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Proceedings Paper

Spatial localization using interfering photon density waves: contrast enhancement and limitations
Author(s): Alexander R. Knuettel; Joseph M. Schmitt; R. Barnes; Jay R. Knutson
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Paper Abstract

In most of the optical methods proposed for imaging an absorbing object embedded in a turbid medium, data is collected using a single source and detector scanned mechanically across the surface of the medium. In this study we exploited destructive interference of diffusive photon- density waves originating from two sources to localize one absorbing (or fluorescent) object in a scattering medium. A frequency-domain instrument is described for scanning several laser- beam spots across the surface of a turbid medium using 1D (or 2D) acousto-optical deflectors and detecting the signals with a gated, intensified CCD camera at a modulation frequency of 246 MHz. The localization of multiple objects arranged in the form of a spatial grating was investigated theoretically with an analytic model by combining the magnitude and phase of the signals detected from the objects. A novel grating pattern comprising several destructively interfering lines, which acts as spatial frequency filter, is discussed. The results were compared with those obtained using a single-source/single-detector scanning configuration. We show that the FWHM (full-width half-maximum) of the signal detected using the single- source/single-detector configuration establishes a limiting spatial scale over which multiple objects can be resolved. Beyond this limit the resolution can only be increased under severe penalty of contrast and signal loss.

Paper Details

Date Published: 14 September 1993
PDF: 12 pages
Proc. SPIE 1888, Photon Migration and Imaging in Random Media and Tissues, (14 September 1993); doi: 10.1117/12.154650
Show Author Affiliations
Alexander R. Knuettel, National Institutes of Health (United States)
Joseph M. Schmitt, National Institutes of Health (United States)
R. Barnes, National Institutes of Health (United States)
Jay R. Knutson, National Institutes of Health (United States)

Published in SPIE Proceedings Vol. 1888:
Photon Migration and Imaging in Random Media and Tissues
Britton Chance; Robert R. Alfano, Editor(s)

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