3D high resolution photoacoustic imaging based on pure optical photoacoustic microscopy with microring resonator

For three-dimensional imaging of optical absorbance, the existing technology of photoacoustic microscopy (PAM) has quite poor axial resolution, the tens of microns to hundreds of microns. This is despite the fact that PAM has recently achieved lateral resolutions on the order of a micron or submicron, comparable to that of optical microscopy. In this paper, a pure optical photoacoustic microscopy (POPAM) with optical rastering of a focused excitation beam and optically sensing of the photoacoustic signal using a microring resonator was developed with the super broad bandwidth of the system more than 350MHz. With unprecedented broad bandwidth of POPAM, 3.8 mu m axial resolution was achieved without deconvolution processing. Sectioning imaging ability along axial direction presenting 3D morphologic features was shown based on imaging printed phantom. The impact of this approach will be similar to how confocal optical microscopy revolutionized the conventional optical microscopy by enabling the axial sectioning capability. Tissue imaging comparing POPAM and conventional PAM based on needle hydrophone demonstrated that though such broad bandwidth compromised the sensitivity of POPAM 4.35 times than that of conventional PAM, the noise equivalent detectable pressure (NEDP) was estimated as 74Pa, still able to get the tissue imaging.