High-amplitude and long-burst pulse transmission array probe for phase-change molecular imaging

Analysis of the breakdown of a conventional imaging probe based on experiments and numerical simulations is described. Both results of simulation and measurements of the electric impedances and round-trip responses of imaging arrays during the breakdown show that the breakdown was caused by peeling of the adhesive between the piezoelectric material and the matching layer. Since the peeling was suppressed by cooling, it was considered to be caused by thermal stress due to the difference in thermal expansion coefficient between these two layers. To increase the maximum transmission ultrasonic power by overcoming this problem, we proposed an imaging array structure with an optimized heat-conductive backing layer connected to a water-cooling bath. Simulation results show that the combination of heat-conductive backing and water cooling can reduce the temperature rise to 1/42 that of the conventional structure. The thickness of the heat-conductive backing layer, consisting of epoxy resin containing graphite fibers, was optimized for heat conductance and pulse response. This proposed structure may be useful for ultrasound molecular imaging using phase-change nanodroplets.