A new coaxial antenna for microwave ablation therapies is proposed. The antenna design includes a miniaturized choke and an arrowhead cap to facilitate antenna insertion into the tissues. Antenna matching and the shape and dimension of the area of ablated tissue (thermal lesion) obtained in ex vivo conditions are evaluated both numerically and experimentally, finding an optimal agreement between numerical and experimental data. Results show that the antenna is well matched, and that it is able to produce a thermal lesion with an average length of 6.5 cm and an average diameter of 4.5 cm in ex vivo bovine liver when irradiates 60 W for 10 min. Finally, the dependence of antenna performances on possible changes in the antenna's structure is investigated, finding an optimal stability with respect to manufacturing tolerances and highlighting the fundamental role played by the antenna's choke.

In addition to an asymmetric substantial shrinkage of the ablated tissue volume, an initial expansion phenomenon occurs during MW ablation. Thus, complex modifications of the tissue close to a radiating antenna will likely need to be taken into account for future methods of real-time ablation monitoring.

Aims:To compare the killing efficacy and the effects exerted by microwaves and conventional heating on structural and molecular components of Bacillus subtilis spores. Methods and Results: A microwave waveguide applicator was developed to generate a uniform and measurable distribution of the microwave electric-field amplitude. The applicator enabled the killing efficacy exerted by microwaves on B. subtilis spores to be evaluated in comparison with conventional heating at the same temperature value. The two treatments produced a similar kinetics of spore survival, while remarkably different effects on spore structures were seen. The cortex layer of the spores subjected to conductive heating was 10 times wider than that of the untreated spores; in contrast, the cortex of irradiated spores did not change. In addition, the heated spores were found to release appreciable amounts of dipicolinic acid (DPA) upon treatment, while extracellular DPA was completely undetectable in supernatants of the irradiated spores. These observations suggest that microwave radiation may promote the formation of stable complexes between DPA and other spore components (i.e. calcium ions); thus, making any release of DPA from irradiated spores undetectable. Indeed, while a decrease in measurable DPA concentrations was not produced by microwave radiation on pure DPA solutions, a significant lowering in DPA concentration was detected when this molecule was exposed to microwaves in the presence of either calcium ions or spore suspensions. Conclusions: Microwaves are as effective as conductive heating in killing B. subtilis spores, but the microwave E-field induces changes in the structural and/or molecular components of spores that differ from those attributable only to heat. Significance and Impact of the Study: This study provides information on the effect of microwaves on B. subtilis spore components.

For the selected MW ablation device, ex vivo data on bovine liver was more predictive of the actual clinical performance on liver malignancies than an in vivo porcine model. Equivalent MW treatments yielded a significantly different response for HCC and metastases at higher deposited energy, suggesting that outcomes are not only device-specific but must also be characterised on a tissue-by-tissue basis.

The proposed model allows the prediction of the shrinkage of liver tissues upon microwave ablation given the extension of the carbonised and coagulated zones. This may be useful in helping to predict whether sufficient tissue volume is ablated in clinical practice.