Abstract: To evaluate the feasibility, accuracy and efficacy of the real time virtual sonography navigation and planning system in radio frequency ablation (RFA) of hepatic colorectal metastases. Methods: Seventeen hepatic colorectal metastases lesions in 12 patients diagnosed pathologically or clinically in Peking University Third Hospital from Oct. 2011 to Apr. 2013 were enrolled, and all the lesions were diagnosed by CT/MRI but invisible in B-mode ultrasound. The patients included 9 males and 3 females, who were 45-82 years old, with an average age of (64.6±19.2) years. Before RFA, the puncture ablation plan of each lesion was made in the planning system, and during RFA the lesion and the 5 mm ablative margin around were ablated according to the puncture ablation plan. After the image fusion between the ultrasound and CT/MRI, the navigation system could decide the location and boundary of the hepatic colorectal metastases in the ultrasound image. Navigation assisted contrast-enhanced ultrasound (CEUS) was employed right after ablation to decide whether the area of the ablative zone had covered the whole tumor. Additional puncture was applied if the ablative zone had not completely covered the tumor. All the patients received CT/MRI one month after ablation to decide whether the carcinoma had been completely ablated. Results: The image fusion was successfully applied in all the 17 hepatic colorectal metastases, and on average, 12 min (8-21 min) was spent in the image fusion. One tumor (1/17, 14.3%) received extra one puncture after navigation assisted CEUS. No severe complications and death occurred in all the 12 patients. Complete ablation of the 17 lesions were observed through CT or MRI scan one month after RFA, showing that all the 17 lesions had been completely ablated. Conclusion: The real time virtual sonography navigation system had high detection rate for invisible focal liver lesions in B-mode ultrasound. Navigation assisted CEUS could decide whether the area of the ablative zone had covered the whole tumor. Ultrasound CT or MRI navigation and planning system is safe, feasible and accurate in assisting ablation of hepatic colorectal metastases lesions with satisfactory clinical efficacy.

Key words: Colorectal neoplasms, Neoplasm metastasis, Catheter ablation, Liver neoplasms, Realtime virtual sonography