Which force does magnetic resonance imaging (MRI) use to align protons in the body?

Magnetic resonance imaging (MRI) primarily utilizes magnets to align protons within the body. In the human body, protons are abundant in water molecules, and when subjected to a strong magnetic field, the magnetic moments of these protons tend to align parallel to the direction of the field. This alignment is crucial for MRI technology, as it allows for the manipulation and measurement of the energy emitted by protons when they return to their original states after being disturbed by a radiofrequency pulse.

The strength and uniformity of the magnetic field play a significant role in the quality of the images produced, allowing for detailed visualization of soft tissues and organs. This reliance on magnetic forces for aligning protons is what distinguishes MRI from other imaging techniques that may utilize different physical principles such as electric fields or radiation.