The characterization of an ultrasound spherical phased array for the ablation of deep-seated tissue

In this paper we have developed and evaluated a spherical phased array ultrasound applicator for deep tissue ablation. The 90-element prototype array has a 21 cm aperture and an 18 cm radius of curvature with a 5 cm wide central hole. Annular distribution with circular elements is used to reduce the number of elements. The array is constructed with piezoelectric (PZT-8) circular planar elements that are 1.4 cm in diameter and 0.2-cm thick. With the water-muscle propagation path, the array offers an effective beam focusing depth of at least 8 cm in the muscle layer. Simulation results show that the array provides good beam focusing and steering capability over a cylindrical volume of approximately π × 1 × 1 × 4 cm3 (up to 10 mm off center over ranges from 15 cm to 19 cm). We also present its beam focusing and steering capability in deep tissue through a series of ex vivo experiments by measuring discoloration areas after sonications. The ex vivo experiments show a similar focal range as that found in the simulations.