Measurement Method Of Vessel Width In Retinal Images And Its Software Realization

Retinal vessels are the only microvascular that can be observed directly and without invasive operation.Vessel width in retinal image is an important indicator for ophthalmic clinical diagnosis,and its changes are closely related to the development of many diseases,such as common glaucoma,cataract and other eye diseases,as well as diabetes,hypertension and other cardiovascular disease.Therefore,quantitative analysis of retinal vessel width is of great significance for the prevention and early diagnosis of diseases.The rapid development of digital image processing technology provides a way for automatic measurement of vascular diameters in retinal images.Existing algorithms focus on the measurement of vessel width in a single retinal image.For retinal image of the same patients taken in different periods(time domain multimodal image),due to difference in imaging equipment,image resolution,focal length and field of view,the retinal images have difference in translation,scaling,rotation,central light reflex,It is therefore not possible to compare the width of the same vessel segment in multiple images horizontally.In addition,the image quality is uneven due to different illumination conditions.Vessel boundary is blurred in low-quality retinal images,and some pathological vessels will have severe central light reflex,resulting in large errors in measuring vessel width.In order to solve above problems,this paper proposes a method for measuring vessel width from multimodal(time domain)retinal image.This method mainly includes two parts: registration algorithm for retinal images and measurement method for vessel width.On this basis,a software for measuring vessel width in retinal images was developed.The software can assist ophthalmologists to analyze the disease progress of patients and the curative effect of medicine,and has practical application value.The main contributions of the present work are:(1)A method for comparing vessel width in multimodal retinal images is presented.The basic idea is: first of all,by measuring the vessel width in the image,the whole vessel information of retinal images was obtained;the images were then registered with those taken in other time periods,to unify the scale space;finally,the measured shape and width of the same vessel in different time periods were comparedand analyzed in the same space.(2)A method is presented to measure the width of pathological vessels.Firstly,Isotropic Undecimated Wavelet Transform combined with threshold segmentation was used to extract the retinal vessels.Secondly,the results of vessel segmentation were morphologically refined to obtain the centerline of the vessel,based on which the parallel model was used to correct the centerline of pathological vessels.Then,the measured axes was generated and the intensity profile over the axes was obtained;Finally,the vessel boundary is determined by K-means clustering algorithm,with which the vessel width was calculated.(3)A method for the registration of retinal images was proposed based on Harris-PIIFD.Firstly,Harris detector was used to detect corner points in the image,and the main direction of corner points was calculated using image gradient;Secondly,PIIFD was extracted around corner points and PIIFD matching was completed by bilateral BBF algorithm;Then the incorrect match was removed according to the main direction of the corner and the geometric distribution of the matched corner pair.The matching optimization was carried out in the neighborhood around the corner;finally,the image transformation mode was selected.(4)Using the REVIEW open database and the clinical ophthalmic data set of a local hospital,the proposed vessel width measuring algorithm and the registration algorithm were tested and compared with expert's manual measurements.The results show that both the proposed method and the ARIA method have high accuracy,with maximal measuring error less than 2 pixels.Compared with ARIA,the proposed method has good performance in the measurement of pathological vessel.The success rate of the proposed registration algorithm is 95%,with fast computing speed.(5)Based on Matlab platform and its excellent GUI function,a software for measuring retinal vessel width was developed.It can be used for measurement of vessel width of single retinal image or registration of retinal images,It can be used to compare the width of the same vessel segment in retinal images taken at different time periods.The practical application requirements are well satisfied.