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Extraction and reconstruction of retinal vasculature

Ahmad Fadzil MH, Izhar LI, Venkatachalam PA, Karunakar TV

J Med Eng Technol, 2007 Nov-Dec;31(6):435-42.
PMID: 17994417 DOI: 10.1080/03091900601111201

Information about retinal vasculature morphology is used in grading the severity and progression of diabetic retinopathy. An image analysis system can help ophthalmologists make accurate and efficient diagnoses. This paper presents the development of an image processing algorithm for detecting and reconstructing retinal vasculature. The detection of the vascular structure is achieved by image enhancement using contrast limited adaptive histogram equalization followed by the extraction of the vessels using bottom-hat morphological transformation. For reconstruction of the complete retinal vasculature, a region growing technique based on first-order Gaussian derivative is developed. The technique incorporates both gradient magnitude change and average intensity as the homogeneity criteria that enable the process to adapt to intensity changes and intensity spread over the vasculature region. The reconstruction technique reduces the required number of seeds to near optimal for the region growing process. It also overcomes poor performance of current seed-based methods, especially with low and inconsistent contrast images as normally seen in vasculature regions of fundus images. Simulations of the algorithm on 20 test images from the DRIVE database show that it outperforms many other published methods and achieved an accuracy range (ability to detect both vessel and non-vessel pixels) of 0.91 - 0.95, a sensitivity range (ability to detect vessel pixels) of 0.91 - 0.95 and a specificity range (ability to detect non-vessel pixels) of 0.88 - 0.94.

Matched MeSH terms: Retinal Vessels/anatomy & histology*
Variability and repeatability of quantitative, Fourier-domain optical coherence tomography Doppler blood flow in young and elderly healthy subjects

Tayyari F, Yusof F, Vymyslicky M, Tan O, Huang D, Flanagan JG, et al.

Invest Ophthalmol Vis Sci, 2014 Dec;55(12):7716-25.
PMID: 25335983 DOI: 10.1167/iovs.14-14430

The purpose of this study was to determine the within-session variability and between-session repeatability of spectral Fourier-domain optical coherence tomography (Doppler FD-OCT) Doppler retinal blood flow measurements in young and elderly subjects.

Matched MeSH terms: Retinal Vessels/physiology*
Fulltext Relationship between retinal blood flow and arterial oxygen

Cheng RW, Yusof F, Tsui E, Jong M, Duffin J, Flanagan JG, et al.

J Physiol, 2016 Feb 01;594(3):625-40.
PMID: 26607393 DOI: 10.1113/JP271182

KEY POINTS: Vascular reactivity, the response of the vessels to a vasoactive stimulus such as hypoxia and hyperoxia, can be used to assess the vascular range of adjustment in which the vessels are able to compensate for changes in PO2. Previous studies in the retina have not accurately quantified retinal vascular responses and precisely targeted multiple PaO2 stimuli at the same time as controlling the level of carbon dioxide, thus precluding them from modelling the relationship between retinal blood flow and oxygen. The present study modelled the relationship between retinal blood flow and PaO2, showing them to be a combined linear and hyperbolic function. This model demonstrates that the resting tonus of the vessels is at the mid-point and that they have great vascular range of adjustment, compensating for decreases in oxygen above a PETCO2 of 32-37 mmHg but being limited below this threshold. Retinal blood flow (RBF) increases in response to a reduction in oxygen (hypoxia) but decreases in response to increased oxygen (hyperoxia). However, the relationship between blood flow and the arterial partial pressure of oxygen has not been quantified and modelled in the retina, particularly in the vascular reserve and resting tonus of the vessels. The present study aimed to determine the limitations of the retinal vasculature by modelling the relationship between RBF and oxygen. Retinal vascular responses were measured in 13 subjects for eight different blood gas conditions, with the end-tidal partial pressure of oxygen (PETCO2) ranging from 40-500 mmHg. Retinal vascular response measurements were repeated twice; using the Canon laser blood flowmeter (Canon Inc., Tokyo, Japan) during the first visit and using Doppler spectral domain optical coherence tomography during the second visit. We determined that the relationship between RBF and PaO2 can be modelled as a combination of hyperbolic and linear functions. We concluded that RBF compensated for decreases in arterial oxygen content for all stages of hypoxia used in the present study but can no longer compensate below a PETCO2 of 32-37 mmHg. These vessels have a great vascular range of adjustment, increasing diameter (8.5% arteriolar and 21% total venous area) with hypoxia (40 mmHg P ETC O2; P < 0.001) and decreasing diameter (6.9% arteriolar and 23% total venous area) with hyperoxia (500 mmHg PETCO2; P < 0.001) to the same extent. This indicates that the resting tonus is near the mid-point of the adjustment ranges at resting PaO2 where sensitivity is maximum.

Matched MeSH terms: Retinal Vessels/physiology*
Diabetic retinopathy: a quadtree based blood vessel detection algorithm using RGB components in fundus images

Reza AW, Eswaran C, Hati S

J Med Syst, 2008 Apr;32(2):147-55.
PMID: 18461818

Blood vessel detection in retinal images is a fundamental step for feature extraction and interpretation of image content. This paper proposes a novel computational paradigm for detection of blood vessels in fundus images based on RGB components and quadtree decomposition. The proposed algorithm employs median filtering, quadtree decomposition, post filtration of detected edges, and morphological reconstruction on retinal images. The application of preprocessing algorithm helps in enhancing the image to make it better fit for the subsequent analysis and it is a vital phase before decomposing the image. Quadtree decomposition provides information on the different types of blocks and intensities of the pixels within the blocks. The post filtration and morphological reconstruction assist in filling the edges of the blood vessels and removing the false alarms and unwanted objects from the background, while restoring the original shape of the connected vessels. The proposed method which makes use of the three color components (RGB) is tested on various images of publicly available database. The results are compared with those obtained by other known methods as well as with the results obtained by using the proposed method with the green color component only. It is shown that the proposed method can yield true positive fraction values as high as 0.77, which are comparable to or somewhat higher than the results obtained by other known methods. It is also shown that the effect of noise can be reduced if the proposed method is implemented using only the green color component.

Matched MeSH terms: Retinal Vessels/physiopathology*
An efficient algorithm for retinal blood vessel segmentation using h-maxima transform and multilevel thresholding

Saleh MD, Eswaran C

Comput Methods Biomech Biomed Engin, 2012;15(5):517-25.
PMID: 21331960 DOI: 10.1080/10255842.2010.545949

Retinal blood vessel detection and analysis play vital roles in early diagnosis and prevention of several diseases, such as hypertension, diabetes, arteriosclerosis, cardiovascular disease and stroke. This paper presents an automated algorithm for retinal blood vessel segmentation. The proposed algorithm takes advantage of powerful image processing techniques such as contrast enhancement, filtration and thresholding for more efficient segmentation. To evaluate the performance of the proposed algorithm, experiments were conducted on 40 images collected from DRIVE database. The results show that the proposed algorithm yields an accuracy rate of 96.5%, which is higher than the results achieved by other known algorithms.

Matched MeSH terms: Retinal Vessels/pathology*
A decision support system for automatic screening of non-proliferative diabetic retinopathy

Reza AW, Eswaran C

J Med Syst, 2011 Feb;35(1):17-24.
PMID: 20703589 DOI: 10.1007/s10916-009-9337-y

The increasing number of diabetic retinopathy (DR) cases world wide demands the development of an automated decision support system for quick and cost-effective screening of DR. We present an automatic screening system for detecting the early stage of DR, which is known as non-proliferative diabetic retinopathy (NPDR). The proposed system involves processing of fundus images for extraction of abnormal signs, such as hard exudates, cotton wool spots, and large plaque of hard exudates. A rule based classifier is used for classifying the DR into two classes, namely, normal and abnormal. The abnormal NPDR is further classified into three levels, namely, mild, moderate, and severe. To evaluate the performance of the proposed decision support framework, the algorithms have been tested on the images of STARE database. The results obtained from this study show that the proposed system can detect the bright lesions with an average accuracy of about 97%. The study further shows promising results in classifying the bright lesions correctly according to NPDR severity levels.

Matched MeSH terms: Retinal Vessels/pathology*
Fulltext A new blood vessel extraction technique using edge enhancement and object classification

Badsha S, Reza AW, Tan KG, Dimyati K

J Digit Imaging, 2013 Dec;26(6):1107-15.
PMID: 23515843 DOI: 10.1007/s10278-013-9585-8

Diabetic retinopathy (DR) is increasing progressively pushing the demand of automatic extraction and classification of severity of diseases. Blood vessel extraction from the fundus image is a vital and challenging task. Therefore, this paper presents a new, computationally simple, and automatic method to extract the retinal blood vessel. The proposed method comprises several basic image processing techniques, namely edge enhancement by standard template, noise removal, thresholding, morphological operation, and object classification. The proposed method has been tested on a set of retinal images. The retinal images were collected from the DRIVE database and we have employed robust performance analysis to evaluate the accuracy. The results obtained from this study reveal that the proposed method offers an average accuracy of about 97 %, sensitivity of 99 %, specificity of 86 %, and predictive value of 98 %, which is superior to various well-known techniques.

Matched MeSH terms: Retinal Vessels/pathology*
Retinal changes and cardiac biomarker assessment in relation to chronic kidney disease: a single centre study

Mustafar R, Hishamuddin KAM, Mohd R, Kamaruzaman L, Halim WHWA, Hsien YM, et al.

BMC Nephrol, 2023 Nov 13;24(1):338.
PMID: 37957551 DOI: 10.1186/s12882-023-03386-w

BACKGROUND: The prevalence of chronic kidney disease (CKD) is rising in Malaysia. Early detection is necessary to prevent disease progression, especially in terms of cardiovascular (CV) risk, the main cause of death in end-stage renal disease (ESRD). Retinal changes have proven to be a good predictor of CKD whereas cardiac biomarkers are useful in cardiovascular risk stratification. We aimed to demonstrate the correlation between retinal changes and cardiac biomarkers with CKD.
METHODS: This single-centre cross-sectional study was conducted among patients with CKD stages 3, 4, and 5 (not on dialysis) from the Nephrology Clinic, Universiti Kebangsaan Malaysia Medical Centre. A total of 84 patients were recruited with an even distribution across all three stages. They underwent fundus photography where images were analysed for vessel calibre (central retinal venular equivalent (CRVE), central retinal arterial equivalent (CRAE), and tortuosity indices. Optical coherence tomography was used to measure macular volume. Blood samples were sent for laboratory measurement of high-sensitivity C-reactive protein (hs-CRP) and asymmetric dimethylarginine (ADMA). These parameters were analysed in relation to CKD.
RESULTS: The mean age was 58.8 ± 11.7 years, with 52.4% male and 47.6% female patients. Among them, 64.3% were diabetics. Retinal vessel tortuosity (r = -0.220, p-value = 0.044) had a negative correlation with the estimated glomerular filtration rate (eGFR). CRVE showed a positive correlation with proteinuria (r = 0.342, p = 0.001) but negative correlation with eGFR (r = -0.236, p = 0.031). Hs-CRP positively correlated with proteinuria (r = 0.313, p = 0.04) and negatively correlated with eGFR (r = -0.370, p = 0.001). Diabetic patients had a higher CRVE compared to non-diabetic patients (p = 0.02). History of ischaemic heart disease was associated with a smaller macula volume (p = 0.038). Male gender (r2 = 0.066, p = 0.031) and HbA1c had a positive influence (r2 = 0.066, p = 0.047) on retinal vessel tortuosity. There was a positive influence of age (r2 = 0.183, p = 0.012) and hs-CRP (r2 = 0.183, p = 0.045) on CRVE. As for macula volume, it negatively correlated with diabetes (r2 = 0.015, p = 0.040) and positively correlated with smoking (r2 = 0.015, p = 0.012).
CONCLUSION: Our study showed that eGFR value affects retinal vessel tortuosity, CRVE and hs-CRP. These parameters bear potential to be used as non-invasive tools in assessing CKD. However, only macula volume may be associated with CVD risk among the CKD population.

Matched MeSH terms: Retinal Vessels
Fulltext Resolution of exudative retinal detachment and regression of retinal macrocyst post-laser in Coats disease

Munira Y, Zunaina E, Azhany Y

Int Med Case Rep J, 2013;6:37-9.
PMID: 23966803 DOI: 10.2147/IMCRJ.S47769

A 15-year-old boy presented with painless progressive blurring of vision in the right eye for 1 year in duration. His visual acuity in the right eye was hand movement. The right fundus showed presence of extensive subretinal exudates at the posterior pole and a retinal macrocyst at the temporal periphery. It was associated with exudative retinal detachment at the inferior periphery of the retina. Fundus angiography revealed telangiectatic retinal vessels at the superotemporal retina. Based on clinical and angiographic findings, a diagnosis of Coats disease was made. He was treated with retinal laser photocoagulation. There was resolution of the exudative retinal detachment, reduction of subretinal exudates, and regression of the retinal macrocyst with improvement of visual acuity to 1/60 post-laser therapy.

Matched MeSH terms: Retinal Vessels
Retinal Vessel Analysis as a Novel Screening Tool to Identify Childhood Acute Lymphoblastic Leukemia Survivors at Risk of Cardiovascular Disease

Azanan MS, Chandrasekaran S, Rosli ES, Chua LL, Oh L, Chin TF, et al.

J Pediatr Hematol Oncol, 2020 08;42(6):e394-e400.
PMID: 32118813 DOI: 10.1097/MPH.0000000000001766

BACKGROUND: Microvascular endothelial dysfunction is central to the pathogenesis of cardiovascular disease (CVD). The eye offers direct access for endothelial health assessment via the retinal microvasculature. The aim of the study was to investigate whether image-based retinal vessel analysis is a feasible method of assessing endothelial health in survivors of childhood acute lymphoblastic leukemia (cALL).
MATERIALS AND METHODS: Cardiovascular risk factors (CRFs) were estimated using the 30-year Framingham Risk Score in 73 childhood leukemia survivors (median age: 25; median years from diagnosis: 19) and 78 healthy controls (median age: 23). Radial arterial stiffness was measured using pulse wave analyzer, while endothelial activation markers were measured by soluble intercellular adhesion molecule 1 (sICAM-1) and soluble vascular cell adhesion molecule 1 (sVCAM-1). Retinal fundus images were analyzed for central retinal artery/vein equivalents (CRAE/CRVE) and arteriolar-venular ratio (AVR).
RESULTS: cALL survivors had higher CRF (P<0.0001), arterial stiffness (P=0.001), and sVCAM-1 (P=0.007) compared with controls. Survivors also had significantly higher CRVE (P=0.021) while AVR was significantly lower (P=0.026) in survivors compared with controls, compatible with endothelial dysfunction. In cALL survivors with intermediate risk for CVD, CRAE, and AVR are significantly lower, while sVCAM-1 and sICAM-1 are significantly higher when compared with survivors with low CVD risk after adjusting with covariates (age, sex, and smoking status).
CONCLUSIONS: cALL survivors have an increased risk of CVD compared with age-matched peers. The survivors demonstrated microvasculopathy, as measured by retinal vascular analysis, in addition to physical and biochemical evidence of endothelial dysfunction. These changes predate other measures of CVD. Retinal vessel analysis may be utilized as a robust screening tool for identifying survivors at increased risk for developing CVD.

Matched MeSH terms: Retinal Vessels/pathology*
The potential for evaluating the effects of intensified antithrombotic therapy using retinal optical coherence tomography angiography

Aik Kah T

Med Hypotheses, 2018 Jun;115:54-57.
PMID: 29685198 DOI: 10.1016/j.mehy.2018.03.022

Oral anticoagulants are widely used in the treatment and prevention of both venous and arterial thromboembolism. They are classified into vitamin K anticoagulants (VKAs) and non-vitamin K antagonist oral anticoagulants (NOACs). The main advantage of NOACs over VKAs is the absence of the need for continuous monitoring. However, there are concerns about their effectiveness and safety in certain clinical situations. In this manuscript, I discussed the possibility of using optical coherence tomography angiography [OCTA] in the monitoring of the activity of NOACs. The rapid development of OCTA technology is very promising. Further research and development will extend its use beyond the realm of ophthalmology.

Matched MeSH terms: Retinal Vessels/drug effects

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