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A. R. Harvey, G. D. Muyo, I. Alabboud, A. Gorman, D. Mordant, A. I. McNaught; Development of a Clinical Snapshot Spectral Imaging Camera for Blood Oximetry. Invest. Ophthalmol. Vis. Sci. 2008;49(13):4256.
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© ARVO (1962-2015); The Authors (2016-present)
Quantitative oximetry of the retinal vasculature using hyperspectral imaging has been shown to provide a means to measuring retinal biochemistry and in particular blood oxygenation. Unfortunately most spectral retinal cameras reported to date are unable to record wide-field spectral images of the retina in a snapshot and hence their use as a clinical tool is severely constrained.
We report the development of a spectral retinal camera that is incorporated into a commercial clinical instrument. Based on the Image Replicating Imaging Spectrometer (IRIS) concept developed initially for real-time multi-spectral surveillance, it employs simultaneous replication and polarising interferometric spectral filtering to record eight spectral images simultaneously on the detector. This is achieved without rejection of light so the light intensity at the retina is minimised. Eight spectral bands were optimised for blood oxymetry in both the larger and smaller blood vessels.The spectral pass-bands for IRIS exhibit minor sidelobes and these have been incorporated into algorithms for determination of semi-quantitative blood oximetry based on spectral unmixing and for quantitative oxymetry based on numerical fitting to an analytical model.
A semi-quantitative oxymetric image of a normal retina is shown below: oxygenated arterial blood is false-coloured white, whilst deoxygenated venous blood is coloured red. Quantitative blood oxygenation employing a an optical model for light propagation in the retina has also been accomplished and validated against an artificial retina containing blood of known oxygenation.
A novel spectral imaging technique has been developed together with associated processing algorithms that offers the real-time and snapshot capability that is highly desirable for accurate oxymetry and usability in a clinical instrument.
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