Magnetic resonance imaging. Magnetic resonance imaging (MRI), also known as spin imaging, is based on the different attenuation of released energy by different structural environments in materials. Using the external gradient magnetic field to detect the emitted electromagnetic wave, we can know the position and type of the nucleus that constitutes this object, and then we can draw the structural image inside the object. MRI can clearly show the location, size and number of gallbladder polyps, so the clip used for gallbladder polypectomy is used.