ABSTRACT
In order to obtain spatial resolution in NMR imaging, magnetic gradients are applied in various directions and pulsed at various time intervals. Various physical characteristics of time-varying magnetic fields are of importance in assessing their biological effects, including the fundamental field frequency, the maximum and average flux density, the presence of harmonic frequencies, and the waveform and polarity of the signal. Bone fracture repair is the result of a multiplicity of physical and chemical events. Bassett et al. found that fractured bones healed more rapidly when low frequency, low intensity pulsed electromagnetic fields were inductively coupled to canine fibulae in vivo. Muscle fibers can be affected by induced electric currents which give rise to muscle contraction. Effects on muscles, particularly the heart, could thus be hazardous if exposure to the rate of change and flux density is high. A biological effect of induced currents applied to the head through capacitive electrodes might be reversible nerve damage.
