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In this study an ultrasound device that uses a toroidal HIFU transducer guided by ultrasound imaging was evaluated clinically for the treatment of liver metastases during an open procedure. Our long-term objective is to associate HIFU with hepatic resection. Here we report the first clinical results obtained on six patients with liver metastases and scheduled for elective surgical resection of their tumors. The principal objective was to validate the effectiveness, tolerance and safety of the HIFU parameters defined during preclinical studies. In addition, the response to HIFU was assessed using the ultrasound imaging probe integrated in the HIFU device and compared directly with histological analysis. It was planned to include 6 patients in this Phase I trial. A 85% ablation rate success was required to continue the study (Phase II). Secondary endpoint was preciseness of ultrasound imaging to visualize HIFU ablations. The transducer has a toroidal shape 70 mm in diameter and is divided into 8 radial ultrasound emitters of 4.16 cm2 each. The radius of curvature is 70 mm to enable treatment of the deepest regions of the liver and each of the 8 emitters is divided into 32 individual transducers operating at 3 MHz. A 7.5 MHz ultrasound imaging probe was placed in the centre of the device to guide the treatment. The imaging plane was aligned with the HIFU focal zone. Two single thermal ablations were created in each patient after laparotomy and just before the planned liver resection. Twelve HIFU lesions were performed. All were visible on ultrasound images. Consistent with our previous experience, the demarcation between ablated and non-ablated tissue was apparent in ultrasound images as a hypoechoic boundary and a large central hyperechoic zone. The dimensions measured on sonograms were correlated (r=0.92) with dimensions measured during histological analysis. The average coagulated volume obtained from a 40 s total exposure in the liver was 5.6 ± - .6 cm3 (1.9 - 11.4) with an average diameter of 21.6 ± 4.5 mm (12.0 - 28.0) and an average depth of 28.4 ± 6.3 mm (20.0 - 43.0). The patients have tolerated the treatment well. There was no hemodynamics and respiratory changes during the HIFU procedure. No HIFU-related complications occurred during surgery and 30 days postoperatively. The average hepatic volume accessible using this device was on average 88%. This HIFU treatment using a toroidal transducer is feasible, safe and well tolerated. The HIFU approach presented in this study is characterized by the brevity of the treatment (40 seconds for one single ablation of 5-6 cm3). This device is capable of achieving selective ablation of predefined liver regions. Ultrasound imaging evidence of complete ablation of the target region can be taken to infer histological success.