Dispersion is a physical phenomenon that refers to the haphazard movement of water molecules. The state of water molecules in normal tissues is close to that of free water, which can move freely without any restriction and without diffusion restriction. However, some special pathophysiological processes can affect the free movement of water molecules, called diffusion restriction, such as ischemia, inflammation, poisoning, infection and malignant tumors. To determine whether a tissue or lesion has diffusion restriction, it can be detected by DWI sequences, which will show corresponding signal changes in DWI and ADC maps, for example, diffusion restriction shows high signal in DWI and low signal in ADC maps. These signal alterations are then used to help the imaging physician make a predictive diagnosis of certain diseases.