What is the frequency called that is perfectly matched to the frequencies of a set of protons?

The term that describes the frequency perfectly matched to the frequencies of a set of protons is known as the resonant frequency. In the context of magnetic resonance imaging (MRI) and nuclear magnetic resonance (NMR), resonant frequency is crucial because it refers to the specific frequency at which protons in a magnetic field absorb energy and transition between different energy states.

When an external RF (radiofrequency) pulse matches this resonant frequency, it excites the protons, causing them to resonate and produce measurable signals. This concept is fundamental to the functioning of MRI, as it allows for the visualization of structures within the body based on the behavior of these protons in response to the applied magnetic field and RF pulse.

Understanding resonant frequency helps in optimizing MRI techniques, including selecting appropriate RF pulse sequences and adjusting the strength of the magnetic field, which directly influences the resonant frequencies of protons in different tissues. Other terms like precessional frequency, angular frequency, and magnetic field frequency relate to different aspects of MRI and magnetic resonance but do not specifically define the condition where excitation occurs at the exact frequency needed for resonance.