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22 February 2010 Optical imaging of structures within highly scattering material using an incoherent beam and a spatial filter
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Angular Domain Imaging (ADI) is a high resolution, ballistic imaging method that utilizes the angular spectrum of photons to filter multiply-scattered photons which have a wide distribution of angles from ballistic and quasi-ballistic photons which exit a scattering medium with a small distribution of angles around their original trajectory. An advantage of the ADI method is that it is suitable with a wide variety of light sources, as it is not sensitive to coherence or wavelength and does not require a pulsed source or a highly collimated beam. We extend the ADI method to transmissive imaging of scattering media using incoherent, collimated sources with a spatial filter comprised of a converging lens (focal distance of 50 to 100 mm) and pinhole aperture (diameter of 100 to 500 μm) giving acceptances angles of 0.06 to 0.6° to produce wide-beam, full-field images of planar, high contrast, phantom test objects through 5 cm thick scattering media at optical depths of up to 14.6 (scattered to ballistic photon ratio ≈ 2×106). Experimental images, obtained using a 12 mm diameter beam produced by a quartz-halogen incandescent source (beam divergence angle 0.52°, beam power < 10 mW), demonstrate the advantages of this combination of broadband, incoherent source and spatial filter: lack of interference artifacts seen with laser sources, ease of changing image magnification, simple correlation between system geometry and resolution, and ease of spectral filtration to obtain multispectral images. Monte Carlo simulation with angular tracking is used to validate the experimental results and determine system tradeoffs.
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Nick Pfeiffer, Glenn H. Chapman, and Bozena Kaminska "Optical imaging of structures within highly scattering material using an incoherent beam and a spatial filter", Proc. SPIE 7562, Optical Interactions with Tissues and Cells XXI, 756208 (22 February 2010);

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