Angular domain fluorescent lifetime imaging in turbid media

We describe a novel florescent lifetime imaging methodology applicable to fluorophores embedded in turbid media. The method exploits the collimation detection capabilities of an angular filter device to extract photons emitted by a fluorophore embedded at depth within the medium. A laser source is used to excite the fluorophore within the medium. Photons emitted by the fluorophore that are not scattered to a high degree pass through the angular filter array and are detected by the intensified CCD camera (200 ps minimum gate width). Scattered photons are rejected by the filter and do not pass through to the camera. We fabricated angular filter arrays using silicon bulk micromachining and found that an array of 80 μm square aperture micro-tunnels, 1.5 cm in length accepted photons with trajectories within 0.4° of the axes of the micro-tunnels. The small acceptance angle rejected most of the scattered light exiting the turbid medium.