MWA with CEUS guidance has demonstrated the potential to dramatically broaden the scope of US diagnosis of hepatic tumors [17, 18] and decrease the number of sessions required for ablation of HCC in difficult cases [19]. Masuzaki et al. [20] reported in a large-scale study that the detectability of tumor nodules was 83.5 % in conventional US and 93.2 % in contrast-enhanced US (P = 0.04). In a randomized controlled study [21], the number of treatment sessions was significantly lower in the contrast harmonic US group (mean, 1.1 ± 0.2 vs. 1.4 ± 0.6, P = 0.037). Treatment analysis showed that the complete ablation rate after a single treatment session was significantly higher in the CEUS group than in the B-mode US group (94.7 % vs. 65.0 %, P = 0.043).

Our previous studies evaluated the efficiency and feasibility of CEUS-guided MWA for hepatocellular carcinoma inconspicuous on conventional US [22]. In that study, we performed MWA under CEUS guidance for 109 patients with 109 HCC nodules inconspicuous on conventional US. We found that CEUS-guided microwave ablation is an efficient and feasible treatment method for patients with HCC inconspicuous on conventional US.

Before its application in MWA, CEUS has been used for a long time in guiding RFA. Other studies reveal that CEUS does allow a reliable and immediate assessment of therapeutic efficacy of percutaneous RFA of malignant liver lesions [23]. Meanwhile, pretreatment evaluation with CEUS is effective for percutaneous RFA of HCCs with poor conspicuity on conventional US [24].

Besides CEUS, CT or MRI guidance can also be used for the guidance of MWA. Compared with other techniques, CEUS guidance has many advantages: (a) US equipment is smaller, which makes it more convenient to use in clinical work. (b) CEUS guidance is real time. (c) CEUS is easy to operate and allows scanning the body from different positions and angles. (d) CEUS emits no ionizing radiation. (e) CEUS is less expensive than other guiding techniques. (f) Few allergies happen during CEUS guidance. (g) The therapeutic effect can be evaluated in real time under CEUS guidance (Table 29.1).

Compared to CEUS, CT and MRI have been used for a long time in guiding MWA (Table 29.2). CT has high spatial resolution, good contrast, wide field of view, good reproducibility, and applicability to bony and air-filled structures. The use of a CT-guided method can be expected to reduce the rate of local tumor progression associated with percutaneous ablation therapy. We reviewed several well-performed studies. Laspas et al. [31] reported that the ablation success rate was 87.3 % (281/322 HCC nodules), and the survival rates at 1 year, 3 years, and 5 years were 94.8, 73.1, and 51.1 %, respectively. Despite the advantages of CT, there are several limitations such as the increased time that is necessary for the procedure and exposure of the patient to ionizing radiation.