An imaging multi-spectral retinal oximeter with intravitrial illumination is used to perform the first in vivo test of the blue-green minima shift oximetry method (BGO) in swine eyes [K. R. Dennighoff, R. A. Chipman, and L. W. Hillman, Opt. Lett. 31, 924–926 (2006); J. Biomed. Opt. 12, 034020 (2007).] A fiber optic intravitreal illuminator inserted through the pars plana was coupled to a monochromator and used to illuminate the retina from an angle. A camera viewing through the cornea recorded a series of images at each wavelength. This intravitreal light source moves the specular vessel glint away from the center of the vessel and directly illuminates the fundus behind most blood vessels. These two conditions combine to provide accurate measurements of vessel and perivascular reflectance. Equations describing these different light paths are solved, and BGO is used to evaluate large retinal vessels. In order to test BGO calibration in vivo, data were acquired from swine with varied retinal arterial oxyhemoglobin saturations (60–100% saturation.). The arterial saturations determined using BGO to analyze the multispectral image sets showed excellent correlation with co-oximeter data (r2=0.98, and residual error ±3.4% saturation) and are similar to results when hemoglobin and blood were analyzed using this technique.
The diffuse fundus reflectance and the spectral transmittance of the swine sensory retina was measured in vivo using intravitreal illumination. Pars plana vitrectomy and intravitreal manipulations were performed on a female American Yorkshire domestic swine. Light from a scanning monochromator was coupled into a fiber optic intraocular illuminator inserted into the vitreous. A 1.93-mm2 region of the illuminated fundus was imaged from an oblique illumination angle. Multispectral retinal images were acquired for four experimental conditions: the eye (1) prior to vitrectomy, (2) after vitrectomy, (3) after insertion of a Spectralon disk super-retinally, and (4) after subretinal insertion of the disk. The absorption of melanin and hemoglobin in the red wavelengths was used to convert relative spectral reflectance to absolute reflectance. The flux scattered from the super-retinal Spectralon was used to correct for scattering in the globe. The transmittance of the sensory retina was measured in vivo using the scatter corrected subretinal Spectralon disk reflectance. The hemoglobin and melanin components of the spectrum due to scattered light were removed from the retinal transmission spectrum. The in vivo spectral transmittance of the sensory retina in this swine was essentially flat across the visible spectrum, with an average transmittance >90%.
We present the implementation of snapshot imaging spectropolarimetry in a short-wave infrared (SWIR) system. It is the first of its kind to provide imaging spectropolarimetry with no moving parts and snapshot capability. This has applications in many fields, such as mining, biomedical imaging, and astronomy. The SWIR Computed Tomographic Imaging Channeled Spectropolarimeter (CTICS) is a snapshot imaging spectropolarimeter with 54X46 pixel spatial resolution and 10-band spectral resolution from 1.25-1.99 μm for the purpose of object identification. First, we present the design of the two main parts: the Computed Tomography Imaging Spectrometer (CTIS) and the channeled spectropolarimetry components. A discussion follows on the reconstruction technique. We then present the final assembled system and testing results.