Microwave Thermal Ablation Near Metallic Bronchial Prostheses: Numerical Models and Experiments

The microwave ablation processes are now extensively used for minimally-invasive interventions on the liver, kidney, lung and other organs using a laparoscopic approach. There is a wide scientific literature focused on the results and clinical expectations of these processes, describing in detail all aspects of the methodology with the aid of numerical simulations or trials on ex-vivo and in-vivo tissues. One aspect not yet explored concerns the electromagnetic (EM) interaction between a microwave antenna and nearby metallic implants that could interfere with the device's radiation mechanism. An example is the transbronchial thermal ablation of the lung tumor tissue that surrounds or invades a metallic bronchial prosthesis. The paper aims to fill this gap by presenting: the electromagnetic analysis of the applicator-prosthesis interaction; the transient thermal simulation; the comparison between the numerical results and those obtained from experiments on an ex-vivo phantom. Simulations firstly analyse the EM interaction of a microwave (MW) applicator with a 12 mm diameter tubular bronchial stent made of a metallic grid. The results show that when the applicator is located in close proximity of the stent or even internally to it, its operation is not substantially perturbed; in fact the reflection coefficient of the applicator is kept below -10 dB in any case. The thermal transient analysis shows that the heating profiles obtained by applying 50 W of input MW power for 60 seconds (3 kJ of energy) are compatible with the clinical needs of obtaining very localized thermal ablations without damaging the surrounding healthy tissues. The experiments performed using a phantom made of fresh ex vivo porcine loin confirm the EM and thermal simulation results.