Ultrahigh-resolution full-field optical coherence tomography for imaging of a developing embryo

Abstract

Optical coherence tomography (OCT) is a new emerging technique for cross-sectional imaging with high spatial resolution of micrometer scale. It enables in vivo and non-invasive imaging with no need to contact the sample and is widely used in biological and clinic application. In this paper a white-light interference microscope is developed for ultrahigh-resolution full-field optical coherence tomography (Full-Field OCT) to implement 3D imaging of biological tissue. The experimental setup is based on a Linnik-type interferometer illuminated by a tungsten halogen lamp via a bundle of fiber. En-face tomographic images are obtained by demodulation of a combination of interferometric images recorded by a CCD camera. We use a PZT synchronized with the CCD in the reference arm to get the modulated interferometric image and use a programmed precisely controlled electric lift stage in the sample arm to get a 3D image. To fulfill the requirement of in vivo measurement and better match the index of bio-tissue, a pair of high numerical-aperture water immersion microscope objectives is used. Spatial resolution of 1.8μm×1.12μm (transverse×axial) is achieved owing to the extremely short coherence length of the light source and optimized compensation of dispersion mismatch. A shot-noise limited detection sensitivity of 80 dB is obtained at an acquisition time of 5 seconds per image. The development of a mouse embryo is studied layer by layer with our ultrahigh-resolution full-filed OCT. 3D imaging of the embryo can be reconstructed by the OCT images. Information of cell shape, centroid, reflectivity, mitosis period in the development process can be obtained. The variance of the relative reflectivity of an oocyte with time is calculated as well. It is found that the reflectivity of a living oocyte is much lower than that of a dead. Therefore the reflectivity of the cytoplasm can be a signal of the cell activity. In fact, all these parameters above could be very useful for distinguishing the healthy embryos from the morbid, showing high potential for early diagnosis of procreation diseases at cellular level in clinic. More experimental study is still in progress.