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Proceedings Paper

Effect of local absorption changes on phase-shift measurement using phase modulation spectroscopy
Author(s): Weijia Cui; Lee E. Ostrander
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Paper Abstract

Recently, researchers have used phase modulation of photons (PMP) at near infrared wavelengths to assess in vivo tissue blood perfusion. The incident light intensity is amplitude modulated in the megahertz to gigahertz range and the phase shift is measured at the detector for the photon waves that have migrated through biological tissue. The obtained phase shift is related to the pathlength for the detected photons. In the past, the models for this process have not considered the effect upon phase produced by inhomogeneities within the in vivo tissue. The phase shift is a function of the distribution of the optical properties within the medium. We used a simple experimental model to investigate the effect upon phase shift of the location for optical changes. A mathematical model has been developed to describe this effect. The results demonstrate that a measured phase shift depends upon the location at which the optical properties are changed, as well as upon the magnitude of change in the optical properties. In vivo tissue is inhomogeneous so that its optical properties are also inhomogeneous. It is therefore important to consider the optical property distribution of the in vivo tissue when assessing blood perfusion using phase modulation measurements.

Paper Details

Date Published: 14 September 1993
PDF: 8 pages
Proc. SPIE 1888, Photon Migration and Imaging in Random Media and Tissues, (14 September 1993); doi: 10.1117/12.154647
Show Author Affiliations
Weijia Cui, Somanetics Corp. (United States)
Lee E. Ostrander, Rensselaer Polytechnic Institute (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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