Abstract
The morphology of embryos produced by in vitro fertilization (IVF) is commonly used to estimate their viability. However, imaging by standard microscopy is subjective and unable to assess the embryo on a cellular scale after compaction. Optical coherence tomography is an imaging technique that can produce a depth-resolved profile of a sample and can be coupled with speckle variance (SV) to detect motion on a micron scale. In this study, day 7 post-IVF bovine embryos were observed either short-term (10 minutes) or long-term (over 18 hours) and analyzed by swept source OCT and SV to resolve their depth profile and characterize micron-scale movements potentially associated with viability. The percentage of en face images showing movement at any given time was calculated as a method to detect the vital status of the embryo. This method could be used to measure the levels of damage sustained by an embryo, for example after cryopreservation, in a rapid and non-invasive way.
Highlights
After fertilization, mammalian zygotes undertake a series of rapid mitotic divisions known as cleavage events which bring them from the original 1 cell to 16-32 cells
12 structural images were displayed in real time in the form of summed voxel projection (SVP), 2 x cross sectional images and 9 x en face images
The volume allowed by the “in-house” acquisition software written in LabVIEW software extends over a voxel size of 200x200x500 pixels
Summary
Mammalian zygotes undertake a series of rapid mitotic divisions known as cleavage events which bring them from the original 1 cell to 16-32 cells In cattle, this phase has a duration of approximately 4 days, after which the embryo undergoes the process of compaction during which it appears as a tight cluster of cells with hardly any distinguishable inter-cellular borders. Bovine blastocysts produced by IVF are screened morphologically at x50 to x100 magnification using a stereomicroscope [5] Whilst this level of investigation is simple and non-invasive, it is highly subjective, gives little indication of intracellular activity [4], and is unable to quantify accurately the percentage of fragmentation (amount of sub-cellular, non-viable material) in the embryo which is known to affect its viability [6]
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