Super-resolution localization photoacoustic microscopy using intrinsic red blood cells as contrast absorbers

Photoacoustic microscopy (PAM) has become a premier microscopy tool that can provide the anatomical, functional, and molecular information of animals and humans in vivo. However, conventional PAM systems suffer from limited temporal and/or spatial resolution. Here, we present a fast PAM system and an agent-free localization method based on a stable and commercial galvanometer scanner with a custom-made scanning mirror (L-PAM-GS). This novel hardware implementation enhances the temporal resolution significantly while maintaining a high signal-to-noise ratio (SNR). These improvements allow us to photoacoustically and noninvasively observe the microvasculatures of small animals and humans in vivo. Furthermore, the functional hemodynamics, namely, the blood flow rate in the microvasculature, is successfully monitored and quantified in vivo. More importantly, thanks to the high SNR and fast B-mode rate (500 Hz), by localizing photoacoustic signals from captured red blood cells without any contrast agent, unresolved microvessels are clearly distinguished, and the spatial resolution is improved by a factor of 2.5 in vivo. L-PAM-GS has great potential in various fields, such as neurology, oncology, and pathology. Photoacoustic microscopy with significantly enhanced temporal and spatial resolution has been demonstrated by scientists in South Korea. Jongbeom Kim and coworkers from Pohang University of Science and Technology (POSTECH) incorporated a fast galvanometer scanner and custom-made scanning mirror into their photoacoustic microscope. The result is an imaging system that is able to visualize very fine blood vessels (microvasculature) in the ear, eye or brain of mice that would usually be very hard to detect or undetectable. The scheme does not require an exogenous contrast agent as the light absorption from red blood cells is sufficiently strong and operates with scan rates of up 500 Hz and with 2.5 times improved spatial resolution by an agent-free localization approach. Potential applications that could benefit from the system include vascularization studies in the areas of dermatology and oncology.