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Dustin L. Pomerleau, Priyatham S. Mettu, Phoebe S. Lin, Ramiro S. Maldonado, Sina Farsiu, Prithvi Mruthyunjaya; Quantitative Analysis of Outer Choroidal Image Contrast on Multiple SD-OCT Systems. Invest. Ophthalmol. Vis. Sci. 2011;52(14):2858.
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© ARVO (1962-2015); The Authors (2016-present)
To quantitatively compare image contrast of the outer choroid using different image-capture techniques across multiple SD-OCT systems.
In a prospective study, 22 eyes of 12 normal subjects underwent upright and inverted imaging using Bioptigen, Heidelberg Spectralis, and Zeiss Cirrus SD-OCT units; eyes also underwent imaging on the Spectralis Enhanced Depth Imaging (EDI) mode. Each 9 mm horizontal line scan centered on the fovea had 1536 (1024 for Cirrus) A-scans per B-scan and 40 (20 for Cirrus) averaged B-scans per image. Manual segmentation of the scan images was performed by two masked graders, identifying the outer aspect of Bruch membrane and the choroid-scleral junction to isolate the choroidal signal. The choroidal signal was further subdivided halfway between boundaries by automated segmentation into inner and outer choroidal signals. Histograms of the represented greyscale pixel values from the outer choroid were generated in MATLAB. The histograms were compared using the full-width at half-maximum (FWHM) value as a metric of relative contrast. Mean FWHM was calculated for upright and inverted modes on each platform as well as for Spectralis EDI mode. Statistical significance was assessed by pairwise Student’s two-tailed t-test. Correlation between observers was assessed by Pearson correlation coefficient.
Outer choroidal signal from the Bioptigen images had a mean (±SD) FWHM of 60.54 ± 13.51 greyscale units (GU) for upright compared to 67.26 ± 20.28 GU for inverted images (p = 0.09). For Cirrus, mean FWHM was 64.43 ± 17.57 GU for upright compared to 65.40 ± 11.64 GU for inverted images (p = 0.83). Mean FWHM for Spectralis was 65.97 ± 26.4 GU for upright compared to 88.13 ± 35.68 GU for inverted images (p = 0.04). Mean FWHM for EDI mode Spectralis images was 84.37 ± 39.43 (p = 0.76 compared to inverted Spectralis, p = 0.08 compared to upright Spectralis). Correlation coefficients between graders were high for Bioptigen upright (0.85) and inverted (0.82), Cirrus upright (0.63), and Spectralis inverted (0.69) and EDI (0.61).
Using these parameters, inverted imaging on Spectralis, compared to upright imaging, had significantly greater outer choroidal image contrast; a similar trend was observed with inverted imaging on Bioptigen and with Spectralis EDI mode. Imaging artifacts in the choroidal region of Cirrus inverted images resulted in falsely high FWHM.
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