Automatic estimation of retinal nerve fiber bundle orientation in SD-OCT images

Abstract

 

Purpose

 

Manual tracing of retinal nerve fiber bundles in fundus images is time consuming, error-prone and grader-dependent. We present a method to automatically estimate the fiber bundle orientation in spectral-domain optical coherence tomography (SD-OCT) images.

 

Methods

 

3D macular OCT scans of two healthy subjects (age 24 and 27) were obtained with a Spectralis SD-OCT system over a field-of-view of 15^ox15^o. The voxel size was 3.9 μm in axial and 11.3 μm in lateral directions. The retinal layers were automatically segmented using by coupled level sets (Novosel, ISBI, 2013) after which an enface image was constructed from a 3.9 μm thin slice located 7.8 μm anterior to the posterior nerve fiber layer interface (Figure 1.a).<br /> A filter-bank of rotated orientation-selective filters (Van Ginkel, SCIA, 2001) was applied to extract the orientation of the bundles. First, the responses resulting from horizontal scanning artifacts were removed. Second, anatomically unlikely orientations (Figure 2) were suppressed. Third, the local bundle orientation was obtained by selecting the orientation corresponding to the maximum filter response. The orientation map was smoothed with a Gaussian kernel of size σ = 90 μm.

 

Results

 

Figure 1.b shows the orientation field representations of the estimated retinal nerve fiber bundle orientation.

 

Conclusions

 

The retinal nerve fiber bundle orientation was estimated from macula-centered en face images around the RNFL-GCL interface by using advanced image filtering. The estimated orientations correlate well with an atlas obtained from manual tracing (Jansonius, Vision Res., 2009) in the temporal region of the macula in the image. Horizontal scanning artifacts hamper reliable estimation of fiber bundle orientation in the nasal region; this may be solved by alternative scanning procedures. In our future work we plan to validate our method by other imaging modalities.  

 

Figure 1.a) The macula-centered en face images of two young normal subjects;<br /> b) Estimated retinal nerve fiber bundle orientation shown with red lines.

 

 

Figure 2. Retinal nerve fiber bundle trajectories obtained from manual tracing (Jansonius, Vision Res., 2009); The white regions in the circles indicate the range of acceptable orientations by the proposed method for each quarter of the image.