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Atherosclerosis: the evolving role of vascular image analysis

Computerized Medical Imaging and Graphics Atherosclerosis: The evolving role of vascular image analysis National Technical University of Athens, School of Electrical and Computer Engineering, Biomedical Simulations and Imaging (BIOSIM) Laboratory, Iroon Polytechniou 9, Zografos 15780, Athens, Greece Atherosclerosis, a chronic systemic degenerative disease involv- hemorrhage, large lipid cores, and heterogeneous material distri- ing the aorta, coronary, carotid, and peripheral arteries, has plagued bution are among the candidate “suspects” for abrupt progression mankind since the beginning of time. Surprisingly enough, it of the disease and plaques prone to rupture. Plaque inflammation has been recently proved that even Egyptian mummies, ancient is also believed to be a main driver of clinical events humans of high social status, had established atherosclerosis in The aforementioned difficulties in current decision making for atherosclerosis hold major risks for patient safety considering that Although atherosclerotic lesions (plaques) may remain “silent” atherosclerosis may not be detected at an early stage, vulnerable for decades, they are considered the leading underlying cause of plaques may not be identified, while patients with stable plaques cardiovascular disease (CVD) which covers a wide range of fatal may unnecessarily undergo a surgical procedure with potential disorders related to the circulatory system, such as coronary heart complications. Furthermore, due to the high cost of revascula- disease (CHD) and stroke. Each year, CVD causes over 1.9 million rization and bypass surgery already unbearable cost of deaths in the European Union (EU); CHD by itself accounts for 15% atherosclerosis is further increased; note that it has recently been and 13% of all deaths among men and women, respectively, while shown that unnecessary carotid revascularization procedures in around one in every twelve men (8%) and one in ten women (11%) asymptomatic patients in the US cost health-care providers US$2 die from stroke same report highlights that CVD costs EU some D 196 billion a year due to healthcare costs (54%), productivity With atherosclerosis being a major cause of morbidity and mor- losses (24%) and spending on informal care (22%). Similar statistics tality, as well as an economic burden worldwide, it is obvious that have also been reported for the United States (US) causes early detection and valid risk stratification for the disease consti- approximately 1.3 million deaths each year in the US, with CHD tute a crucial public health challenge. In recent decades, advances and stroke accounting for 17% and 6% of all deaths, respectively.
in medical imaging technology and computer vision have allowed The annual direct and indirect financial cost of CVD in the US is for valuable contribution of image analysis toward this direction. By estimated $297.7 billion due to healthcare expenditures (60%) and continuously revealing several new morphological or composition- related markers, vascular image analysis plays a multifaceted role In current clinical practice, atherosclerotic patients are offered which focuses on accurately detecting the presence of atheroscle- either an invasive procedure, such as artery revascularization rosis in individuals, defining the burden of the disease before they (endarterectomy or angioplasty with stenting) and bypass surgery, develop clinical events, and evaluating the efficacy of therapies.
or a more conservative therapy with medications, physical exercise Computed tomography (CT) of the chest, in particular, has pro- and dietary therapeutic decision is traditionally made judg- vided a real breakthrough in the evaluation of coronary artery ing on symptom status and the image-measured degree of artery calcification (CAC) used for detecting the presence of atheroscle- stenosis, which, however, is not always sufficient Specifi- rosis in the artery. Furthermore, CAC score has been shown to be cally, it has been observed that severe carotid artery stenosis may able to assess cardiovascular risk, adding prognostic information remain asymptomatic carotid atherosclerotic plaques to the Framingham risk score CT image analy- causing a low degree of stenosis can result in symptoms sis has also shown great potential in detecting significant coronary nary atherosclerotic plaques being less than 50% occlusive have artery stenoses identifying the composition of plaques also been reported to cause acute coronary and cerebrovascular and assessing the response to anti-inflammatory drugs syndromes observations arise from the fact that plaque’s Similar findings have been reported regarding the role of mag- material (calcium, fibers, blood components, lipids, etc.) composi- netic resonance imaging (MRI) in optimal management of the tion appears to be a critical determinant of the risk for future events disease. Besides the ability of MRI image analysis to clearly identify the absence of calcification, thin fibrous caps, intra-plaque vessel boundaries, thereby allowing highly accurate measurements of plaque burden histological studies have shown that it also offers a comprehensive structural plaque characterization More interestingly, experiments have associated the iden- tification of a ruptured fibrous cap in MRI images with a recent K.S. Nikita / Computerized Medical Imaging and Graphics 37 (2013) 1–3 history of ischemic event MRI image analysis of would offer optimal data management, knowledge discovery and atherosclerosis can also provide useful information about the effect sharing, as well as easy comparisons with similar prior cases for Nuclear imaging modalities, i.e. positron emission tomogra- However, translating biomedical research into beneficial com- phy (PET) and single-photon emission computed tomography mercial and profitable products is often difficult due to different (SPECT), can provide a valuable tool for functional evaluation of expertise and the mutual understanding of objectives and the atherosclerotic disease. PET and SPECT can demonstrate signif- requirements of the scientific community, clinicians and indus- icant artery stenoses, while co-registration with other modalities try. Therefore, partnerships and information exchange among (PET-CT, PET-MRI, SPECT-CT) is widely used enabling a com- academic, medical and industrial institutions are necessary in bined study of plaques’ structure and function developing systems which will be incorporated in current clin- 18F-fluorodeoxyglucose nuclear image analysis has been used to ical practice, thereby optimizing the delivery of healthcare for identify inflamed atherosclerotic plaques detect signs of atherosclerosis. Such systems are expected to significantly con- biological effects of experimental drugs tribute to the vision of occidental countries to manage prevalent Intravascular ultrasound (IVUS) has emerged as a valuable imag- chronic diseases, enhance patient safety through prediction, opti- ing modality for atherosclerosis, especially for the assessment of mized treatments, and fewer medical errors, halt the rising cost of ambiguous lesions, as those located in the left main coronary artery healthcare without compromising quality and efficiency, bridge the or at bifurcation sites. Measurements on IVUS images are able to gap between research and medical practice, and realize the health demonstrate changes in plaque lesion size with time and treatment IVUS studies are more limited because of the finan- To conclude, given that atherosclerosis holds a major risk for cial cost, the increase in the time of the procedure, and the fact that both public health and state economies, and the current ‘one-size- it is considered an interventional procedure.
fits-all’ approach has been shown to be inadequate and inefficient, Because of its low cost, non-invasiveness and short time of it is crucial to reveal novel, personalized and low-cost markers that examination, duplex ultrasound is commonly used in monitor- will upgrade the medical practice for the disease. Computerized ing and tracking progression of atherosclerotic disease. Analysis of analysis of vascular images, and particularly ultrasound ones, plays ultrasound images of the neck allows measurements of (i) the thick- a valuable role in this field and is expected to continue receiving ness of two layers of the wall of the carotid artery (the so-called significant attention by future research.
carotid intima-media thickness) which has emerged as one of the most powerful tools for the evaluation of subclinical atherosclero- sis drug response (ii) texture indices of carotid References
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