Dual frequency imaging and therapeutic transducer using an acoustic band-pass filter for application to endoscopic surgery

A HIFU and imaging hybrid transducer with stacking structure for endoscopic application was described. In our previous study, a bi-laminar transducer involved an imaging and a therapeutic array transducers and a polymer layer working as an acoustic band-pass filter (ABPF) between both transducers was developed^[1]. Because the ABPF passes through the lower frequency therapeutic beam and reflects the higher frequency imaging beam, the imaging array was isolated from the therapeutic transducer. Because this prototype transducer was designed to realize ultrasound clot solution, therapeutic output was lower than that of HIFU. In this study, frequency and power optimizations are required. Based on simulation optimization, a prototype transducer consisting of a spherical HIFU transducer and a concave imaging array stacking on the HIFU transducer was fabricated. The fractional bandwidth at -20 dB of imaging pulses was 100%. The transmittance of the HIFU beam through the imaging array was 0.6. The measured bandwidth of the imaging pulse is sufficient to obtain a high resolution US image. An estimated peak intensity of HIFU beam transmitted from the prototype structure was 60% higher than that of the conventional HIFU transducer with a center hole to mount the imaging array, whose outer diameter of aperture is the same as that of the prototype structure.