Synthetic multi-focus optical-resolution photoacoustic microscope for large volumetric imaging

Photoacoustic microscopy is becoming an important tool for the biomedical research. It has been widely used in biological researches, such as structural imaging of vasculature, brain structural and functional imaging, and tumor detection. The conventional optical-resolution photoacoustic microscopy (OR- PAM) employs focused gaussian beam to achieve high lateral resolution by a microscope objective with high numerical apertures. Since the focused gaussian beam only has narrow depth range in focus, little detail in depth direction can be revealed. Here, we developed a synthetic multi-focus optical-resolution photoacoustic microscope using multi-scale weighted gradient-based fusion. Based on the saliency of the image structure, a gradient-based multi-focus image fusion method is used, and a multi-scale method is used to determine the gradient weights. We pay special attention to a dual-scale scheme, which effectively solves the fusion problem caused by anisotropic blur and registration error. First, the structure-based large-scale focus measurement method is used to reduce the effect of anisotropic blur and registration error on the detection of the focus area, and then the gradient weights near the edge wave are used by applying the small-scale focus measure. Simulation was performed to test the performance of our method, different focused images were used to verify the feasibility of the method. Performance of our method was analyzed by calculating Entropy, Mean Square Error (MSE) and Edge strength. The result of simulation shown that this method can extend the depth of field of PAM two times without the sacrifice of lateral resolution. And the in vivo imaging of the zebra fish further demonstrates the feasibility of our method.