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Journal of Biomedical Optics • Open Access

On the geometry dependence of differential pathlength factor for near-infrared spectroscopy. I. Steady-state with homogeneous medium
Author(s): Daqing Piao; Randall L. Barbour; Harry L. Graber; Daniel C. Lee

Paper Abstract

This work analytically examines some dependences of the differential pathlength factor (DPF) for steady-state photon diffusion in a homogeneous medium on the shape, dimension, and absorption and reduced scattering coefficients of the medium. The medium geometries considered include a semi-infinite geometry, an infinite-length cylinder evaluated along the azimuthal direction, and a sphere. Steady-state photon fluence rate in the cylinder and sphere geometries is represented by a form involving the physical source, its image with respect to the associated extrapolated half-plane, and a radius-dependent term, leading to simplified formula for estimating the DPFs. With the source-detector distance and medium optical properties held fixed across all three geometries, and equal radii for the cylinder and sphere, the DPF is the greatest in the semi-infinite and the smallest in the sphere geometry. When compared to the results from finite-element method, the DPFs analytically estimated for 10 to 25 mm source–detector separations on a sphere of 50 mm radius with μa=0.01  mm1 and μs=1.0  mm1 are on average less than 5% different. The approximation for sphere, generally valid for a diameter ≥20 times of the effective attenuation pathlength, may be useful for rapid estimation of DPFs in near-infrared spectroscopy of an infant head and for short source–detector separation.

Paper Details

Date Published: 14 October 2015
PDF: 14 pages
J. Biomed. Opt. 20(10) 105005 doi: 10.1117/1.JBO.20.10.105005
Published in: Journal of Biomedical Optics Volume 20, Issue 10
Show Author Affiliations
Daqing Piao, Oklahoma State Univ. (United States)
Randall L. Barbour, SUNY Downstate Medical Ctr. (United States)
NIRx Medical Technologies, LLC (United States)
Harry L. Graber, NIRx Medical Technologies, LLC (United States)
Daniel C. Lee, The Univ. of Oklahoma College of Medicine (United States)

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