Читать книгу Essentials of MRI Safety - Donald W. McRobbie - Страница 56

Maxwell’s fourth equation, or Ampere’s Law, tells us that magnetic fields can be generated both by electric currents and by time‐varying electric fields, allowing for the existence of electro‐magnetic waves – everything in the electromagnetic spectrum: gamma rays, X‐rays, ultraviolet, visible light, infrared, microwaves, and radiowaves (Figure 2.4). It has consequences for the more “wave‐like” behavior of the B₁ excitation field at higher frequencies. It also results in field exposures from the gradients being higher than intuitively anticipated.

Figure 2.4 Electromagnetic wave: the magnetic and electric fields are orthogonal to each other and to the direction of propagation.