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. 2018 Apr 18;7(2):23.
doi: 10.1167/tvst.7.2.23. eCollection 2018 Apr.

Combining ODR and Blood Vessel Tracking for Artery-Vein Classification and Analysis in Color Fundus Images

Minhaj Alam  1 , Taeyoon Son  1 , Devrim Toslak  1 , Jennifer I Lim  2 , Xincheng Yao  1   2
Affiliations

Combining ODR and Blood Vessel Tracking for Artery-Vein Classification and Analysis in Color Fundus Images

Minhaj Alam et al. Transl Vis Sci Technol. .

Abstract

Purpose: This study aims to develop a fully automated algorithm for artery-vein (A-V) and arteriole-venule classification and to quantify the effect of hypertension on A-V caliber and tortuosity ratios of nonproliferative diabetic retinopathy (NPDR) patients.

Methods: We combine an optical density ratio (ODR) analysis and blood vessel tracking (BVT) algorithm to classify arteries and veins and arterioles and venules. An enhanced blood vessel map and ODR analysis are used to determine the blood vessel source nodes. The whole vessel map is then tracked beginning from the source nodes and classified as vein (venule) or artery (arteriole) using vessel curvature and angle information. Fifty color fundus images from NPDR patients are used to test the algorithm. Sensitivity, specificity, and accuracy metrics are measured to validate the classification method compared to ground truths.

Results: The combined ODR-BVT method demonstrates 97.06% accuracy in identifying blood vessels as vein or artery. Sensitivity and specificity of A-V identification are 97.58%, 97.81%, and 95.89%, 96.68%, respectively. Comparative analysis revealed that the average A-V caliber and tortuosity ratios of NPDR patients with hypertension have 48% and 15.5% decreases, respectively, compared to that of NPDR patients without hypertension.

Conclusions: Automated A-V classification has been achieved by combined ODR-BVT analysis. Quantitative analysis of color fundus images verified robust performance of the A-V classification. Comparative quantification of A-V caliber and tortuosity ratios provided objective biomarkers to differentiate NPDR groups with and without hypertension.

Translational relevance: Automated A-V classification can facilitate quantitative analysis of retinal vascular distortions due to diabetic retinopathy and other eye conditions and provide increased sensitivity for early detection of eye diseases.

Keywords: blood vessel tracking; diabetic retinopathy; optical density ratio; vein–artery classification.

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Figures

Figure 1
Figure 1
Core steps of A-V identification.
Figure 2
Figure 2
(A1) Original fundus image. (A2) Red channel. (A3) Green channel. (A4) Blue channel. (B) Intensity histogram of three channels. (C) Enhanced green channel. (D) Vessel map. (E) Skeleton.
Figure 3
Figure 3
Comparing ODR in arteries and veins. (A) Scatter plot illustrates ODR values of identified blood vessels in perifoveal retina of a single fundus image. A threshold can be added easily to clearly distinguish arterial and venous ODRs. (B) Average arterial and venous ODR values in a single fundus image. (C) Average arterial and venous ODR values for 50 fundus images used in this study. The average values are presented with corresponding standard deviations. ***P < 0.001 from Student's t-test.
Figure 4
Figure 4
Core steps of BVT algorithm.
Figure 5
Figure 5
Steps of vessel tracking. (A) A source node is identified with the cross. (B) The main branch of the vessel is tracked; the red dots represent all the possible branch nodes. (C) The process of choosing the forward path in the vessel map is shown in this enlarged window. (D) All the possible branches are identified; only four-way cross sections are marked with red crosses. (E) The decision taken on the four-way cross sections and whole vessel is identified. (F) Vein (blue) and artery (red) identified in the skeleton. (G) Classified vein and artery map.
Figure 6
Figure 6
The comparison of mean ROC curves for A-V classification. The dashed line represents the trade-off resulting from random chance.
Figure 7
Figure 7
Quantitative comparison between patients without hypertension and with hypertension. (A) A-V caliber ratio. (B) A-V tortuosity ratio. (C) Average caliber of the whole vessel map. (D) Average tortuosity of the whole vessel map. Error bars are standard deviations; the significance of Student's t-test is marked as *P < 0.05; **P < 0.01; ***P < 0.001.
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