What role does the RF pulse play in MRI?

The role of the RF pulse in MRI is fundamental to the imaging process, specifically in the manipulation of the net magnetization vector (NMV). When an RF pulse is applied, it interacts with the magnetic moments of the hydrogen protons in the body. This interaction causes the NMV to flip away from its aligned position with the static magnetic field (B0) and enter a state of precession.

The RF pulse is typically at the resonant frequency of the hydrogen nuclei, which allows for efficient energy transfer. The flip angle determined by the duration and strength of the RF pulse is crucial because it influences the signal characteristics that are detected during the imaging process. When the NMV is flipped and precesses, it generates a measurable signal as it returns to equilibrium, which is collected to create images.

In contrast, the alignment of the NMV with B0 is primarily accomplished during the initial application of the static magnetic field, rather than through the RF pulse itself. The RF pulse does not create a static magnetic field; that function is fulfilled by the magnet itself. Additionally, while certain aspects of the MRI process may involve heat management to prevent overheating of equipment, the RF pulse is not explicitly responsible for dissipating heat in the coils.