Todoidal transducer with two large focal zones for increasing the coagulated volume

Spherical transducers used for HIFU therapy produce small single lesions that are ellipsoidal in shape. These lesions must be placed side by side systematically to treat the tumor with safety margins. This can be difficult to produce in moving organs like the liver. It has been shown that a toroidal transducer makes it possible to significantly increase the focal zone. A toroidal HIFU transducer geometry generates simultaneously a first ring-shaped focal zone and an overlap of ultrasound beams beyond this first focal plane. This particular focalization allows the creation of 7 cm³ ablated volume in 40 seconds. Although these large single lesions contributes to reduce treatment time, it is still needed to juxtapose 4 to 9 single lesions to treat one liver metastases of 2 cm in diameter with safety margins. In order to improve this treatment, a new toroidal geometry of transducer was developed. The difference is that the overlap of ultrasound beams is now between the transducer and the focal ring. The objective of this work is to combine this new geometry of transducer and the use of electronic focusing in order to create without any mechanical displacement of the device a coagulated volume sufficient for the destruction of a metastasis of 2 to 3 cm in diameter. In vitro tests were conducted to validate the treatment parameters determined using a software developed in the laboratory. The diameter and the depth of the lesion obtained were 40 and 38 mm respectively. In conclusion, these results indicate that the treatment of a metastasis up to 3 cm in diameter in the liver with safety margins is conceivable using this device and no need to juxtapose single lesions.