Endoscopic electronic-speckle-pattern interferometry - Application to non-destructive quality control in industry and medicine

The method of endoscopic electronic-speckle-pattern interferometry (ESPI) is a too] for detection and visualization of deformations and movements in technical cavities as well as for non-destructive minimal invasive diagnostics within body cavities. Here, a spatial phase shifting (SPS) method is chosen for additional quantitative determination of the object phase, which requires a considerable less stability of the experimental setup and the investigated specimen in comparison to temporal phase shifting techniques. With a simple arrangement, the SPS technique is adapted to the special conditions of standard endoscopic optical imaging, The characterization and optimization of the interferometer is carried out on technical specimen. To demonstrate possible applications of endoscopic ESPI and spatial phase shifting endoscopic ESPI on biological tissues, non-destructive investigations of biological heart valve pro,;theses (in-vitro) are performed. The quality of the obtained phase difference fringes is sufficient for phase unwrapping and for visualization as well as quantitative evaluation. In conclusion, the results of the investigations show that it is possible to detect structural differences in tissue underneath the visible surface ("endoscopic taction") by application of SPS endoscopic ESPI even of biological specimen with a wet and low reflecting surface.