Flexible $3\times3$ Mueller Matrix Endoscope Prototype for Cancer Detection

In this paper, we research and design a flexible head-modulated polarization endoscope system prototype for early cancer detection in vivo. The new idea of our design is the implementation of the distal tip of the endoscope structure, that is, the distal tip has integrated the polarization state generator (PSG) and polarization state analyzer (PSA), the illumination fiber, and image capture device. A closed-loop motion control system was adopted to accurately rotate the linear polarizers in PSG and PSA. A high-definition image capture and transfer system was used to capture the polarized images. By this design, a $3\times 3$ Mueller matrix could be calculated through such an endoscope head. Furthermore, the measurement process would not be influenced by the polarization disturbance induced to the pathway of light transmission. A state of polarization calibration process was carried out on the PSG and PSA to keep a high degree of accuracy and repeatability of described rotation-based polarization, and the results showed its effectiveness. Finally, our endoscope head was used to measure the nude mice skin with subcutaneous implantation of HeLa cells in vivo. The corresponding Mueller matrix decomposition and Mueller matrix transformation parameters extracted showed that our proposed device can clearly and stably distinguish the cancerous and normal tissues. The results prove that the polarization endoscope system has its potential application in early cancer detection.