Self-focusing ultrasound phased arrays for noninvasive surgery

Abstract

Modern transducer technology is providing phased arrays with high-power, relatively large fractional bandwidth, and low cross coupling between array elements. As a result, it is possible to use these arrays in a dual imaging/therapy mode. We have recently demonstrated this using a 64-element 1-MHz array with 1.5×50 mm2 elements on a spherical shell with a 100-mm radius of curvature. In the therapy mode, the array was shown to be capable of producing focal intensities in excess of 10<th>000 W/cm2 and cause well-defined lesions in tissue at depth. In the imaging mode, the array was shown to be capable of forming images of acceptable quality in a region covering ±35 mm axially and ±25 mm laterally around its geometric center. In this paper, we describe new algorithms for using this array in self-focusing mode based on acoustic feedback from the intended focal region. Two modes of acoustic feedback will be described and compared, specifically, direct hydrophone measurements at the desired focus and backscatter from the focal region (collected in imaging mode). Experimental data are given to demonstrate optimal focusing of phased array systems in the presence of strongly scattering objects, e.g., the ribcage.