Design and experiment of 256-element ultrasound phased array for noninvasive focused ultrasound surgery

A 256- element phased array high intensity focused ultrasound system has been designed and constructed in our laboratory. The 256-element spherical- section ultrasound phased array made from piezocomposite material operates at 1.1 MHz with 11- cm radius of curvature, 14- cm outer diameter, and 3.4- cm diameter central hole for mounting diagnostic ultrasound imaging probe. First, the explicit sound field calculation approach for the spherical- section phased array and the genetic optimal algorithm are briefly introduced as the optimal focus pattern control methods. Then, the design guidelines of 256- element spherical- section focused ultrasound phased array and 256- channel driver system are given. The results of single on and off axial focus, multiple on and off axial foci, half sub- array focus pattern provide further evidence for the 3D focus steering and sub- array mode for avoiding obstacles in focused ultrasound surgery. The multi- foci pattern can enlarge the treatment volume to 22 times larger than that of a single focus in one sonication. Finally, in vitro and transparent tissue- mimicking phantom experiment results confirm the ability of 256- element spherical- section phased array system to induce thermal lesions for noninvasive ultrasound surgery. (c) 2006 Elsevier B. V. All rights reserved.