A new design method for extracorporeal high-intensity focused ultrasound annular array

Considering the damage to normal tissues during the high-intensity focused ultrasound ablation of the tumor is important. The purpose of this work was to design the annular array under the considerations of preventing the skin burn and damage to normal tissues behind the tumor target. Based on the Rayleigh-Summerfield pressure integral, the numerical acoustic intensity field of a spherical bowl annular array with a diameter of 12 cm and a radius of curvature of 12 cm was obtained by using the MATLAB software. An absorbed intensity ratio of the normal tissue to target was proposed to define the allowable grating lobe for determining the focusing range. The analytic results showed that for the treatment of uterine fibroids, the focusing range increased as the number of the element increased from 9 to 22 and the 14-ring array at the operating frequency of 0.8, 0.9 or 1.0 MHz had a focusing range larger than 5.5 cm when the range was only 4 cm at 1.2 MHz. For the treatment of medullary carcinoma and scirrhous carcinoma in breast, the focusing range of the 0.9-MHz, 14-ring annular array was 8-12 and 8-14 cm, respectively.