Ultrasound Asymptomatic Carotid Plaque Image Analysis for the Prediction of the Risk of Stroke
High-resolution vascular B-mode and Doppler ultrasound provide information not only on the degree of carotid artery stenosis but also on the characteristics of the arterial wall including the size and consistency of atherosclerotic plaques [1 ]. Carotid s
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1 Introduction High-resolution vascular B-mode and Doppler ultrasound provide information not only on the degree of carotid artery stenosis but also on the characteristics of the arterial wall including the size and consistency of atherosclerotic plaques [1]. Carotid stenosis alone has limitations in predicting risk and does not show plaque vulnerability and instability, thus other ultrasonographic plaque morphologic characteristics have been studied for better prediction of the risk stroke. Plaque echogenicity as assessed by B-mode ultrasound has been found to reliably predict the content of soft tissue and the amount of calcification in carotid plaques. Additionally, it has been reported that subjects with echolucent atherosclerotic plaques have increased risk of ischemic cerebrovascular events [2]. More recent studies by Nicolaides et al. [3] Topakian et al. [4] and Kyriacou et al. [5], showed that plaque echolucency and plaque morphology can be used to predict stroke. Other studies have reported that plaques that are more echolucent and heterogeneous are often associated with higher cerebrovascular risk and the development of ipsilateral neurological symptoms [3, 6–10]. In contrast, homogeneous hypoechoic and hyperechoic plaques without evidence of ulceration usually remain asymptomatic. Prediction of risk is important as it will aid clinicians in the selection of asymptomatic cases at higher risk. Equally important is the establishment of a method that
C. P. Loizou (B) Department of Electrical Engineering, Computer Engineering and Informatics, Cyprus University of Technology, Limassol, Cyprus e-mail: [email protected] E. Kyriacou Department of Computer Science and Engineering, Frederick University, Nicosia, Cyprus e-mail: [email protected] © Springer Nature Singapore Pte Ltd. 2019 S. Golemati and K. S. Nikita (eds.), Cardiovascular Computing—Methodologies and Clinical Applications, Series in BioEngineering, https://doi.org/10.1007/978-981-10-5092-3_16
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will allow for objective and quantitative evaluation of high risk cases, that are the ones that would most benefit from endarterectomy. Atherosclerosis of the internal carotid artery (ICA) is known to be an important risk factor for stroke. Using the NASCET [11] method for the determination of stenosis the risk of stroke has been shown to range between 0.1–1.6% per year for asymptomatic individuals with ICA stenosis 60–70% (using the NASCET method) carotid endarterectomy reduced the risk of stroke from 2 to 1% per year. However, in these trials carotid endarterectomy was associated with a 2–3% perioperative rate of stroke or death making it marginally effective for asymptomatic patients. This chapter presents methods that can be used for evaluation of high cerebrovascular risk using image normalization, despeckling, segmentation, texture and morphological appearance of plaques in combination with a number of clinical factors for the estimation of the stroke risk. Images and results presented are based on
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