Carotid Ultrasound for Stroke Prediction

Introduction: The aims of this thesis were to identify if carotid endarterectomy was cost-effective and affordable in the United Kingdom and secondly to explore the potential of contrast enhanced ultrasound and plaque texture analysis for risk stratification in asymptomatic patients with carotid atherosclerosis. Methods: A cost-utility analysis based on results from the Asymptomatic Carotid Surgery Trial was performed using a Markov transition state model. Three cross-sectional studies of symptomatic and asymptomatic individuals with 50-99% carotid stenosis were performed for late phase and dynamic phase contrast enhanced ultrasound, followed by plaque texture analysis. Results: There was a high probability of surgical endarterectomy lying under the £20-30, 000 per quality adjusted life year National Institute for Health and Clinical Excellence acceptability threshold in the United Kingdom. In men under 75 years of age, the cost per quality adjusted life year gained was lower and in women there was improved effectiveness with reduced long-term costs. Late phase contrast enhanced ultrasound imaging of carotid atherosclerosis suffered from a tissue suppression artefact which limited its ability to image microbubble retention. Quantification of plaque perfusion using low mechanical index imaging demonstrated a pseudoenhancement phenomenon from non-linear propagation, which artificially increased far wall intensity, again limiting its use for quantification of plaque perfusion. Semi-quantitative grading of plaque perfusion revealed no significant difference in generalised plaque perfusion between symptomatic and asymptomatic individuals, however detection of ulceration using dynamic contrast enhanced ultrasound showed a trend towards an association with symptomatic status. Type II plaque showed a significant independent association with symptomatic status. Conclusion: Carotid endarterectomy is likely to be cost-effective in those under 75 years of age, particularly women. However, without further selection, the upfront costs and high number needed to treat with endarterectomy limit its potential as a large scale strategy. Improvements in non-linear pulse sequencing are required before quantitative contrast enhanced ultrasound can reliably be used for functional imaging of carotid atherosclerosis. Qualitative assessment of plaque perfusion is unlikely to gain widespread use due to its high subjectivity. However assessment of plaque type and to a lesser extent imaging of ulceration using contrast enhanced ultrasound are promising and reproducible imaging biomarkers for further study. Validation of these markers with histology and then prospective study of individuals with these plaque phenotypes is proposed. In the future individuals with a recent transient ischaemic attack and moderate (50-69%) stenosis may prove to be an ideal group for risk stratification

Carotid Artery Disease

This book will bring out the state of art of carotid stenosis in the basic and clinical approaches for better understanding of the mechanisms and useful therapies for these disease. We hope that would be a new current trend understanding new aspects regarding this scientific problematic involving not only anatomical, functional but also clinical questions

Multimodality carotid plaque tissue characterization and classification in the artificial intelligence paradigm: a narrative review for stroke application

Cardiovascular disease (CVD) is one of the leading causes of morbidity and mortality in the United States of America and globally. Carotid arterial plaque, a cause and also a marker of such CVD, can be detected by various non-invasive imaging modalities such as magnetic resonance imaging (MRI), computer tomography (CT), and ultrasound (US). Characterization and classification of carotid plaque-type in these imaging modalities, especially into symptomatic and asymptomatic plaque, helps in the planning of carotid endarterectomy or stenting. It can be challenging to characterize plaque components due to (I) partial volume effect in magnetic resonance imaging (MRI) or (II) varying Hausdorff values in plaque regions in CT, and (III) attenuation of echoes reflected by the plaque during US causing acoustic shadowing. Artificial intelligence (AI) methods have become an indispensable part of healthcare and their applications to the non-invasive imaging technologies such as MRI, CT, and the US. In this narrative review, three main types of AI models (machine learning, deep learning, and transfer learning) are analyzed when applied to MRI, CT, and the US. A link between carotid plaque characteristics and the risk of coronary artery disease is presented. With regard to characterization, we review tools and techniques that use AI models to distinguish carotid plaque types based on signal processing and feature strengths. We conclude that AI-based solutions offer an accurate and robust path for tissue characterization and classification for carotid artery plaque imaging in all three imaging modalities. Due to cost, user-friendliness, and clinical effectiveness, AI in the US has dominated the most

The identification of the vulnerable carotid plaque and haemodynamic compromise of the brain in carotid artery stenosis

Introduction: Carotid stenosis plays a large role in the aetiology of ischaemic stroke. The main mechanism of carotid stenosis causing stroke is the forming of thrombus and consequently embolus formation. Another mechanism is the compromise in haemodynamics: reduced blood flow distal from the stenosis causing hypoperfusion of the brain. This work investigates the current prevalence of carotid stenosis in ischaemic stroke. It also explores the role of transcranial Doppler (TCD) and brain perfusion imaging with magnetic resonance imaging in patients with carotid stenosis. Methods: The current prevalence of carotid stenosis was assessed in a comprehensive Central London hyper-acute stroke unit and a systematic review with meta-regression analysis was conducted on the prevalence of carotid stenosis. Patient individual risk factors and morphological characteristics of the carotid plaque were associated with the presence of micro-embolic signals on TCD. The perfusion of the brain was assessed in patients with carotid stenosis and those who underwent carotid endarterectomy (CEA). Results: The prevalence of carotid stenosis 350% in the local stroke unit was 19.0%, including 7.9% with symptomatic stenosis. The pooled prevalence estimate of carotid stenosis, described in 37 studies in the literature, was 16.0% and has not declined over time. Intraplaque haemorrhage was associated with a higher risk of future stroke by detection of micro-embolic signals on TCD. Haemodynamic factors played a great role in stroke, especially in patients with stenosis 370%. Cerebral perfusion improved significantly in patients who underwent CEA, especially in those who initially had 370% stenosis. Conclusion: Morphology of the plaque, more than the degree of stenosis, is an important predictive feature of the unstable carotid plaque, whilst the degree of stenosis is more relevant to the hypoperfused brain. There is evidence for a synergic role of embolism and haemodynamic compromise as a mechanism of ischaemic stroke in carotid stenosis