A time-resolved, multi-wavelength, fluorescence, diffuse optical tomography system for small animal imaging

摘要

A tomographic approach, relying on diffuse near infrared photons to image the optical properties of tissues and the inner distribution of fluorescent probes is described. The method should improve the spatial resolution and quantification of fluorescence signals, thanks to multiple-projection acquisitions and to a reconstruction procedure using the principles of diffuse optical tomography. The scanner assembled uses picosecond laser diodes, an eight-anode photo-multiplier tube (PMT) and time-correlated single photon counting. Two sets of laser heads, each operating at four wavelengths, are fitted with furcated optical fibers, providing two sequential sources of light positioned on the animal or object studied. Multimode optical fibers are used to detect light at eight output points on the animal or object. These fibers are connected to the PMT, with an air-gap allowing the insertion of an optical filter to reject the excitation wavelength. The light sources and detectors can be rotated to increase the number of projections recorded. For the reconstruction process, the coordinates of the body surface of the animal to be imaged are necessary. These are acquired by interferometry, using a conoscope and an XY scanning system, before the animal is entered in the scanner. The profiles measured at the excitation wavelengths are used to compute absorption and reduced scattering images and perfusion/oxygenation images of the animal. Fluorescence images, free from diffusion and absorption artefacts, can then be computed with a-priori knowledge of the optical images of the animal. The scanner, its performances and images of light-scattering and fluorescent phantoms are presented.