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. 2018 Sep:11039:328-335.
doi: 10.1007/978-3-030-00949-6_39. Epub 2018 Sep 14.

2D Modeling and Correction of Fan-beam Scan Geometry in OCT

Min Chen  1 , James C Gee  1 , Jerry L Prince  2 , Geoffrey K Aguirre  3
Affiliations

2D Modeling and Correction of Fan-beam Scan Geometry in OCT

Min Chen et al. Comput Pathol Ophthalmic Med Image Anal (2018). 2018 Sep.

Abstract

A-scan acquisitions in OCT images are acquired in a fan-beam pattern, but saved and displayed in a rectangular space. This results in an inaccurate representation of the scan geometry of OCT images, which introduces systematic distortions that can greatly impact shape and morphology based analysis of the retina. Correction of OCT scan geometry has proven to be a challenging task due to a lack of information regarding the true angle of entry of each A-scan through the pupil and the location of the A-scan nodal points. In this work, we present a preliminary model that solves for the OCT scan geometry in a restricted 2D setting. Our approach uses two repeat scans with corresponding landmarks to estimate the necessary parameters to correctly restore the fan-beam geometry of the input B-scans. Our results show accurate estimation of the ground truth geometry from simulated B-scans, and we found qualitatively promising result when the correction was applied to longitudinal B-scans of the same subject. We establish a robust 2D framework that can potentially be expanded for full 3D estimation and correction of OCT scan geometries.

Keywords: Distortion Correction; OCT; Retina.

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Figures

Fig. 1.
Fig. 1.
Tw o examples of simulated OCT scans and the effect of the scan geometry distortion on a flat object. (a) shows the relative positioning between the fan-beam and the object. Blue represents the scan area acquired in the OCT image, and green is the non-acquired region between the nodal point and OCT image. (b) shows the resulting OCT B-scan of the object, where each column in the image corresponds with a blue A-scan line in the respective image in (a).
Fig. 2.
Fig. 2.
Diagram of the OCT fan-beam geometry in our model. C is the location of the nodal point, R is a constant distance from C to the beginning of the OCT scan. For the nth A-scan, rn is the distance from the retina to the beginning of the scan and ϕn is the polar angle of the A-scan.
Fig. 3.
Fig. 3.
Diagram of our approach for using two scans to solve for the nodal points CA and CB and, R, the constant distance from each OCT scan to its nodal point.
Fig. 4.
Fig. 4.
Histogram of the estimated R across 10000 random trials using simulated OCT images with a ground truth R = 500.
Fig. 5.
Fig. 5.
Example of the proposed scan correction on a pair of longitudinal B-scans from the same subject. Yellow arrows indicate the two pairs of vessel locations used as corresponding landmarks for our method. (a) shows the two original B-scan images. (b) shows the resulting images after correcting for the scan geometry.
See this image and copyright information in PMC

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