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BLOOD VESSEL ENHANCEMENT AND SEGMENTATION USING WAVELET TRANSFORM
BLOOD VESSEL ENHANCEMENT AND SEGMENTATION USING WAVELET TRANSFORM
Submitted by
RAHUL RAJAN
DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING
SREE CHITRA THIRUNAL COLLEGE OF ENGINEERING, THIRUVANANTHAPURAM - 695 018.
SEPTEMBER 2010

ABSTRACT


Retinal vessel segmentation is an essential step for the diagnoses of various eye diseases. An

automated tool for blood vessel segmentation is useful to eye specialists for purpose of patient screening and clinical study. Vascular

Pattern is normally not visible in retinal images. In this paper, we present a method for

enhancing, locating and segmenting blood vessels in images of retina. We present a method that

uses 2-D Gabor wavelet and sharpening filter to enhance and sharpen the vascular pattern

respectively. This technique locates and segments the blood vessels using edge detection

algorithm and morphological operations. This technique is tested on publicly available STARE

database of manually labeled images which has been established to facilitate

comparative studies on segmentation of blood vessels in retinal images. The validation of our

retinal image vessel segmentation technique is supported by experimental results.

Keywords—Vascular pattern, retinal images, vessel segmentation

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1.INTRODUCTION




Retinal image processing is greatly required in diagnosing and treatment of many diseases

affecting the retina and the choroid behind it [1]. Diabetic retinopathy is one of the

complications of diabetes mellitus affecting the retina and the choroid. In this condition, a

network of small blood vessels, called choroidal neovascularization (CNV), arises in the

choroid and taking a portion of the blood supplying the retina. As the amount of blood supplying

the retina is decreased, the sight may be degraded and in the severe cases, blindness may occur .

The eye is a window to the retinal vascular system which is uniquely accessible for the study of

a continuous vascular bed in humans. Retinal image processing is greatly required in diagnosing

and treatment of many diseases affecting the retina and the choroid behind it [1]. Diabetic

retinopathy is one of the complications of diabetes mellitus affecting the retina and the choroid.


In this condition, a network of small blood vessels, called choroidal neovascularization (CNV),

arisesin the choroid and taking a portion of the blood supplying the retina. As the amount of

blood supplying the retina is decreased, the sight may be degraded and in the severe cases,

blindness may occur . The eye is a window to theretinal vascular system which is uniquely

accessible for the study of a continuous vascular bed in humans [1]. The detection and

measurement of blood vessels can be used to quantify the severity of disease, as part of the

process of automated diagnosis of disease or in the assessment of the progression of therapy [2].

Retinal bloodvessels have been shown to have measurable changes in diameter, branching

angles, length , as a result of a disease.


Thus a reliable method of vessel segmentation would be valuable for the early detection and

characterizationofchanges due to such diseases [2]. Retinal vascular pattern facilitates the

physicians for the purposes of diagnosing eye diseases, patient screening, and clinical study [3].

Inspectionof blood vessels provides the information regarding pathological changes caused by

ocular diseases includingdiabetes, hypertension, stroke and arteriosclerosis [4]. The hand

Retinal vessel segmentation may be used for automatic generation of retinal maps for the

treatment of age-related macular degeneration [6], extraction of characteristic points of the

retinal vasculature for temporal or multimodal image registration [7], retinal image mosaic

synthesis,identification of the optic disc position [8], and localization of the fovea [9].




The challenges faced in automated vessel detection include wide range of vessel widths, low

contrastwith respect with background and appearance of variety of structures in the image

including the optic disc, the retinal boundary and other pathologies [10].



















1.1 PROCEDURE


Different approaches for automated vessel segmentation have been proposed. Methods based on

vessel tracking to obtain the vasculature structure, along with vessel diameters and branching

points have been proposed by [12]-[17]. Tracking consists of following vessel center

lines guided by local information. In [23], ridge detection was used to form line elements and

partition the image into patches belonging to each line element. Pixel features were

then generated based on this representation. Many features were presented and a feature

selection scheme is used to select those which provide the best class separability. Papers

[18]-[21] used deformable models for vessels segmentation. Chuadhuri et al. [22] proposed a

technique using matched filters to emphasize blood vessels. An improved region

based threshold probing of the matched filter response technique was used by Hoover et al. [24].

In this paper, we present the colored retinal image vessel segmentation technique that enhances

and sharpens the vascular pattern using 2-D Gabor wavelet and sharpening filters.



Our technique creates a binary mask for vessel segmentation applying edge detection algorithm

on sharpened retinal image and a fine segmentation mask is

obtained by applying morphological dilation operation. The paper is organized in four sections.

In Section II, a schematic overview of our implementation methodology is illustrated. Section II

also presents the step by step

techniques required for colored retinal image vessels segmentation. Experimental results of the

tests on the images of the STARE database and their analysis are given in Section III followed by

conclusion in Section IV.











1.2 BLOOD VESSEL ENHANCEMENT AND SEGMENTATION


A schematic overview of proposed blood vessel enhancement and segmentation method is

illustrated here.

The monochromatic RGB retinal image is taken as an input and 2-D Gabor wavelet is used to

enhance the vascular pattern especially the thin and less visible vessels are

enhanced using Gabor wavelet [25]. Before extracting vessels from enhanced

retinal image, the blood vessels are sharpened using sharpening filter [26].

Vessels segmentation binary mask is created by detecting vessels edges from

sharpened image. The blood vessels are marked by the masking procedure which assign

one to all those pixels which belong to blood vessels and zero to non vessels pixels. Final

refined vessel segmentation mask is created by applying morphological dilation operator

[26].
Fig. 2 shows the complete flow diagram of proposed blood vessel enhancement and

segmentation technique.












1.3 EXPERIMENTAL RESULTS



The tests of proposed technique are performed with respect to the vessel segmentation accuracy

and their standard deviation using publicly available STARE database [11]. The STARE database

consists of 20 RGB color images

of the retina. The images are of size 605×700 pixels, 24 bits per pixel (standard RGB). There are

two hand-labeling available for the 20 images of made by two different human observers. The

manually segmented images by 1st human observer are used as ground truth and the

segmentations of set B aretested against set A, serving as a human observer reference for

performance comparison truth. The segmentations of set B are tested against those of A, serving

proposed technique with the accuracies of the methods of Hoover et al. [24], Staal et al. [23] and

Soares et al. [28]. Table I summarizes the results of vessel

segmentation for above mentioned methods. It shows the results in term of average accuracy and

their standard deviation. Fig. 6 illustrates the blood vessel segmentation results for proposed

method.














1.4RESULT

The problem with retinal images is that the visibility of vascular pattern is usually not good. So,

it is necessary toenhance the vascular pattern. In this paper, a wavelet based colored retinal

image blood vessel segmentation technique is proposed. Vascular pattern is enhanced and

edge detection algorithm and morphological dilation operator respectively. We have tested our

technique on publicly available STARE database of manually labeled images. Experimental

results show that our method performs well in enhancing and segmenting the vascular pattern.







2.LITERATURE SURVEY


Diabetes affects almost one million Australians, and has associated complications such as vision

loss, heart failure and stroke. Any improvement in early diagnosis would therefore represent a

significant gain with respect to reducing the morbidity and mortality of the Australian

population. This work describes one step along the path to providing automated diagnostic

support tools for the early detection of diabetes associated retinal pathology. We focus on the

blood vessel network in the retina that is affected by diabetes. Currently, the

correct assessment of these images using fluorescein requires a specialist, which presents

difficulties in remote or rural areas and is also a relatively invasive and dangerous procedure.

The alternative is to use non-mydriatic colour images that although more difficult to interpret, are

more desirable for use in remote or rural areas as they can be obtained by trained rural health
professionals.The alternative is to use non-mydriatic colour images that although more difficult

to interpret, are more desirable for use in remote or rural areas as they can be obtained by trained

rural health professionals.

Non-mydriatic camera images were analysed in an attempt to fine tune and improve the quality

of retinal blood vessel detection in medical imaging. For this purpose we used the Morlet

wavelet as a tool for segmenting retinal blood vessels in combination with adaptive thresholding,

supervised classification and supervised classifier probabilities combined with

adaptivethresholding. The advantage of wavelet analysis is its multiscale analysing capability in

tuning to specific frequencies, allowing noise filtering and blood vessel enhancement in a

single step. Twenty non-mydriatic camera images of the retinal fundus were analysed, from the

Stare database (http://www.parl.clemson.edu/stare). The results were compared against

the corresponding gold-standard images indicating the true location of vessels as determined by

two ophthalmologists and presented in the manner of free-response receiver operator

characteristic (FROC) curves.


Diabetes is a chronic disease that affects the body’s capacity to regulate the amountof sugar in

the blood. One in twenty Australians are affected by diabetes, but thisfigure is conservative, due

to the presence of subclinical diabetes, where the diseaseis undiagnosed, yet is already damaging

the body without manifesting substantial symptoms.

This incidence rate is not confined to Australia, but is typical of de-veloped nations, and even

higher in developing nations. Excess sugar in the bloodresults in metabolites that cause vision

loss, heart failure and stroke, and damage to peripheral blood vessels.These problems contribute

significantly to themorbid-ity and mortality of the Australian population, so that any

improvement in earlydiagnosis would therefore represent a significant gain. The incidence is
projected to rise, and has already become a major epidemic [16]

The most common diagnostic test for diabetes is measurement of blood sugar,but this is only

effective when the disease has already made substantial progres-sion. However, because of the

effect of diabetes on peripheral vessels, it is possibleto detect diabetes by examining these

vessels. One of the most suitable areas tomake such an observation is the retina, where small

blood vessels are arrangedon the surface, and visual inspection is possible through the pupil

itself. Thistechnique is well developed, with ophthalmologists routinely employing manual

inspection of the retina for diagnosing diabetic retinopathy, which is causedby diabetes, and

leads to significant vision degeneration without prompt treat-ment. In addition cameras can

capture an image of the retina for examination byophthalmologists or for telemedicine as well as

for providing records over time.The requirement of specialists to make an accurate diagnosis

does make retinalphotography prohibitive in cost as a screening tool for the general population

especially in rural or remote regions.


Images containing labelled blood vessels can be derived by injecting a fluorescent dye into the

person being examined, so that blood vessels can be observedwith higher contrast. This

technique, know as fluorescein imaging, is invasiveand brings some risk. As it also requires the

presence of an ophthalmologist, it isnot suitable for rural and remote screening programmes.

Images taken withoutfluorescent dye and pupil dilation are known as non-mydriatic, and are also

lessinvasive with good contrast due to the high resolution cameras available. These

are therefore desirable for use in remote or rural areas as they can be obtained

by trained rural health professionals such as indigenous health workers, diabetes

educators and community nurses.The aim of this work is first, to improve the accuracy and speed

of vessel segmentation using non-mydriatic retinal images, by the application of advanced

image processing techniques; and second, to apply machine intelligence tech-niques to offer

decision support and reduce the burden on specialist interpretation. Starting with a non-mydriatic

image, our aim is to provide an assessmentof risk of diabetes for the person being examined.





3.METHOD STUDY


Identification of anomalies in retinal blood vessels, associated with diabeteshealth care,

represents a large portion of the assessment carried out by ophthalmologists, which is time

consuming and in many cases does not show anyanomalies at the initial visit. Utilizing non-

specialist health workers in identifying diabetic eye disease is an alternative but trials have

shown that correctidentification of retinal pathology may be poor (i.e. only 50% of the cases).

Thissuccess rate decreases for early proliferative retinopathy stages. Telemedicine isan attractive

approach. However, this procedure is not time effective and doesnot lessen the burden on a

comparatively small number of ophthalmologistsin rural areas that need to assess the images. In

addition significant technicalproblems lessen the availability of telemedicine




3.1 Image processing for medical diagnosis


Identification of vascular anomalies associated with diabetes health care represents a large

portion of the assessment carried out by ophthalmologists, which is time consuming and in

many cases does not show any anomalies at the initial visit. Utilizing non-specialist health

workers in identifying diabetic eye disease is an alternative but trials have shown that correct

identification of retinal pathology may be poor (i.e. only 50% of the cases). This success rate

decreases for early proliferative retinopathy stages. Telemedicine is an attractive approach.

However, this procedure is not time effective and does not lessen the burden on a

comparatively small number of ophthalmologists in rural areas that need to assess the images. In

addition significant technical problems lessen the availability of telemedicine (Yogesan et 2000).

Automated assessment of blood vessel patterns that can be used by rural health

professionals is now being extended from fluorescein-labelled to non-mydriatic

camera images

Automated assessment of blood vessel patterns that can be used by rural healtprofessionals is

now being extended from fluorescein-labelled to non-mydriaticcameraimages (Cesar &Jeline

2003; McQuellin et al., 2002). This work presents the evolution ofretinal blood vessel

segmentation as a function of the effectiveness of the wavelet transform.We outline the use of the

wavelet transform combined with mathematical morphology, supervised training algorithms and

adaptivethresholding.

Several methods for segmenting blood vessels using either rule-based or supervised methods

have recently been reported for both fluorescein and non-mydriatic colour retinal

images (Leandro et al., 2003; Sinthanayothin et al., 1999; Staal et al., 2004). Mathematical

morphology, which is a rule-based method, has previously revealed itself as a very useful

digital image processing technique for detecting and counting microaneurysms in fluorescein and

non-mydriatic camera images (Cree et al., 2004; Spencer et al., 1996). Wavelet transformtheory

has grown rapidly since the seminal work by Morlet and Grossman, finding applications in

several realms (Goupillaud et al., 1984). The wavelets space-scale analysis

capability can be used to “decompose” vessel structures into differently scaled Morlet wavelets,

so as to segment them from the retinal fundus.

Automated assessment of blood vessel patterns that can be used by rural health

professionals is now being extended from fluorescein-labelled to non-mydriatic

camera images [3, 15]. This has the advantage of a less invasive and risky proce-

dure, making possible a screening procedure for the general population. A signif-

icant problem in these non-mydriatic images, however, is the ability to identify

the blood vessels in low vessel to background contrast and diverse pathology,

and to separate (segment) them from the background image (fundus). In this

work we present the evolution of retinal blood vessel segmentation, using the

wavelet transform combined with mathematical morphology, supervised train-

ing algorithms and adaptive thresholding. Once the vessels have been success-

fully segmented, it is possible to apply automated measures, such as morphology

measures, then to use further automated methods to identify anomalies.

further processing is outside the scope of this paper, as we concentrate on the

vessel segmentation only.

Several methods for segmenting items of interest have been reported, using

either rule-based or supervised methods for both fluorescein and non-mydriatic

colour retinal images [14, 17, 19]. Mathematical morphology, which is a rule-

based method, has previously revealed itself as a very useful digital image pro-

cessing technique for detecting and counting microaneurysms in fluorescein and

non-mydriatic camera images [4, 12, 18]. Wavelet transform theory has grown

rapidly since the seminal work by Morlet and Grossman, finding applications in

many realms (e.g. [9]). The wavelets space-scale analysis capability can be used

to decompose vessel structures into differently scaled Morlet wavelets, so as to

segment them from the retinal fundus.

The recognition of images, or parts of images as possessing pathologies, has

responded well to automated classification techniques. Here the key is to deter-

mine some relationship between a set of input vectors that represent stimuli, and

a corresponding set of values on a nominal scale that represent category or class.

The relationship is obtained by applying an algorithm to training samples that

are 2-tuples (u,z), consisting of an input vector u and a class label z. The learned

relationship can then be applied to instances of u not included in the training

set, in order to discover the corresponding class label z


The learned relationship can then be applied to instances of u not included in the training

set, in order to discover the corresponding class label z [6]. This process, known

as supervised classification, requires manually labelled images for training the

model, and also requires suitable measures to form the vector u. These measures

can be derived from the previously discussed techniques, including mathematical

morphology and the wavelet transform. After training, the model can then be

used to classify previously unseen images. Alternatively, it is possible to classify

individual pixels as either belonging to a vessel or to the background of the im-

age. The classification technique can include Artificial Neural Networks or many

others from the range of techniques available.




4.0Supervised classification


In methods 2 and 3, supervised classification was applied to obtain the final segmentation,

with the pixel classes defined as C1 = vessel-pixels and C2 = non-vessel pixels using the

Bayesian classifier consisting of a mixture of Gaussians (Theodoridis, 1999). In order to obtain

the training set, retinal fundus images have been manually segmented, thus allowing the creation

of a labelled training set into 2 classes C1 and C2 (i.e. vessels and non-vessels).

In this work, the hand-drawn vascular tree provided by the ophthalmologist has been used – our

training pattern – so that we obtained its feature space. Two different strategies for deriving the

training set were applied:

1. Some images were completely segmented by an expert and a random sub-set of their

pixelswas used to train the classifier.

2. Only a small portion (window) of a sample image was manually segmented. The labelled

pixels are then used to train the classifier, which is applied to the same image in order to
conclude its segmentation.

3. This 2ndstrategy has been devised so that a semi-automated fundus segmentation

software can be developed, in which the operator only has to draw a small portion of the

vessels over the input image or simply click on several pixels associated with the vessels









5.Comparison


The results were obtained in the form of segmented images and compared by the experts. Here

we present the results in the manner of FROC curves to assess the trade off between true-

positive fraction and false-positive fraction of our methods in detecting the pixels associated

with the vessel patterns.






6.Methods


In this work we assess the relative merits of several techniques for segmentation

of blood vessels from colour retinal images. Twenty digital images were used from

the Stare database [11]. This database also includes the opinions of two experts

who had indicated the position of the vessels from colour images to establish

two “gold standards” as separate images.Our strategy was to use three methods for segmenting

retinal blood vesselsfrom directly digitized colour retinal images. The experimental procedure

followed was to pre-process the images first to optimise the use of the wavelet

transforms. The methods tested were:

1. Wavelet transform plus adaptive thresholding,

2. Wavelet transform plus supervised classifiers,

3. Wavelet transform plus pixel probabilities combined with adaptivethresholding.


In addition, we compared two training techniques: training on one or more

complete images, then classifying the remaining images, and training on a win-

dow of the image then classifying the remainder of the same image.

Initially the methods were compared qualitatively, but the best of these methods were selected

and compared numerically by plotting on a graph of true positive against false positive results

from the classification. This graph resembles

a free-response receiver operating characteristic (FROC) curve to aid the readerin its

interpretation.

True positives occur when the classifier labels a pixel as

belonging to a vessel and the gold standard segmentation also labels the pixelas vessel.

In order to reduce the noise effects associated with the processing, the inputimage was pre-

processed by a mean filter of size 5×5 pixels. Due to the circularshape of the non-mydriatic

image boundary, neither the pixels outside the region of-interest nor its boundary were

considered, in order to avoid boundary effects.For our wavelet analysis we used the green

channel of the RGB components ofthe colour image as it displayed the best vessels/background

contrast.






6.1 Pre-processing

In order to reduce the noise effects associated with the processing, the input image was pre –

processed by a mean filter of size 5x5 pixels. Due to the circular shape of the non-mydriatic

image boundary, neither the pixels outside the region-of-interest nor its boundary were

considered, in order to avoid boundary effects. For our wavelet analysis we used the green

channel of the RGB components of the colour image as it displayed the best
vessels/background contrast.







6.2 Continuous wavelet transform plus adaptive thresholding


Applying the continuous wavelet transform approach provides several benefits but resulted in

some loss of detail as the scale parameter was fixed. We therefore adopted a pixel

thresholding approach that represented each pixel by a feature vector including colour

information, measurements at different scales taken from the continuous wavelet (Morlet)

transform and the Gaussian Gradient, as well as from mean filtering applied to the green

channel. The resulting feature space was used to provide an adaptive local threshold to assign

each pixel as either a vessel-pixel or a non-vessel pixel.


The real plane RR × is denoted as

2R , and vectors are represented as bold letters, e.g.

2, R ∈ b x . Let

2L f ∈ be an image represented as a square integrable (i.e. finite energy)
function defined over 2

R (Arnéodo et al., 2000). The continuous wavelet transform (CWT) is
defined as:


Applying the continuous wavelet transform approach provides several benefits

but resulted in some loss of detail as the scale parameter was fixed. We therefore

adopted a pixel thresholding approach that represented each pixel by a feature

vector including colour information, measurements at different scales taken from

the continuous wavelet (Morlet) transform and the Gaussian Gradient, as well

as from mean filtering applied to the green channel. The resulting feature space

was used to provide an adaptive local threshold to assign each pixel as either a

vessel-pixel or a non-vessel pixel.



















7. Feature Extraction



The pixel feature space was formed by Morlet wavelet responses (taken at dif-

ferent scales and elongations), Gaussian Gradient responses (taken at different

scales) and colour information, which determine each pixel’s colour. This re-

sulted in a computationally demanding high dimensional feature space. At the

same time, Morlet responses taken at close scales are highly correlated, as are

the Gaussian Gradient responses for similar scales. Therefore we used a feature

extraction approach to obtain a lower dimensional feature space, while trying

to preserve structure important for discrimination. Feature extraction was per-

formed by a linear mapping provided by nonparametric discriminant analysis

[7]. Nonparametric discriminant analysis consists of building two matrices. The

first is a nonparametric between-class scatter matrix, constructed using k-nearest

neighbour techniques, which defines the directions of class separability. The sec-

ond is the within-class scatter matrix, which shows the scatter of samples around

their mean class vectors. These matrices were built based on the labelled training

samples. The two matrices are then used to find a projection (given by a linear

mapping) that maximizes class separability while minimizing the within-class

scatter in the projected feature space.






We have used 2-D Gabor wavelet to enhance the

vascular pattern and thin vessels [25]. 2-D Gabor wavelet is used due to its directional

selectiveness capability of detecting oriented features and fine tuning to specific frequencies

[25], [27].










7.1VESSEL ENHANCEMENT


Fig. 3 shows the enhanced vascular pattern afterapplying Gabor wavelet. Fig. 3(b) shows the

enhancedvascular pattern using Hoover et al. method [24] while fig.

3© shows the vascular pattern enhanced using waveletmethod and there is a clear improvement

inenhancementusing wavelet method.












7.2 Sharpening Filter


We used unsharp masking [26] on enhanced vessel retinal image to sharpen the vascular pattern

. The application of Gabor wavelet on colored retinal image enhances the vascular pattern but the

resulting image is a

little blurred so we have used unsharp filter to sharpen the vascular edges. This helps in reliable
extraction of vessels from the colored retinal image. Fig. 4(a) shows enhanced retinal image and

fig. 4(b) shows sharpened retinal image. It is clearly visible that the vessels are much more

prominentthan they were in the original image.




7.3Vessel Segmentation Mask


Vessels segmentation mask is created by extracting vessels boundaries using edge detection

algorithm and then

by applying morphological dilation operator [26]. In this paper, we have used canny edge

detector [29]. Canny operator simultaneously optimizes three criteria: detection criterion,

localization criterion, and elimination of multiple responses and these rules also become a

standard to evaluate edge detection algorithm performance [29]. The vessels extracted using edge

detection algorithm are

refined using standard morphological dilation operator [26]. Dilation will fill the gaps between

vessel boundaries detected by edge detection algorithm.





Fig 4.1






















7.4 MORPHOLOGICAL DIALATION OPERATION




Fig 5.0
















8. Results


Before we present the results of the experiments comparing the different applications of the

segmentation procedures, we provide for comparison an example of the application of the

wavelet transform to fluorescein images (Leandro et al., 2001). Figure 1(a) shows a typical

image of the retinal fundus with the optic disk on the right hand side and the protruding blood

vessels that course throughout the image. Figure 1 (b) shows the result of image segmentation

using the Morlet wavelet transform. The latter shows the difficulty in obtaining a clear

segmentation. Background noise and variable grey levels across the image introduce artefacts. In

particular, this method did not remove the optic disc located on the right hand side of the image

and was very susceptible to hue variation that resulted in the large grey area to the left of the

image.



Fig.6





9. ANALYSIS


We have demonstrated some new techniques for the automated processing of non-mydriatic

images in the study of diabetic retinopathy that can certainly be extended to other contexts in

pattern recognition. The results we have obtained so far suggest that pixel classification, in

conjunction with wavelet transform and adaptive thresholding, can provide noise-robust vessel

segmentation. The approach reported here improved on previous results by reducing

the level of interaction required with the segmentation program, providing a useful tool for non-

specialists such as community health workers in assessing fundus complications associated with

diabetes (Antoine et al., 1997; Cesar &Jelinek, 2003; da Costa, 2001; Grossmann, 1988; Zana&
Klein, 2000).

Wavelets are especially suitable for detecting singularities (e.g. edges) in signals,

extracting instantaneous frequencies, and performing fractal and multifractal analysis (Antoine et

al., 1997; Grossmann, 1988). Applying the wavelet transform allows noise filtering and blood

vessel enhancement in a single step. Our results indicate that for the same false-positive fraction,

the supervised learning with adaptive thresholding obtained a greater than 75% sensitivity

compared to the ophthalmologist with approximately 90%. Future research is now focused on

fine tuning our algorithms on a larger data set.









10. CONCLUSION

The problem with retinal images is that the visibility of vascular pattern is usually not good. So,

it is necessary to enhance the vascular pattern. In this paper, a wavelet based

colored retinal image blood vessel segmentation technique is proposed. Vascular pattern is

enhanced and sharpened prior to their detection. Vessel and located and segmentation

mask is created using edge detection algorithm and morphological dilation operator

respectively. We have

tested our technique on publicly available STARE database of manually labeled images.

Experimental results show that our method performs well in enhancing and segmenting the

vascular pattern.




11. REFERENCE



M. S. Mabrouk, N. H. Solouma and Y. M. Kadah,

“Survey of retinal image segmentation and registration” , GVIP Journal, vol. 6, No.2,

September, 2006.

[2] M. E. Martnez-Prez, A. D. Hughes, S. A. Thom, A.

A. Bharath and K. H. Parker, “Retinal Blood Vessel Segmentation by Means of Scale-Space
B.
C. Analysis and Region Growing ”, Medical Image Computing and Computer-Assisted
D.
E. Intervention MICCAI99, pp. 90-97, 1999.
F.
[3] J. KansKy, Clinical Opthalmology, Butterworh-

Heinmann , London, 1994.

[4] T. Teng, M. Lefley and D. Claremont, “Progress towards automated diabeticocular

screening: A review of image analysis and intelligent systems

for diabetic retinopathy,” Med. Biol. Eng. Comput., vol. 40, pp. 2-13, 2002.

[5] E. J. Susman, W. J. Tsiaras, and K. A. Soper,

“Diagnosis of diabetic eye disease,” JAMA, vol. 247, pp. 3231-3134, 1982.

[6] A. Pinz, S. Bernogger, P. Datlinger and A. Kruger,

“Mapping the human retina,” IEEE Trans. Med. Imag., vol. 17, no. 4, pp. 606-619, Aug. 1998.

[7] C.L. Tsai, C. V. Stewart, H. L. Tanenbaum and B. Roysam, “Modelbased method for

improving the accuracy and repeatability of estimating vascular bifurcations and crossovers from

retinal fundus

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RE: BLOOD VESSEL ENHANCEMENT AND SEGMENTATION USING WAVELET TRANSFORM
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