 The resonant frequency, energy of the radiation absorbed, and the intensity of the signal are proportional to the strength of the magnetic field.For example, in a 21 Tesla magnetic field, hydrogen atoms (commonly referred to as protons) resonate at 900 MHz.It is common to refer to a 21 T magnet as a 900 MHz magnet since hydrogen is the most common nucleus detected, however different nuclei will resonate at different frequencies at this field strength in proportion to their nuclear magnetic moments.