Label-free optical-resolution photoacoustic endomicroscopy in vivo

Intravital microscopy techniques have become increasingly important in biomedical research because they can provide unique microscopic views of various biological or disease developmental processes in situ. Here we present an opticalresolution photoacoustic endomicroscopy (OR-PAEM) system that visualizes internal organs with a much finer resolution than conventional acoustic-resolution photoacoustic endoscopy systems. By combining gradient index (GRIN) lens-based optical focusing and ultrasonic ring transducer-based acoustic focusing, we achieved a transverse resolution as fine as similar to 10 mu m at an optical working distance of 6.5 mm. The OR-PAEM system's high-resolution intravital imaging capability is demonstrated through animal experiments.