Brain tumors are mainly divided into two categories in terms of origin: one is primary brain tumors that originate from intracranial tissues including brain tissues, meninges, cranial nerves and pituitary gland; the other is brain metastases that originate from other systems and invade or metastasize into the skull; in terms of malignancy, they are divided into benign tumors and malignant tumors; in terms of time of occurrence, they are divided into congenital tumors and acquired tumors. With the development of modern medicine, especially the development of medical imaging, the diagnosis of brain tumor has been greatly improved, especially the emergence of CT and MRI, which are of revolutionary importance and have greatly improved the diagnostic accuracy of brain tumor. However, from the perspective of clinical treatment, medical imaging is required not only to detect lesions at an early stage, but also to do the following: 1) to determine the diagnosis; 2) to reflect the biological characteristics of tumors; 3) to guide the treatment; 4) to evaluate the effect of treatment in time; 5) to judge the prognosis of tumors. In fact, although there are various imaging examinations, such as magnetic resonance imaging, which can diagnose many diseases, they still cannot fully meet the above requirements. Specifically, there are many shortcomings in the existing imaging examinations, such as: high sensitivity but insufficient specificity, inability to accurately distinguish the nature of all tumors, inability to guide specific targeted therapy, and inability to predict the success or failure of treatment and judge the prognosis at an early stage. The current international gold standard for the diagnosis of brain tumors is still histopathological diagnosis. Therefore, in some cases, it is not surprising that histopathological examination is still needed for the nature of lesions that cannot be determined after MRI and other examinations. Nowadays, there are various medical imaging examinations to diagnose brain tumor, not to mention ordinary people, even general professional doctors do not fully grasp the indications of these imaging examinations, let alone being able to diagnose the disease more accurately. Therefore, when an MRI image is shown to different doctors, they may come to different diagnostic conclusions. However, as a patient, it is important to know about these imaging tests and to objectively consider the doctor’s diagnosis, which is necessary to choose the right treatment. Here I will give you a brief introduction of imaging examinations commonly used in brain tumor diagnosis. 1. Anatomical imaging examination 1. Cranial CT: also called X-ray computerized body scan, divided into plain scan and enhanced scan, can also be used for cerebrovascular imaging (CTA), which is simple and fast, and can clearly show bony structure and intracranial hemorrhage is its biggest advantage, but it is the second place in brain tumor diagnosis, not as clear as magnetic resonance. Currently, it is mainly used for physical examination, diagnosis of cranial trauma and cerebrovascular diseases. It is also necessary to perform examinations after brain tumor surgery, mainly for exploring acute complications of surgery, such as hemorrhage, infarction, brain swelling or tension pneumothorax, and for preliminary evaluation of the extent of surgical resection. 2.Magnetic resonance imaging (MRI): divided into plain scan and enhanced scan, is the first in the diagnostic value of brain tumor, and its sensitivity and specificity are obviously better than CT, but it requires longer examination time and cannot show the cranial structure, which is its main shortcoming. In recent years, the technology of magnetic resonance has been developed rapidly. In addition to the traditional examination sequence, MRA (showing cerebral vessels), cerebral perfusion imaging and diffusion tension imaging, and MRS (spectral analysis) technology have also appeared. Metabolic imaging 1, PET/CT: also known as positron emission/computerized tomography, by applying radioisotopes to determine the metabolism of the lesion, the main tracers used internationally are FDG (18F-Fluorodeoxyglucose), MET (11C-Methionine) and FLT (18F- PET/CT has certain significance in determining the benignity and malignancy of tumors, determining the residual tumor, and identifying tumor recurrence and radiation necrosis. The biggest advantage is that it can simultaneously perform whole body scanning, which is of high value in the diagnosis of brain metastases. The disadvantage is that it requires the application of radioisotopes and is more expensive. 2.MRS: also known as magnetic resonance spectroscopy, is a non-invasive method to study the metabolism, biochemical changes and quantitative analysis of compounds in living organ tissues by using magnetic resonance, which is mainly used in the diagnosis of brain diseases. (3) Cr level is a marker of energy metabolism; (4) Lac level is a product of anaerobic metabolism. The changes in these biochemical parameters are of clinical significance in determining the metabolic status of the lesion, especially in identifying glioma recurrence from radiation necrosis and malignancy from inflammation. The disadvantage is that the examination time is long, and many MRI machines are not equipped with the appropriate system software, so it is not possible to perform MRS examination with MRI.