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6 December 1996 Continuous spectrum near-infrared spectroscopy approach in functional activation studies in the human adult
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In contrast to the conventional approaches using single wavelengths the whole spectrum approach monitors optical changes across a continuous spectrum in the near infrared. By fitting the spectra of oxygenated and deoxygenated haemoglobin into the spectrum the changes in the concentration of these parameters can be calculated in an extension of the known near-infrared spectroscopy (NIRS) algorithms. By twice differentiating both chromophore and recorded attenuation spectra the offset and wavelength dependent influence of scattering (assumed to be linear) cancels out. Since oxygenated haemoglobin (oxy-Hb) and cytochrome oxidase (Cyt-02) spectra have essentially featureless second differentials a fitting procedure using the second differentials of water and deoxygenated haemoglobin (deoxy-Hb) result in a ratio of the compounds' contribution to the spectrum. This corresponds to the ratio of their concentrations in the tissue. Assuming a known and constant concentration of water (deoxy-Hb) can be quantified. On the basis of this theory previously described the paper shows that the response to a motor stimulation paradigm is consistent with data reported with a conventional NIRS monitor (n equals 8ss). Data suggest that signal to noise is greater for the new approach. A concentration of 10.5 μm is found for the adult human brain (n equals 6ss). Exploring the temporal resolution of the method the contribution of the different compounds to the optical changes evoked by the heart beat are examined (n equals 5ss).
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Hellmuth Obrig, Hauke R. Heekeren, Jan Ruben, Rudiger Wenzel, J.-P. Ndayisaba, Ulrich Dirnagl, and Arno Villringer M.D. "Continuous spectrum near-infrared spectroscopy approach in functional activation studies in the human adult", Proc. SPIE 2926, Optical Biopsies and Microscopic Techniques, (6 December 1996);

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