High-resolution mapping of embryo mechanical properties during development with reverberant OCE

Abstract

Many embryonic developmental processes are inherently mechanical, such as elongation, neural tube closure, and cardiogenesis. Any disruption or failure of these events can lead to debilitating or even fatal pathologies, e.g., anencephaly. While much is known about the genetic and molecular mechanisms underlying these processes, there remains a significant knowledge gap about the associated biomechanical parameters due to the lack of noninvasive high-resolution mechanical imaging techniques, particularly in live samples. In this work, we demonstrate completely noninvasive, label-free, highresolution, and three-dimensional mapping of mouse embryo stiffness at several critical stages of embryogenesis based on reverberant shear wave optical coherence elastography (Rev-OCE). Mouse embryos at various developmental stages (embryonic day 9.5, 10.0, 10.5, 11.0, and 11.5) were dissected out and placed on an optical window during imaging. The samples were encompassed in embryo culture media to preserve the integrity of the delicate embryo tissues. The optical window was attached to a piezoelectric bender, which vibrated the optical window at 1 kHz. M-C-mode imaging was performed with a phase-sensitive spectral domain OCT system operating in the common-path configuration. Standard reverberant OCE processing steps were applied, and the local autocorrelation was fitted to the analytical solution of the reverberant shear field. The local shear wave speed was then mapped in 3D. The results show that the stiffness of the spine, heart, and brain all increased as the embryo developed.