title: The calculation of induced currents and absorbed power in a realistic, heterogeneous model of the lower leg for applied electric fields from 60 Hz to 30 MHz.
abstract: The ankle consists mainly of bone and tendon with little muscle. Currents will tend to preferentially flow through the high-conductivity muscle and this can result in very high local values of the specific energy-absorption rate (SAR). This paper presents a finite-difference method to calculate SAR in a realistic, heterogeneous model of the leg below the knee. The structure of the leg is defined by cross-sectional slices from an anatomical atlas which are converted into a 3D model of over 14,000 cells. Four types of tissue are included in the model--muscle, cortical bone, trabecular bone and connective tissue. Displacement as well as ionic currents are considered in a complex potential representation. The current to be injected into the limb model is obtained from the computed coupling of an applied vertical electric field with a 1.8 m tall, homogeneous phantom. Values of the maximum current density and SAR in the ankle from 60 Hz to 30 MHz are presented. Field limits based on a maximum SAR of 20 W kg-1 averaged over 1 g of tissue are given. Sensitivity analyses with regard to the range of tissue electric properties and the ankle cross-sectional area are performed.
authors.affiliation: National Radiological Protection Board, Chilton, Didcot, Oxfordshire, UK.
authors.forename: P J
authors.initials: PJ
authors.lastname: Dimbylow
mesh_terms: D000842:Ankle / Q000502:physiology*; D004553:Electric Conductivity; D004560:Electricity; D004594:Electrophysiology; D006801:Humans; D008954:Models, Biological