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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 73 (2002), S. 2917-2922 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Low light-level ultraviolet and optical imaging with a photon counting image intensifier coupled to a charge coupled device camera generally results in varying levels of fixed pattern noise in the image. Here, we demonstrate that this can be minimized by the appropriate choice of photon event centroiding algorithm. We compare the fixed pattern noise generated by a center of gravity centroiding algorithm, a Gaussian centroiding algorithm, and a hybrid centroiding algorithm which uses center of gravity centroiding when one wing is zero, and Gaussian centroiding otherwise. This approach yields the best image quality with a lower fixed pattern noise parameter (9.99%) than the sole use of Gaussian centroiding (16.4%), and there is no need for a look-up table correction. In addition, the hybrid algorithm also yields maximum detective quantum efficiency by overcoming small pulse centroiding failure associated with Gaussian centroiding. The digitization error when recording the events is modeled with a Monte Carlo simulation and discussed. It is found that a center of gravity algorithm produces not only significant fixed pattern noise, but also pulse height dependent x¯ positions. For a Gaussian centroiding algorithm the x¯ positions are independent of the pulse height, the fixed pattern noise is low and the digitization error only yields a small increase of the fixed pattern noise parameter. This shows that while there is a limit to centroiding accuracy due to the digitization error, the appropriate choice of centroiding algorithm is a much more important factor to minimize fixed pattern noise. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1600-065X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Summary: As T cells and natural killer (NK) cells survey the surface of other cells, cognate receptors and ligands are commonly organized into distinct micrometer-scale domains at the intercellular contact, creating an immune or immunological synapse (IS). We aim to address the still unanswered questions of how this organization of proteins aids immune surveillance and how these domains are biophysically constructed. Molecular mechanisms for the formation of the IS include a role for the cytoskeleton, segregation of proteins according to the size of their extracellular domains, and association of proteins with lipid rafts. Towards understanding the function of the IS, it is instructive to compare and contrast the supramolecular organization of proteins at the inhibitory and activating NK cell IS with that at the activating T cell IS. Finally, it is essential to develop new technologies for probing molecular recognition at cell surfaces. Imaging parameters other than fluorescence intensity, such as the lifetime of the fluorophore's excited state, could be used to report on protein environments.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We report the operation of a new type of fluorescence lifetime imaging camera based on the time-correlated single-photon counting (TCSPC) technique. To the best of our knowledge the application-specific integrated circuit (ASIC) used in the camera is the first ASIC designed for the field of fluorescence. The ASIC also forms the basis for the first read-out system for single-photon timing array detectors and is capable of multiplexing and routing counts from up to sixteen detection channels, while preserving their timing characteristics with picosecond resolution. In conjunction with an array detector such as a multianode MCP-PM this ASIC allows multiple fluorescence decays to be routinely and simultaneously acquired using a single set of TCSPC timing electronics. To demonstrate one practical application of this technology, we have observed for the first time the spatial distribution of fluorescence lifetime contours through a strongly self-absorbing sample, and the effects observed demonstrate how differences in optical geometry can contribute to the lack of consistency between results obtained in different laboratories. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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