Optical coherence microscopy as a novel, non-invasive method for the 4D live imaging of early mammalian embryos

Abstract

Imaging of living cells based on traditional fluorescence and confocal laser scanning microscopy has delivered an enormous amount of information critical for understanding biological processes in single cells. However, the requirement for a high numerical aperture and fluorescent markers still limits researchers’ ability to visualize the cellular architecture without causing short- and long-term photodamage. Optical coherence microscopy (OCM) is a promising alternative that circumvents the technical limitations of fluorescence imaging techniques and provides unique access to fundamental aspects of early embryonic development, without the requirement for sample pre-processing or labeling. In the present paper, we utilized the internal motion of cytoplasm, as well as custom scanning and signal processing protocols, to effectively reduce the speckle noise typical for standard OCM and enable high-resolution intracellular time-lapse imaging. To test our imaging system we used mouse and pig oocytes and embryos and visualized them through fertilization and the first embryonic division, as well as at selected stages of oogenesis and preimplantation development. Because all morphological and morphokinetic properties recorded by OCM are believed to be biomarkers of oocyte/embryo quality, OCM may represent a new chapter in imaging-based preimplantation embryo diagnostics.

Speckle variance OCT for depth resolved assessment of the viability of bovine embryos

“…To date, a limited number of reports have focused on applying functional OCT imaging to study early mammalian embryos [18,24,25]. However, to our best knowledge, this is the first time OCT and SV have been applied to a day 7 post-IVF mammalian embryo to resolve its 3D structure and quantify micron-scale movement.…”

“…OCT has already found some limited application in developmental biology in model organisms like Xenopus laevis [16], and Rattus norvegicus [17]. Recently, high-resolution intracellular imaging on live mouse and pig oocytes and embryos has been reported [18]. In this context, the fundamental advantages of OCT are its ability to image embryos without labels, and its use of low power light sources as compared to confocal systems.…”

“…In this context, the fundamental advantages of OCT are its ability to image embryos without labels, and its use of low power light sources as compared to confocal systems. The use of low power optical beams reduces the chance of damaging the embryo during observation [18,19]. However, no study so far has applied the motion detection principles of OCTA to early stage embryos, like blastocysts, to assess their viability.…”

Assessing embryo development using swept source optical coherence tomography

“…Micron-sized axial and lateral resolutions are achievable. Moreover, OCT has been used to study several aspects of embryo development, such as those connected to the heart or the vasculature system [10,11]. OCT can provide 3D images of the full embryo non-invasively.…”

Enhancing microvasculature maps for Optical Coherence Tomography Angiography (OCT-A)

“…Some recent improvements include speckle-modulation OCT (SM-OCT), which has demonstrated superiority by revealing anatomical features previously hidden by speckle noise [3]. Moreover, there have also been advancements in 4D live imaging using OCT [4]. The major disadvantage of OCT is that it is impossible to visualize microvasculature in real time from the raw OCT data.…”