ارتقاء كيفيت تصاوير سي تي اسكن مغز به منظور تشخيص زود هنگام ايسكمي مغزي

چكيده انگليسي :

Enhancement of Brain CT Images and Applications in Early Detection of Ischemic Stroke Mehdi Sajjadi m sajjadi@ec iut ac ir Date of Submission 2011 04 20 Department of Electrical and Computer Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language FarsiSupervisor Rasoul Amirfattahi fattahi@cc iut ac ir Mohammad Reza Ahmadzadeh ahmadzadeh@cc iut ac irAbstract Ischemic stroke is one of the major causes of mortality and accounts for most of adult disabilitieshappening worldwide Early detection of ischemic stroke is of great importance since prolonged interruptionof cerebral blood flow causes irreversible damage to brain tissues This will lead to permanent disabilities oreven death Stroke diagnosis is mainly done using imaging systems CT scan and MRI play a significant rolein CVA detection Non enhanced CT is often the first radiologic examination performed in case of suspicionof stroke Compared to MRI brain imaging with CT is more accessible less expensive and quicker Nevertheless the signs of ischemia in few hours after onset are quite subtle on CT or practically invisible Contrast is an important factor in subjective evaluation of image quality In present thesis we concentratedon contrast enhancement of brain CT images so that subtle signs of ischemia become more visible toradiologist To this end numerous methods of contrast enhancement were evaluated In medical image processing multi scale transforms are being used for different purposes These transformsare able to extract image details and edges in different size and scales So they provide a flexible frameworkfor image analysis and modification For example by appropriate amplification of specific sub bands coefficients using linear or non linear mapping functions we are able to emphasize on desired image detailswith specific size This is our general approach in brain CT image enhancement These transforms arecompletely characterized by their corresponding set of basis functions and this set can be redundant or not By allowing redundancy it is possible to enrich the set of basis functions so that the transform is moreefficient in capturing some signal behavior In addition redundant transforms are generally more flexible andeasier to design In applications such as denoising enhancement and contour detection a redundant transformcan significantly outperform a non redundant one These redundant transforms are often translation invariant This feature is of unique importance in many image processing tasks In this thesis we used four different redundant multi scale transforms to enhance brain CT images Redundant Dyadic Wavelet Transform RDWT Laplacian Pyramid LP Nonsubsampled Pyramid NSP and Nonsubsampled Contourlet Transfrom NSCT Except Laplacian Pyramid the other three transformsare also translation invariant At the end we show that by using these transforms and proper selection of sub bands and mapping functions it is possible to suitably enhance brain CT images so that ischemic sensitivebrain tissues e g gray matter basal ganglia and sulcus become more visible We applied our method to 35 normal and 35 pathologic cases All of 35 pathologic cases hadn t any notablesymptoms of stroke and specialist s diagnosis was normal in first examination Pathology of abnormal caseswas diagnosed by means of a second CT scan examination performed several hours after the first one Allnormal and pathologic images were enhanced by means of proposed method and delivered to specialist forreassessment After second evaluation 19 out of 35 pathologic cases were detected to be abnormal and 3 outof 35 normal cases mistakenly diagnosed to be abnormal Keywords stroke ischemia contrast enhancement CT scan Wavelet NSWT NSCT Laplacian Pyramid

سجادي، مهدي

ارتقاء كيفيت تصاوير سي تي اسكن مغز به منظور تشخيص زود هنگام ايسكمي مغزي

سكته مغزي , ارتقاء كنتراست , موجك , RDWT , NSCT