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A. R. Harvey, E. Theofanidou, I. Al_Abboud, M. Graham, A. C. Hargreaves; Spectral Imaging of the Rat Retina. Invest. Ophthalmol. Vis. Sci. 2007;48(13):3844.
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Spectral imaging has been demonstrated to provide useful quantitative mapping and classification of scene constituents in applications ranging from geographical remote sensing through medical imaging to bio photonics. The basic principle involves the recording of images in multiple spectral bands followed by appropriate spectral processing. We have previously described the application of this technique to human retinal imaging where it shows promise for non-invasive mapping of, for example, blood oxygenation and consequently offers promise for detecting and monitoring a range of diseases including diabetic retinopathy and glaucoma.
The ability to detect retinal disease in rats at an early stage is of great significance to drug discovery programmes where toxicity-induced retinal disease may be evident at an earlier stage in spectral images of the retina, than from time-consuming and costly histological studies of the retina. We report here on the development of instrumentation and methodology for recording and processing spectral images of rat retinas Spectral images of rats were recorded using a modified conventional non-mydriatic fundus camera designed for use with humans. Integration of a liquid crystal tuneable filter so as to spectrally filter the flash illumination enabled time-sequential and spectrally randomised acquisition of spectral images of rat retinas with a spectral resolution of 7nm.
Automated computer algorithms corrected for image-to-image rotational and translational misregistration and for spatial variations in illumination. Pixel-based processing of the spectral data cube using commercial spectral processing software (ENVI) enabled a map of spectral signatures to be constructed that provides a semi-quantitative map of biochemical chromaphore concentrations, whilst a physical model of light propagation in the retina enabled quantification of retinal blood oxygenation.
The principal spectral signatures recorded were associated with the changes in oxygenation of haemoglobin and changes in the vascular structure. Spectral imaging of the retina shows promise for the early detection of retinal damage in drug discovery programmes.
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