Novel noninvasive multispectral snapshot imaging system to measure and map the distribution of human vessel and tissue hemoglobin oxygen saturation

Abstract

AIM: To design and implement a snapshot imaging system capable of mapping oxygen saturation of retinal vessels and tissue clinically for the first time.

MATERIALS AND METHODS: Our image-splitting design is attached to the imaging portions of a fundus camera. A relay subsystem and reimaging system convert reflected white light from the eye into seven monochromatic images simultaneously. Our algorithm uses intensity information at each of these discrete wavelengths to approximate the area between the oxy- and deoxyhemoglobin spectral curves, which has been shown to be proportional to oxygen saturation. We used Matlab to convert this information into color-coded oxygen saturation maps of the optic nerve head. We validated our system by using it on a model eye with a capillary of known blood oxygen saturation, then used it in vivo to obtain quantitative values of human oxygen saturation for veins and tissue.

RESULTS: By collecting seven images simultaneously with one snapshot, our system is the first to document and map oxygen saturation of the retinal vessels and tissue. Our system’s calculations agree with co-oximeter readings of blood in a model eye capillary mimicking a vessel. The quantitative calculations from the healthy subject, as well as the qualitative oxygen saturation maps, show oxygen saturation levels consistent with those in the literature.

CONCLUSION: This system is clinically valuable for diagnosing and monitoring diseases affecting ocular oxygen saturation, such as glaucoma, diabetic retinopathy, age-related macular degeneration, and others. Retinal tissue often becomes hypoxic in such diseases, and our reliable method is capable of documenting tissue oxygenation.

KEY WORDS: Multispectral, Oxygen Saturation, Snapshot, Noninvasive, Hemoglobin