A new design approach for dual-mode ultrasound arrays

Advances in piezocomposite transducer technology have made it possible to design and fabricate therapeutic phased arrays with sufficiently high bandwidth and low element cross coupling to produce high-quality HIFU beams. These improvements have also allowed for the use of such arrays in dual-mode operation as imaging and therapy arrays. We have reported on a 1-MHz, 64- element concave dual-mode ultrasound array (DMUA) prototype with 100-mm radius of curvature. However, the imaging capabilities of this prototype remain limited by the coarse sampling of the large, concave aperture, i.e. the therapeutic performance of the DMUA was maintained at the expense of degradation in the imaging performance. We have conducted a simulation study of a new design approach for DMUAs that significantly improves their imaging performance without compromising their therapeutic capabilities. The approach is based on the use a finely sampled aperture in imaging mode (to optimize the spatial and contrast resolutions) and a coarsely sampled aperture in therapeutic mode (to optimize the therapeutic gain and driver efficiency). We will describe a 128 × 8 DMUA structure that can be configured as a 64 × 1 array in therapeutic mode and 128 ×1 in imaging mode. Pulse-mode simulations of wire targets and cyst phantoms using the Field II program show that the new DMUA design offers significant improvement in both spatial and contrast resolutions compared to the existing prototype design. These results provide initial validation of our approach toward the design and fabrication of piezocomposite DMUAs which are simultaneously optimized for therapeutic and imaging operations.