同轴数字全息用于血吸虫尾蚴检测研究

由于水的表面易出现抖动或波动情况,而传统的显微镜成像需要精确的光学焦聚过程,因此不适于观察漂浮于水表面的血吸虫尾蚴.本文论述了用同轴数字全息检测血吸虫尾蚴的基本原理.通过对再现像进行小波分析发现,偏离焦点时的小波变换高频系数的幅值比聚焦时要小得多.针对这一特点,本文对小波变换清晰度评价函数进行了改进,将原来利用高频系数之和改为利用聚焦窗口中高频系数的最大幅值为清晰度评价依据.在模拟实验结果中清晰度评价函数极大值出现在再现距离与记录距离相等处,说明了该算法的准确性.建立了用于血吸虫尾蚴检测的实验装置,可方便获取普通显微图像及数字全息图.实验结果表明,本文提出的算法能实现实际情况下的数字全息自动聚焦,其再现像的分辨率与装有1倍显微镜头的数码显微镜分辨率相当,足以清晰地分辨出血吸虫尾蚴的尾部分叉特征.利用同轴数字全息技术可在水面与图像传感器之间的距离不确定的情况下实现对血吸虫尾蚴的检测.

Digital In-line Holography for Schistosoma Cercariae Detection

The traditional microscope is not suitable to observe the schistosoma cercariae which usually floating on the water surface, because it needs an optical focusing process and the wobble or fluctuation of the water surface is difficult to avoid. The basic concept and procedure of digital in-line holography based on convolution are shown mainly for schistosoma cercariae detection. An auto-focus algorithm based on wavelet transform was improved. The max amplitude of high-frequency coefficients in the focal windows was used to evaluate the definition of the reconstructed image instead of the sum of high-frequency coefficients. The evaluation function was maximal only when the reconstructed distance equal to the recording distance in the simulated experiment, which shows the accuracy of the improved algorithm. The experimental device of digital in-line holography was designed for schistosoma cercariae detection. The experimental results show that the auto-focusing method based on wavelet transform can be used in digital holography, and the digital in-line holography can be used to detect schistosoma cercariae when the water surface is fluctuant. The reconstructed image resolution is equivalent to the resolution of digital microscope with 1X micro lens, and the bifurcated tail of schistosoma cercariae can be observed clearly.