A Directional Interstitial Antenna for Microwave Tissue Ablation: Theoretical and Experimental Investigation

Abstract

Microwave ablation (MWA) is a minimally invasive thermal therapy modality increasingly employed for the treatment of tumors and benign disease. For successful treatment, complete thermal coverage of the tumor and margin of surrounding healthy tissue must be achieved. Currently available interstitial antennas for MWA have cylindrically symmetric radiation patterns. Thus, when treating targets in proximity to critical structures, caution must be taken to prevent unintended thermal damage. A novel coaxial antenna design for MWA with an asymmetrical cylindrical heating pattern is presented in this paper. This radiation pattern is achieved by employing a hemicylindrical reflector positioned at a critical distance from a conventional coaxial monopole antenna. Finite-element method simulations were employed to optimize the geometric dimensions of the antenna with the objective of minimizing the antenna reflection coefficient at the 2.45-GHz operating frequency, and maximizing volume of the ablation zone. Prototype antennas were fabricated and experimentally evaluated. Simulations indicated an optimal S11 of -32 dB at 2.45 GHz in close agreement with experimental measurements of -29 dB. Ex vivo experiments were performed to validate simulations and observe effects to the antennas' heating pattern with the varying input power and geometry of the reflector. Ablation zones up to 20 mm radially were observed in the forward direction, with minimal heating (less than 4 mm) behind the reflector.

Physical modeling of microwave ablation zone clinical margin variance

“…43 Nevertheless, the parameterization described in Eq. (5) (perfusion as a step function of temperature, with a 60 • C threshold for the transition) has been used by several groups to simulate perfusion during MWA, 44,45…”

Analysis of microwave ablation antenna optimization techniques

“…As many liver, lung, and kidney tumors are spherical, elongated ablation zones can cause unnecessary damage in adjacent healthy tissues, and complicate the planning and execution of ablation procedures . For this reason, a number of microwave ablation antenna developments have recently focused on controlling the shape of the ablation zone …”

“…16 For this reason, a number of microwave ablation antenna developments have recently focused on controlling the shape of the ablation zone. [17][18][19][20][21] The antenna structure dictates the shape of heating produced by a microwave ablation antenna and, by extension, the shape of the resulting ablation zone. Many variants of monopole, dipole, triaxial, choke, slot, and floating sleeve antennas have been described, most of which have been designed to minimize the antenna reflection coefficient (CÞ or minimize backward heating along the antenna shaft.…”

Computational modeling of 915 MHz microwave ablation: Comparative assessment of temperature‐dependent tissue dielectric models

“…Mathematical models of the processes that occur during MWA have been employed during the design and optimization of devices for MWA. [12][13][14][15][16] These models use numerical techniques to solve the partial differential equations which govern electromagnetic propagation, power deposition, and bioheat transfer to estimate the treatment zone following a defined microwave exposure. 17,18 Recently, there has been renewed interest in the development of modeling techniques for predictive planning of ablation treatments.…”