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Simultaneous measurement of oxygen saturation and vessel diameter by imaging spectrometry

An imaging spectrometer, developed at the University of Jena, enables locally resolved spectral measurements at the fundus of the human eye. From the measured profile of a blood vessel the value of vessel diameter may be detected and the weakening of intensity is a result of wavelength- dependent absorption and scattering in blood. Although extinction spectra of hemolyzed oxygenated and reduced hemoglobin are known very exactly, in vivo measurements of oxygen saturation at streaming whole blood in single vessels are difficult. The extension of Lambert-Beer's law by a scattering part is used as an attempt for the calculation of the oxygen saturation from the locally resolved reflectance spectra of the fundus. Measurements of vessel diameter according to the principle of optical centroid are insensitive to variations of real illumination. This principle results in exact values if there are at least three observations in each edge of vessel profile. Practical measurements of oxygen saturation over vessel cross section and of vessel diameter are given.