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Naoki Takeno, Shinya Iwata, Ryosuke Shiba, Koichi Ito, Masaaki Hanebuchi; Full Range Optical Coherence Tomography by Optical Path Difference Sweep. Invest. Ophthalmol. Vis. Sci. 2019;60(9):141.
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© ARVO (1962-2015); The Authors (2016-present)
In principle, Fourier domain optical coherence tomography (FD-OCT) generates complex conjugate artifacts (mirror images) resulting in the availability of only half of the depth range of the OCT (Fig. 1A). This depth range is often insufficient in the peripheral regions to capture wide-field fundus images. Additionally, overlapping of the mirror image with the real image remains a problem. We propose a method to achieve full range imaging without using any additional optical mechanisms. This method uses the observation that the distance between the real image and mirror image changes depending on the optical path difference (OPD) between the sample arm and the reference arm of the OCT (Fig. 1B).
The RS-3000 Advance 2 (Nidek, Aichi, Japan) spectral domain OCT (a type of FD-OCT), and a prototype wide-field OCT were used. Normally, the device removes the depth region containing the mirror image. For this study, modifications allowed retention of the region with the mirror image. After capturing the first OCT image, the OPD was shifted, and a second OCT image was captured. In this manner, images were repeatedly captured while changing the OPD to obtain multiple OCT images. Subsequently, the real images were aligned based on the correlation between the images, and statistics such as the average were calculated to obtain a full range image. Extracting the region with the mirror image and excluding this region from statistical processing minimized the influence of this artifact.
Full range images were obtained by capturing OCT images of the fundus while varying the OPD and by processing these images as explained above (Fig. 2). By using information from multiple images, not only mirror images were removed, but also the signal-to-noise ratio (SNR) was improved. In addition, variability of the SNR due to sensitivity roll-off was mitigated.
Full range images were obtained with the FD-OCT without using any additional optical mechanisms capturing multiple fundus images while varying the OPD between the sample arm and reference arm.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
An example of the OCT image of the fundus. Normally, only the half of the image below the zero-delay line (the middle yellow broken line) is extracted for use. Varying the OPD changes the positions of the real image from “A” to “B” as shown above.
Image created by combining six images with different OPDs from which the mirror image was removed.
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