High-resolution volumetric imaging with optically encoded photoacoustic microscopy (openPAM)

Photoacoustic microscopy (PAM) is a functional volumetric imaging technique that achieves optical diffraction-limited lateral resolution through confined optical excitation and axial profiling via acoustic time-of-flight detection. However, the diffraction-limited lateral resolution is maintainable only within a depth of field of approximately 100 μm, and the axial resolution is restricted to tens of micrometers due to the finite bandwidth of acoustic signals. To overcome these limitations, we developed optically encoded PAM (openPAM), which sculpts the illumination light into a fractional vortex beam to encode the object to be imaged. The resultant measurements are then resolved into high-resolution volumetric images over a large axial range using an efficient neural decoding algorithm. To demonstrate the superior performance of openPAM, we performed in vivo volumetric imaging of animal vasculature and cancer models, achieving an unprecedented isometric 3.5-μm resolution over an extended depth of 1.0 mm, significantly outperforming conventional PAM. The synergy of optical encoding and time-of-flight detection offers a new solution for optical sectioning and can broadly benefit fast and high-resolution volumetric microscopy.