Tomographie optique des photons diffusés et de fluorescence : un appareil dédié au petit animal

Abstract

Various optical approaches have been used to image fluorescence in vivo, ranging from confocal microscopy, to observe markers close to the surface, to photographic macroscopic systems, to probe deeper tissues. We developed a tomographic approach that uses diffuse near infrared and fluorescence photons to image the optical properties of tissues and the fluorescent probes distribution. This method uses multiple-projections acquisition and a reconstruction procedure based on the principles of diffuse optical tomography. The scanner assembled uses 8 ps laser diodes, an eight-anode photo-multiplier tube (PMT) and time-correlated single photon counting. Two sets of four laser heads, at four wavelengths, are fitted with furcated optical fibers, providing sequential sources of light. Eight multimode optical fibers are used to detect light. These fibers are connected to the PMT with an air-gap allowing the insertion of an optical filter to reject the excitation wavelengths. The light sources and detectors can be rotated to increase the number of projections recorded. An interferometry technique using a conoscope and a XY scanning system records the coordinates of the body surface, required for the reconstruction process, before entering the animal in the scanner. Excitation profiles are used to compute absorption and reduced scattering images of the animal. Fluorescence images, free from diffusion and absorption artefacts, are then computed with a-priori knowledge of the optical images of the animal. The scanner, its performances and images of light scattering and fluorescent phantoms will be presented.