Computational Refractive Index Light-sheet Microscopy (CORILIM)

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Developing future therapies, the first of EPSRC's Healthcare Technologies Grand Challenges, is essential to keep the National Health Service sustainable. Currently, an estimated 70% of the UK's healthcare expenditure goes towards the management of chronic diseases. Regenerative medicine is expected to significantly reduce costs as it can turn chronic, degenerative, diseases into curable conditions. Realising this potential requires the right tools to study the biological development process as it progresses from the single cell to the complex structure of entire organs.The invention of the optical microscope, and in particular the phase contrast microscope, made it possible to highlight the fine features of living cells with unprecedented clarity. However, cells isolated on a microscope slide often do not behave as tissue in its natural, three-dimensional, environment. The recent development of the planar illumination light-sheet microscope enabled the visualisation of the intact, fluorescently-labelled, organisms during development. While light-sheet microscopy is highly successful for transparent zebrafish or chemically cleared tissue, many tissues are too opaque to be studied beyond the first layer of cells. A prime example is the chick embryo in its early stages of development. The complex collective behaviour of the cells in the initial layer can be studied in exquisite detail, yet as soon as the primitive streak forms, to grow the embryo in the third dimension, we lack the tools to keep track of the cell migration and differentiation. The images are too blurred.Correlative refractive index light-sheet microscopy aims to make the invisible visible. It is based on the realization that the turbidity of biological samples is due to the same refractive index variations that yield structural information in phase-contrast microscopy. The distribution of optical properties within the specimen not only contains valuable structural information for the biologist, it also enables the adaptive wavefront correction needed for high resolution fluorescence imaging. By developing a hybrid instrument that maps the optical property distribution in parallel with the fluorescence image, this proposal will enable high-resolution deep-tissue imaging in turbid biological specimen. A direct view into the inner workings of the biological development process is essential to develop effective regenerative-medicine therapies.