Research On Photoacoustic Wavefront Shaping Microscopic Imaging Based On The Superpixel Method And DMD

Based on the photoacoustic effect,photoacoustic imaging(PAI)can reconstruct the light absorption contrast images of the samples with photoacoustic signal excited by laser pulse.Thus it has the advantages of both light contrast and sound penetration.However,as the imaging depth is further increased,the incident light is affected by scattering,which causes the excited photoacoustic signal to be weak or even unable to excite the photoacoustic signal.The development of photoacoustic imaging has therefore been seriously hindered.Wavefront shaping methods can overcome multiple light scattering and control the transmission of light in the scatter at a certain extent.Especially the iterative optimization wavefront shaping method is simple,easy to implement and has high robustness.The optical modulation device is the core device for wavefront shaping.Digital micromirror device(DMD)has the outstanding advantages of high refresh rate,wide applicable bandwidth,excellent performance and moderate price.DMD is a binary amplitude modulation device,and the phase modulation using DMD can be realized with the superpixel method.This paper presents a photoacoustic wavefront shaping method which combines the superpixel method and DMD.For the first time,DMD is used to modulate the phase and amplitude of the incident light in photoacoustic wavefront shaping experiment.The photoacoustic signal is extracted from the initial signal which contains much noise through the combination of wavelet denoising and correlation detection.By combining the superpixel method and DMD,the amplitude and phase of the incident light can be modulated together with the photoacoustic signal served as the feedback signal.The genetic algorithm(GA)is used to control the iterative optimization process.Combining the superpixel method and DMD,we first conduct a singlepoint focusing experiment through photoacoustic wavefront shaping.After completing the iterative optimization of the wavefront of the incident light,the enhancement factor of the photoacoustic signal reaches 10.46,which is much higher than the theoretical enhancement factor of pure amplitude modulation with DMD.This confirms the advantages of combining the superpixel method and DMD in modulation effect.Then we performed scanning imaging.The optimal mask loaded on the DMD keeps unchanged after the iterative optimization is completed.We move the sample for scanning imaging and collect the photoacoustic signals with which a clear photoacoustic image with a contrast of 8.57 is reconstructed.However,the photoacoustic signal before optimization is weak and the signal-to-noise ratio is low that the light absorption contrast image of the sample cannot be reconstructed.The method proposed in this paper opens up a new path for photoacoustic imaging with low signal-tonoise ratio photoacoustic signals and effectively improves the depth of photoacoustic imaging.