Nguyen, T.H. et al. Nat. Commun. 8, 210 (2017).

Quantitative phase imaging (QPI) is a label-free imaging approach that offers advantages over conventional phase and differential interference contrast (DIC) imaging for quantitative analyses, such as measuring the local thickness and refractive index of the imaged structure. However, QPI does not work well for thick specimens, because multiple scattering caused by the specimen results in an incoherent background that degrades image contrast. Nguyen et al. addressed this problem by developing gradient light interference microscopy (GLIM). GLIM combines DIC microscopy with low-coherence interferometry and holography; this combination leads to rejection of much of the incoherent background, which results in high-contrast images of thick specimens. To demonstrate their approach, the researchers carried out 3D imaging of bovine embryos during early development and showed that GLIM could be used to assay embryo viability.