title: A method to estimate the ratio of absorption coefficients of two wavelengths using phase modulated near infrared light spectroscopy.
abstract: Near infrared spectroscopy provides a very useful tool to monitor the oxygen saturation of the living tissue non-invasively. We can calculate the hemoglobin oxygen saturation within the tissue, using the ratio of the absorption coefficient (mu a) at two different wave lengths of light. Biological tissue has a very high effective scattering factor (mu s), which elongates an optical path length and makes it difficult to compute the mu a by the conventional method using continuous light. Phase Modulated Spectroscopy (PMS) measures the path length which is a complex function of the mu a and mu s. To get the ratio of the mu a, we have to eliminate the effects of the mu s from the obtained value by the PMS method. In this report, we present a theory and an experimental result which show that the inverse of the squared ratio of two phase angle differences at two different separations obtained by two different light wavelengths provides a good estimate of the ratio at these wavelength.
authors.affiliation: Johnson Research Foundation, Department of Biochemistry and Biophysics, School of Medicine, University of Pennsylvania, Philadelphia 19104-6089.
authors.forename: M
authors.initials: M
authors.lastname: Haida
authors.forename: B
authors.initials: B
authors.lastname: Chance
mesh_terms: D000465:Algorithms; D055592:Biophysical Phenomena; D001703:Biophysics; D002244:Carbon; D004396:Coloring Agents; D005217:Fat Emulsions, Intravenous; D008962:Models, Theoretical; D055095:Optics and Photonics; D010100:Oxygen / Q000032:analysis*; D010108:Oxyhemoglobins / Q000378:metabolism; D012542:Scattering, Radiation; D013055:Spectrophotometry, Infrared / Q000379:methods*
chemical_list: D004396:Coloring Agents; D005217:Fat Emulsions, Intravenous; D010108:Oxyhemoglobins; C028433:chinese ink; D002244:Carbon; D010100:Oxygen