Picosecond Kerr gated imaging of phantoms in turbid media.
Item
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Title
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Picosecond Kerr gated imaging of phantoms in turbid media.
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Identifier
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AAI9605679
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identifier
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9605679
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Creator
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Wang, Leming.
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Contributor
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Co-Advisers: R. R. Alfano | P. P. Ho
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Date
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1995
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Language
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English
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Publisher
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City University of New York.
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Subject
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Engineering, Electronics and Electrical
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Abstract
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The focus of this thesis is to characterize, understand, and improve upon a picosecond time-gated optical imaging method to localize hidden objects inside turbid media with sub-millimeter resolution. It was found that imaging information can be transported through the scattering medium by early-arriving ballistic and snake photons. Effective improvements of the image spatial resolution, dynamic range, contrast and signal to noise ratio of phantoms hidden in biomedical turbid media were achieved using a picosecond time- and space-gated imaging system. The rejection rate of diffusive photons provided by the time and space imaging system was {dollar}{lcub}\sim{rcub}10\sp{10}{dollar} to select the early light. The spatial resolution of image signal through turbid media was experimentally determined by estimating FWMH of point spread function of a point source. The spatial Fourier spectrum of turbid media with and without hidden object were examined. The minimum detectable contrast difference of {dollar}\Delta{dollar}OD = {dollar}\sim{dollar}0.14 or scattering coefficient difference {dollar}\Delta\mu{dollar} = 0.05mm{dollar}\sp{lcub}-1{rcub}{dollar} was demonstrated in a 50-mm thick highly scattering media with 1{dollar}\rm \sb{lcub}t{rcub}{dollar} = 4.6mm. Early-time-detected scattering attenuation coefficients of Intralipid solution was found. Images of translucent objects hidden in thick turbid media were obtained.;The thesis is divided into ten chapters. In the first chapter, the scientific background to field is introduced, which includes: several key issues to be investigated using the early light detection and spatial Fourier spectrum analysis in optical imaging in turbid media. In Chapter II, the operational principles behind the experimental arrangements, in which the time- and non-time-resolved imaging methods, transmission characters of the imaging set up are discussed. In this chapter, (1) a traditional continuous wave (CW) transillumination imaging method (Diaphanography); (2) a picosecond Kerr time-resolved imaging system without spatial gate (Kerr imaging); (3) a continuous wave spatial gate imaging system (CW-F); (4) a time-resolved Fourier gate imaging system (K-F); and (5) a double-stage optical Kerr gate imaging system are discussed. In the chapter III, the optical properties of biomedical media are discussed at different wavelengths. In the chapter IV, the transmission of the image signal of a point source, as the basic element of an image, is presented. In chapter V, the spatial Fourier transform of turbid media using a time-resolved imaging system and its application to image quality improvement are introduced, which includes Fourier spectrum of turbid media, the frequency filtering effect of an aperture on the image contrast and the temporal intensity distribution of the image signal through turbid media. Chapter VI focuses on the illumination intensity dependence of the image contrast in turbid media. The experimental results of the image contrast for both 1054nm and 527nm are described. In chapter VII, three basic influences onto the image quality in thick turbid media are discussed: (1) the size of the target; (2) the target depth (location) inside turbid media; (3) the minimum irradiation difference (the object contrast or contrast resolution) between the target object and the surroundings. The conclusion and future-direction of this work are found in Chapter VIII. The appendix is in Chapter IX. The last two sections of this thesis are Bibliography and list of my publications.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
