MR imaging involves the use of a strong magnetic field. This magnetic field pulls on many metal objects. Thus, for safety reasons, the MR staff must determine if you unknowingly have metal in your body. Some patients may have small pieces of metal in their eyes, a metal implant, a prosthetic device that may contain metal, surgical clips or other implanted objects that may be susceptible to the magnetic field. After asking you a few questions, x-ray imaging may be necessary to screen for metallic items prior to the MR examination.
If they don't ask you, you ask them if there is reason to do an x-ray check before the MRI. Once you are cleared for MRI, there is no reason to be scared anymore.