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H. Ishikawa, G. Wollstein, H. Ishikawa, M.L. Gabriele, A.A. Bonfioli, R.J. Noecker, D. Greenfield, C. Mattox, R. Varma, J.S. Schuman; Signal Strength Outperformed Signal to Noise Ratio in Evaluating StratusOCT Image Quality . Invest. Ophthalmol. Vis. Sci. 2005;46(13):2496.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To compare a newly introduced image quality parameter, signal strength (SS) with the conventional signal to noise ratio (SNR), for optical coherence tomography (OCT; Stratus OCT, Carl Zeiss Meditec, Inc., Dublin, CA) images. Methods: StratusOCT images (linear macular scan and peripapillary circular scan) were analyzed using Stratus 4.0 software. SS and SNR were calculated for each image. Images without any processing (cross–correlation and/or border detection) were exported to an IBM compatible PC, and a software evaluation program was developed so that OCT experts could see StratusOCT images one at a time on a computer monitor while categorizing them by subjective 3–level–grading (excellent, acceptable, and poor). Four OCT experts independently evaluated these images in a randomized fashion, and the outcome results were compared with SS and SNR. Results:270 images of 90 subjects (30 each for normal, early, and advanced glaucoma) were enrolled in this study. Subjects were selected in a consecutive and retrospective fashion from our OCT imaging database. There were significant differences in SS and SNR between each of the categories (excellent vs. poor, acceptable vs. poor, and excellent vs. acceptable) (all p≤0.0003, Wilcoxon test). Areas under the receiver operating characteristic (ROC) curve for discrimination of poor from excellent and acceptable images were 0.89 (SNR) and 0.95 (SS) (p=0.002). The suggested cutoff of SS was 6.28 achieving the best specificity and sensitivity (0.88 and 0.86, respectively). Conclusions: SS was better than SNR in terms of discrimination of poor images. Although the operating manual states that SS of 5 or better can be acceptable, based on the results of this study it is recommended that only images with SS of 6 or greater be used clinically.
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