Ultraviolet photoacoustic microscopy (UV-PAM) has emerged as a promising medical imaging technique for alternative histopathology, relying on the inherent optical absorption of DNA/RNA. However, traditional UV-PAM faces resolution challenges compared to clinical histological methods, limiting the observation of cellular structures. This limitation stems from the constraints of conventional reflection-mode UV-PAM systems, utilizing opto-ultrasound beam combiners or ring-shaped ultrasound transducers. These components impose constraints on numerical apertures (NA), thereby limiting spatial resolution. On the flip side, transmission-mode UV-PAM encounters difficulties in imaging thick specimens due to signal attenuation. In this study, we introduce an innovative solution – the development of an ultraviolet-transparent ultrasound transducer (UV-TUT) – overcoming these limitations and enabling high-resolution UV-PAM system. The UV-TUT significantly enhances both NA and lateral resolution, outperforming previous reflection-mode UV-PAM systems. With an impressive light transmission efficiency in the UV region and sensitivity four times greater than traditional ring-shaped ultrasound transducers, the UV-TUT lays the foundation for improved imaging capabilities. Leveraging the capabilities of the UV-TUT, we exploited a UV-PAM system, showcasing superior performance for imaging mouse brain tissue sections compared to conventional opto-ultrasound beam combiner-based UV-PAM. Furthermore, our application of photoacoustic histopathology on uterine cancer tissue sections demonstrated image quality comparable to microscopy images, providing valuable insights for accurate histopathological analysis. This work signifies a significant advancement in UV-PAM system, holding the promise to enhance the clinical utility of alternative histopathology with unprecedented resolution and imaging capabilities.
Photoacoustic (PA) imaging has become one of the promising biomedical imaging technologies in the past decade, thanks to its advantages of structural, functional, imaging capabilities and seamless integration with conventional ultrasound imaging. Endoscopic photoacoustic and ultrasound (ePAUS) is the combination of PA imaging technology and endoscopic ultrasound (EUS). In the design of the ePAUS, it is ideal to align the optical beam of the laser and the acoustic beam of the transducer on the same axis to achieve high spatial resolution and long imaging range. Existing ePAUS uses a ring transducer or a beam combiner to obtain a coaxial or rather an off-axis arrangement. However, the ring transducer has a problem in that the diameter and acoustic side lobes are large, and the beam combiner has a disadvantage in that the structure is complicated and the acoustic loss due to multiple acoustic reflections is large. Our approach to solving this problem is the development of ePAUS based on a miniaturized transparent ultrasonic transducer (TUT). In this study, lead-magnesium- niobate lead-titanate and Indium Tin Oxide-based ultra-small TUT was fabricated, and the performance of center frequency of 28.1 MHz and bandwidth of 51.5% was obtained. Thereafter, quasi-focus was used by combining a multimode optical fiber and a gradient index lens, and coaxial alignment was achieved by arranging the optical axis perpendicular to the optically transparent TUT. This results in high spatial resolution and long imaging distances, and the imaging performance of the probe is demonstrated by imaging the rectum and vagina of the rat in vivo.
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