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Rafael Grytz, Preston Fuchs, Mustapha El Hamdaoui, Ryan P McNabb, Anthony N Kuo, Brian C Samuels; Empirical Distortion Correction for Posterior Segment SD-OCT Images in Small Animals. Invest. Ophthalmol. Vis. Sci. 2020;61(7):4778.
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© ARVO (1962-2015); The Authors (2016-present)
Develop an empirical distortion correction approach for commercial posterior segment SD-OCT devices that use a fan scanning pattern but otherwise undisclosed optical details.
Based on the assumption that the A-Scan rays that make up a single B-scan converge at one pivot point in space, the image space is mapped to the object space by a nonlinear transformation defined by three unknown variables: axial and angular scaling factors, and pivot point location. We used two types of data sets to empirically estimate these parameters in 3 tree shrew eyes: (i) MRI images of each tree shrew eye were obtained and the curvature of the posterior ocular coats were manually delineated. (ii) Glass beads of known diameter (100±2.7 μm) were implanted on top of or into the retina. The Spectralis OCT2 (Heidelberg Engineering) was used to acquire B-scans through the center of the implanted beads while varying camera settings (camera position, scan focus, and reference arm position [RAP]). The glass bead diameter and RPE were manually delineated from 120 B-Scans. The unknown transformation parameters were identified by matching the mapped bead diameter and RPE curvature for each B-scan to the known diameter and MRI-based curvature, respectively. The proposed method was validated against distorted images of the optic nerve head (ONH) by imaging the same ONH at baseline position and after moving the camera 5 mm anterior or posterior.
The algorithm used was able to restore the bead diameter and RPE curvature in the optically distorted OCT images. A clear non-linear correlation between the angular scaling factor and the pivot point location was identified (R2: 0.997). The axial scaling factor was independent of the device settings. The angular scaling factor was correlated with two scan parameters: scan focus and RAP (R2: 0.687). Based on the identified correlations, anatomically corrected ONH images were restored from the distorted OCT scans.
No commercial OCT device provides anatomically correct images. We have proposed an empirical approach to compensate for non-linear distortions in SD-OCT images from commercial devices that use fan scanning. Our method does not require knowledge of the device’s optical system.
This is a 2020 ARVO Annual Meeting abstract.
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