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Proceedings Paper

Spatial localization of discrete fluorescent inclusions with early photons: an analysis on the stability with respect to variations of optical properties
Author(s): Geoffroy Bodi; Yves Bérubé-Lauzière
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Paper Abstract

We recently developed a time-domain technique for localizing in 3D discrete fluorescent inclusions embedded in a scattering medium. It exploits early photon arrival times (EPATs), that is the time of flight of early arriving photons at a detector determined via numerical constant fraction discrimination. Our localization technique requires the knowledge of the speed of propagation of diffuse light pulses in the turbid medium to convert measured propagation times to distances. We have developed an experimental method for measuring the speed of propagation of such pulses. We have shown that time differences between a reference detector position and other positions around the medium allow finding the position of the inclusion. Our technique allows localizing inclusions to millimeter precision in a thick 5 cm diameter turbid medium. Herein, we analyze the stability of EPAT differences introduced above and propagation speeds with respect to changes in the medium's optical properties for optical properties typical of biological tissues. As we target small animal imaging, we concentrate on optical properties of mouse organs and tissues. Our objective is to determine bounds to be expected on the precision that can be achieved when media properties can vary and determine the limits of validity of our localization technique. Our results show that EPAT differences and propagation speeds obtained by our approach can vary; these values depend on the medium. We study 5 kinds of mouse organs and tissues. Propagations speeds are between 2.97 × 107ms-1 and 5.52 × 107ms-1. Thus, it becomes important to evaluate the discrepancy between true geometrical distance differences and distances as obtained by our approach using a constant propagation speed and the measurement of EPAT differences. It is such discrepancies that ultimately determine the localization accuracy of our algorithm because if distance differences based on EPATs are far from true distances, our algorithm although it has a certain tolerance will have to consider that. The distance error and so the localization accuracy of our algorithm is between 2.5mm and 8.6mm.

Paper Details

Date Published: 4 August 2009
PDF: 9 pages
Proc. SPIE 7386, Photonics North 2009, 73860H (4 August 2009); doi: 10.1117/12.840049
Show Author Affiliations
Geoffroy Bodi, Univ. de Sherbrooke (Canada)
Yves Bérubé-Lauzière, Univ. de Sherbrooke (Canada)

Published in SPIE Proceedings Vol. 7386:
Photonics North 2009
Réal Vallée, Editor(s)

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