DWI diffusion restriction is not cancer, but is caused by brain cell edema. It is a special imaging method to determine whether there is a new lesion by the response of DWI diffusion restriction. It is mainly used in the acute phase of cerebral infarction to determine whether there is an acute cerebral ischemic lesion by whether the DWI diffusion is limited or not, and the judgment is based on the phenomenon of bound and free water. The DWI image changes are judged to be caused by the acute phase of cerebral ischemic infarction or by the chronic resultant changes. The DWI diffusion can clearly reflect the early response of acute cerebral infarction as a high signal change. Of course, many acute diseases causing brain cell edema, including multiple sclerosis, encephalitis, and brain tumor compression of brain tissue, will show symptoms of DWI diffusion restriction, which is a change reflecting brain cell edema caused by acute brain damage.