Clinical value of CT/MR-US fusion imaging for radiofrequency ablation of hepatic nodules.

OBJECTIVE The aim of this study was to determine the registration error of an ultrasound (US) fusion imaging system during an ex vivo study and its clinical value for percutaneous radiofrequency ablation (pRFA) during an in vivo study. MATERIALS AND METHODS An ex vivo study was performed using 4 bovine livers and 66 sonographically invisible lead pellets. Real-time CT-US fusion imaging was applied to assist the targeting of pellets with needles in each liver; the 4 sessions were performed by either an experienced radiologist (R1, 3 sessions) or an inexperienced resident (R2, 1 session). The distance between the pellet target and needle was measured. An in vivo study was retrospectively performed with 51 nodules (42 HCCs and 9 metastases; mean diameter, 16 mm) of 37 patients. Fusion imaging was used to create a sufficient safety margin (>5 mm) during pRFA in 24 nodules (group 1), accurately target 21 nodules obscured in the US images (group 2) and precisely identify 6 nodules surrounded by similar looking nodules (group 3). Image fusion was achieved using MR and CT images in 16 and 21 patients, respectively. The reablation rate, 1-year local recurrence rate and complications were assessed. RESULTS In the ex vivo study, the mean target-needle distances were 2.7 mm±1.9 mm (R1) and 3.1±3.3 mm (R2) (p>0.05). In the in vivo study, the reablation rates in groups 1-3 were 13%, 19% and 0%, respectively. At 1 year, the local recurrence rate was 11.8% (6/51). In our assessment of complications, one bile duct injury was observed. CONCLUSION US fusion imaging system has an acceptable registration error and can be an efficacious tool for overcoming the major limitations of US-guided pRFA.