PET, known as Positron Emission Computed Tomography, was invented in the 1970s and was named one of the top ten inventions in the field of medicine in the last century. Initially, PET examination was limited to basic scientific research due to the high cost of PET auxiliary drugs and instruments. In recent years, with the development of modern science and technology, the cost of preparing PET examination auxiliary drugs has decreased and the performance of PET examination instruments has improved dramatically, so PET examination is widely used in the field of clinical medicine. Due to the superiority of PET imaging compared with other examinations in many aspects, it has now become a very important diagnostic tool in clinical work, especially in the early diagnosis of cancer and functional imaging of the brain. It is also the gold standard for evaluating the vitality of the heart muscle by its results on the vitality of the heart muscle. The principle of PET examination After the positron isotope labeled drug is injected into the body from a vein, the emitted positrons interact with the electrons in the neighboring tissues to produce a pair of gamma photons. the PET scanning probe detects the gamma photon signal and gives the signal to the computer for processing. The radiation dose from a PET scan is very small, less than a gastrointestinal imaging, and even less than a CT scan. Also, the drugs used for the test are glucose and amino acids, so the PET test has very little effect on the human body. PET examinations can detect cancer very early Cancer is one of the major causes of human death. To reduce deaths caused by malignant tumors, it is necessary to achieve early detection, early diagnosis and early treatment of cancer. PET examination is highly sensitive and can show the metabolism, function, blood flow, cell proliferation and receptor distribution of the body and focal tissue cells at the molecular level, so that the disease can be detected at an extremely early stage. It helps to determine the surgical plan and reduce the number of unhelpful invasive procedures; it helps to assess the prognosis before surgery; and it helps to evaluate the efficacy of treatment. For example, PET examination has a very high sensitivity for lung cancer diagnosis, and more than 95% of lung cancer patients can be accurately detected by it. For lung cancer patients with mediastinal lymph node metastasis, the survival rate after 5 years is only 5%; if there is no mediastinal lymph node metastasis, the survival rate after 5 years can reach 50%; for those lung cancer patients with extensive mediastinal lymph node metastasis, PET examination can reduce unnecessary surgery. In addition, PET examination is important for cancer grading and localization of lesions. The development of PET/CT now has raised this diagnostic tool to a higher level, making the functional imaging of PET and CT anatomical imaging perfectly combined, which can solve most of the difficult clinical cases in one examination. PET examination can detect psychiatric diseases PET examination is also widely used in neuropsychiatric diseases and functional brain imaging.PET imaging can observe the features of abnormal brain glucose metabolism. PET examination has unique advantages in the diagnosis and staging of certain psychiatric diseases, the study of drug treatment and drug mechanisms, and the etiological discovery of psychiatric diseases. For example, in the elderly population, dementia and depression are two of the most common psychiatric disorders, and the treatments for both differ greatly. The atypical presentation of symptoms in some patients makes the diagnosis very difficult. PET examination, on the other hand, is a good way to identify dementia and depression, which brings a great help to clinical treatment. PET can show the biochemical activity of the brain very well, and it is possible to obtain a functional localization of the whole brain in a single examination. This is the outstanding advantage of PET and makes it an ideal tool for functional brain imaging. It is thanks to PET technology that for the first time ever, researchers have been able to observe, non-invasively, changes in the corresponding functional areas of the brain in the human body during behavioral or mental activity states such as visualization, hearing, and physical movement, or memory and anxiety. Some scientists even predict that PET examinations can help psychiatrists and psychologists to analyze mental illnesses, and even through PET imaging, police officers can visually determine whether a suspect is lying and thus identify possible criminals. PET combines the best of nuclear physics, radiochemistry, medical imaging, molecular biology and other technologies, and is recognized as the crown of contemporary medical high technology. It is currently a very important screening tool for early diagnosis of cancer and functional brain imaging. With the continuous progress of PET technology, it will play a greater role in the medical field and better benefit mankind.