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Proceedings Paper

Changes in cytochrome-oxidase oxidation in the occipital cortex during visual simulation: improvement in sensitivity by the determination of the wavelength dependence of the differential pathlength
Author(s): Matthias Kohl-Bareis; Christian Nolte; Hauke R. Heekeren; Susanne Horst; J. Scholz; Hellmuth Obrig; Arno Villringer
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Paper Abstract

In this study we assess changes in the hemoglobin oxygenation (oxy-Hb, deoxy-Hb) and the Cytochrome-C-Oxidase redox state (Cyt-ox) in the occipital cortex during visual stimulation by near infrared spectroscopy. For the calculation of changes in oxy-Hb, deoxy-Hb and Cyt-ox from attenuation data via a modified Beer-Lambert equation, the wavelength dependence of the differential pathlength factor (DPF), i.e. the ratio of the mean optical pathlength and the physical light-source-detector separation, has to be taken into account. The wavelength dependence of the DPF determines the crosstalk between the different concentrations and is therefore essential for a high sensitivity. Here a simple method is suggested to estimate the wavelength dependence of the DPF((lambda) ) from pulse induced attenuation changes measured on the head of adult humans. The essence is that the DPF is the ratio of the attenuation changes over absorption coefficient changes and the spectral form of the pulse correlated absorption coefficient change is proportional to the extinction coefficient of blood. Indicators for the validity of the DPF((lambda) ) derived for wavelengths between 700 and 970 nm are the stability of the calculated oxy-Hb, deoxy-Hb and Cyt-ox signals with variations of the wavelength range included for their calculation and its overall agreement with the data available from the literature. The DPF derived from pulse measurements was used for the analysis of attenuation data from cortical stimulations. We show that Cyt-ox in the occipital cortex of human subjects is transiently oxidized during visual stimulation.

Paper Details

Date Published: 1 January 1998
PDF: 10 pages
Proc. SPIE 3194, Photon Propagation in Tissues III, (1 January 1998); doi: 10.1117/12.301055
Show Author Affiliations
Matthias Kohl-Bareis, Humboldt Univ. Berlin (Germany)
Christian Nolte, Humboldt Univ. Berlin (Germany)
Hauke R. Heekeren, Humboldt Univ. Berlin (Germany)
Susanne Horst, Humboldt Univ. Berlin (Germany)
J. Scholz, Humboldt Univ. Berlin (Germany)
Hellmuth Obrig, Humboldt Univ. Berlin (Germany)
Arno Villringer, Humboldt Univ. Berlin (Germany)

Published in SPIE Proceedings Vol. 3194:
Photon Propagation in Tissues III
David A. Benaron; Britton Chance; Marco Ferrari, Editor(s)

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