title: The effect of basic assumptions on the tissue oxygen saturation value of near infrared spectroscopy.
abstract: Tissue oxygen saturation (StO(2)), a potentially important parameter in clinical practice, can be measured by near infrared spectroscopy (NIRS). Various devices use the multi-distance approach based on the diffusion approximation of the radiative transport equation [1, 2]. When determining the absorption coefficient (μ (a)) by the slope over multiple distances a common assumption is to neglect μ (a) in the diffusion constant, or to assume the scattering coefficient (μ(s)) to be constant over the wavelength. Also the water influence can be modeled by simply subtracting a water term from the absorption. This gives five approaches A1-A5. The aim was to test how these different methods influence the StO(2) values. One data set of 30 newborn infants measured on the head and another of eight adults measured on the nondominant forearm were analyzed. The calculated average StO(2) values measured on the head were (mean ± SD): A1: 79.99 ± 4.47%, A2: 81.44 ± 4.08%, A3: 84.77 ± 4.87%, A4: 85.69 ± 4.38%, and A5: 72.85 ± 4.81%. The StO(2) values for the adult forearms are: A1: 58.14 ± 5.69%, A2: 73.85 ± 4.77%, A3: 58.99 ± 5.67%, A4: 74.21 ± 4.76%, and A5: 63.49 ± 5.11%. Our results indicate that StO(2) depends strongly on the assumptions. Since StO(2) is an absolute value, comparability between different studies is reduced if the assumptions of the algorithms are not published.
authors.affiliation: Biomedical Optics Research Laboratory, Division of Neonatology, University Hospital Zurich, Zurich, Switzerland. andreas.metz@usz.ch.|Zurich Center for Integrative Physiology, University Zurich, Frauenklinikstrasse 10, 8091, Zürich, Switzerland. andreas.metz@usz.ch.
authors.forename: Andreas Jaakko
authors.initials: AJ
authors.lastname: Metz
authors.affiliation: Biomedical Optics Research Laboratory, Division of Neonatology, University Hospital Zurich, Zurich, Switzerland.|Zurich Center for Integrative Physiology, University Zurich, Frauenklinikstrasse 10, 8091, Zürich, Switzerland.
authors.forename: Martin
authors.initials: M
authors.lastname: Biallas
authors.affiliation: Biomedical Optics Research Laboratory, Division of Neonatology, University Hospital Zurich, Zurich, Switzerland.|Zurich Center for Integrative Physiology, University Zurich, Frauenklinikstrasse 10, 8091, Zürich, Switzerland.
authors.forename: Carmen
authors.initials: C
authors.lastname: Jenny
authors.affiliation: Biomedical Optics Research Laboratory, Division of Neonatology, University Hospital Zurich, Zurich, Switzerland.|Zurich Center for Integrative Physiology, University Zurich, Frauenklinikstrasse 10, 8091, Zürich, Switzerland.
authors.forename: Thomas
authors.initials: T
authors.lastname: Muehlemann
authors.affiliation: Biomedical Optics Research Laboratory, Division of Neonatology, University Hospital Zurich, Zurich, Switzerland.|Zurich Center for Integrative Physiology, University Zurich, Frauenklinikstrasse 10, 8091, Zürich, Switzerland.
authors.forename: Martin
authors.initials: M
authors.lastname: Wolf
mesh_terms: D000328:Adult; D001921:Brain / Q000098:blood supply* / Q000378:metabolism*; D005542:Forearm / Q000098:blood supply*; D006257:Head / Q000098:blood supply*; D006801:Humans; D007231:Infant, Newborn; D008875:Middle Aged; D008962:Models, Theoretical; D010100:Oxygen / Q000378:metabolism*; D019265:Spectroscopy, Near-Infrared / Q000379:methods*
chemical_list: D010100:Oxygen