In fact, although PET-CT has a high detection rate for cancerous tumors, it cannot completely detect cancerous tumors throughout the body and needs to be complemented by other screening devices such as CT and MRI, etc. PET-CT is a functional imaging technology that can show the specific location of tumors in the body. However, since not all tumors have specific markers, some tumors are better differentiated and relatively easy to distinguish, while others are not easy to detect, such as those that are not metabolically active enough or those that are slow to proliferate and divide, plus the low level of glycolysis in these tumors, PET-CT alone may not be able to accurately detect them. In addition, PET-CT can also have false positives, such as some inflammatory diseases, tuberculosis, etc., which can be metabolically positive and easily misdiagnosed as tumors. At present, PET-CT examination is mainly used in three fields: tumor, brain and heart. In tumor, PET-CT can reflect the metabolic information of tissues and lesions, which provides important information for early diagnosis and differential diagnosis of tumor as well as finding the primary lesion of tumor. At present, PET-CT is becoming more and more valuable in tumor diagnosis as more and more molecular probes are available, such as PSMA imaging for prostate cancer and FES-PET imaging for ER and PR positivity of breast endocrine receptors, etc. The emergence of new detection probes makes PET-CT more and more valuable in tumor diagnosis; in brain, PET-CT can detect abnormal brain discharge lesions in epilepsy patients, which provides a favorable basis for developing brain surgery In the brain, PET-CT can detect abnormal brain discharges in patients with epilepsy, providing a favorable basis for the development of brain surgery plans, etc. In the heart, PET-CT can visually express valve lesions and blood perfusion in the form of images. In addition, PET-CT can provide accurate clues for treatment planning and help doctors to adjust treatment plans in a timely manner. It is important to note that a high fasting glucose level during PET-CT may cause bias in PET-CT results. Therefore, it is recommended to fast for at least 8 hours before the examination so that the blood glucose level does not affect the normal development of the contrast agent.