SignificanceAdaptive optics (AO) has been implemented on several microscopy setups and has proven its ability to increase both signal and resolution. However, reported configurations are not suited for fast imaging of live samples or are based on an invasive or complex implementation method.AimProvide a fast aberration correction method with an easy to implement AO module compatible with light-sheet fluorescence microscopy (LSFM) for enhanced imaging of live samples.ApproachDevelopment of an AO add-on module for LSFM based on direct wavefront sensing without requiring a guide star using an extended-scene Shack-Hartmann wavefront sensor. The enhanced setup uses a two-color sample labeling strategy to optimize the photon budget.ResultsFast AO correction of in-depth aberrations in an ex-vivo adult Drosophila brain enables doubling the contrast when imaging with either cell reporters or calcium sensors for functional imaging. We quantify the gain in terms of image quality on different functional domains of sleep neurons in the Drosophila brain at various depths and discuss the optimization of key parameters driving AO.ConclusionWe developed a compact AO module that can be integrated into most of the reported light-sheet microscopy setups, provides significant improvement of image quality and is compatible with fast imaging requirements such as calcium imaging.
Optical microscopy allows to perform structural and functional imaging within large volume of tissues with subcellular resolution. Non-linear microscopy allows the interrogation of neuronal activity in mammalian brains but remains limited because of scattering and optical aberrations. To overcome these issues, Adaptive Optics (AO) strategies have been implemented to retrieve the microscope imaging quality while addressing important imaging depths.
A first AO strategy implemented in non-linear microscopy relies on a sensorless configuration, but is a time-consuming iterative process hardly compatible with photobleaching issues. A second approach is based on direct wavefront sensing using Shack-Hartmann wavefront sensors and has proved its efficiency on in vivo experiments. However, this method fails at large depths because of the strong scattering of the emitted fluorescence. A method for direct wavefront sensing more resilient to scattering of the fluorescence emission would therefore facilitate the use of AO in optical microscopy.
This work proposes an alternative method of direct wavefront measurement, which relies on the cross-correlation of images of an extended source obtained through a microlens array. This extended-source Shack-Hartmann wavefront sensor (ESSH) requires to be coupled to an optical sectioning method. Its efficiency has been proven when coupled to Light Sheet Fluorescence Microscopy in the adult drosophila brain in weekly scattering conditions. Here, we show that it allows quantitative aberration measurements through highly scattering fixed brain slices, up to four times the scattering length of the tissue. We demonstrate that it is more resilient to scattering compared to the current centroid-based approach. Taking advantage of its geometry, this new wavefront sensor also provides scattering coefficient measurements of biological tissues. Finally, we present its implementation on a two-photon microscope within a closed–loop configuration for in depth neuroimaging in mouse brain and compare its performances in scattering media to the classical centroid approach.
This conference presentation, “Axially-swept adaptive optics light sheet fluorescence microscopy for high resolution neuroimaging in the drosophila brain” was recorded for the Biomedical Spectroscopy, Microscopy, and Imaging II conference at SPIE Photonics Europe 2022.
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