Photoacoustic imaging (PAI) uniquely combines optics and ultrasound, presenting a promising role in biomedical imaging as a non-invasive and label-free imaging technology. As the traditional opaque ultrasound (US) transducers could hinder the transportation of the excitation light and limit the performance of PAI system, piezoelectric transparent ultrasonic transducers (TUTs) with indium tin oxide (ITO) electrodes have been developed to allow light transmission through the transducer and illuminate the sample directly. Nevertheless, without having transparent matching materials with appropriate properties, the bandwidth of those TUTs was generally narrow. In this work, we propose to employ polymethyl methacrylate (PMMA) as the matching layer material to improve the bandwidth of lithium niobate (LN)-based TUTs. The effects of PMMA matching layer on the performance of TUTs have been systematically studied. With the optimized PMMA matching layer, the very wide bandwidth of > 50 % could be achieved for the TUTs even with different transducer frequencies, leading to the great enhancement of axial resolution when compared to the similar reported work. In addition, the imaging performance of the developed TUT prototype has been evaluated in a PAI system and demonstrated by both phantom and small animal imaging.

中文翻译：

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以聚甲基丙烯酸甲酯作为匹配层的宽带透明超声换能器，用于体内光声显微镜

光声成像（PAI）独特地结合了光学和超声，作为一种非侵入性、无标记的成像技术，在生物医学成像中发挥着广阔的前景。由于传统的不透明超声 (US) 换能器可能会阻碍激发光的传输并限制 PAI 系统的性能，因此开发了具有氧化铟锡 (ITO) 电极的压电透明超声换能器 (TUT)，以允许光通过换能器传输并直接照射样品。然而，如果没有具有适当特性的透明匹配材料，这些 TUT 的带宽通常很窄。在这项工作中，我们建议采用聚甲基丙烯酸甲酯（PMMA）作为匹配层材料来提高基于铌酸锂（LN）的TUT的带宽。系统研究了PMMA匹配层对TUT性能的影响。通过优化的 PMMA 匹配层，即使具有不同的换能器频率，TUT 也可以实现 > 50% 的非常宽的带宽，与类似的报道工作相比，轴向分辨率大大提高。此外，所开发的 TUT 原型的成像性能已在 PAI 系统中进行了评估，并通过体模和小动物成像进行了证明。