A Method to Estimate the Ratio of Absorption Coefficients of Two Wavelengths Using Phase-Modulated Near Infrared Light Spectroscopy
✍ Scribed by M. Haida; M. Miwa; A. Shiino; B. Chance
- Publisher
- Elsevier Science
- Year
- 1993
- Tongue
- English
- Weight
- 253 KB
- Volume
- 208
- Category
- Article
- ISSN
- 0003-2697
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✦ Synopsis
Near infrared spectroscopy is a very useful tool for monitoring the oxygen saturation of living tissue noninvasively. We can calculate the hemoglobin oxygen saturation within tissue, using the ratio of the absorption coefficients (\left(\mu_{a}\right)) at two different wave lengths of light. Biological tissue has a very high effective scattering factor (\left(\mu_{s}^{\prime}\right)), which elongates an optical path length and makes it difficult to compute the (\mu_{\mathrm{a}}) by the conventional method using continuous light. Phase-modulated spectroscopy (PMS) measures the path length which is a complex function of the (\mu_{\mathrm{a}}) and (\mu_{\mathrm{s}}^{\prime}). To obtain the ratio for (\mu_{\mathrm{a}}), we have to eliminate the effects of the (\mu_{\mathrm{s}}^{\prime}) 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 wavelengths. (c) 1983 Academic Press, Inc.