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Y. Hirohara, Y. Okawa, T. Yamaguchi, H. Aoki, Y. Tsuruga, T. Mihashi, S. Ninomiya, N. Maeda, I. Uchida, T. Fujikado; Validity of Oxygen Saturation Analysis With Hyperspectral Fundus Camera . Invest. Ophthalmol. Vis. Sci. 2005;46(13):4281.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Methods to measure the oxygen saturation in the retina are principally based on the fact that the absorptive properties of oxy– and deoxyhemoglobin are different in thevisible spectral range. To investigate the validity of absorption analysis by hyperspectral imaging, images of the retina and those of artificial capillaries filled with blood were obtained by the hyperspectral fundus camera and the absorption properties were analyzed. Methods: The apparatus for hyperspectral imaging consisted of a fundus camera (TRC–50LX, Topcon) and a liquid crystal tunable filter (VariSpec, CRI) (Hirohara Y, ARVO 2004). The spectral range for this measurement was from 500 to 720 nm and the spectral band width of the tunable filter was 20 nm. Wavelengths of the tunable filter were scanned at10 nm intervals..(I hope I have understood this correctly!) Five dilated normal eyes were measured. The intensities of the images of the artery, of the vein and of the area around those vessels were measured and the absorptions of the vessels were analyzed. The absorption ratio (Rab) of the artery and the vein over two spectral ranges, from 500 to 580 nm (range 1) and from 600 to 720 nm (range 2), were compared. Images of artificial capillaries filled with blood circulated by oxygen or nitrogen were also analyzed. Analyzed data were compared with the absorption of oxy– and deoxyhemoglobin calculated from reported data of oxy– and deoxyhemoglobin extinction rate (S. Prahl http://omlc.ogi.edu/spectra/hemoglobin/summary.html). Results: For all measurements, the Rab of range 1 was larger than that of range 2. The difference of the average of Rab between range 1 and range 2 was 0.388 ± 0.159 for the retinas (p<0.01) and was 0.191 (p<0.01) for the artificial capillaries. The difference of the average of Rab between range 1 and 2 calculated from the reported data was 0.807. We speculated the reason why the calculated data was larger than the data for the retinas and capillaries was that scatter and reflection of various blood components and scatter of the vessel and of the capillary were ignored in the calculation. Conclusions: It was confirmed by in–vivo and in–vitro experiment that the absorption coefficient obtained by hyperspectral fundus camera corresponds to the spectral characteristics of oxy– and deoxyhemoglobin.
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