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Photoacoustic microscopy (PAM) based on the photoacoustic (PA) effect showed the ability of anatomical, functional, metabolic and pathological imaging of animals and humans in vivo. However, the developed PAM systems have not achieved a fast temporal resolution and a high spatial resolution due to physical constraints. To overcome this, microelectromechanical systems (MEMS) scanners have been used for fast scanning speed and super-resolution technologies have been applied for the high spatial resolution. However, the MEMS scanners have shown unstable scanning patterns, and the super-resolution methods have slowed down imaging and required an external contrast agent. Here, we report an agent-free super-resolution high-speed PAM based on a fast scanner (AF-SR-PAM) that overcomes both the spatial and temporal resolution limitations. The scanner was used to steer the optical beam and acoustic wave together, achieving a high signal-to-noise ratio and a B-mode image rate of 500 Hz. Furthermore, by applying our super-resolution method, unresolved micro-vessels in a conventional PAM system are separated in the PA images of AF-SR-PAM. This improvement enables the observation of microvasculature in animals in vivo.

In this study, we developed an imaging device for preclinical and clinical application using photoacoustic effect. The photoacoustic effect is to make ultrasound images using light as its name illustrates. Light irradiated in a short time (nano seconds) is absorbed by the tissue, and the local pressure is generated by the thermo-elastic expansion. The photoacoustic effect is a safe method of imaging because it uses an endogenous chromophore in the human body without the use of an external contrast agent. In this study, the image uses an optical-resolution photoacoustic microscope (OR-PAM) which has a resolution of 12 ¥im. The conventional or-pam has the disadvantage of being slow and bulky using mechanical motors. To overcome this problem, our research team developed a photoacoustic imaging system that uses a MEMS scanner to equip a fast image capability into a compact handheld probe.