MRI has no radiation and is not harmful to humans. However, if the patient has non-magnetic metals in the body or a pacemaker implant, MRI must be prohibited to avoid accidents. The principle of MRI is to put the human body in a special magnetic field, and use radio frequency pulses to excite the nucleus of hydrogen atoms in the human body, causing them to resonate and inhale energy. Since MRI is magnetic field imaging, not X-rays, there is no radioactivity, so it is harmless to human body and very safe. However, some metallic substances and things that can be subjected to magnetic fields, such as radio equipment, watches and other devices with metals, as well as metal medical devices with implants in the body, such as pacemakers, stents, and denture, such substances can affect the image clarity of MRI and may also cause damage to the patient. In addition, there is a titanium alloy that can be used for MRI, but it needs to be confirmed by the MRI examiner. Titanium devices, such as spinal stents, can do MRI, but they may also cause distortion and artifacts in the MRI image near the bone stent, which in turn may affect the effectiveness of the examination.