Which statement about RF pulses in MRI is true?

• A. They heat tissues to enhance signal
• B. They deposit energy to excite hydrogen nuclei
• C. They produce ionizing radiation
• D. They measure electrical potential in nerves

Answer: (B)

RF pulses in MRI deliver energy at the Larmor frequency to flip the net magnetization of hydrogen protons. This energy transfer excites the spins from a lower-energy state toward a higher-energy state, producing transverse magnetization that the receiver coils detect as the MR signal. This process is non-ionizing—MRI does not produce ionizing radiation. Any heating of tissue is incidental and managed as a safety concern (SAR), not the mechanism by which signals are generated. The idea of heating tissues to boost signal isn’t how MRI works, and measuring electrical potentials in nerves is outside MRI’s function.