We report a novel transparent ultrasound transducer (TUT) platform for low intensity pulsed ultrasound (LIPUS) stimulation of cells and simultaneously imaging live cell fluorescent calcium dynamics using time lapse microscopy. By culturing cells directly on the biocompatible TUT surface, this platform eliminated the need for additional acoustic coupling and reduced the risk of contamination. High light transmission (> 80%) and compact size of TUTs allowed easy integration with state-of-the-art microscopy for high-resolution imaging of cells in both bright and fluorescent modes while stimulating with optimal LIPUS stimulation conditions. Quantitative single cell fluorescence analysis results demonstrated that the proposed TUT allows uniform and high-throughput stimulation of all plated cells. Dead cell assay results confirmed cell viability after LIPUS. In the future, the TUT based platform can be combined with optical cell imaging and manipulation technologies to favor many biomedical applications and help gain insights into the mechanobiology of cells.
An integrated functional ultrasound (fUS) and photoacoustic (PA) imaging modality is favorable for obtaining multiparametric functional information of deep vasculature. fUS maps blood volume changes of microvasculature using power Doppler frames generated from multiple plane-wave angles with high spatiotemporal resolution, while PA complements vascular oxygen saturation images. In this work, we demonstrated that fUS, ultrasound, and PA imaging can be performed in real-time with a single ultrasound transducer probe. For this, we attached a custom-designed fiber optic illuminator to the fUS probe to optimally deliver light for deep tissue PA imaging. Validation studies on blood flow phantoms and in vivo finger images with a compact imaging head show reduced motion artifacts and ease out the acoustic coupling challenges, making it suitable for multimodal US, fUS and PA imaging of microvasculature.
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.
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