The principle of MRI is the signal generated by the nucleus of hydrogen atom in the magnetic field, and the computer reconstruction processing imaging a way of examination, the content of hydrogen atoms in the human body is high and widely distributed, we can treat it as a small magnet, the distribution and arrangement of the spin axis of the small magnet is chaotic, if we put the human body within a strong magnetic field, then this small magnet it will be in accordance with the direction of the magnetic field in a regular Arrangement, this time we then apply a radio frequency pulse that affects the magnetic field, while absorbing the energy released in the form of radio frequency signal. This RF signal is received, reconstructed by computer, and then converted into an image, which is the MRI image we usually see.