Conventional label-based contrast enhancement techniques (e.g., fluorescence) frequently modify the genetic makeup of tagged cells, making them poor candidates for use in in-vitro fertilization applications. Instead, we choose a label-free form of contrast, based on interferometric imaging, sensitive to optical path length differences. Compared to, single HeLa cells, typical mammalian ova and embryos are more than an order of magnitude thicker. As a result, regions of large phase variation lead to phase wrapping and an overall reduction in signal intensity occurs due to multiple scattering. These effects manifest themselves in low-spatial frequencies (blurs), with the desired details buried in the background. We present a phase shifting interferometer that yields the derivative of the phase, a quantity whose value is particularly sensitive to local variations and fine details. We demonstrate that our new real-time imaging platform is valuable in measuring the multiday development of bovine embryos. Reconstructing the derivative of the image phase and amplitude, we characterize the motion of previously low-contrast structures, which are relevant for embryo viability tests.

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Mikhail E. Kandel, Marcello Rubessa, Daniel Fernandes, Tan H. Nguyen, Matthew B. Wheeler, and Gabriel Popescu, "Monitoring in-vitro bovine embryo development during the first days after fertilization (Conference Presentation)," Proc. SPIE 9718, Quantitative Phase Imaging II, 97180M (Presented at SPIE BiOS: February 15, 2016; Published: 27 April 2016); https://doi.org/10.1117/12.2217122.4848767816001.