The unique role of PET is based on metabolic imaging and quantitative analysis, applying the short-lived nuclides that make up the main elements of the human body, such as 11C, 13N, 15O, 18F, and other positronic nuclides as tracers, which not only can rapidly obtain multilayered tomographic images, three-dimensional quantitative results, and three-dimensional whole-body scanning, but also can be dynamically observed at the molecular level to see the physiological and biochemical changes of the metabolites or drugs in the body, which can be used to study physiological, biochemical, chemical transmitters, receptors, and even genetic changes. It can also dynamically observe the physiological and biochemical changes of metabolites or drugs in the human body at the molecular level, which can be used to study the physiology, biochemistry, chemical transmitters, receptors, and even genetic changes in the body. In recent years, PET has shown unique superiority in diagnosing and guiding the treatment of tumors, coronary heart disease and brain diseases.