There is no difference between an MR exam and an MRI, which is the abbreviation for magnetic resonance imaging. The basic principle of MRI is that the body is placed in a special magnetic field and radiofrequency pulses are used to excite the hydrogen nuclei in the body, causing them to resonate and absorb energy. After the radio frequency pulse is stopped, the nucleus emits an electrical signal at a specific frequency and releases the absorbed energy, which is collected by an external receiver and processed by an electronic calculator to obtain an image, i.e., an MRI. MRI is currently more advanced, scientific, and has no radiological damage to the human body. MRI examinations are performed by capturing the values of changes in the tissues of the body under a strong magnetic field, and are analyzed and organized by a computer to display them in the form of images. Therefore, the examination can effectively distinguish soft tissue damage such as muscle, ligament and nerve compared to CT and X-ray, and has a very high clinical diagnostic value especially for early brain hemorrhage and cerebral infarction.