Magnetic resonance imaging: calculation of rates of energy absorption by a human-torso model.

The three-dimensional impedance method was used to estimate specific absorption rate (SAR) in a human-torso model during exposure to the time-varying and static magnetic fields used in magnetic resonance imaging (MRI). Analytical data for discrete tissues as well as the entire torso are presented. Generalized equations were derived that enable calculation of whole-torso SAR over a broad range of conditions. In addition, the impedance method can generate data about internal distributions of SAR, which are needed to predict critical organs that might undergo excessive elevations of temperature. Fair to good agreement was found between impedance-method SAR and those predicted by simple phenomenological models.