Section: Scientific Foundations
Image restoration for high-resolution microscopy
Optical Wide-Field microscopy.
(Fluorescence Lifetime Microscopy Imaging): imaging of fluorescent molecule lifetimes.
(Förster Resonance Energy Transfer): energy transfer between neighbouring molecules.
(Photo-Activated Localization Microscopy): high-resolution microscopy using stochastic photo-activation of fluorophores and adjustment of point spread functions [20] .
(Structured Illumination Microscopy): high-resolution light microscopy using structured patterns and interference analysis [27] .
(Total Internal Reflectance): 2D optical microscopy using evanescent waves and total reflectance [19] .
(Cryo-Electron Tomography): 3D representation of sub-cellular and molecular objects of 5-20 nanometres, frozen at very low temperatures, from 2D projections using a transmission electron microscope.
In order to produce images compatible with the dynamic processes in living cells as seen in video-microscopy, we study the potential of denoising approaches and non-iterative algorithms [6] , [2] , [7] , [4] . The major advantage of these approaches is to acquire images at very low SNR while recovering denoised 2D+T(ime) and 3D+T(ime) images [1] . Such post-acquisition treatment can improve the rate of image acquisition by a factor of 100 to 1000 times [5] , reducing the sensitivity threshold and allowing imaging for long time regime without cytotoxic effect and photodamages. This approach has been successfully applied to wide-field, Nipkow disk based confocal [1] , TIRF (Total Internal Reflection Fluorescence [19] microscopy), fast live imaging and 3D-PALM using the OMX system in collaboration with J. Sedat and M. Gustafsson at UCSF [5] . The nd-safir software (see Section 5.1 ) has been licensed to a large set of laboratories over the world (see Figure 1 ). New developments are required in the future to be compatible with “high-throughput microscopy” since we need to analyse several hundred of cells at the same time and since the exposure times are typically reduced.
Meanwhile, improving the resolution beyond 200 nm diffraction limit while retaining the advantages of light microscopy and the specificity of molecular imaging is a long-standing goal in optics. Recent advances have been achieved using 3D-SIM (Structured Illuminated Microscopy) [27] . While being probably less effective in “breaking the resolution barrier” than other optical sub-diffraction limited techniques (e.g. STED [29] , PALM [20] ), SIM approach has the strong advantage of versatility when considering the photo-physical properties of the fluorescent probes. Nevertheless, in their classical form, SIM is poorly compatible with time regimes expected in most live cell imaging, which restrict their application to fixed samples. Advances in information restoration and image denoising should make SIM imaging compatible with the imaging of molecular dynamic in live cells.