The feasibility of developing a 64-elements cylindrical phased array for intraductal thermal ablation

In this study, the feasibility of a cylindrical phased array (10-mm O.D.) has been evaluated for intraductal thermal ablation. The principle of this applicator is to generate electronically rotating plane waves. A plane propagation is generated by exciting eight successive elements with appropriate excitation delay times. The shot direction was changed by exciting a different set of eight elements. In the future, the final applicator will be composed of 64 elements arranged all over the periphery of the cylinder. This study present a cylindrical prototype (10.6-mm O.D.) which is composed of 16 transducers working at 4.55 MHz and arranged on a quarter of the cylinder. The dimension of each transducer is 15 /spl times/ 0.45 mm/sup 2/ and the distance between two consecutive elements is 70-/spl mu/m. The mechanical strength of the device was reinforced by mounting a rigid damper structure on the rear face of the active part. Heat dissipation is favoured by the thermal properties of the backing. The active part is covered by a latex balloon and cooled internally and externally by a continuous flow of degassed water. This study showed that the ultrasound beam generated by eight elements excited with appropriated delay times is plane. Ex vivo experiments were carried out on pig liver and permit to generated three reproducible well-defined lesions up to 14-mm, separated from each other by a 23/spl deg/ angle.