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M. Zhao, Y. K. Tao, J. A. Izatt; High-Speed Fiber-Based Polarization Sensitive Retinal SDOCT. Invest. Ophthalmol. Vis. Sci. 2007;48(13):2615.
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© ARVO (1962-2015); The Authors (2016-present)
Spectral domain optical coherence tomography (SDOCT) has recently emerged as a powerful new tool for noninvasive human retinal imaging. SDOCT permits much faster image acquisition rates (up to 20,000 - 50,000 A-scans/sec in commercially available systems) than the conventional time-domain approach. Polarization sensitive OCT (PSOCT) provides additional contrast for retinal imaging and has been shown to be sensitive to the orientation and density of fibers in the RNFL and Henle’s fiber layer. Most previously reported PSOCT implementations have been modifications of much slower time-domain systems. A few preliminary spectral domain PSOCT systems have recently been reported, however they have included either multiple expensive spectrometers or complex bulk optics, and have not approached the acquisition rates which are now commonplace in SDOCT. We have constructed and tested a compact, high-speed polarization sensitive SDOCT (PS-SDOCT) system for retinal imaging which is a simple modification of a state-of-the-art SDOCT system which operates at 1/3 the rate of the SDOCT system, or up to 17,000 A-scans/sec.
The sample arm of a state-of-the-art SDOCT retinal system was modified by addition of a high speed EOM and a vertical linear polarizer to modify the sample illumination polarization state between linear, right-hand elliptical and left-hand elliptical for three repeated A-scans at each lateral sample position. Modified commercial software (Bioptigen, Inc.) was used to collect repeated A-scans at the maximum readout rate of a 1024-pixel line scan camera (51.9 kHz), and custom software was developed to transform the repeated A-scan data into images of reflectivity, birefringence, and fast axis orientation.
The PS-SDOCT system was tested at 20 kHz A-scan rate using a quarter wave plate phantom. The average error and standard deviation of retardation measurements was 5.4 and 3.5 degrees, respectively, and of fast axis orientation was 8.1 and 0.62 degrees. A mathematical model was created to analyze the relationship between SNR, axis orientation and retardation. Experimental results confirm the accuracy of the theoretical model. The system is currently being modified for real-time in vivo retinal PS-SDOCT operation.
A fiber-based polarization sensitive SDOCT system using a single spectrometer has been developed for high-speed characterization of birefringence and fast axis orientation at a composite rate of 17,000 A-Scans/second, which will enable densely sampled retinal imaging (1000 A-scans/B-scan) at 17 B-scans/sec. The measured accuracy of the system is comparable to previous time-domain PSOCT implementations.
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