The imaging principle of MRI is that when the human body is examined, it is in a special magnetic field and reacts to the influence of electromagnetic waves. The MRI system collects information about the body’s reaction in the magnetic field and processes it, and then images it. The images are used to determine whether abnormalities occur in the body’s tissues, organs and structures. Unlike CT examinations, MRI does not require radiation and there is no ionizing radiation, so there is no radiation effect on pregnant women and fetuses, and it can be used for fetal examinations. MRI can be used to check many diseases, such as placenta praevia and abnormal fetal development.