MRIs also notice the strength of these radio signals. Where there is a lot of water, for example in muscle, the signal is strong, and where there is less water, for example in bone, the signal is weak. The different strengths of the radio waves enable the MRI to fill in the image with the proper shades of gray.An MRI is noisy because its magnetic field is created by running electrical current through a coiled wire—an electromagnet. When the current is switched on, there is an outward force all along the coil.And because the magnetic field is so strong, the force on the coil is very large.he frequency of the proton's radio wave is determined by its wobbling rate; so the protons in water emit a radio frequency of about 50 million cycles per second. The heart of an MRI is basically just a strong magnet and a radio transmitter and receiver, plus a lot of electronics to coordinate their operation.