Diffusion function should refer to diffusion function imaging. On MRI, there are T1 phase, T2 phase, FLAIR phase, diffusion-weighted imaging, and diffusion-weighted imaging, which is also called DWI phase. Cerebral infarction is a disease with a very high incidence nowadays, and the lesions can only be seen through other phases, but it is not possible to distinguish which is a new lesion and which is an old lesion. With the extension of time, the lesions become less and less bright, and gradually become chronic, so diffusion-weighted imaging is still very important in clinical practice.