Brain MRI can detect a variety of intracranial lesions, most commonly cerebral infarction, cerebral hemorrhage, brain tumors and so on. 1. Cerebral infarction: MRI is more sensitive and can detect tiny lesions, such as lacunar cerebral infarction, and it can also distinguish between different periods, and the signals change in different periods, such as the signal changes of T₁WI and T₂WI are not obvious in the hyper-acute period, and DWI can show high signals, while infarcts in the acute period show iso-T₁ or slightly longer T₁ or longer T₂ signals, and DWI can show high signals. 2. Cerebral hemorrhage: MRI signals of cerebral hemorrhage are different at different periods, depending on the changes of oxygenated hemoglobin, deoxyhemoglobin, methaemoglobin and ferritin. Generally speaking, within 7 days after hemorrhage, T₁WI shows equal signal and T₂WI shows low signal; 1-4 weeks after hemorrhage, T₁WI and T₂WI both show high signal; after 1 month after hemorrhage, T₁WI shows low signal, and T₂WI shows central high signal and peripheral low signal. 3. Brain tumor: Occupying lesions can be suggested on MRI. According to the different nature of the tumor, its signal intensity and value presented on MRI are also different. In addition to the above problems, cranial MRI can also detect cerebral white matter lesions and demyelinating diseases, intracranial infections, neurodegenerative diseases, etc., which need to be analyzed by professional doctors.