Positron Emission Computed Tomography (PET)

PET translated in Chinese as "Pat", is a non-invasive imaging technique for detecting the distribution of radioactive nuclei in the body. The "positron" in its full name. Traditional medical imaging techniques show anatomical and structural changes caused by disease, while PET shows changes in the function of the human body. In other words, if the anatomy of the human body has not changed, traditional imaging techniques are powerless for the diagnosis of the disease. Basic Information Specialist classification: neurological examination classification: X-ray Applicable gender: whether women are fasting: fasting Tips: Fasting for 6-8 hours before scanning, you can drink a small amount of boiled water, and ban coffee, tea and alcoholic beverages for two days before the heart check. Do not do strenuous activities 1 day before scanning. Normal value PET is particularly useful for early diagnosis of disease, discovery of subclinical lesions, and evaluation of therapeutic effects without morphological changes. At present, PET has shown important value in the diagnosis and treatment of three major diseases, such as tumor, coronary heart disease and brain disease. Clinical significance Traditional medical imaging techniques show anatomical and structural changes caused by disease, while PET shows changes in the function of the human body. In other words, if the anatomy of the human body has not changed, traditional imaging techniques are powerless for the diagnosis of the disease. In fact, the occurrence of diseases is accompanied by functional changes in biochemical processes, which often precede changes in anatomical structure; there are also some diseases such as Alzheimer's disease, Parkinson's disease, etc., which have no obvious structural changes, traditional Medical imaging cannot show changes in these functions. PET is uniquely able to show functional changes, and thus has an unparalleled advantage for early detection and diagnosis of diseases. In addition, PET can perform three-dimensional dynamic and whole-body imaging, and can find problems that cannot be found by other inspections. “—Leaf obstacles, not seeing Mount Tai”, make up for the shortcomings of traditional medical imaging. Precautions 1. You must register at the Tumor Radiotherapy Center according to the appointment time and cooperate with the doctor to prepare for the examination. If you fail to arrive on time, you will be arranged to check first and your inspection will be postponed. 2, fasting 6-8 hours before scanning, can drink a small amount of boiled water, two days before the heart check forbidden coffee, tea and alcohol-based beverages, do not do strenuous activities 1 day before scanning. 3. Please bring your medical records and X-ray films, CT films, MRI films, etc. At that time, the doctors in the PET-CT room will ask and record your medical history, treatment status and allergies. Blood sugar will be tested for you before scanning. If you have a history of diabetes, please let us know. 4. Due to the production, transportation and other unpredictable factors of PET-CT imaging positron drugs, your inspection may be postponed or postponed. Please understand and support. The PET-CT room staff will complete the inspection as soon as possible. 5, you need to receive intravenous injection of positron drugs, please rest assured that the radiation dose of these drugs is within the safe range. After the injection, you must sit in the PET-CT waiting room for about 60 minutes. After the drug is metabolized in the body, PET-CT scan is performed. When scanning, the bed should be placed on the flat bed, and the body position cannot be moved during the examination. 6. After the scan, please do not leave the PET-CT waiting room by yourself. The medical staff will inform you if you need to leave further inspection according to the situation. Please complete the examination and leave with the permission of the medical staff. 7. If you have any other questions, please ask the staff. 8. If you need to postpone or cancel the inspection due to special circumstances, please be sure to notify the appointment room 24 hours before, so as not to affect your or others' visits. Inspection process 1, brain glucose metabolism imaging: human brain blood supply accounts for 15% of cardiac output, oxygen consumption accounts for 20% of the whole body, about 40ml of oxygen, 70mg of glucose per minute. Glucose metabolism is almost the only source of brain energy. The rate of glucose metabolism in the brain can reflect the brain function. Whether it is the physiological activity or pathological process of the brain, it is accompanied by changes in the level of glucose metabolism. Glucose is degraded by phosphorylase in brain cells to become glucose-6-phosphate, and carbon dioxide and water are finally formed along the glycolysis pathway. 2-deoxyglucose (DG) and fluorinated deoxyglucose (FDG) can also enter the brain through the blood-brain barrier (BBB), and are phosphorylated by glycogen kinase to become DG-6-PO4. And FDG-6-PO4, but unlike natural glucose, these two molecules can not continue to metabolize along the glycolysis pathway, and can not quickly diffuse out of the BBB, so stay in the brain tissue for a period of time (at least 45min) . Using 18F-FDG for PET brain imaging, although it can not trace the whole process of natural glucose metabolism in the brain, it can be retained in the brain for a period of time, not only can obtain reliable radioactive distribution images, but also It specially designed physiological and mathematical models to determine the local and whole brain glucose metabolic rate, and then display different metabolic quantities in different colors to obtain local brain glucose metabolism function images. 2, cerebral oxygen consumption imaging: normal human brain oxygen consumption 40ml per minute, oxygen consumption is an indicator of brain energy metabolism and function, with 15O2 (half-life 2min) inhalation (continuous inhalation or one dose) for PET Imaging, the brain oxygen metabolism rate (CM-RO2), combined with cerebral blood flow and blood oxygen concentration determination, can calculate the oxygen extraction fraction (OEF, OEF = CMRO2 / CBF), according to CMRGLU and CMRO2, can calculate the whole brain and The local cerebral oxygen/glucose utilization ratio can be used to study the mismatch between blood flow and metabolism and the relationship between oxidation and glucose metabolism under pathological conditions. 3, brain protein metabolism imaging: PET can display and determine the utilization of substance metabolism, including sugar, fat and amino acids, the former two reflect the energy supply, the latter reflects the level of DNA metabolism. Currently used to study amino acid protein metabolism are mainly 1-11C-leucine and 11C-methyl-L-methionine. Methionine is easily introduced into the brain through BBB, and the kinetic data of methionine uptake and protein synthesis in the brain can be obtained by fitting a three-compartment model with 11C-methionine imaging. The basis of tumor cell proliferation is amino acid metabolism (or DNA metabolism). 11C-methionine can be used to examine tumors and their metastases, and the tumor proliferation rate can be evaluated according to their aggregation in tumor tissues, especially to evaluate the proliferation rate of deep tumors. A non-invasive method. 4. Neuroreceptor imaging: At present, more than 40 kinds of natural neurotransmitters and their receptors have been found in the brain tissue of mammals. The content of receptors in the brain is very small, only in picomoles (pmol). One millionth of the brain's weight. Therefore, the key to receptor imaging is to prepare labeled ligands with high affinity and high specific activity, and require few non-specific binding. These specific labeling ligands are agonists or antagonists of receptors, mostly antagonists. Because of the minimal amount of chemical, it does not cause pharmacological effects and behavioral changes. The imaging agent is combined with the neuroreceptor after the brain, and the dynamic planar or tomographic imaging is performed by using PET to obtain the anatomical distribution image of the neuroreceptor. With the compartment model, the binding density and binding solution of the imaging agent and the receptor can be estimated. The constant is used to reflect the number of receptors and the activity of the receptor. By intervening in known antagonists, the binding specificity of the imaging agent to the receptor and its subtypes can be evaluated. Not suitable for the crowd 1. Pregnant and lactating women: In principle, it is not recommended for PET examination. The gamma rays produced by FDG drugs may have certain effects on the fetus, especially those with gestational age not exceeding three months. For breastfeeding women, FDG can enter the baby through the milk, which may cause unnecessary exposure. If a PET-CT is required for the diagnosis, the benefit of the test should be greater than the adverse effects on the fetus or infant and avoid breastfeeding during this period. 2. A claustrophobia.

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