available. The improved resolution permitted better study to be made as to the area of the brain activated by a particular task.