High-contrast imaging based on wavefront shaping to improve low signal-to-noise ratio photoacoustic signals using superpixel method

Photoacoustic(PA) imaging has drawn tremendous research interest for various applications in biomedicine and experienced exponential growth over the past decade. Since the scattering effect of biological tissue on ultrasound is two-to three-orders magnitude weaker than that of light, photoacoustic imaging can effectively improve the imaging depth.However, as the depth of imaging further increases, the incident light is seriously affected by scattering that the generated photoacoustic signal is very weak and the signal-to-noise ratio(SNR) is quite low. Low SNR signals can reduce imaging quality and even cause imaging failure. In this paper, we proposed a new wavefront shaping and imaging method of low SNR photoacoustic signal using digital micromirror device(DMD) based superpixel method. We combined the superpixel method with DMD to modulate the phase and amplitude of the incident light, and the genetic algorithm(GA) was used as the wavefront shaping algorithm. The enhancement of the photoacoustic signal reached 10.46. Then we performed scanning imaging by moving the absorber with the translation stage. A clear image with contrast of 8.57 was obtained while imaging with original photoacoustic signals could not be achieved. The proposed method opens new perspectives for imaging with weak photoacoustic signals.

Wavefront Shaping for Fast Focusing Light through Scattering Media Based on Parallel Wavefront Optimization and Superpixel Method

When light travels in biological tissues,it undergoes multiple scattering and forms speckles,which seriously restricts the penetration depth of optical imaging in biological tissues.With wavefront shaping method,by modulating the wavefront of incident light to compensate for the wavefront aberration,light focusing and scanning imaging through scattering media can be achieved.However,wavefront shaping must be accomplished within the speckle decorrelation time.Considering the short speckle decorrelation time of living tissues,the speed of wavefront shaping is rather essential.We propose a new iterative optimization wavefront shaping method to improve the speed of wavefront shaping in which the existing parallel optimization wavefront shaping method is improved and is combined with the superpixel method.Compared with the traditional multi-frequency parallel optimization method,the modulation rate of our method is doubled.Moreover,we combine the high frame rate amplitude modulator,i.e.,the digital micromirror device(DMD),with the superpixel method to replace the traditional phase modulator(i.e.,spatial light modulator),which further increases the optimization speed.In our experiment,when the number of the optical modes is 400,light focusing is achieved with only 1000 DMD superpixel masks and the enhancement factor reaches 223.Our approach provides a new path for fast light focusing through wavefront shaping.