5A-4 Thermal Ablation by Ultrasound: Increasing the Coagulated Volume

Here, we report that a new design of High Intensity Focused Ultrasound transducer can significantly enlarge the coagulated volume over short periods of time. Our long-term objective is to develop a device that can be used during a surgery, for eventual clinical use in conjunction with hepatic resection. Eight ultrasound emitters, divided into 256 elements, were created by sectioning a single toroid piezocomposite transducer. The focal zone was conical in shape and located 70 mm from the transducer; enabling the treatment of deep-seated tumors. A single thermal lesion was created when the eight emitters performed alternative and consecutive 5s ultrasound exposures. This paper presents in vivo evidence that the coagulated volume obtained from a 40 s total exposure in the liver was 7.0 plusmn 2.5 cm3 (1.5 - 20.0 cm³) with an average diameter of 19.5 plusmn 3.8 mm (10.0 - 29.0 mm). All lesions were visible with high contrast on sonograms. The correlation between the diameter of lesions observed on sonograms and during gross examination was 92%. This method also allowed the user to easily enlarge the coagulated volume by juxtaposing single lesions.