Refractive index reconstruction of biological samples from multimodal phase microscopy

Abstract

The extraction of quantitative information is important to better understand cellular activity in biological processes. In particular the optical refractive index can be used to analyze the results of cellular processes such as the average dry mass of biological samples. Phase microscopy modalities are widely used to image unstained biological samples because of their ability to obtain high-contrast images without introducing exogenous agents. The most common phase modalities are predominantly qualitative. However quantitative phase microscopy can provide more specific information about optical thickness and refractive index. In biological samples with several internal inhomogeneities and thickness variations, refractive index calculation becomes challenging to achieve by direct analysis of the images. Here we present a multimodal iterative method to reconstruct the spatial distribution of refractive index, combining information from two phase microscopy techniques. We use a constrained boundary iterative method under the assumption that the index of refraction inside the object can be approximated as piecewise constant. The boundary locations of all inhomogeneities are obtained by leveraging measurements from DIC and quantitative phase imaging modalities, and then the index of refraction is estimated based on those boundaries and a quantitative forward model for one modality. Simulations have confirmed the reliability of the proposed method. Experiments with measurement from mouse embryos at several development stages show that the proposed approach can reconstruct the distribution of the refractive index of these samples.