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Makoto Saika, Yoko Hirohara, Toshifumi Mihashi, Hiroyuki Kanda, Tomomitsu Miyoshi, Takashi Fujikado; Measurements of Oxygen Saturation in Cat Retina Using a Near Infrared Snapshot HYperspectral Imaging Fundus Camera. Invest. Ophthalmol. Vis. Sci. 2012;53(14):2171.
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© ARVO (1962-2015); The Authors (2016-present)
To measure oxygen saturation changes in retinal vessel noninvasively for early diagnosis of retinal vascular diseases using near infrared snapshot hyperspectral imaging fundus camera.
Six cats under general anesthesia were used as an acute ischemia-reperfusion model. Retinal arterial oxygen saturation (SpO2) was varied by changing the ratio of oxygen and nitrogen gasses while a pulse oximeter placed on the tongue monitored SpO2. Retinal images over the range 700-900 nm were obtained by a fundus camera attached with the snapshot system (Saika M, 2011 ARVO). Ninty-two×92 spatial images with 10 nm spectral-sampling were reconstructed by the MART algorithm. To estimate oxygen saturation, a multivariate regression model based on a modified Lambert-Beer law (Cohen AJ, 1976 IEEE) was used. The signal intensities from the hyperspectral images within the central area of artery and retinal area without vessels were used to calculate the oxygen saturation.
The correlation between the SpO2 and the hyperspectral measurements was shown in Fig.1 (R2=0.37, p<0.01). The retinal image of a cat and the maps of snapshot hyperspectral oxygen saturation changes in retina at various SpO2 conditions were shown in Fig.2. The oxygen saturations in arteries were higher than those in the veins. In this model, the oxygen saturation maps were not correctly evaluated in area in that vessel diameter varied but the vessel diameter was assumed to be a constant.
Retinal oxygen saturation measured by a near infrared snapshot hyperspectral imaging fundus camera correlated significantly with that by pulse oximeter. The results suggest that the oxygen saturation maps in retinal vessels are able to be obtained by this method if the diameters of vessels are properly calibrated.
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