High-Resolution Photoacoustic Microscopy Based on a Transparent Ultrasonic Transducer

Photoacoustic microscopy (PAM), a fusion of light and ultrasound, is a non-invasive and label-free imaging method that provides high resolution and high optical contrast. Based on the intrinsic absorbance of hemoglobin itself, PAM is drawing attention as an angiogram because it can provide an image of blood vessels without exogenous agents. To acquire a high signal-to-noise ratio (SNR) photoacoustic image, it is a key point to precisely alignment between laser and ultrasonic focus. This can be achieved by coaxial positioning of the laser beam and the ultrasonic detector, but the conventional ultrasonic transducer itself is opaque and cannot be confocaled coaxially with the laser. Recently, we have developed an optically transparent ultrasonic transducer (TUT) that can be an alternative to this problem. In this study, we present high-resolution and high-SNR in vivo vascular imaging of the mouse eye, and brain with PAM integrated with the TUT. First, we observed microvessels in a chemically damaged mouse eye model. In particular, the performance of PAM as a comprehensive eye disease diagnosis tool was demonstrated by observing not only corneal neovascularization, but also iris blood vessels and hemorrhages in a cloudy state of the corneal. Second, we delineated in vivo mouse brain vascular imaging at high resolution, and encoded a depth map. We believe that TUT-based PAM is expected to meet the demands of various biomedical imaging fields that require more compact and high SNR.