Hyperspectral Computed Tomographic Imaging Spectroscopy of Vascular Oxygen Gradients in the Rabbit Retina In Vivo

Abstract

Diagnosis of retinal vascular diseases depends on ophthalmoscopic findings that most often occur after severe visual loss (as in vein occlusions) or chronic changes that are irreversible (as in diabetic retinopathy). Despite recent advances, diagnostic imaging currently reveals very little about the vascular function and local oxygen delivery. One potentially useful measure of vascular function is measurement of hemoglobin oxygen content. In this paper, we demonstrate a novel method of accurately, rapidly and easily measuring oxygen saturation within retinal vessels using in vivo imaging spectroscopy. This method uses a commercially available fundus camera coupled to two-dimensional diffracting optics that scatter the incident light onto a focal plane array in a calibrated pattern. Computed tomographic algorithms are used to reconstruct the diffracted spectral patterns into wavelength components of the original image. In this paper the spectral components of oxy- and deoxyhemoglobin are analyzed from the vessels within the image. Up to 76 spectral measurements can be made in only a few milliseconds and used to quantify the oxygen saturation within the retinal vessels over a 10–15 degree field. The method described here can acquire 10-fold more spectral data in much less time than conventional oximetry systems (while utilizing the commonly accepted fundus camera platform). Application of this method to animal models of retinal vascular disease and clinical subjects will provide useful and novel information about retinal vascular disease and physiology.

Normative Values and Predictors of Retinal Oxygen Saturation

“…For decades, the level of oxygen has been estimated by either indirect 1 or invasive methods. 2,3 Recently, direct and noninvasive quantitative measurement of oxygen saturation (SO 2 ) levels in human retinal vessels has been made possible using various techniques, [4][5][6][7][8] including retinal oximetry by spectrophotometry.…”

Hyperspectral imaging of retinal microvascular anatomy

“…Previously, the HCTIS oximetry method had been validated in animal models [14,39,40] . Snapshot hyperspectral imaging as a tool for evaluating macular pigment and understanding age-related macular degeneration (AMD) is already underway [41,42] .…”

Imaging of Hypoxia in Retinal Vascular Disease

“…Since then, full spectral imaging has developed into hyperspectral imaging (HSI) with algorithms used to construct a two dimensional image in order to visualize the data as an oxygen map [87][88][89]. Whereas this process originally took several seconds due to sequential acquisition of many single-dimension images, new technology allows for enough images to be taken to cover a 15 degree field with good spatial resolution in only a few milliseconds [90]. Today, HSI has been further developed into hyperspectral computed tomographic imaging spectroscopy (HCTIS), which in addition to giving detailed oxygen saturation maps, can give information about changes in the retina such as lesions, perfusion, and pigment density [90,91].…”