Complete Angle Small Animal Fluorescence Imaging with Early-Arriving Photons

Fluorescence mediated tomography allows quantitative, three-dimensional imaging of optical reporter probes in whole animals and is therefore emerging as a powerful molecular imaging tool. The achievable image quality in fluorescence tomography is limited by the high-degree of light scatter in biological tissue. Time-gated detection of early-arriving and therefore minimally-scattered photons transmitted through diffusive tissue is one strategy for minimizing the effects of light scatter. In this work, we performed full-angle tomographic imaging of mice implanted with fluorescent tubes using time-gated detection of early- and later-arriving photons. This was achieved using a femtosecond laser and a high-speed, time-gated intensified CCD imager. We demonstrate that the early-transmitted fluorescent photons allow improved visualization of the fluorescence distribution, even when considering individual projections through the animal. High-fidelity image reconstruction using 72 projections in 5-degree steps using early-arriving photons is also demonstrated.