Abstract
We present a new phase unwrapping approach, which allows reconstruction of optically thick objects that are optically thin from at least one viewing angle, by considering the information stored in the object phase maps captured from consecutive angles. Our algorithm combines 1-D phase unwrapping in the angular dimension with conventional 2-D phase unwrapping, to achieve unwrapping of the object from the optically thick perspective. We thus obtain quantitative phase imaging of objects that were previously impossible to image in certain viewing angles. To demonstrate our approach, we present both numerical simulation and experimental results for quantitative phase imaging of biological cells.
Highlights
Imaging biological cells in vitro is useful for both medical diagnosis and biological research
The new approach for angular phase unwrapping presented in this paper enables the phase unwrapping of optically thick objects, using the projections of the object from other perspectives, assuming that they meet two basic criteria
The second requirement is that the phase gradient between most corresponding pixels in consecutive acquisition angles does not exceed an absolute value of π radians, a requirement that can be achieved for most biological samples, provided that the angular increments are small enough
Summary
Imaging biological cells in vitro is useful for both medical diagnosis and biological research. Isolated cells in vitro are mostly transparent, and cannot be imaged well via standard bright-field microscopy. Quantitative phase-contrast interferometric microscopy enables the imaging of isolated cells in vitro, without the use of cell staining, by measuring how much the light is delayed when passing through the sample [1, 2]. The reconstruction process includes the retrieval of the 2-D quantitative phase map from an interferogram [3], which is an ill posed problem. While retrieving the initial phase map from an interferogram is a fairly simple process [4, 5], the phase obtained is wrapped, meaning that it is bounded in the range [ 0 , 2π ], and contains 2π jumps in spatial locations where the optical path difference (OPD) is larger than the illumination wavelength. For optically thick objects, where this requirement is not met, it is impossible to differentiate between full multiplications of 2π from the information present in the 2-D wrapped phase map, resulting in an erroneous calculation of the final phase map
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