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Usefulness of the Extracted-Overlay Function in CT/MR-Ultrasonography Fusion Imaging for Radiofrequency Ablation of Hepatocellular Carcinoma

Objectives: We developed a novel technique of the extracted-overlay function in CT/MR-ultrasonography (US) fusion imaging for radiofrequency ablation (RFA), in which only a tumor extracted from CT/MR images with a virtual ablative margin of arbitrary thickness is overlaid on US. The usefulness of this function is investigated in this preliminary report. Methods: The volume data of the extracted tumor with a virtual ablative margin were created on an image-processing workstation, and transported into a US unit equipped with a CT/MR-US fusion imaging system. After the positional registration of US and transported images, the extracted tumor with an ablative margin could be overlaid on US. In RFA, using this function, an electrode was inserted targeting the overlaid tumor with an ablative safety margin of 5 mm on US, and the treatment effect was evaluated by dynamic CT. Treatment results of 23 consecutive hepatocellular carcinomas (HCCs) that underwent RFA using this function were retrospectively analyzed. Results: Complete tumor ablation was achieved in 22 (95.7%) and 1 (4.3%) HCCs in 1 and 2 treatment sessions, respectively. Conclusions: Due to the visualization of an extracted tumor with an ablative safety margin on a US image, even during and after ablation, this function is useful for treatment planning and guidance of RFA.