A novel translucent ultrasound transducer approach for dual-modality ultrasound and photoacosutic imaging

The transparent ultrasound transducer (TUT) has recently emerged as an attractive platform for development of multiscale photoacoustic imaging (PAI) systems. TUT allows an easy co-alignment of optical illumination and acoustic detection paths on the tissue surface, averting the complex beam arrangements employed by the current PAI systems that use opaque conventional ultrasound transducers. However, TUTs suffer from narrow bandwidth and low sensitivity due to the lack of suitable transparent acoustic matching and backing layers. To address the above challenges, in this study we explored a novel optically translucent acoustic matching layer made out of glass beads suspended in transparent epoxy to improve both the transducer bandwidth/sensitivity and light fluence on the tissue surface. Our experiments with 13 MHz center frequency TUTs coated with varying glass bead concentration demonstrated that both pulse-echo bandwidth and sensitivity increases with glass bead concentration. Approximately 3.3 fold improvement in bandwidth and a 2.5 times higher pulse-echo sensitivity was measured with TUT fabricated with an acoustic matching layer of 40%GB. Optical measurements were conducted to confirm that the translucent glass bead layer can act as a light diffuser to help achieve uniform light distribution on the tissue surface.