Photoacoustic microscopy with transmissive adaptive optics using liquid crystal

Photoacoustic microscopy (PAM) is a biological visualization technique that can provide high spatial resolution and high contrast images of deep structures in living tissues. In PAM, the lateral resolution is determined by the size of the focus spot. Generally, because the wavefront aberration, due to the difference of refractive index between samples and air (water) and the shape of samples, enlarges the focus spot, obtained deep images are blurred or distorted. In order to solve this problem, we corrected the wavefront aberration occurring in samples using a transmissive liquid-crystal adaptive optics (AO) element. Our AO element consists of three liquid-crystal layers which have different ITO (indium tin oxide) patterns and are controlled independently. Their patterns are designed to correct the wavefront aberration suitable for a 40X water-immersion objective lens. The AO element with transmissive and thin structure is easily installed in the PAM system. Also, our AO element is inexpensive and has low power consumption. In this study, we compared photoacoustic images obtained without and with the AO element for a USAF test target, polystyrene beads diffused in glycerol and various tissue specimens. As a result, we found that the use of transmissive AO element improves the lateral resolution and signal-to-noise ratio in PAM.