Imagerie

Résumé

L’imagerie consiste en la conception, la fabrication et le commerce des s. À la fin du , le terme désigne un ensemble d'objets sculptés qui représentent des êtres ou des choses. La fabrication se faisait soit à la main, soit par impression mécanique. À partir de la fin du , elle se fait principalement par ordinateur et imprimante. L'imagerie définit aussi simplement un ensemble d'images ayant soit une même origine et un style défini (par exemple, l'), soit un même style et un même genre (par exemple, l'). Le sens du mot image ayant connu des développements, le terme imagerie l'a suivi. Elle désigne donc également un ensemble de figures et de métaphores dans le domaine de la langue, ou d'un ensemble d' et psychiques qui se forment dans l'esprit. Dans le domaine scientifique, le terme est fort utilisé : l' est possible grâce à la radiologie, l' relève de la microscopie, l' concerne les satellites, l' englobe l', etc. Voir aussi Bibliographie * Articles c

Source officielle

https://fr.wikipedia.org/wiki/Imagerie

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Uncovering the neural substrates of communication between the brain and ventral nerve cord in Drosophila melanogaster (italic)

Florian Aymanns

Despite a long history of research in motor control, the exact mechanism of how the brain communicates with the the invertebrate ventral nerve cord (VNC) and the vertebrate spinal cord on a single neuron basis remains largely elusive.Drosophila melanogaster is an ideal model organism to address the role of individual neurons, thanks to its stereotyped nervous system.Descending neurons (DNs), interneurons in the brain that project to the invertebrate ventral nerve cord or vertebrate spinal cord, have been shown to elicit specific behaviors upon optogenetic activation in Drosophila.These results suggest that behavior is controlled by sparse sets of command neurons, each eliciting a particular behavior.However, it remains to be seen how many DNs are involved in the control of naturalistic behaviors and what other information they might encode.In order to avoid commands leading to physically impossible or destabilizing actions, the brain has to be aware of the current behavior state.Ascending neurons (ANs), interneurons in the invertebrate ventral nerve cord or vertebrate spinal cord projecting to the brain, are likely conveying this information to the brain.To which degree of fidelity and in what way ANs encode behavior state remains unclear.To address these questions, we developed a dissection approach that allows functional imaging of ANs and DNs in the cervical connective.This dissection gives us optical access to the cervical connective and parts of the VNC in behaving adult Drosophila such that a two-photon fluorescence microscope can be used to image neural activity via calcium indicators.We began by imaging a new library of sparse split GAL4 driver lines targeting ANs.Our recordings from 247 genetically identifiable ANs revealed neurons encoding walking, resting, turning, eye grooming, and foreleg movements.Anatomical characterization of these ANs showed that they predominantly project to two brain regions: the anterior ventrolateral protocerebrum (AVLP) and the gnathal ganglion (GNG).Our results suggest that ANs encoding the motion of the animal with respect to the surrounding environment (self-motion) predominantly project to the AVLP, an integrative sensory hub. ANs projecting to the GNG mostly encode discrete actions.We then proceeded to image populations of DNs.The majority of DNs we recorded encoded walking behavior, with smaller fractions encoding resting and head grooming.Some of these neurons are likely to drive walking, but we also identified neurons encoding walking speed and turning.This suggests that a core set of DNs drives a behavior whose features can be modulated by additional DNs.Besides encoding behaviors, some DNs encode sensory information, including the presence of odors and deflection of the antennae.

EPFL2022

Chargement

Imaging methods to capture the beating and developing heart inside embryonic animal models such as the zebrafish are a key component for the study of fundamental biological processes such as cardiac birth defects or tissue regeneration. However, live heart imaging is subject to many challenges that limit the achievable spatial and temporal resolutions. While many commonly available microscopes offer the necessary optical sectioning capabilities to produce slices or volumes at the required scale, they often lack the necessary speed to seamlessly resolve the beating heart within a still frame, the entire heartbeat, or over a complete developmental sequence. In this thesis, I aim to assemble dynamic image series of the heart by using a wide range of microscopes, including, in particular, scanning microscopes---which are widely available but slow---and microscopes with a slow framerate. First, I considered the problem of reconstructing an image sequence covering one heartbeat from still images arbitrarily triggered throughout multiple cardiac cycles, when the underlying cardiac motion is temporally asymmetrical. I proposed to sort the images such as to maximize the overall similarity between contiguous frames, which I formulated as a TSP. The performance of the method increases with the number of images. I reconstructed image sequences of the heart at a virtual frame-rate of up to 300 frames per second. Second, to resolve the ill-posedness of the sorting problem when identical object poses appear multiple times in one cycle, I proposed to illuminate alternate frames with a temporally-asymmetric pattern. Sorting issues are mitigated at the cost of a custom setup and additional light exposure, without adversely affecting the reconstructed sequence. Third, I considered the problem of imaging the beating heart on conventional scanning confocal microscopes (LSM) that have a frame scanning rate comparable to the heartbeat rate. My approach takes a set of arbitrarily triggered images that may contain scanning aberrations and assembles it into a sequence that covers one heartbeat. Reconstructing scanning-aberrated frames offers a robust alternative for LSM. The quality of recovered cardiac heartbeat dynamics is comparable to that obtained by fast microscopes. Finally, I considered the problem of building smooth time-lapse sequences in the cardiac phase versus development or imaging depth spaces, based on a set of still images captured at weakly-constrained times within the heartbeat and over the course of development or at various depths. This method determines a smooth path in cardiac phase-development or depth space enforcing neighborhood similarity via a within-stage (or within-depth) sorting followed by a cyclical least-squares phase alignment approach that I formulated as a mixed integer linear problem. Constraining the paths of time-lapses by providing key-points while enforcing local similarity successfully stabilizes the the excursion error from which recursive registration approaches suffer. The results suggest that reliably imaging the heart on a wide range of microscopes is possible, provided the heart motions are stereotypical and that minimal sampling constraints are met. The newly gained possibility of using conventional instruments may be particularly relevant for applications with emerging modalities that do not allow wide-field capture.

EPFL2021

Chargement

Advanced Techniques in Optical Diffraction Tomography

Ahmed Bassam Sayed Ayoub Mohamed Emam

In this thesis, we study the 3 challenges described above. First, we study different reconstruction techniques and assess the fidelity of each reconstruction results by means of structured illumination and phase conjugation. By reconstructing the 3D refractive index of the sample using different algorithms (i.e. Born, Rytov, and Radon) and then perform a numerical back-propagation of experimentally measured structured illumination pattern we are able to assess the fidelity of each reconstruction algorithms without prior information about the 3D RI distribution of the sample.The second part of the thesis is concerned with the 3D reconstruction of samples using intensity-only measurements which the need to holographically acquire them. We show that using intensity-only measurements, we could still be able to reconstruct the 3D volume of the sample with edge-enhanced effects which was proven useful for drug delivery applications in which nano-particles were identified on the cell membrane of immune T-cells in a drug delivery studies. Such reconstruction technique would result in more robust imaging system where the commercial imaging microscope systems can be incorporated with LEDs for high-quality speckle noise-free imaging systems. In addition, we show that under certain conditions, we can be able to reconstruct the 3D refractive index distribution of different samples.The third part of the thesis is contributing to high-speed complex wave-front shaping using DMDs. In that part, new modulation technique is demonstrated that can boost the speed of the current time-multiplexing techniques by a factor of 32. The modulation technique is based on amplitude modulation where an amplitude modulator is synchronized withvthe DMD to modulate the intensity of each bit-plane of an 8-bit image and then all the modulated bit-planes are linearly added on the detector. Such modulation technique can be used not only for structured illumination microscopy but also for high-speed 3D printing applications as well as projectors.The last part is concerned with using deep learning approaches to solve the missing cone problem usually accompanied with optical imaging due to the limited numerical aperture of the imaging system. Two techniques are discussed; the first is based on using a physical model to enhance the quality of the 3D RI reconstruction and the second is based on using deep neural network to solve the missing cone problem.

EPFL2022

Chargement

EPFL2021

Uncovering the neural substrates of communication between the brain and ventral nerve cord in Drosophila melanogaster (italic)

Florian Aymanns

EPFL2022

Advanced Techniques in Optical Diffraction Tomography

Ahmed Bassam Sayed Ayoub Mohamed Emam

EPFL2022