MRI is magnetic resonance imaging, which uses the principle of magnetic field to place the human body in a strong and uniform static magnetic field, and changes the regional magnetic field through specific radio wave pulses, which excites the hydrogen proton nuclei in human tissues to produce resonance phenomena and generate signals by computer processing and imaging. The imaging principle of magnetic resonance is different from that of X-ray and nuclear medicine examinations, thus avoiding the damage of radiation to the human body and being non-invasive. Because different tissues in the human body contain different hydrogen protons, different signals are generated when MRI is performed. The soft tissue resolution of MRI is higher than that of CT, and it is commonly used in clinical practice for the examination of lesions in the central system, cardiovascular system, joints, soft tissues, and pelvic organs, and is superior for the examination of the skull, mediastinum, and substantial organs of the abdominal cavity.