Microwave Antenna Design for Cardiovascular Applications: A Comparison Between a Balanced and Unbalanced Microwave Ablation Antenna

Abstract

Objective: To determine whether an irrigatedunbalanced antenna can create larger ablations than a conventional microwave antenna without overheating. Method: The microwave and ablation characteristics of a previously published multi-ring slot array (MRSA) ablation antenna, optimized for intravascular environments, were compared with a dielectric-insulated monopole antenna with no matching or balancing elements, creating the unbalanced monopole antenna. The two antennae were numerically simulated in an intravascular environment and tested inside a gel phantom for five repetitions for comparison. Each antenna assembly was $\text{900 mm}$ long, with a $\text{2.45 GHz}$ ablatingfrequency, with a microwave input power of $\text{60 W}$ for $\text{120 s}$ via a patient cable. Results: Gel experiments were consistent with numerical simulations, with the unbalanced monopole antenna possessing better microwave and ablative characteristics than the MRSA in a biological environment. Microwave input power to the device connector was attenuated from $\text{60 W}$ to $\text{40 W}$ due to patient cable losses. Removing matching elements improved input impedance at the test plane (Real, 52.20 $\pm$ $5.90 \;\Omega$ vs. 74.22 $\pm$ $43.25 \;\Omega$ , p = 0.05648; Imaginary, −23.50 $\pm$ $2.63 \;\Omega$ vs. 14.92 $\pm$ $51.10 \;\Omega$ , p = 0.1333) and the return loss (−12.79 $\pm$ $\text{0.45 dB}$ vs. 6.51 $\pm$ $\text{0.25 dB}$ , p = $2.521 \times 10^{-7}$ ). The unbalanced monopole antenna created wide (18.28 $\pm$ $\text{0.57 mm}$ vs. 13.38 $\pm$ $\text{0.60 mm}$ , p = $2.482 \times 10^{-5}$ ) and deeper (11.87 $\pm$ $\text{0.88 mm}$ vs. 9.41 $\pm$ $\text{0.98 mm}$ , p = $1.616 \times 10^{-2}$ ) ablation lesions than the MRSA. Clinical Impact: Removing elements from an MRSA created an unbalanced monopole antenna that creates larger ablation lesions with improved microwave characteristics.