Nearly spherical ablation zone with minimally invasive microwave ablation: Analysis and experimental characterization of a tapered-tip symmetric dipole antenna

Abstract

Microwave ablation (MWA) is a widely used technology for tumors treatments. The reported asymmetric dipole antennas were not ideal in ablation zone. Although some methods were proposed to improve the ablation performance, other important characteristics were still not satisfactory enough, such as poor impedance matching, increased invasion diameter, or additional insertion devices. In this paper, a minimally invasive antenna with a nearly spherical ablation zone for microwave ablation is presented by a tapered-tip symmetric dipole structure with a sleeve. The tapered-tip symmetric dipole, fed by a coaxial line, are composed of a tapered-tip cylinder arm and a hollow cylinder arm. Both of the lengths of the two arms are approximately equal to a quarter of wavelength. The proposed antenna provides good matching at resonating frequency without any extra impedance matching network. Moreover, the tapered-tip structure enables the proposed MWA antenna be inserted into the tissues directly without an additional needle-shape catheter. Furthermore, the sleeve structure, electrically isolated from the dipole and the coaxial feed line, is employed to prevent the current and thermal from flowing along the feed line. A minimally invasive antenna with a diameter of only 1.9 mm working at 2.45 GHz is designed and fabricated for verification, in which different input power and heating time are taken into account. The temperature evolution in four locations of the liver tissue is recorded by using a 4-channel temperature monitoring system. The comparison with a commercial MWA antenna of the same diameter is also included. Simulation and experiment results show that the proposed MWA antenna create nearly spherical ablation zones. The proposed MWA antenna would be promising for minimally invasive medical applications.