BACKGROUND: Local cryoablation guided by CT or ultrasound has been widely applied in the treatment of hepatocellular carcinoma. However, it is still difficult to apply this technique in certain regions such as the diaphragm dome, the first hepatic hilum, and regions adjacent to the gallbladder. This study aimed to evaluate the safety and efficacy of using magnetic resonance imaging (MRI)-guided percutaneous cryoablation as well as the effect of using an open MRI system in guiding and monitoring the treatment of hepatocellular carcinoma in these regions. METHODS: Cryoablation, guided by an open 0.35T MRI scanner and with the assistance of an MRI-compatible optical navigation system, was performed on 32 patients with hepatocellular carcinoma at the diaphragm dome, the first hepatic hilum, and regions adjacent to the gallbladder. Each patient had one or two tumors. The total number of tumors treated was 36. The tumor diameters ranged from 2.5 to 10.0 cm (mean 4.7±1.8 cm). The cryosurgical system was MRI-compatible and equipped with cryoprobes 1.47 mm in outside diameter. Under the guidance of MRI in combination with the optical navigation system, the cryoprobes were introduced percutaneously into a tumor at the planned targeting points while critical organs or tissues were avoided. Each cryoablation procedure included two freezing-thawing cycles, and MRI images were acquired dynamically to monitor the ablation of the tumor from time to time during the operation. In order to investigate the therapeutic effects of a cryoablation procedure, AFP measurements and liver- enhanced MRI or CT-enhanced scans were performed at regular times.RESULTS: MRI and optical navigation system-guided cryoablation procedures were successfully performed on all 32 patients (36 tumor sites) and no serious complications occurred. The follow-up period ranged from 5 to 12 months. The 6- and 12-month overall survival rates were 96.8% and 90.6%, respectively. According to the diagnosis of liver- enhanced MRI scans, 10 patients (31.3%) had complete ablation, 18 (56.3%) partial ablation (>80%), 3 (9.4%) stable disease (>50% ablation), and 1 (3.1%) progressive disease (a new tumor site in the liver). The overall efficacy was 87.5%. CONCLUSIONS: MR-guided percutaneous cryoablation using optical navigation is a safe and effective minimally invasive procedure for the treatment of hepatocellular carcinoma at certain special regions, which is difficult to treat with other imaging guidance approaches. With its unique and superb imaging functions, MRI plays an important role in the display, guidance, and monitoring of the cryoablation procedure in treating hepatocellular carcinoma at these special regions. Equipped with an MRI-compatible optical navigation system, MRI-guided therapy makes the cryoablation procedure more precise and safe. BACKGROUND: Local cryoablation guided by CT or ultrasound has been greatly applied in the treatment of hepatocellular carcinoma. However, it is still difficult to apply this technique in certain regions such as the diaphragm dome, the first hepatic hilum, and regions adjacent to the gallbladder . This study aimed to evaluate the safety and efficacy of using magnetic resonance imaging (MRI) -guided percutaneous cryoablation as well as the effect of using an open MRI system in guiding and monitoring the treatment of hepatocellular carcinoma in these regions. METHODS: Cryoablation, guided by an open 0.35T MRI scanner and with the assistance of an MRI-compatible optical navigation system, was performed on 32 patients with hepatocellular carcinoma at the diaphragm dome, the first hepatic hilum, and regions adjacent to the gallbladder. Each patient had one or both tumors. The total number of tumors treated was 36. The tumor diameters ranged from 2.5 to 10.0 cm (mean 4.7 ± 1.8 cm). The cryosurgica l the system was MRI-compatible and equipped with cryoprobes 1.47 mm in outside diameter. Under the guidance of MRI in combination with the optical navigation system, the cryoprobes were introduced percutaneously into a tumor at the planned targeting points while critical organs or tissues were avoided. Each cryoablation procedure included two freezing-thawing cycles, and MRI images were acquired dynamically to monitor the ablation of the tumor from time to time during the operation. In order to investigate the therapeutic effects of a cryoablation procedure, AFP measurements and liver-enhanced MRI or CT-enhanced scans were performed at regular times .RESULTS: MRI and optical navigation system-guided cryoablation procedures were successfully performed on all 32 patients (36 tumor sites) and no serious issues occurred. The follow-up period ranged from 5 to 12 The 6- and 12-month overall survival rates were 96.8% and 90.6%, respectively. According to the diagnosis of liver-en hAnced MRI scans, 10 patients (31.3%) had complete ablation, 18 (56.3%) partial ablation (> 80%), 3 a new tumor site in the liver. The overall efficacy was 87.5%. CONCLUSIONS: MR-guided percutaneous cryoablation using optical navigation is a safe and effective minimally invasive procedure for the treatment of hepatocellular carcinoma in certain special regions, which is difficult to treat with its unique and superb imaging functions, MRI plays an important role in the display, guidance, and monitoring of the cryoablation procedure in treating hepatocellular carcinoma at these special regions. Equipped with an MRI-compatible optical navigation system, MRI-guided therapy makes the cryoablation procedure more precise and safe.