Microwave Tissue Ablation: Biophysics, Technology, and Applications

Abstract

Microwave ablation is an emerging treatment option for many cancers, cardiac arrhythmias and other medical conditions. During treatment, microwaves are applied directly to tissues to produce rapid temperature elevations sufficient to produce immediate coagulative necrosis. The engineering design criteria for each application differ, with individual consideration for factors such as desired ablation zone size, treatment duration, and procedural invasiveness. Recent technological developments in applicator cooling, power control and system optimization for specific applications promise to increase the utilization of microwave ablation in the future. This article will review the basic biophysics of microwave tissue heating, provide an overview of the design and operation of current equipment, and outline areas for future research for microwave ablation.

Percutaneous Tumor Ablation Tools: Microwave, Radiofrequency, or Cryoablation—What Should You Use and Why?

“…Microwave energy produces faster and hotter ablation zones than does RF current. (24,25). Many antennae produce an elongated ablation zone (as long as 6 cm) that may increase the risk for burns to the body wall and other structures, so newer designs aim for more rounded and forward-weighted heating that is amenable to treating smaller tumors (Fig 3) (26,27).…”

“…Overall, the potential advantages of microwave over RF ablation include faster ablations (typically 2-8 minutes with high-powered systems), higher temperatures without the limitations related to electric impedance, less sensitivity to tissue type with more consistent results (which may be beneficial in treating some tumors that are resistant to treatment with RF, such as sarcomas and hemangiopericytomas), a relative insensitivity to "heat sinks" compared with RF, and the ability to create much larger ablation zones if needed (ablation zones as long as 8 cm have been achieved without applicator repositioning) (22,25,33,39,40). The continued challenges of microwave ablation are as follows: (a) Because microwave ablation is relatively new, clinical data and experience are minimal; (b) a learning curve is associated with using microwave ablation safely because of the potentially larger ablation zones compared with RF ablation; and (c) the clinical systems are heterogeneous in terms of antenna design, wavelength, frequency, power, and cooling, which leads to different performance characteristics and confusion regarding the interpretation of clinical results and the predictability of results between systems from different manufacturers.…”

Microwave ablation of renal tumors: state of the art and development trends

“…Microwave energy is distinct from other energies for thermal therapy in a number of ways. The most important feature is that microwaves propagate through all types of tissues and non-metallic materials including water vapor, dehydrated, charred and desiccated tissues created during the ablative process [16]. Dielectric properties of biological tissues, as permittivity and conductivity, allow the transmission and absorption of the electromagnetic energy.…”

Non-Invasive in vivo Loss Tangent Imaging: Thermal Sensitivity Estimation at the Larmor Frequency

“…Hyperthermic ablation is a widely used therapeutic tool for cardiac arrhythmias and cancers of the liver, lung, kidney, and bone (6)(7)(8)(9). RF and microwave ablation utilize the thermal sensitivity differences between tumor and normal tissue, which are primarily determined by the electrical properties (i.e., permittivity and conductivity).…”