Figure 1.

A subject is being prepared for a magnetic resonance examination. The subject lies in front of the magnetic resonance instrument on a movable bed. His head is encircled by an electronic device, which serves both to transmit low-energy radio frequency (RF) waves to hydrogen or phosphorus nuclei in the head and to receive the energy emitted from these nuclei. For the examination, the bed on which the subject lies is moved into the tunnel so that the magnet completely surrounds the subject’s head. The magnetic field affects all nuclei in the body so that they will absorb and emit RF energy.