Optimized optical-acoustic combiner for high-sensitivity, high-speed three-dimensional photoacoustic microscopy.

We present a high-speed three-dimensional optical-resolution photoacoustic microscopy (OR-PAM) system featuring an optimized optical-acoustic combiner (OAC) and a novel, to our knowledge, curved scanning strategy. To enhance acoustic detection sensitivity, four OAC configurations were systematically evaluated. The design employing a spherically focused ultrasound transducer and a 45° glass reflector achieved the highest sensitivity. To address the limited depth of focus (DOF) in conventional OR-PAM, we developed a curved scanning method that extends the DOF from 1.74 mm to ~10 mm. The integrated system enables high-resolution, volumetric imaging with uniform high lateral resolution over an extended DOF. Phantom and <i>in vivo</i> experiments, including mouse ear and brain vasculature imaging, demonstrate significantly improved structural visibility and vessel density compared to planar scanning. The compact OAC design and fiber-optic light delivery offer the potential for handheld implementation. This work establishes a sensitive, large-DOF OR-PAM platform for high-quality vascular imaging of biological tissues.