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15 April 2005 Angular domain image detectability with changing turbid medium scattering coefficients
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Optical tomography within highly scattering media has usually employed coherence domain and time domain imaging, which observe the shortest path photons over the dominant randomly scattered background light. An alternative, Angular Domain Imaging, employs micromachined collimators which detect photons within a small angle of the aligned laser light source. These angular filters consist of micromachined silicon collimator channels 51 micron wide by 10 mm long on 102 micron spacing giving an acceptance angle of 0.29 degrees at a CCD detector. Phantom test objects were observed in turbid mediums ranging from 1 to 5 cm thick at effective scattered to ballistic ratios from 1:1 to greater than 100,000,000:1. Simple line and space test objects detection limits are set by detector pixel size not collimator hole spacing. Restricting the light emission to only the collimating array hole area provides increased detectability by reducing the amount of scattered light background. This is best done using cylindrical spherical cylindrical lens beam expanders/shrinkers to create a wide line of light of small thickness aligned to the collimator array. As object locations within the medium are moved closer to the detector/collimator, image detectability appears to depend on the scattering ratio after the test object rather than the total medium scattering. Hence, objects located closer to the detector than the middle of the medium are observed at a much higher scattering levels than those nearer the light source.
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Glenn H. Chapman, Paulman K. Y. Chan, Jozsef Dudas, Josna Rao, and Nick Pfeiffer "Angular domain image detectability with changing turbid medium scattering coefficients", Proc. SPIE 5695, Optical Interactions with Tissue and Cells XVI, (15 April 2005);

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