A highly sensitive and wideband transparent ultrasound transducer designed for advanced in-vivo ultrasound and photoacoustic imaging

In this study, a novel approach is presented to overcome the challenge of replacing conventional opaque ultrasound transducers (OUTs) with transparent ultrasound transducers (TUTs) that seamlessly integrate optical and ultrasound components. TUTs offer a design that seamlessly combines optical and ultrasound modalities, providing a convenient solution to overcome challenges such as beam combiner or off-axis problems. However, their performance has been significantly limited due to acoustic impedance mismatch. To address the acoustic impedance mismatch problem, transparent composite-based matching and backing layers are utilized with acoustic impedances exceeding 7 and 4 MRayl, respectively. These layers facilitate the development of an ultrasensitive and wideband TUT with a single resonance frequency and a pulse-echo bandwidth of over 60%, equivalent to traditional OUTs. The TUT demonstrates exceptional performance, with over 80% optical transparency, maximizing acoustic power transfer efficiency, maintaining spectrum flatness, and minimizing ringdowns. Such capabilities enable high-contrast and high-definition dual-modal ultrasound and photoacoustic imaging in both animals and humans. Notably, these imaging modalities achieve a penetration depth of over 15 mm, utilizing a 30MHz TUT. We believe this advancement opens up new possibilities for non-invasive imaging applications, offering enhanced diagnostic capabilities and potential insights into biological structures at greater depths.