Dynamic cell imaging by iterative phase retrieval microscopy

Most living cells exhibit low contrast under bright field microscopy as they do not significantly absorb the visible spectrum of radiation. The captured intensity images lack information about the specimen thereby preventing a detailed examination. Obtaining phase information provides better insight into the specimen as it offers more important information in comparison to intensity images. Various approaches such as Holography, deterministic and iterative algorithms, etc. have been used to extract the phase information which has its own advantages and disadvantages. This paper focuses on the application of the iterative phase retrieval technique which works by using multiple intensity (diffraction) patterns recorded at different axial planes with angular spectrum propagation for obtaining quantitative phase contrast images of Red Blood Cells (RBCs). It is a single-beam non-interferometric system and therefore relatively simple, inexpensive, and doesn’t require a reference beam like in the case of the interferometric technique. The iterative phase retrieval technique is also employed to study low-frequency thickness fluctuations of RBCs. The ability and efficiency of the system can be further improved by increasing the translation speed for capturing intensity images at several axial planes.