Laser speckle imaging (LSI) is a full-field blood flow imaging technique with high spatio-temporal resolution and easily controlled imaging area. It has attracted extensive attention in biomedical application, such as intraoperative imaging, mechanism of neurovascular coupling and evaluating drug efficiency. However, this method suffers from the problem of shallow sampling depth of blood flow, so it mainly reflects the superficial blood flow information of biological tissue. The main reason is scattering effect of biological tissue, which disturbs the waveftront of the incident laser and severely influences the imaging quality and the detection of the flow signal under the deep tissue. Recently, some methods used to improve the sampling depth of flow signal have been reported, such as the optical clearing method. However, it has not been clearly investigated to apply the iterative wavefront shaping technique in laser speckle imaging through scattering medium.
Prof. Pengcheng Li’s group from Wuhan National Lab for Optoelectronics (WNLO) proposed to combine the iterative wavefront shaping technique with laser speckle contrast analysis method to detect the relative speed changes of moving objects through scattering medium. Phantom experiments were performed to validate our method. After compensating the wavefront distortion caused by scattering medium with SLM, an object can be imaged through the scattering system, such as diffuser. When the object is moving, the motion of scattering particles can cause spatial-temporal intensity fluctuations of imaged speckle when a coherent light is incident on a dynamic turbid medium. The speed map can then be obtained with the laser speckle temporal contrast analysis method. The method may have potential implications in astronomy, biomedical imaging, security system and other related engineering field.
This work, published in Optics Express (Vol. 24, No. 8, pp. 8382-8390, 2016), was supported in part by the National Natural Science Foundation of China (Grant Nos. 91332121, 31471083, 61405065) and the Director Fund of Wuhan National Laboratory for Optoelectronics.
Fig. 1. Experimental setup for speed detection of moving object through scattering medium
Fig. 2. The raw images and the speed maps of moving object through diffuser with wavefront correction and without wavefront correction