**4. Microwave ablation**

#### **4.1. Overview**

Microwave ablation (MWA) is a hyperthermic ablative technique that is similar in many ways to RFA. MWA was introduced in the 1980s and 1990s and showed potential, but suffered from problems controlling the emitted field. There was a relatively high complication rate with MWA, thus RFA became the dominant ablative technique [80, 81]. While the early MWA systems had higher complication rates, since then newer designs have significantly decreased the complication rates. Recent retrospective and prospective studies have proven the efficacy and safety of MWA for not only HCC lesions but also other hepatic lesions [82–85].

From a procedural point of view, MWA and RFA are performed similarly under image guidance. The operator guides a MWA antenna toward the targeted lesion using their favored imaging modality (**Figure 2**). Unlike RFA, MWA does not require the use of grounding pads to establish an electrical circuit. MWA uses dielectric hysteresis to produce heat. An oscillating field, typically 900–2500 MHZ, is applied forcing polar molecules (such as water) to continuously move and realign in the field creating kinetic energy and ultimately raising the temperature of the tissue. Microwaves are able to propagate through a variety of tissues, even those with low electrical conductivity, high impedance, or low thermal conductivity. This makes MWA more versatile [86].
