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David Alonso-Caneiro, Scott A Read, Michael J Collins; Automatic choroidal thickness segmentation in optical coherence tomography. Invest. Ophthalmol. Vis. Sci. 2014;55(13):4795.
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© ARVO (1962-2015); The Authors (2016-present)
Choroidal thickness (ChT) provides valuable information regarding the eye’s anatomy and physiology. A fully automatic method to segment the choroid in OCT images is presented and evaluated in a healthy pediatric population (10-16 years of age) with a range of refractive errors.
The automated segmentation method uses graph-search theory to delineate the inner choroidal boundary (ICB) and the outer choroidal boundary (OCB) to obtain the ChT profile from OCT images (Fig 1). Before the segmentation, the B-scan is pre-processed to enhance the boundaries and to minimize the artifacts produced by surrounding features. Based on our previous method (Alonso-Caneiro et al. BOE 2013), the technique was tested on a substantially larger dataset containing 3205 B-scans (3x the original dataset), which had been manually segmented by an experienced observer.
Two common measurements of error were used to evaluate the performance of the automatic method with respect to the manual segmentation, the mean and the [absolute mean] errors. The ICB, which presents a well-defined boundary, had mean measurement errors of 2.33 [2.69]μm, respectively. The less distinct OCB had higher mean measurement errors of 5.51 [13.02]μm. Analysis of the ChT, which is more clinically relevant, revealed errors of -3.18 [12.63]μm. The manual and automatic methods were highly correlated with an r2=0.98 (Fig 2A). The Bland-Altman plot (Fig 2B) illustrates good agreement between the two methods, and does not exhibit an obvious bias or association between the measurement error and the mean ChT. The mean difference between methods was 2.51±17.68μm (95% C.I. 37.88 to -32.85μm). Taking into consideration that the axial resolution is 3.9μm/pixel, the performance of the automatic method shows a close agreement with the experienced human observer.
The results demonstrate that the proposed method provides robust detection of the ChT in a large dataset of images with a diverse range of choroidal morphologies.
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