scholarly journals The impact of different thresholds on optical coherence tomography angiography images binarization and quantitative metrics

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Alessandro Arrigo ◽  
Emanuela Aragona ◽  
Andrea Saladino ◽  
Alessia Amato ◽  
Francesco Bandello ◽  
...  
Keyword(s):  
Optical Coherence Tomography ◽  
Optical Coherence Tomography Angiography ◽  
Foveal Avascular Zone ◽  
Optical Coherence ◽  
Image Binarization ◽  
Quantitative Metrics ◽  
Avascular Zone ◽  
The Status ◽  
The Impact ◽  
Retinal Capillaries

AbstractOptical coherence tomography angiography (OCTA) provides several data regarding the status of retinal capillaries. This information can be further enlarged by employing quantitative metrics, such as vessel density (VD). A mandatory preliminary step of OCTA quantification is image binarization, a procedure used to highlight retinal capillaries on empty background. Although several binarization thresholds exist, no consensus is reached about the thresholding technique to be used. In this study, we tested thirteen binarization thresholds on a dataset made by thirty volunteers. The aim was to assess the impact of binarization techniques on: (I) detection of retinal capillaries, assessed by the calculation of overlapping percentages between binarized and original images; (II) quantitative OCTA metrics, including VD, vessel tortuosity (VT) and vessel dispersion (Vdisp); (III) foveal avascular zone (FAZ) detection. Our findings showed Huang, Li, Mean and Percentile as highly reliable binarization thresholds (p < 0.05), whereas the worst binarization thresholds were Intermodes, MaxEntropy, RenylEntropy and Yen (p < 0.05). All the thresholds variably underestimated VD metric and FAZ detection, with respect to the original OCTA images, whereas VT and Vdisp turned out to be more stable. The usage of a Fixed threshold resulted extremely useful to reduce VD and FAZ underestimations, although bound to operators’ experience.

Different effect of media opacity on automated and manual measurement of foveal avascular zone of optical coherence tomography angiographies

2020 ◽  
pp. bjophthalmol-2019-315780 ◽  
Author(s):  
Jinyu Zhang ◽  
Fang Yao Tang ◽  
Carol Cheung ◽  
Xiaolin Chen ◽  
Haoyu Chen
Keyword(s):  
Optical Coherence Tomography ◽  
Quantitative Measurement ◽  
Optical Coherence Tomography Angiography ◽  
Signal Strength ◽  
Normal Subjects ◽  
Foveal Avascular Zone ◽  
Elderly Subjects ◽  
Optical Coherence ◽  
Avascular Zone ◽  
The Impact

BackgroundOptical coherence tomography angiography (OCTA) provides not only visualisation but also quantitative measurement of foveal avascular zone (FAZ). Media opacity is common in elderly subjects with cataracts. This study aimed to investigate the impact of media opacity on automated and manual FAZ measurement.MethodsCirrus 5000 OCTA and Triton OCTA were used to image FAZ using a 3×3 mm scanning protocol from 30 eyes of 30 healthy normal subjects. Media opacity was simulated with neutral-density filters (optical density (OD): 0.10–0.48 in Cirrus 5000 and 0.15–0.51 in Triton). Signal strength (SS) and signal strength intensity (SSI) were provided by the built-in software in Cirrus 5000 and Triton, respectively. FAZ area, perimeter and circularity were measured automatically using the built-in software as well as a customised MATLAB program. FAZ metrics were also measured manually. The correlations between the OD, SS/SSI and FAZ metrics were analysed using Spearman correlation.ResultsIncreased OD significantly correlated with decreased SS/SSI (rs=−0.602 and −0.925, respectively, both p<0.001), decreased automated FAZ area (rs=−0.344 and −0.766, respectively, both p<0.001), but increased manual FAZ area in both Cirrus 5000 and Triton (rs=0.423 and 0.543, respectively, both p<0.001). Similar results were found for FAZ perimeter and circularity. There was a positive correlation between SS/SSI with the automated FAZ area but negative correlation with the manual FAZ area.ConclusionsThe effect of media opacity on quantitative measurement of FAZ is different between automated and manual measurements. Cautions must be taken when interpreting FAZ measurement in eyes with media opacity.

Foveal avascular zone in oculocutaneous albinism

2021 ◽  
Vol 14 (5) ◽  
pp. e240208
Author(s):  
Hana A Mansour ◽  
Sami Uwaydat ◽  
Muhamad H Yunis ◽  
Ahmad M Mansour
Keyword(s):  
Optical Coherence Tomography ◽  
Optical Coherence Tomography Angiography ◽  
Oculocutaneous Albinism ◽  
Foveal Avascular Zone ◽  
Optical Coherence ◽  
Retinal Capillary ◽  
Avascular Zone ◽  
Capillary Plexus ◽  
Foveal Hypoplasia

Optical coherence tomography angiography imaging in two patients with oculocutaneous albinism, one with severe nystagmus, showed persistence of both the superficial and the deep retinal capillary plexus adding another vascular feature to the foveal hypoplasia.

scholarly journals Automatic segmentation of foveal avascular zone based on adaptive watershed algorithm in retinal optical coherence tomography angiography images

2021 ◽  
Author(s):  
Jian Liu ◽  
Shixin Yan ◽  
Nan Lu ◽  
Dongni Yang ◽  
Chunhui Fan ◽  
...  
Keyword(s):  
Optical Coherence Tomography ◽  
Healthy Subjects ◽  
Optical Coherence Tomography Angiography ◽  
Automatic Segmentation ◽  
Qualitative Evaluation ◽  
Foveal Avascular Zone ◽  
Watershed Algorithm ◽  
Strong Positive Correlation ◽  
Optical Coherence ◽  
Avascular Zone

The size and shape of the foveal avascular zone (FAZ) have a strong positive correlation with several vision-threatening retinovascular diseases. The identification, segmentation and analysis of FAZ are of great significance to clinical diagnosis and treatment. We presented an adaptive watershed algorithm to automatically extract FAZ from retinal optical coherence tomography angiography (OCTA) images. For the traditional watershed algorithm, “over-segmentation” is the most common problem. FAZ is often incorrectly divided into multiple regions by redundant “dams”. This paper analyzed the relationship between the “dams” length and the maximum inscribed circle radius of FAZ, and proposed an adaptive watershed algorithm to solve the problem of “over-segmentation”. Here, 132 healthy retinal images and 50 diabetic retinopathy (DR) images were used to verify the accuracy and stability of the algorithm. Three ophthalmologists were invited to make quantitative and qualitative evaluations on the segmentation results of this algorithm. The quantitative evaluation results show that the correlation coefficients between the automatic and manual segmentation results are 0.945 (in healthy subjects) and 0.927 (in DR patients), respectively. For qualitative evaluation, the percentages of “perfect segmentation” (score of 3) and “good segmentation” (score of 2) are 99.4% (in healthy subjects) and 98.7% (in DR patients), respectively. This work promotes the application of watershed algorithm in FAZ segmentation, making it a useful tool for analyzing and diagnosing eye diseases.

Optical coherence tomography angiography in diabetic patients without diabetic retinopathy

2019 ◽  
Vol 30 (6) ◽  
pp. 1418-1423 ◽  
Author(s):  
Claudio Furino ◽  
Grazia Montrone ◽  
Maria Vittoria Cicinelli ◽  
Stefania Balestra ◽  
Maria Oliva Grassi ◽  
...  
Keyword(s):  
Optical Coherence Tomography ◽  
Diabetic Retinopathy ◽  
Optical Coherence Tomography Angiography ◽  
Vessel Density ◽  
Foveal Avascular Zone ◽  
Diabetic Patients ◽  
Optical Coherence ◽  
Avascular Zone ◽  
Capillary Plexus ◽  
Superficial Capillary Plexus

Purpose: To investigate a subset of diabetic patients without diabetic retinopathy with optical coherence tomography angiography, assessing the differences in macular perfusion between diseased eyes and healthy controls. Methods: Monocentric cross-sectional study, including 86 eyes from 43 diabetic patients with no clinical signs of diabetic retinopathy and 78 eyes from 39 controls. Patients underwent 3.0 × 3.0 mm and 4.5 × 4.5 mm swept-source optical coherence tomography angiography. Vessel density (%), foveal avascular zone area (mm2), and avascular density (%) were provided for the superficial capillary plexus and the deep capillary plexus. Results: The foveal avascular zone area at the superficial capillary plexus was larger in the study group compared to controls, irrespective of the area of the slab considered. A meaningful difference was found in the vessel density at the deep capillary plexus of the 3.0 × 3.0 mm slab (p = 0.03). Almost all the variables considered in the study showed a significant within-subject effect. Age significantly correlated with vessel density of superficial capillary plexus on 4.5 × 4.5 mm in both control and diabetic eyes. Conclusion: Diabetic patients with subclinical diabetic retinopathy feature a larger foveal avascular zone at the superficial capillary plexus compared with controls, as well as relative reduction of the vessel density at the deep capillary plexus. These findings might serve as the basis for screening between normal and diabetic subjects.

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