On the Use of Cloverleaf Coils to Induce Therapeutic Heating in Tissues

Abstract

Current-carrying multi-leaf planar coils fed by radio-frequency generators are frequently employed to induce eddy currents and therapeutic ohmic heating in biological tissues. Previous studies have shown that adjusting the current direction in the neighboring leaves of a two- or four-leaf structure makes it possible to enhance the focality and selectivity of the diathermic treatment, but the electric field-strength induced in the issue, as well as the associated specific absorption rate (SAR), are far less than those achievable with a simple round coil of the same size. The aim of this paper is to prove that, for a fixed power supply, replacing a round coil with a four times larger four-leaf one makes it possible to significantly increase the deposited peak SAR and, at the same time, assuring a fairly good field localization. What is more, it is found that closing together four round units allows to obtain the same peak SAR provided by each unit considered alone with a reduction of the energy consumption by at least 30%. This demonstrates that the cloverleaf applicator can be successfully employed for heating deep afflicted tissue areas.