Accurate quantitative phase imaging by differential phase contrast with partially coherent illumination: beyond weak object approximation

Quantitative phase imaging (QPI) by differential phase contrast (DPC) with partially coherent illumination provides speckle-free imaging and lateral resolution beyond the coherent diffraction limit, demonstrating great potential in biomedical imaging applications. Generally, DPC employs weak object approximation to linearize the phase-to-intensity image formation, simplifying the solution to the phase retrieval as a two-dimensional deconvolution with the corresponding phase transfer function. Despite its widespread adoption, weak object approximation still lacks a precise and clear definition, suggesting that the accuracy of the QPI results, especially for samples with large phase values, is yet to be verified. In this paper, we analyze the weak object approximation condition quantitatively and explicitly give its strict definition that is applicable to arbitrary samples and illumination apertures. Furthermore, an iterative deconvolution QPI technique based on pseudo-weak object approximation is proposed to overcome the difficulty of applying DPC to large-phase samples without additional data acquisition. Experiments with standard microlens arrays and MCF-7 cells demonstrated that the proposed method can effectively extend DPC beyond weak object approximation to high-precision three-dimensional morphological characterization of large-phase technical and biological samples. (c) 2023 Chinese Laser Press

Automated summary

Quantitative phase imaging (QPI) by differential phase contrast (DPC) with partially coherent illumination shows potential in biomedical imaging, with speckle-free imaging and improved lateral resolution. This paper analyzes the weak object approximation condition and provides a precise definition applicable to all samples and illumination apertures. An iterative deconvolution QPI technique based on pseudo-weak object approximation is proposed to overcome the limitations of DPC for large-phase samples without additional data acquisition. Experiments demonstrate the effectiveness of the proposed method for high-precision three-dimensional morphological characterization of large-phase technical and biological samples.