Projet ANR-06-BLAN-0394 – SYDIMEN : SYstèmes DIscrets et Micro Endoscopie Non linéaire
Programme : Programme blanc (BLANC) 2006
Année de financement : 2006
Coordinateur du projet : UNIVERSITE DE LIMOGES (UNIVERSITE DE LIMOGES)
Partenaires : Institut Curie; Université Lille 1 - Sciences technologies; Université de Limoges
Montant : 550000.0 euros
Date de début : 2006
Durée : 36 mois
Résumé : SYDIMEN SYstèmes DIscrets et Micro-Endoscopie Non linéaire   The project concerns an innovative and flexible optical imaging system dedicated to in vivo and in situ microscopy of biological samples through a specific optical fibre image guide. More particularly the system will suit the requirements of high resolution nonlinear imaging techniques such as two photon fluorescence (TPF) microscopy, second and third harmonic generation microscopy, etc...  1-Introduction  1-1 Context: flexible micro-endoscopy  Confocal fluorescence microscopy has been very helpful in biology, and opened the way to major discoveries in cell biology. The availability of femtosecond turn-key laser sources in the last ten years has expanded the benefits of laser scanning microscopies toward dynamic and in vivo imaging, with strong benefits in neurobiology, immunology, cell biology, and developmental biology [1]. The interaction between the femtosecond excitation and the sample only occurs in a sharp volume at the focus of the imaging objective where the intensity is sufficiently high to produce two photon absorption or second harmonic generation. Optical signals classically come as the response of extrinsic fluorescent chromophores that specifically reveals the features of the sample (GFP, FITC-derived molecules, ion indicators, ...). An other possibility is to make use of the intrinsic resonant (fluorescence) or non-resonant response (Raman, optical harmonics) of biomolecules and their assemblies (collagen, NADH, ....) [2]. Nonlinear optical excitation significantly reduces phototoxicity, allows for deeper tissue imaging, offers a high signal to noise ratio for detection, and the larger stokes shift helps better signal collection. Many teams are now exploring the applications of non-linear imaging to medical diagnostic imaging (oncology, ophthalmology, dermatology, neurodegenerative diseases, ...). A major challenge consists in bringing the imaging device as close as possible to the living environment, but current achievements remains limited to rather external accesses to the body (brain surface through the skull, skin flaps on the back), and rather on anesthetized animals than vigil humans ! The main limit arises from the bulky size of objectives and scanning devices. On the other hand, endoscopy is now a well established medical tool for diagnostic macroscopy and surgery, with bundles of optical waveguides that give images from the inside of the human body. The spatial resolution is far from that required to visualize the cells with subcellular resolution. This situation is probably changing (see the confocal endoscope of Optiscan Ltd. & Pentax).  It is our goal here to develop a system that would permit nonlinear microscopy in vivo without these drawbacks. Our system will provide remote imaging and even internal imaging of the body through a special flexible optical fibre waveguide. It will make the link between the laser source and the imaging set-up within the living body. Such an equipment does not exist yet neither on the market nor in research laboratories.   Three main reasons make it difficult to associate fibre image guides and nonlinear microscopy:  (1) It is now familiar that endoscopes, a bundle of optical waveguides, give images from the inside of the human body. They are used in hospital for diagnosis and surgery. Their spatial resolution is far by orders of magnitudes from that required to visualize the cells. New waveguides must be designed and fabricated. (2) For nonlinear imaging, bright and ultra-short (~100 fs) pulses in the infra-red (~800 nm) must be delivered to the tissues. It is well known that optical fibres, usually made of silica, disperse the spectral component of the pulse which broadens to several picosecond durations after one meter propagation only. Self-phase modulation in the first stage of the propagation broadens the spectrum and increases further the pulse duration at high power level. Techniques must be imp...