Bayes clustering and structural support vector machines for segmentation of carotid artery plaques in multicontrast MRI.

Accurate segmentation of carotid artery plaque in MR images is not only a key part but also an essential step for in vivo plaque analysis. Due to the indistinct MR images, it is very difficult to implement the automatic segmentation. Two kinds of classification models, that is, Bayes clustering and SSVM, are introduced in this paper to segment the internal lumen wall of carotid artery. The comparative experimental results show the segmentation performance of SSVM is better than Bayes.Peer Reviewe

Automated image segmentation and registration of vessel wall MRI for quantitative assessment of carotid artery vessel wall dimensions and plaque composition

The main goal of this thesis was to develop methods for automated segmentation, registration and classification of the carotid artery vessel wall and plaque components using multi-sequence MR vessel wall images to assess atherosclerosis. First, a general introduction into atherosclerosis and different stages of the disease were described including the importance to differentiate between stable and vulnerable plaques. Several non-invasive imaging techniques were discussed and the advantages of multi-sequence MRI were highlighted. Different novel automated image segmentation and registration techniques for analysis of the MRI images have been developed. A 3D vessel model to automatically segment the vessel wall was presented. Automated image registration was applied to correct for patient movement during the acquisition of an MRI scan and between MRI scans. The last topic is the automatic classification of the different plaque components which can be present inside the vessel wall. All techniques were developed and validated using relevant patient data and reference standards. The work presented is an important contribution to the automated analysis of multi-sequence MR vessel wall imaging of the carotid artery. These techniques can speed up the current manual analysis and are potentially more accurate and more reproducible.ASCI research school. Bontius Stichting inz. Doelfonds beeldverwerking. Library of the University of Leiden. Medis medical imaging systems bv, Leiden. Pie Medical Imaging BV, MaastrichtUBL - phd migration 201

Three-dimensional Quantitative Magnetic Resonance Imaging of Carotid Atherosclerotic Plaque

Stroke is one of the leading causes of death and disability worldwide with 20% of ischemic strokes attributed to carotid atherosclerosis. In recent years, morphological characteristics of atherosclerotic plaque such as a thin fibrous cap, large lipid-rich necrotic core, intraplaque haemorrhage and ulceration have shown correlations with subsequent clinical events. High resolution, multi-contrast magnetic resonance imaging (MRI) can qualitatively identify these features and monitor disease progression. Compared to traditional contrast weighted imaging, quantitative MRI could provide an objective assessment of disease. Therefore, the general hypothesis investigated in this thesis is: Quantitative MRI methods can be used to acquire objective biomarkers of carotid vessel wall and atherosclerotic plaque, with high accuracy and good repeatability. The research presented in this thesis describes the use of multiple quantitative MRI methods to evaluate the carotid vessel wall. These include dynamic contrast-enhanced (DCE) MRI analysis for the assessment of plaque inflammation/neovascularization and the development of black-blood quantitative T2/T2* mapping sequences for plaque component characterisation. The acceleration of the sequences was also investigated using a combination of compressed sensing (CS) and parallel imaging (PI). Chapter 3 investigated the hypothesis that plaque functional characteristics and surface morphology can be evaluated using a high temporal and spatial resolution 4D contrast-enhanced MRI/MR angiography (MRA) sequence. Chapter 4 tested the hypothesis that magnetisation prepared 3D fast-spin-echo (FSE) is the best sequence for in vivo T2 mapping. Four different black-blood T2 mapping sequences were developed and compared in phantom and volunteers. Chapter 5 tested the hypothesis that the optimised iMSDE 3D FSE T2 mapping sequence can be combined with CS and PI to further reduce the acquisition time without significantly affecting image quality and the measured T2 relaxation times. Chapter 6 investigated the hypothesis that compressed sensing can be used to reduce the overall examination time of a comprehensive multi-contrast MRI protocol, comprising black-blood T1 weighted, T2 weighted and proton density weighted sequences. Finally, Chapter 7 investigated the hypothesis that accurate 3D vessel wall R2* mapping can be achieved through black-blood preparation. In summary, this thesis investigated the use of multiple quantitative MRI methods in evaluating the carotid vessel wall and atherosclerotic plaque. The results demonstrate that quantitative MRI is an accurate and reproducible method for the carotid plaque characterization

Review of Journal of Cardiovascular Magnetic Resonance 2014

There were 102 articles published in the Journal of Cardiovascular Magnetic Resonance (JCMR) in 2014, which is a 6 % decrease on the 109 articles published in 2013. The quality of the submissions continues to increase. The 2013 JCMR Impact Factor (which is published in June 2014) fell to 4.72 from 5.11 for 2012 (as published in June 2013). The 2013 impact factor means that the JCMR papers that were published in 2011 and 2012 were cited on average 4.72 times in 2013. The impact factor undergoes natural variation according to citation rates of papers in the 2 years following publication, and is significantly influenced by highly cited papers such as official reports. However, the progress of the journal’s impact over the last 5 years has been impressive. Our acceptance rate is <25 % and has been falling because the number of articles being submitted has been increasing. In accordance with Open-Access publishing, the JCMR articles go on-line as they are accepted with no collating of the articles into sections or special thematic issues. For this reason, the Editors have felt that it is useful once per calendar year to summarize the papers for the readership into broad areas of interest or theme, so that areas of interest can be reviewed in a single article in relation to each other and other recent JCMR articles. The papers are presented in broad themes and set in context with related literature and previously published JCMR papers to guide continuity of thought in the journal. We hope that you find the open-access system increases wider reading and citation of your papers, and that you will continue to send your quality papers to JCMR for publication

Computational studies of blood flow at arterial branches in relation to the localisation of atherosclerosis

Atherosclerotic lesions are non-uniformly distributed at arterial bends and branch sites, suggesting an important role for haemodynamic factors, particularly wall shear stress (WSS), in their development. Using computational flow simulations in idealised and anatomically realistic models of aortic branches, this thesis investigates the role of haemodynamics in the localisation of atherosclerosis. The pattern of atherosclerotic lesions is different between species and ages. Such differences have been most completely documented for the origins of intercostal arteries within the descending thoracic aorta. The first part of the thesis deals with the analysis of wall shear stresses and flow field near the wall in the vicinity of model intercostal branch ostia using high-order spectral/hp element methods. An idealised model of an intercostal artery emerging perpendicularly from the thoracic aorta was developed, initially, to study effects of Reynolds number and flow division under steady flow conditions. Patterns of flow and WSS were strikingly dependent on these haemodynamic parameters. Incorporation of more realistic geometrical features had only minor effects. The WSS distribution in an anatomically correct geometry of a pair of intercostal arteries resembled in character the pattern seen in the idealised geometry. Under unsteady and non-reversing flow conditions, the effect of pulsatility was small. However, significantly different patterns were generated for reversing aortic near-wall flow and reversing side branch flow. The work was extended to study the wall shear stress distribution within the aortic arch and proximal branches of mice, in comparison to that of men. Mice are increasingly used as models to study atherosclerosis and it has been shown that, in knockout mice lacking the low density lipoprotein receptor and apolipoprotein E, lesions develop in vivo at the proximal wall of the entrance to the brachiocephalic artery. Three aortic arch geometries from wild-type mice were reconstructed from MRI images using in-house and commercial software, and the WSS distribution was calculated under steady flow conditions to establish the mouse haemodynamic environment and mouse-to-mouse variability. Approximated human aortic arch geometries were further considered to enable comparison of the flow and WSS fields with that of mice. The haemodynamic environment of the aortic arch varied between the two species. The overall distribution of wall shear stress was more heterogeneous in the human aortic arch than in the mouse arch, although some features were similar. Intraspecies differences in mice were small and influenced primarily by the detailed anatomical geometry and the Reynolds number. A number of simplifications were made in the above flow analyses, and clearly, relaxing these assumptions would increase complexity. Nonetheless, this thesis demonstrates the fundamental features of flow, which underlie the disparate patterns of WSS in different species and/or ages, for simplified cases, and the results are expected to be relevant to more complex ones. Aspects of the observed WSS patterns in the simplified model of intercostal artery correlate with, and may explain, some of the lesion patterns in human, rabbit and mouse aortas. WSS distributions in the aortic arch of wild-type mice associate with lesion locations seen in diseased mice.Open acces