Multispectral angular domain imaging with a tunable pulsed laser

Angular Domain Imaging (ADI) is an imaging technique that is capable of generating three dimensional images of attenuating targets embedded in a scattering medium. In ADI, an angular filter is positioned between the sample and the detector to discriminate between quasi-ballistic photons and scattered photons. Quasi-ballistic photons have undergone relatively few forward directed scattering events, and can be used to generate a projection image representative of the imaging target. Scattered photons have undergone many scattering events and contain little information regarding the imaging target, thereby leading to decreased image contrast. Our implementation of ADI utilizes a silicon micro-channel array to reject scattered photons based on the angle at which they exit the sample. The objective of this work was to collect ADI images with a tunable pulsed laser within the visible range. Samples were illuminated at 13 wavelengths between 460 nm and 700 nm. An angular filter array of 80 μm × 80 μm tunnels 2-cm long was used to select the quasiballistic photons. Images were detected with a linear 16-bit linear CCD. The phantom consisted of a 0.7 mm attenuating target submerged in one of four IntralipidR dilutions (0.15%-0.3%) contained within a 1 cm path length cuvette. Image contrast ranged from 0.02 at 460 nm and 0.3% IntralipidR to 1 at 680 nm at 0.15% IntralipidR. For a given scattering level, contrast increased at longer wavelengths. Resolution varied minimally with wavelength. The results suggested that multispectral ADI with a tunable pulsed laser is feasible and may find utility in imaging thin tissue samples in the future.