Restricted Summed-Area Projection for Geographic Atrophy Visualization in SD-OCT Images.
OBJECTIVE
To enhance the rapid assessment of geographic atrophy (GA) across the macula in a single projection image generated from three-dimensional (3D) spectral-domain optical coherence tomography (SD-OCT) scans by introducing a novel restricted summed-area projection (RSAP) technique.


METHODS
We describe a novel en face GA visualization technique, the RSAP, by restricting the axial projection of SD-OCT images to the regions beneath the Bruch's membrane (BM) boundary and also considering the choroidal vasculature's influence on GA visualization. The technique analyzes the intensity distribution beneath the retinal pigment epithelium (RPE) layer to fit a cross-sectional surface in the sub-RPE region. The area is taken as the primary GA projection. A median filter is then adopted to smooth the generated GA projection image. The RSAP technique was evaluated in 99 3D SD-OCT data sets from 27 eyes of 21 patients presenting with advanced nonexudative age-related macular degeneration and GA. We used the mean difference between GA and background regions and GA separability metric to measure GA contrast and distinction in the generated images, respectively. We compared our results with two existing GA projection techniques, the summed-voxel projection (SVP) and Sub-RPE Slab techniques.


RESULTS
Comparative results demonstrate that the RSAP technique is more effective in displaying GA than the SVP and Sub-RPE Slab. The average of the mean difference between GA and background regions and the GA separability based on SVP, Sub-RPE Slab, and RSAP were 0.129/0.880, 0.238/0.919, and 0.276/0.938, respectively.


CONCLUSIONS
The RSAP technique was more effective for GA visualization than the conventional SVP and Sub-RPE Slab techniques. Our technique decreases choroidal vasculature influence on GA projection images by analyzing the intensity distribution characteristics in sub-RPE regions. The generated GA projection image with the RSAP technique has improved contrast and distinction.


CONCLUSIONS
Our method for automated generation of GA projection images from SD-OCT images may improve the visualization of the macular abnormalities and the management of GA.
School of Computer Science and Engineering, Nanjing University of Science and Technology, Nanjing, China.
Qiang
Q
Chen
School of Computer Science and Engineering, Nanjing University of Science and Technology, Nanjing, China.
Sijie
S
Niu
School of Computer Science and Engineering, Nanjing University of Science and Technology, Nanjing, China.
Honglie
H
Shen
Byers Eye Institute at Stanford, Stanford University School of Medicine, Palo Alto, CA, USA.
Theodore
T
Leng
Department of Radiology and Medicine (Biomedical Informatics Research), Stanford University School of Medicine, Stanford, CA, USA.
Luis
L
de Sisternes
Department of Radiology and Medicine (Biomedical Informatics Research), Stanford University School of Medicine, Stanford, CA, USA.
Daniel L
DL
Rubin
choroidal vasculature; geographic atrophy visualization; geographic separability; restricted summed-area projection; spectral domain optical coherence tomography