What occurs to hydrogen protons as a result of resonance?

Resonance in the context of MRI refers to the interaction between the hydrogen protons in a magnetic field and a specific frequency of electromagnetic radiation, typically from an RF (radio frequency) pulse. When the right frequency is applied during the MRI process, the hydrogen protons absorb energy and transition to a higher energy state.

As a result of this energy absorption, the magnetic moments of these protons, which are essentially tiny magnetic fields that align with the external magnetic field, start to synchronize — or move into phase with each other. This means that they rotate in concert rather than randomly, which enhances the overall signal produced when the RF pulse is turned off and the protons return to their lower energy state. The synchronization of the magnetic moments allows for a stronger and more coherent signal that can be detected and used to create images.

The other options do not accurately reflect the effects of resonance on hydrogen protons: while magnetic moments can change, the key feature of resonance is this alignment or phasing together of the magnetic moments, which is vital for the imaging process in MRI.