ABSTRACT
In both NMR imaging and NMR spectroscopy, oscillating magnetic fields in the Rf range of 1 to 70 MHz are used for the excitation of the nuclear spin. Thus, in clinical NMR examinations the human body is exposed to intense pulses of Rf fields. The fundamental physical representation of electromagnetic fields is given by the well-known Maxwell equations. These equations also describe the interaction of electromagnetic fields with matter. The specific absorption rate “SAR” corresponds to the rate of specific absorbed electromagnetic power in tissue. The most significant result of such work is the demonstration that there is a characteristic resonant frequency for each subject at which plane-wave exposure will result in a significantly higher level of total absorbed energy than that which occurs at other frequencies. The majority of NMR antennas or probes that generate a magnetic field perpendicular to their geometric axis have two symmetrical surfaces, each composed of an appropriate number of plates and conductors.
