Wide-field photoacoustic microscopy of oxygen saturation at 1-MHz A-line rate

We report wide-field polygon-scanning optical-resolution photoacoustic microscopy (OR-PAM) that achieves 1-MHz A-line rate of oxygen saturation in vivo. We develop a polygon-scanning imaging probe. Using stimulated Raman scattering and optical delay in fiber, we develop a dual-wavelength pulsed laser that has proper wavelengths, sufficient pulse energy, high pulse repetition rate, and sub-microseconds wavelength switching time for fast imaging of oxygen saturation. The OR-PAM system offers a 478-Hz B-scan rate and a 1-Hz volumetric imaging rate over a 12×5 mm2 scanning area. We demonstrate dynamic imaging of oxygen saturation of fast response to epinephrine injection in the mouse ear. Results show fast hemodynamic and functional changes in centimeter-sized areas.