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Sanam Mozaffari, Volker Jaedicke, Francesco LaRocca, Pavan Tiruveedhula, Austin Roorda; Multi-detection Scheme for Enhancing the Signal-to-Noise Ratio in Adaptive Optics Scanning Laser Ophthalmoscopy. Invest. Ophthalmol. Vis. Sci. 2018;59(9):4633.
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© ARVO (1962-2015); The Authors (2016-present)
Conventional confocal Adaptive Optics Scanning Laser Ophthalmoscopy (AOSLO) uses a pinhole in the detection path to reject out-of-focus light and improve resolution. The pinhole size can be increased to improve signal-to-noise ratio (SNR) or decreased to improve resolution. To circumnavigate this tradeoff, we incorporated a multi-detector scheme into an AOSLO consisting of a fiber bundle with each fiber acting as a pinhole to collect light from seven locations simultaneously.
A fiber bundle, consisting of seven fibers arranged in a hexagonal pattern, was placed at a retinal conjugate plane. The other end of the fiber bundle fanned out into separate fibers each of which were coupled to a photomultiplier tube to produce simultaneous videos. Each fiber acted as a pinhole collecting light from a 1/3 Airy-disk-diameter area to maintain resolution. Since the outer fibers collect light from slightly translated locations, the recorded images need to be shifted according to the physical distance between the outer and central fiber. These shifts were applied to each frame of the seven videos and recombined into a single video. A series of images from one subject was used to demonstrate the benefits.
Pooling the data from each imaging channel into a single video yielded a higher SNR video with no loss in resolution. A direct comparison of the foveal video acquired from a single channel and the multi-detector setup is displayed in Figure 1. The improved SNR enabled more accurate and robust correction for distortions caused by eye motion, which in turn led to improved images shown in Figure 2.
This multi-detector design improves AOSLO imaging SNR without sacrificing resolution. The increase in SNR improves the eye motion correction resulting in better image quality when averaging multiple frames. Improved eye motion correction is crucial for imaging low-reflectivity regions in the retina or studying clinical pathophysiology on subjects with poor fixation. Since the permissible retinal light exposure is limited, especially for shorter wavelengths, this detection scheme enables a safer alternative without compromising image quality or resolution.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
Figure 1 compares the number of frames averaged using a single detector vs the multi-detector, which pools data from seven imaging channels.
Figure 2 exhibits the improvement in eye motion correction after enhancing the SNR.
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