Image contrast enhancement during time-angular domain imaging through turbid media by estimation of background scattered light

Time-angular domain imaging (TADI) employs an angular filter array, which functions to accept quasi-ballistic photons with trajectories near the axis of a collimated light source. At high scattering coefficients, image contrast declines due to background signals from scattered photons that have trajectories compatible with the angular filter array. We attempted to correct for the background signal using a temporal discrimination technique and image subtraction. During TADI through turbid media, photons at early arrival times represent a mixture of quasi-ballistic and scattered photons, while late arriving photons represent scattered photons. We captured two TADI images of a resolution target suspended midway through a 2 cm thick cuvette filled with 0.30% Intralipid (TM). A 780 nm, 100 ps pulsed laser (PicoTA, PicoQuant) was used to trans-illuminate the cuvette. Detection was performed after the angular filter array (500 elements with 60 mu m x 60 mu m square-shaped cross section and 1 cm length) with a gated camera (Picostar HR, LaVision). The first TADI image was collected at a short gate delay with respect to the minimum transit time, and resulted in a projection of the target. A long gate delay was used to collect the second TADI image and the projection of the target was not apparent. A corrected image (two - one) was digitally computed. Analysis of the first image compared to the corrected image revealed a 2.1-fold increase in contrast-to-noise ratio for the corrected image. Therefore, images collected with TADI were improved by processing successive images at different gate delays.