Abstract
Scanning laser ophthalmoscopy (SLO) and optical coherence tomography (OCT) are widely used retinal imaging modalities that can assist in the diagnosis of retinal pathologies. The combination of SLO and OCT provides a more comprehensive imaging system and a method to register OCT images to produce motion corrected retinal volumes. While high quality, bench-top SLO-OCT systems have been discussed in the literature and are available commercially, there are currently no handheld designs. We describe the first design and fabrication of a handheld SLO/spectral domain OCT probe. SLO and OCT images were acquired simultaneously with a combined power under the ANSI limit. High signal-to-noise ratio SLO and OCT images were acquired simultaneously from a normal subject with visible motion artifacts. Fully automated motion estimation methods were performed in post-processing to correct for the inter- and intra-frame motion in SLO images and their concurrently acquired OCT volumes. The resulting set of reconstructed SLO images and the OCT volume were without visible motion artifacts. At a reduced field of view, the SLO resolved parafoveal cones without adaptive optics at a retinal eccentricity of 11° in subjects with good ocular optics. This system may be especially useful for imaging young children and subjects with less stable fixation.
Highlights
Scanning laser ophthalmoscopy (SLO) and optical coherence tomography (OCT) are widely used retinal imaging modalities that can assist in the diagnosis of retinal pathologies
We demonstrate lateral motion correction of OCT B-scans based on motion estimates determined from concurrently acquired SLO images using a modified version of the patch-based cross correlation image registration technique [19,20,21,22,23,24,25,26]
We used 500 A-scans per B-scan, 500 B-scans per volume, and a delay equivalent to 50 A-scan integration times per return path of the galvanometer mirrors between B-scans. This corresponded to a fast scan of 40 Hz and a slow scan of ~0.073 Hz giving ~220 SLO images per OCT volume
Summary
Scanning laser ophthalmoscopy (SLO) and optical coherence tomography (OCT) are widely used retinal imaging modalities that can assist in the diagnosis of retinal pathologies. SLO is a confocal imaging technique that produces real-time, high contrast 2-D en-face retinal images by raster scanning illumination and detecting backscattered light through a pinhole [1]. OCT, like SLO, utilizes raster scanning and confocal detection and employs coherence gating in the axial direction, which allows for high resolution depth sectioning [2]. Current-generation clinical spectral domain OCT (SD-OCT) systems utilize rapid acquisition along the depth axis (depth-priority scanning) at 20 - 50 kHz line rates to produce high-resolution 2-D crosssectional images (B-scans) near video rate; 3-D volumes comprising hundreds of Bscans require several seconds to acquire. Current-generation SLO systems utilize rapid acquisition along the lateral axis (lateral-priority scanning) at multi-kHz rates to obtain 2D en-face retinal images near video rate. OCT and SLO provide complimentary lateral image information at different time scales such that when combined, rapidly acquired 2-D en-face SLO images may be used to register volumetric OCT B-scans to correct for patient motion within an OCT volume
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