Dual applicator thermal ablation at 2.45 GHz: a numerical comparison and experiments on synchronous versus asynchronous and switched-mode feeding

Abstract

Purpose: This paper compares the results obtained with numerical simulations and ex vivo experiments involving a dual applicator microwave thermal ablation system operating at a 2.45 GHz frequency, both in synchronous and asynchronous modes. Our purpose was to demonstrate that at this frequency an asynchronous or switched-mode system performs essentially as well as the synchronous one, in spite of the prevailing belief that coherence would assure better thermal (TH) synergy. Numerical analysis: The calculations of temperature fields were based on the Pennes bioheat equation, taking into account the effects of blood perfusion by means of a full-wave 3D simulator that allows numerical electromagnetic (EM) and TH analyses. Materials and methods: Experiments were done using a 100 W microwave (MW) power generator and a fast switched-mode sequential ‘active’ power splitter. By adding a further passive power splitter we arranged a test bed for an accurate experimental comparison of synchronous versus switched-mode TH ablations. Results: The experimental ablation zones produced by a dual applicator array on ex vivo swine tissue corresponded well with the simulated ones, confirming that the simplifications assumed in the full-wave analysis were compatible with the aim of our work. Conclusions: Numerical simulations and experiments show that at a 2.45 GHz industrial, scientific and medical (ISM) frequency, synchronous, asynchronous and switched-mode multi-probe systems are substantially equivalent in terms of ablative performance. Moreover, the switched-mode solution offers simpler operation along with lesser sensitivity to the placement of applicators in the tissue.