Effects of Frequency and Number of Elements on Acoustic Fields Generated by a Spherical Ultrasound Phased Array Hyperthermia Applicator

Understanding the effect of frequency and number of elements on suppressing the grating lobes is of importance for the design of the phased array. In this study, acoustic field simulation model of a spherical phased array for focused ultrasound surgery is described. The influence on performance of frequency (0.8 to 1.5 MHz) and number of circular elements (45 to 90) in the array is investigated for elements distributed quasi-randomly on a spherical shell (radius of curvature, 180 mm). The grating lobes and depth of focal region in the simulated acoustic fields are relatively sensitive to the increase of frequency. For a spherical phased array, decrease in frequency could suppress the grating lobes and enlarge the focused volume when focusing the array away from its center of curvature. For single focus pattern, a significant decrease in the number of elements could be made without degrading the quality of the intensity distribution. However, that could shift the focal region away from the array. The results of simulations offer useful suggestions for the optimization of the array to suppress the grating lobes and ablate the target tissue.