The Performance of Higher Frequency Microwave Ablation in the Presence of Perfusion

Objective: In this paper, we investigate the impact of perfusion on the performance of microwave ablation across a large frequency range. Methods: We designed multiple microwave ablation antennas to operate in liver tissue at discrete frequencies in the range 1.9-18 GHz. We performed electromagnetic simulations to calculate microwave power absorption patterns. Five-minute, 25 W ablation experiments were performed at each frequency in perfused and nonperfused ex vivo porcine livers, and thermal lesion dimensions were measured. Results: The volume of greatest microwave power absorption shrinks by two orders of magnitude as the frequency is increased from 1.9 to 18 GHz. Mean thermal lesion volumes are consistent across the frequency range for a given perfusion state and are about three times smaller under active perfusion. Typical thermal lesion diameters (perpendicular to the antenna axis) were 24 mm and 16 mm for nonperfused and perfused ablations, respectively. No significant differences in axial ratio were observed among different frequency groups in active-perfusion experiments. Conclusion: Higher-frequency microwave ablation produces thermal lesions with volumes comparable to those achieved at lower frequencies, even in strongly perfused environments. Significance: Higher-frequency microwave ablation is appealing because it allows for more flexibility in antenna design. A critical issue concerning the feasibility of higher frequency microwave ablation, considering its strong dependence on heat diffusion to grow thermal lesions, is its performance in strongly perfused environments. This paper shows that higher frequency microwave ablation achieves thermal lesions comparable to those from microwave ablation performed at conventional frequencies in both non- and strongly perfused environments.