Limits on focused power deposition for electromagnetic hyperthermia

Abstract

Computations of SAR distributions in homogeneous regions and in multilayered concentric cylindrical models of the torso are presented to illustrate how an increase in the localization of the fields and/or a decrease in attentuation of the fields in one dimension is accompanied by a decrease in the localization and/or an increase in the attenuation in the other dimensions. Sharp gradients that may exist in the EM intensity patterns at the surface of a body become less pronounced further into the body because the wave components having higher spatial frequencies are most rapidly attenuated.

4. Summary

By considering the possible EM fields, independent of particular sources, it is possible to obtain alternative perspectives on antenna design for hyperthermia, and to better understand the fundamental limitations on the localization of fields and power deposition in source free regions. In this paper computations of EM fields in homogeneous regions and in multilayered concentric cylinders are used to illustrate the following points. As the fields are more confined in one direction an increase in the attenuation and/or decrease in localization occurs in other directions. Also, as the fields propagate into the body, those waves having higher spatial frequencies are attenuated more rapidly than waves having lower spatial frequencies. Consequently, in applicator design it is desirable to avoid fields having sharp gradients near the surface because such fields have increased attentuation in other directions and cause most of the power to be concentrated at the outer layers (fat, skin). Also, in numerically modelling applicator. It is desirable to avoid gradients of the fields that are more rapid than those actually generated by the devices that are modelled.

Key Words:

• Hyperthennia
• electromagnetic fields
• focused power
• cylindrical models
• non-invasive