How is signal detected in an MRI system?

In an MRI system, signal detection occurs through the process of detecting induced magnetization that precesses in the X-Y plane. When a patient is placed in the magnetic field, the protons in the body align with the static magnetic field (B0). An RF pulse is then applied, which tips these protons out of alignment. After the pulse is turned off, the protons begin to relax back to their original alignment, and as they do, they generate a signal.

This signal occurs as the magnetization of the protons precesses around the direction of the magnetic field, which takes place in the X-Y plane (also known as the transverse plane). The precession creates oscillating magnetic fields that can be detected by the MRI system’s receiver coils. This is fundamentally how the information is gathered to construct the images.

The other options reflect aspects of MRI technology but do not describe the actual mechanism of signal detection. Measuring the static magnetic field relates to maintaining the magnetic environment but does not involve signal acquisition. Synchronizing the RF pulse with B0 pertains to the timing of the RF pulse application, which influences the effectiveness of excitation but is not the signal detection itself. Lastly, the use of light sensors in the magnet does not play