High-speed adaptive photoacoustic microscopy

Optical-resolution photoacoustic microscopy (OR-PAM) is capable of observing the distribution of optical absorbers inside bio-tissues with a high spatial resolution of micrometers. Unfortunately, due to the employment of a tight optical focus, it suffers from a limited depth of field (DOF), making it challenging to achieve high-resolution imaging of targets with arbitrary surfaces. Here, we propose a high spatiotemporal adaptive photoacoustic focusing mechanism through integrating a high-speed optical focuser, a time-of-flight contour deriving algorithm, and the rotary-scanning photoacoustic microscopy. The developed system, named high-speed adaptive photoacoustic microscopy (HA-PAM), features an ultrashort focus-shifting time of 5 ms and an enlarged DOF of up to 5 mm. With the assistance of the proposed mechanism, we can achieve a homogeneous lateral resolution of 6 μm over a 10 mm circular imaging domain within 5 s. We demonstrate the advantages of HA-PAM through imaging phantoms with curved surfaces, subcutaneous tumor-bearing mice, resected rabbit kidneys, and pulsating mouse brains. The imaging results suggest that this approach provides a high and consistent spatial resolution for imaging bio-tissues with arbitrary surfaces without sacrificing the imaging speed, and has the potential to extend the fundamental and clinical applications of OR-PAM.