Wide-field optical-resolution optoacoustic microscopy utilizing a stationary silicon-photonics acoustic detector for reflection and transmission imaging configurations

We present a novel OR-OAM system with a stationary silicon photonics acoustic detector (SPADE) with semi-isotropic sensitivity, enabling high-resolution, large-field imaging without acoustic path scanning. This advances clinical translation through a compact, miniature probe design. Optical-resolution optoacoustic microscopy (OR-OAM) enables label-free imaging of microvasculature by leveraging optical pulse excitation and subsequent acoustic wave detection. This process typically employs a focused optical beam and ultrasound transducer, necessitating a coaxial configuration where the optical and acoustic paths are aligned. However, this setup often leading to a bulky setup that requires physically scanning the ultrasound transducer to achieve a large field of view (FOV). In this study, we present an advanced OR-OAM configuration that circumvents the need for physically scanning the ultrasound transducer or the acoustic beam path. Our system adopts a non-coaxial configuration, utilizing a silicon photonics acoustic detector (SPADE) featuring semi-isotropic sensitivity. SPADE, based on a micro-ring resonator, fabricated in silicon nitride with a 30 μm diameter, provides a bandwidth of 120 MHz and a noise-equivalent pressure of 7 mPa/-Hz, enabling detection from multiple directions and facilitating static detection during imaging. This innovative setup allows the optical beam alone to be scanned across the sample. The system is operable in both epi and trans-illumination configurations. In epi-illumination, SPADE and the optical elements are co-located on the same side of the sample, while in transillumination, they are positioned on opposite sides. In both configurations SPADE remains stationary during the imaging procedure and only the optical excitation beam is scanned. The system is showcased for imaging resolution targets and for the in vivo visualization of the micro-vasculature in a mouse ear. Optoacoustic imaging with focal spots down to 1.3 μm, lateral resolution of 4 μm, and a field of view higher than 4 mm in both lateral dimensions were demonstrated as seen in Figures 1-3. Our new OR-OAM design enables relatively large fields of view without scanning the acoustic detector or acoustic beam path. Furthermore, it offers the potential for high-speed imaging within compact, miniature probe and could potentially facilitate the clinical translation of OROAM technology.