In vivo accuracy of multisequence MR imaging for identifying unstable fibrous caps in advanced human carotid plaques

The Effect of PCSK9 Inhibition on the Stabilization of Atherosclerotic Plaque Determined by Biochemical and Diagnostic Imaging Methods

Atherosclerosis is a multifactorial, progressive, chronic inflammatory disease. Ultrasound and magnetic resonance imaging are the most accurate predictors of atherosclerotic plaque instability (MRI). Cytokines such as osteopontin, osteoprotegerin, and metalloproteinase 9 could be used as the most recent markers to identify and track the efficacy of anti-atherosclerotic therapy. Patients with USG and MRI-verified unstable atherosclerotic plaque were included in the study. Biomarker concentrations were measured and compared before and after PCSK9 inhibitor therapy. Additionally, concentrations prior to treatment were correlated with MRI images of the carotid artery. After treatment with alirocumab, the concentrations of MMP-9 (p < 0.01) and OPN, OPG (p < 0.05) decreased significantly. Furthermore, the results of OPN, OPG, and MMP 9 varied significantly depending on the type of atherosclerotic plaque in the MRI assay. In stable atherosclerotic plaques, the concentrations of OPN and OPG were greater (p < 0.01), whereas the concentration of MMP9 correlated with the instability of the plaque (p < 0.05). We demonstrated, probably for the first time, that alirocumab therapy significantly decreased the serum concentration of atherosclerotic plaque markers. In addition, we demonstrated the relationship between the type of atherosclerotic plaque as determined by carotid MRI and the concentration of these markers.

Vessel Wall Imaging in Cryptogenic Stroke

Cryptogenic strokes are symptomatic cerebral ischemic infarcts without a clear etiology identified following standard diagnostic evaluation and currently account for 10% to 40% of stroke cases. Continued research is needed to identify and bridge gaps in knowledge of this stroke grouping. Vessel wall imaging has increasingly shown its utility in the diagnosis and characterization of various vasculopathies. Initial promising evidence suggests rational use of vessel wall imaging in stroke workup may unravel pathologies that otherwise would have been occult and further improve our understanding of underlying disease processes that can translate into improved patient outcomes and secondary stroke prevention.

The Role of High-Resolution Magnetic Resonance Imaging in Cerebrovascular Disease: A Narrative Review

High-resolution magnetic resonance imaging (HRMRI) is the most important and popular vessel wall imaging technique for the direct assessment of vessel wall and cerebral arterial disease. It can identify the cause of stroke in high-risk plaques and differentiate the diagnosis of head and carotid artery dissection, including inflammation, Moya Moya disease, cerebral aneurysm, vasospasm after subarachnoid hemorrhage, reversible cerebral vasoconstriction syndrome, blunt cerebrovascular injury, cerebral arteriovenous malformations, and other stenosis or occlusion conditions. Through noninvasive visualization of the vessel wall in vitro, quantified assessment of luminal stenosis and pathological features of the vessel wall can provide clinicians with further disease information. In this report, technical considerations of HRMRI are discussed, and current clinical applications of HRMRI are reviewed.

Evidence of Carotid Atherosclerosis Vulnerability Regression in Real Life From Magnetic Resonance Imaging: Results of the MAGNETIC Prospective Study

Background Atherosclerosis vulnerability regression has been evidenced mostly in randomized clinical trials with intensive lipid-lowering therapy. We aimed to demonstrate vulnerability regression in real life, with a comprehensive quantitative method, in patients with asymptomatic mild to moderate carotid atherosclerosis on a secondary prevention program. Methods and Results We conducted a single-center prospective observational study (MAGNETIC [Magnetic Resonance Imaging as a Gold Standard for Noninvasive Evaluation of Atherosclerotic Involvement of Carotid Arteries]): 260 patients enrolled at a cardiac rehabilitation center were followed for 3 years with serial magnetic resonance imaging. Per section cutoffs (95th/5th percentiles) were derived from a sample of 20 consecutive magnetic resonance imaging scans: (1) lipid-rich necrotic core: 26% of vessel wall area; (2) intraplaque hemorrhage: 12% of vessel wall area; and (3) fibrous cap: (a) minimum thickness: 0.06 mm, (b) mean thickness: 0.4 mm, (c) projection length: 11 mm. Patients with baseline magnetic resonance imaging of adequate quality (n=247) were classified as high (n=63, 26%), intermediate (n=65, 26%), or low risk (n=119, 48%), if vulnerability criteria were fulfilled in ≥2 contiguous sections, in 1 or multiple noncontiguous sections, or in any section, respectively. Among high-risk patients, a conversion to any lower-risk status was found in 11 (17%; P=0.614) at 6 months, in 16 (25%; P=0.197) at 1 year, and in 19 (30%; P=0.009) at 3 years. Among patients showing any degree of carotid plaque vulnerability, 21 (16%; P=0.014) were diagnosed at low risk at 3 years. Conclusions This study demonstrates with a quantitative approach that vulnerability regression is common in real life. A secondary prevention program can promote vulnerability regression in asymptomatic patients in the mid to long term.

Chronic kidney disease, atherosclerotic plaque characteristics on carotid magnetic resonance imaging, and cardiovascular outcomes

Background

It is unclear whether faster progression of atherosclerosis explains the higher risk of cardiovascular events in CKD. The objectives of this study were to 1. Characterize the associations of CKD with presence and morphology of atherosclerotic plaques on carotid magnetic resonance imaging (MRI) and 2. Examine the associations of baseline CKD and carotid atherosclerotic plaques with subsequent cardiovascular events.

Methods

In a subgroup (N = 465) of Systolic Blood Pressure Intervention Trial.

(SPRINT) participants, we measured carotid plaque presence and morphology at baseline and after 30-months with MRI. We examined the associations of CKD (baseline eGFR < 60 ml/min/1.73m²) with progression of carotid plaques and the SPRINT cardiovascular endpoint.

Results

One hundred and ninety six (42%) participants had CKD. Baseline eGFR in the non-CKD and CKD subgroups were 77 ± 14 and 49 ± 8 ml/min/1.73 m², respectively. Lipid rich necrotic-core plaque was present in 137 (29.5%) participants. In 323 participants with both baseline and follow-up MRI measurements of maximum wall thickness, CKD was not associated with progression of maximum wall thickness (OR 0.62, 95% CI 0.36 to 1.07, p = 0.082). In 96 participants with necrotic core plaque at baseline and with a valid follow-up MRI, CKD was associated with lower odds of progression of necrotic core plaque (OR 0.41, 95% CI 0.17 to 0.95, p = 0.039). There were 28 cardiovascular events over 1764 person-years of follow-up. In separate Cox models, necrotic core plaque (HR 2.59, 95% CI 1.15 to 5.85) but not plaque defined by maximum wall thickness or presence of a plaque component (HR 1.79, 95% CI 0.73 to 4.43) was associated with cardiovascular events. Independent of necrotic core plaque, CKD (HR 3.35, 95% CI 1.40 to 7.99) was associated with cardiovascular events.

Conclusions

Presence of necrotic core in carotid plaque rather than the presence of plaque per se was associated with increased risk of cardiovascular events. We did not find CKD to be associated with faster progression of necrotic core plaques, although both were independently associated with cardiovascular events. Thus, CKD may contribute to cardiovascular disease principally via mechanisms other than atherosclerosis such as arterial media calcification or stiffening.

Trial Registration

NCT01475747, registered on November 21, 2011.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12882-021-02260-x.

Evolving determinants of carotid atherosclerosis vulnerability in asymptomatic patients from the MAGNETIC observational study

MRI can assess plaque composition and has demonstrated an association between some atherosclerotic risk factors (RF) and markers of plaque vulnerability in naive patients. We aimed at investigating this association in medically treated asymptomatic patients. This is a cross-sectional interim analysis (August 2013-September 2016) of a single center prospective study on carotid plaque vulnerability (MAGNETIC study). We recruited patients with asymptomatic carotid atherosclerosis (US stenosis > 30%, ECST criteria), receiving medical treatments at a tertiary cardiac rehabilitation. Atherosclerotic burden and plaque composition were quantified with 3.0 T MRI. The association between baseline characteristics and extent of lipid-rich necrotic core (LRNC), fibrous cap (CAP) and intraplaque hemorrhage (IPH) was studied with multiple regression analysis. We enrolled 260 patients (198 male, 76%) with median age of 71-y (interquartile range: 65-76). Patients were on antiplatelet therapy, ACE-inhibitors/angiotensin receptor blockers and statins (196-229, 75-88%). Median LDL-cholesterol was 78 mg/dl (59-106), blood pressure 130/70 mmHg (111-140/65-80), glycosylated hemoglobin 46 mmol/mol (39-51) and BMI 25 kg/m² (23-28); moreover, 125 out of 187 (67%) patients were ex-smokers. Multivariate analysis of a data-set of 487 (94%) carotid arteries showed that a history of hypercholesterolemia, diabetes, hypertension or smoking did not correlate with LRNC, CAP or IPH. Conversely, maximum stenosis was the strongest independent predictor of LRNC, CAP and IPH (p < 0.001). MRI assessment of plaque composition in patients on treatment for asymptomatic carotid atherosclerosis shows no correlation between plaque vulnerability and the most well-controlled modifiable RF. Conversely, maximum stenosis exhibits a strong correlation with vulnerable features despite treatment.

Magnetic resonance imaging of carotid plaques: current status and clinical perspectives

Rupture of a vulnerable carotid plaque is one of the leading causes of stroke. Carotid magnetic resonance imaging (MRI) is able to visualize all the main hallmarks of plaque vulnerability. Various MRI sequences have been developed in the last two decades to quantify carotid plaque burden and composition. Often, a combination of multiple sequences is used. These MRI techniques have been extensively validated with histological analysis of carotid endarterectomy specimens. High agreement between the MRI and histological measures of plaque burden, intraplaque hemorrhage (IPH), lipid-rich necrotic core (LRNC), fibrous cap (FC) status, inflammation and neovascularization has been demonstrated. Novel MRI sequences allow to generate three-dimensional isotropic images with a large longitudinal coverage. Other new sequences can acquire multiple contrasts using a single sequence leading to a tremendous reduction in scan time. IPH can be easily identified as a hyperintense signal in the bulk of the plaque on strongly T₁-weighted images, such as magnetization-prepared rapid acquisition gradient echo images, acquired within a few minutes with a standard neurovascular coil. Carotid MRI can also be used to evaluate treatment effects. Several meta-analyses have demonstrated a strong predictive value of IPH, LRNC, thinning or rupture of the FC for ischemic cerebrovascular events. Recently, in a large meta-analysis based on individual patient data of asymptomatic and symptomatic individuals with carotid artery stenosis, it was shown that IPH on MRI is an independent risk predictor for stroke, stronger than any known clinical risk parameter. Expert recommendations on carotid plaque MRI protocols have recently been described in a white paper. The present review provides an overview of the current status and applications of carotid plaque MR imaging and its future potential in daily clinical practice.

CT imaging features of carotid artery plaque vulnerability

Despite steady advances in medical care, cardiovascular disease remains one of the main causes of death and long-term morbidity worldwide. Up to 30% of strokes are associated with the presence of carotid atherosclerotic plaques. While the degree of stenosis has long been recognized as the main guiding factor in risk stratification and therapeutical decisions, recent evidence suggests that features of unstable, or ‘vulnerable’, plaques offer better prognostication capabilities. This paradigmatic shift has motivated researchers to explore the potentialities of non-invasive diagnostic tools to image not only the lumen, but also the vascular wall and the structural characteristics of the plaque. The present review will offer a panoramic on the imaging modalities currently available to characterize carotid atherosclerotic plaques and, in particular, it will focus on the increasingly important role covered by multidetector computed tomographic angiography.

Significance of high resolution MRI in the identification of carotid plaque

The stability of carotid artery plaque serves a key role in the occurrence of stroke. The present study was based on the recruitment of patients with acute ischemic cerebrovascular disease. High-resolution magnetic resonance imaging (HR-MRI) was used to identify the nature of carotid artery plaque, and the results were then used to manage the high-risk group of stroke. The patients were divided equally into a symptomatic group (36 cases) and an asymptomatic group (36 cases). According to the degree of carotid artery stenosis, the patients were divided into mild, moderate and severe stenosis groups, each group comprising 12 patients, and HR-MRI was performed. The proportion of patients with vulnerable plaque in the symptomatic group was higher compared with that in the asymptomatic group (P<0.05). The more severe the stenosis, the higher the proportion of vulnerable plaque that was identified (P<0.05). Compared with carotid ultrasound, HR-MRI was indicated to have the capability to both identify and quantify the different components in the plaque, allowing an assessment of its properties. In conclusion, the present study demonstrated that carotid HR-MRI is able to distinguish and quantify the different components of plaque, which may prove to be helpful for the hierarchical management of a population at high risk of stroke.

The Role of Carotid and Femoral Plaque Burden in the Diagnosis of Coronary Artery Disease

PURPOSE OF REVIEW

With limitations of cardiovascular disease risk stratification by traditional risk factors, the role of noninvasive imaging techniques, such as vascular ultrasound, has emerged as a prominent utility for decision-making in coronary artery disease. A review of current guidelines and contemporary approaches for carotid and femoral plaque assessment is needed to better inform the diagnosis, management, and treatment of atherosclerosis in clinical practice.

RECENT FINDINGS

The recent consensus-based guidelines for carotid plaque assessment in coronary artery disease have been established, supported by some outcomes-based research. Currently, there is a gap of evidence on the use of femoral ultrasound to detect atherosclerosis, as well as predict adverse cardiovascular outcomes. The quantification and characterization of individualized plaque burden are important to stratify risk in asymptomatic or symptomatic atherosclerosis patients. Standardized quantification guidelines, supported by further outcomes-based research, are required to assess disease severity and progression.

Recommendations for the Assessment of Carotid Arterial Plaque by Ultrasound for the Characterization of Atherosclerosis and Evaluation of Cardiovascular Risk: From the American Society of Echocardiography

Atherosclerotic plaque detection by carotid ultrasound provides cardiovascular disease risk stratification. The advantages and disadvantages of two-dimensional (2D) and three-dimensional (3D) ultrasound methods for carotid arterial plaque quantification are reviewed. Advanced and emerging methods of carotid arterial plaque activity and composition analysis by ultrasound are considered. Recommendations for the standardization of focused 2D and 3D carotid arterial plaque ultrasound image acquisition and measurement for the purpose of cardiovascular disease stratification are formulated. Potential clinical application towards cardiovascular risk stratification of recommended focused carotid arterial plaque quantification approaches are summarized.

Carotid plaque imaging profiling in subjects with risk factors (diabetes and hypertension)

Carotid artery stenosis (CAS) due to the presence of atherosclerotic plaque (AP) is a frequent medical condition and a known risk factor for stroke, and it is also known from literature that several risk factors promote the AP development, in particular aging, smoke, male sex, hypertension, hyperlipidemia, smoke, diabetes type 1 and 2, and genetic factors. The study of carotid atherosclerosis is continuously evolving: even if the strategies of treatment still depends mainly on the degree of stenosis (DoS) determined by the plaque, in the last years the attention has moved to the study of the plaque components in order to identify the so called "vulnerable" plaque: features like the fibrous cap status and thickness, the volume of the lipid-rich necrotic core and the presence of intraplaque hemorrhage (IPH) are risk factors for plaque rupture, that can be studied with modern imaging techniques. The aim of this review is to give a general overview of the principle histological and imaging features of the subcomponent of carotid AP (CAP), focalizing in particular on the features of CAP of patients affected by hypertension and diabetes (in particular type 2 diabetes mellitus).

Imaging of inflammatory cellular protagonists in human atherosclerosis: a dual-isotope SPECT approach

Purpose

Atherosclerotic plaque development and progression signifies a complex inflammatory disease mediated by a multitude of proinflammatory leukocyte subsets. Using single photon emission computed tomography (SPECT) coupled with computed tomography (CT), this study tested a new dual-isotope acquisition protocol to assess each radiotracer’s capability to identify plaque phenotype and inflammation levels pertaining to leukocytes expressing leukocyte function-associated antigen-1 (LFA-1) and the leukocyte subset of proinflammatory macrophages expressing somatostatin receptor subtype-2 (SST₂). Individual radiotracer uptake was quantified and the presence of corresponding immunohistological cell markers was assessed.

Methods

Human symptomatic carotid plaque segments were obtained from endarterectomy. Segments were incubated in dual-isotope radiotracers [¹¹¹In]In-DOTA-butylamino-NorBIRT ([¹¹¹In]In-Danbirt) and [^99mTc]Tc-[N^0–1₄,Asp⁰,Tyr³]-octreotate ([^99mTc]Tc-Demotate 2) before scanning with SPECT/CT. Plaque phenotype was classified as pathological intimal thickening, fibrous cap atheroma or fibrocalcific using histology sections based on distinct morphological characteristics. Plaque segments were subsequently immuno-stained with LFA-1 and SST₂ and quantified in terms of positive area fraction and compared against the corresponding SPECT images.

Results

Focal uptake of co-localising dual-radiotracers identified the heterogeneous distribution of inflamed regions in the plaques which co-localised with positive immuno-stained regions of LFA-1 and SST₂. [¹¹¹In]In-Danbirt and [^99mTc]Tc-Demotate 2 uptake demonstrated a significant positive correlation (r = 0.651; p = 0.001). Fibrous cap atheroma plaque phenotype correlated with the highest [¹¹¹In]In-Danbirt and [^99mTc]Tc-Demotate 2 uptake compared with fibrocalcific plaques and pathological intimal thickening phenotypes, in line with the immunohistological analyses.

Conclusion

A dual-isotope acquisition protocol permits the imaging of multiple leukocyte subsets and the pro-inflammatory macrophages simultaneously in atherosclerotic plaque tissue. [¹¹¹In]In-Danbirt may have added value for assessing the total inflammation levels in atherosclerotic plaques in addition to classifying plaque phenotype.

Understanding Atherosclerosis Through an Osteoarthritis Data Set

Atherosclerotic cardiovascular disease remains a worldwide epidemic and one of the leading causes of death nowadays. Vessel wall imaging can be used to understand the development and progression of atherosclerosis, but it is rarely done because of the high cost. We recently identified the Osteoarthritis Initiative, a large prospective cohort study of knee osteoarthritis, which might serve as a valuable source for atherosclerosis research with its serial knee magnetic resonance imaging data. We have found that these images are suitable for vessel wall image analysis of the lower extremity arteries. Here, we will introduce the Osteoarthritis Initiative data set and explain why it could be used for cardiovascular research purposes. Also, we will briefly comment on peripheral artery atherosclerosis as it is covered in the Osteoarthritis Initiative image data set and review the use of vessel wall imaging for studying atherosclerosis. We think data mining of imaging studies, not originally designed on cardiovascular research, can not only maximize the value of the imaging data set but also boost our understanding of atherosclerosis.

Noninvasive Imaging Biomarkers of Vulnerable Coronary Plaques – a Clinical Update

Atherosclerosis is a slow, progressive disease, its most common manifestation and most severe consequence being coronary artery disease, one of the main causes of mortality and morbidity worldwide. The vast majority of cardiovascular deaths are caused by complications of atherosclerosis, most often being represented by the rupture of an unstable coronary plaque, regularly triggered by inflammation. A vulnerable plaque is characterized by a large, lipid-rich necrotic core, a thin fibrous cap with macrophage infiltration, and the presence of multiple specific biomarkers such as positive remodeling, irregular calcifications, and low attenuation visible with coronary computed tomography angiography (CCTA). Identifying biomarkers that could predict the risk of plaque rupture with high accuracy would be a significant advance in predicting acute cardiac events in asymptomatic patients, furthermore guiding treatment of patients with this disease. The main indication of noninvasive imaging is to identify patients at risk based on the presence or absence of symptoms that can be related to myocardial ischemia. The diagnostic objective is to confirm or to exclude the presence of coronary plaques. Coronary imaging in asymptomatic individuals is used to estimate the risk of future cardiac events through the identification of non-obstructive high-risk plaques. The possibility to monitor the evolution of vulnerable plaques via noninvasive imaging techniques, prior to the occurrence of an acute clinical event, is the main goal in plaque imaging. This manuscript will be focusing on recent advances of noninvasive imaging of vulnerable coronary plaques.

Correlation between significant asymptomatic carotid artery stenosis and severity of peripheral arterial occlusive disease in the lower limb: a retrospective study on 200 patients

Background

The aim of this study was to evaluate the correlation between significant asymptomatic carotid artery stenosis (ACAS) and severity of peripheral arterial occlusive disease (PAOD) in the lower limb, and to investigate the risk factors for significant ACAS in patients with lower limb PAOD.

Methods

Two hundred patients with lower limb PAOD were retrospectively reviewed. Baseline data, medical history and potential risk factors were collected. Lower limb PAOD was classified as stage IIA, stage IIB, stage III and stage IV. The carotid artery stenosis was classified as significant ACAS and non-significant ACAS. Multiple logistic regression estimated odds ratio of the risk factors.

Results

Compared to patients with non-significant ACAS, the patients with significant ACAS were significantly older in age and had greater percentage of cigarette-smoking andalcohol beverage consumption, and higher levels of total cholesterol and fibrinogen. There was no significant difference in sex, diabetes, hypertension, coronary heart disease and triglyceride between the two groups. The prevalence rate of significant ACAS increased with the stage of lower limb PAOD and with age. Advanced age and hypercholesteremia were risk factors for significant ACAS in this cohort. The prevalence rate of stroke increased with ACAS stage.

Conclusion

The results suggested that the prevalence rate of significant ACAS was positively correlated with the severity of lower limb PAOD and age. Advanced age and hypercholesteremia appeared to be potential risk factors for significant ACAS in patients with lower limb PAOD.

Intraplaque Microvascular Flow Signal in Superb Microvascular Imaging and Magnetic Resonance Imaging Carotid Plaque Imaging in Patients with Atheromatous Carotid Artery Stenosis

Carotid artery atherosclerosis is one of the major risk factors for ischemic stroke. Intraplaque neovascularization (IPN) is one of the steps toward the development of vulnerable plaque. Superb microvascular imaging (SMI) is a new ultrasonographic technique for visualizing low-velocity and microvascular flow by clutter suppression to extract flow signals from large to small vessels and enables visualization of intraplaque microvascular flow (IMVF) without echo contrast media. We aimed to investigate the association between IMVF signal in SMI and MRI plaque imaging among patients with atherosclerotic carotid stenosis. We prospectively enrolled patients (>18 years old) with mild to severe carotid stenosis (more than 50% in cross-sectional area) diagnosed by carotid ultrasonography between August 2017 and April 2018, irrespective of sex and history of stroke. A total of 40 patients (31 men, 9 women; mean age, 75.1 ± 10.0 years) were enrolled. SMI revealed IPN findings in 21 patients. SMI clearly visualized the direction of pulsatile flow movement in microvessels and IPN was easily classified into the two types of Type V (n=2) and Type E (n=19). Multivariate logistic regression analysis presented that microvascular flow signal in carotid plaque on SMI was identified as a significant predictor of intraplaque hemorrhage as evaluated by MRI (OR, 8.46; 95%CI, 1.44-49.9; p=0.018). This study demonstrated a significant association between the presence of IMVF signal in SMI and intraplaque hemorrhage characterized by high-intensity lesions on MRI T1-FFE images.

Risk prediction of cerebrovascular events with carotid plaque magneitc resonance analysis: A meta-analysis

BACKGROUND AND PURPOSE

It is not conclusive that magnetic resonance (MR)-based carotid atherosclerotic plaque assessment identifies high-risk features associated with cerebrovascular events. We aimed to systematically summarize the association of MR imaging (MRI)-determined intraplaque hemorrhage (IPH), lipid-rich necrotic core (LRNC), and thinning/rupture of the fibrous cap (TRFC) with subsequent ischemic events.

MATERIALS AND METHODS

We performed a comprehensive literature search evaluating the association of MRI-based carotid plaque composition with ischemic outcomes. We included cohort studies examining IPH, LRNC, or TRFC with mean follow-up of≥6 months and an outcome measure of ipsilateral ischemic events. A meta-analysis was done according to the Cochrane guideline.

RESULTS

We identified 13 studies including 1.150 patients and 1.208 analyzed carotid arteries, with mean follow-up of 21.1 months. The hazard ratios (HR) for IPH, LRNC, and TRFC as predictors of subsequent ischemic events were 4.41 (95% CI: 2.87, 6.79), 3.00 (95% CI: 1.51, 5.95), and 5.94 (95% CI: 2.66, 13.28), respectively. The predictive value of carotid plaque MRI for ischemic events was acceptable, with sensitivity of 0.80 (95% CI: 0.66, 0.90) and specificity of 0.63 (95% CI: 0.57, 0.68). However, it was limited to confirm or exclude future ischemic events in clinical context, with positive likelihood ratio (LR) of 2.2 (95% CI: 1.9, 2.5) and negative LR of 0.31 (95% CI: 0.18, 0.55). No statistically significant heterogeneity or publication bias was observed.

CONCLUSION

The presence of IPH, LRNC, and TRFC determined by MRI is associated with increased risk of future ischemic events, but its predictive value is moderate and should not be used for confirmation or exclusion of future ischemic events in clinical context.

Noninvasive Coronary Plaque Imaging

Early identification of high-risk or vulnerable atherosclerotic plaques prone to rupture and performing preemptive therapy prior to catastrophic cardiovascular events are optimal goals of plaque imaging. Despite the advances in imaging modalities to identify vulnerable characteristics, the predictive value of the imaging techniques in the clinical setting is still developing. In this regard, reliable and high-sensitive imaging modalities identifying vulnerable plaque characters that may lead to future cardiovascular events will be useful. In this review article, we describe a current non-invasive plaque imaging technique to identify high-risk coronary plaque features.

Learning-based automated segmentation of the carotid artery vessel wall in dual-sequence MRI using subdivision surface fitting

PURPOSE

The quantification of vessel wall morphology and plaque burden requires vessel segmentation, which is generally performed by manual delineations. The purpose of our work is to develop and evaluate a new 3D model-based approach for carotid artery wall segmentation from dual-sequence MRI.

METHODS

The proposed method segments the lumen and outer wall surfaces including the bifurcation region by fitting a subdivision surface constructed hierarchical-tree model to the image data. In particular, a hybrid segmentation which combines deformable model fitting with boundary classification was applied to extract the lumen surface. The 3D model ensures the correct shape and topology of the carotid artery, while the boundary classification uses combined image information of 3D TOF-MRA and 3D BB-MRI to promote accurate delineation of the lumen boundaries. The proposed algorithm was validated on 25 subjects (48 arteries) including both healthy volunteers and atherosclerotic patients with 30% to 70% carotid stenosis.

RESULTS

For both lumen and outer wall border detection, our result shows good agreement between manually and automatically determined contours, with contour-to-contour distance less than 1 pixel as well as Dice overlap greater than 0.87 at all different carotid artery sections.

CONCLUSIONS

The presented 3D segmentation technique has demonstrated the capability of providing vessel wall delineation for 3D carotid MRI data with high accuracy and limited user interaction. This brings benefits to large-scale patient studies for assessing the effect of pharmacological treatment of atherosclerosis by reducing image analysis time and bias between human observers.

Multimodality ultrasound imaging in stroke: current concepts and future focus

INTRODUCTION

Stroke is a leading cause of disability and mortality worldwide. Ultrasound is a real-time imaging technique that is inexpensive, portable, non-invasive, and safe, with high diagnostic accuracy. Ultrasonic imaging can provide useful direct and indirect information about the characteristics of various vessels in the both intracranial and extracranial segments. Areas covered: In this review, we will discuss multimodal applications of ultrasonic imaging in stroke prevention and management including checking carotid intima-media thickness progression, evaluating the plaque morphology, calibrating the degree of stenosis, detecting the presence of patent foramen ovale, monitoring microembolization, and screening for stroke risk in patients with sickle cell disease. We present the conventional ultrasonography as well as the novel ultrasound techniques including gray scale median, 3-dementional ultrasound, elastography, intravascular ultrasound, and contrast-enhanced ultrasound. Expert commentary: Ultrasonography is a non-invasive, low-cost, safe, fast, and real-time imaging technology for stroke risk assessment. Each modality has its own advantage as well as limitation. Future research should be focused on developing new technologies that can improve the quality of imaging and accuracy of diagnosis.

Review: Mechanical Characterization of Carotid Arteries and Atherosclerotic Plaques

Cardiovascular disease (CVD) is a leading cause of death and is in the majority of cases due to the formation of atherosclerotic plaques in arteries. Initially, thickening of the inner layer of the arterial wall occurs. Continuation of this process leads to plaque formation. The risk of a plaque to rupture and thus to induce an ischemic event is directly related to its composition. Consequently, characterization of the plaque composition and its proneness to rupture are of crucial importance for risk assessment and treatment strategies. The carotid is an excellent artery to be imaged with ultrasound because of its superficial position. In this review, ultrasound-based methods for characterizing the mechanical properties of the carotid wall and atherosclerotic plaque are discussed. Using conventional echography, the intima media thickness (IMT) can be quantified. There is a wealth of studies describing the relation between IMT and the risk for myocardial infarction and stroke. Also the carotid distensibility can be quantified with ultrasound, providing a surrogate marker for the cross-sectional mechanical properties. Although all these parameters are associated with CVD, they do not easily translate to individual patient risk. Another technique is pulse wave velocity (PWV) assessment, which measures the propagation of the pressure pulse over the arterial bed. PWV has proven to be a marker for global arterial stiffness. Recently, an ultrasound-based method to estimate the local PWV has been introduced, but the clinical effectiveness still needs to be established. Other techniques focus on characterization of plaques. With ultrasound elastography, the strain in the plaque due to the pulsatile pressure can be quantified. This technique was initially developed using intravascular catheters to image coronaries, but recently noninvasive methods were successfully developed. A high correlation between the measured strain and the risk for rupture was established. Acoustic radiation force impulse (ARFI) imaging also provides characterization of local plaque components based on mechanical properties. However, both elastography and ARFI provide an indirect measure of the elastic modulus of tissue. With shear wave imaging, the elastic modulus can be quantified, although the carotid artery is one of the most challenging tissues for this technique due to its size and geometry. Prospective studies still have to establish the predictive value of these techniques for the individual patient. Validation of ultrasound-based mechanical characterization of arteries and plaques remains challenging. Magnetic resonance imaging is often used as the "gold" standard for plaque characterization, but its limited resolution renders only global characterization of the plaque. CT provides information on the vascular tree, the degree of stenosis, and the presence of calcified plaque, while soft plaque characterization remains limited. Histology still is the gold standard, but is available only if tissue is excised. In conclusion, elastographic ultrasound techniques are well suited to characterize the different stages of vascular disease.

On the Feasibility of Quantifying Fibrous Cap Thickness With Acoustic Radiation Force Impulse (ARFI) Ultrasound

Acute cerebrovascular accidents are associated with the rupture of vulnerable atherosclerotic plaques in the carotid arteries. Fibrous cap (FC) thickness has been shown to be an important predictor of plaque rupture but has been challenging to measure accurately with clinical noninvasive imaging modalities. The goals of this investigation were first, to evaluate the feasibility of using transcutaneous acoustic radiation force impulse (ARFI) ultrasound to quantify FC thickness and second, to optimize both imaging and motion-tracking parameters to support such measurements. FCs with varying thickness (0.1-1.0 mm) were simulated using a simple-layered geometry, and their mechanical response to an impulse of radiation force was solved using finite-element method (FEM) modeling. Ultrasound tracking of FEM displacements was performed in Field II utilizing three center frequencies (6, 9, and 12 MHz) and eight motion-tracking kernel lengths ( 0.5λ-4λ). Additionally, FC thickness in two carotid plaques imaged in vivo was measured with ARFI and compared to matched histology. The results of this study demonstrate that 1) tracking pulse frequencies around 12 MHz are necessary to resolve caps around 0.2 mm; 2) large motion-tracking kernel sizes introduce bias into thickness measurements and overestimate the true cap thickness; and 3) color saturation settings on ARFI peak displacement images can impact thickness measurement accuracy substantially.

Imaging Modalities to Identity Inflammation in an Atherosclerotic Plaque

Atherosclerosis is a chronic, progressive, multifocal arterial wall disease caused by local and systemic inflammation responsible for major cardiovascular complications such as myocardial infarction and stroke. With the recent understanding that vulnerable plaque erosion and rupture, with subsequent thrombosis, rather than luminal stenosis, is the underlying cause of acute ischemic events, there has been a shift of focus to understand the mechanisms that make an atherosclerotic plaque unstable or vulnerable to rupture. The presence of inflammation in the atherosclerotic plaque has been considered as one of the initial events which convert a stable plaque into an unstable and vulnerable plaque. This paper systemically reviews the noninvasive and invasive imaging modalities that are currently available to detect this inflammatory process, at least in the intermediate stages, and discusses the ongoing studies that will help us to better understand and identify it at the molecular level.

Characterization of intracranial atherosclerotic stenosis using high-resolution MRI study--rationale and design

BACKGROUND

Intracranial atherosclerosis is a leading cause of stroke, but little is known about the composition of the intracranial atherosclerotic lesion and how intracranial plaque morphology is related to the risk of stroke. High-resolution magnetic resonance imaging (HR MRI) has been used in patients with extracranial carotid atherosclerosis as an in vivo tool to identify, with high-interrater agreement, histologically defined plaque components (i.e., intraplaque hemorrhage, fibrous cap, and lipid core), which have been shown to be predictors of recurrent stroke. With careful imaging the components of atherosclerotic plaque can be visualized in the intracranial arteries using HR MRI, but there are no reports of reproducibility or interrater reliability.

METHODS/STUDY DESIGN

The Characterization of intracranial atherosclerotic stenosis using high-resolution MRI (CHIASM) study is a single-center NIH-funded prospective observational study, to (1) demonstrate high -interrater agreement for identifying intracranial plaque components on HR MRI, (2) determine the frequency of these components in symptomatic versus asymptomatic plaques, and (3) estimate the 1-year rate of stroke in the territory of high-risk plaque components. CHIASM will recruit 90 patients with 50-99% intracranial atherosclerosis to undergo HRMRI of the intracranial artery plaque at enrollment and 1-year follow-up. Both symptomatic and asymptomatic subjects will be recruited.

CONCLUSION

Determination of good interrater reliability is an important first step in the development of HR MRI as a tool to predict risk in patients with intracranial atherosclerosis. This study will inform the design of future multicenter studies to determine the prevalence and prognosis of intracranial atherosclerotic plaque components. Such studies could lead to new understanding of the pathophysiological mechanisms of cerebral ischemia in patients with atherosclerotic intracranial stenosis, improvements in risk stratification, and potentially to new treatments of this common and serious disease.

Analysis of Multicontrast Carotid Plaque MR Imaging

Plaque imaging by MR imaging provides a wealth of information on the characteristics of individual plaque that may reveal vulnerability to rupture, likelihood of progression, or optimal treatment strategy. T1-weighted and T2-weighted images among other options reveal plaque morphology and composition. Dynamic contrast-enhanced-MR imaging reveals plaque activity. To extract this information, image processing tools are needed. Numerous approaches for analyzing such images have been developed, validated against histologic gold standards, and used in clinical studies. These efforts are summarized in this article.

Advanced MRI for carotid plaque imaging

Atherosclerosis is the ubiquitous underling pathological process that manifests in heart attack and stroke, cumulating in the death of one in three North American adults. High-resolution magnetic resonance imaging (MRI) is able to delineate atherosclerotic plaque components and total plaque burden within the carotid arteries. Using dedicated hardware, high resolution images can be obtained. Combining pre- and post-contrast T1, T2, proton-density, and magnetization-prepared rapid acquisition gradient echo weighted fat-saturation imaging, plaque components can be defined. Post-processing software allows for semi- and fully automated quantitative analysis. Imaging correlation with surgical specimens suggests that this technique accurately differentiates plaque features. Total plaque burden and specific plaque components such as a thin fibrous cap, large fatty or necrotic core and intraplaque hemorrhage are accepted markers of neuroischemic events. Given the systemic nature of atherosclerosis, emerging science suggests that the presence of carotid plaque is also an indicator of coronary artery plaque burden, although the preliminary data primarily involves patients with stable coronary disease. While the availability and cost-effectiveness of MRI will ultimately be important determinants of whether carotid MRI is adopted clinically in cardiovascular risk assessment, the high accuracy and reliability of this technique suggests that it has potential as an imaging biomarker of future risk.

Advances in MRI for the evaluation of carotid atherosclerosis

Carotid artery atherosclerosis is an important source of mortality and morbidity in the Western world with significant socioeconomic implications. The quest for the early identification of the vulnerable carotid plaque is already in its third decade and traditional measures, such as the sonographic degree of stenosis, are not selective enough to distinguish those who would really benefit from a carotid endarterectomy. MRI of the carotid plaque enables the visualization of plaque composition and specific plaque components that have been linked to a higher risk of subsequent embolic events. Blood suppressed T1 and T2 weighted and proton density-weighted fast spin echo, gradient echo and time-of-flight sequences are typically used to quantify plaque components such as lipid-rich necrotic core, intraplaque haemorrhage, calcification and surface defects including erosion, disruption and ulceration. The purpose of this article is to review the most important recent advances in MRI technology to enable better diagnostic carotid imaging.

Non-invasive molecular imaging of vulnerable atherosclerotic plaques

The growing discoveries coming from clinical and basic research during the past decades have revolutionized our knowledge regarding pathophysiologic mechanisms underlying the atherosclerotic process and its thrombotic complications. The traditional view focusing on the severity of stenosis of atherosclerotic plaque has given way to the evidence that the clinical complications of atherosclerotic vascular disease, particularly the propensity to develop thrombotic complications, are determined mainly by the biological composition of the plaque. This paradigm shift has reinforced the need to move from the sole anatomical assessment toward combined anatomic and functional imaging modalities enabling the molecular and cellular characterization of the disease on top of its structural properties. Together, the progress to identify molecular targets related to plaque vulnerability and the improvement of imaging techniques for the detection of such molecular targets have allowed us to obtain new important pathophysiological information. This might allow better patient stratification for the identification of subjects at high risk to develop premature atherosclerosis who might need an aggressive therapeutic approach. Nuclear techniques, magnetic resonance imaging, computed tomography angiography, and contrast-enhanced ultrasound represent the currently available non-invasive imaging modalities for molecular imaging which can provide different and complementary insights into the biological features of the atherosclerotic process. This clinical review will discuss the evidence and potential translational applications of the individual imaging techniques particularly concerning their ability to detect the main atherosclerotic features related to plaque vulnerability, such as plaque inflammation and intertwined neovascularization.

Imaging the intracranial atherosclerotic vessel wall using 7T MRI: initial comparison with histopathology

BACKGROUND AND PURPOSE

Several studies have attempted to characterize intracranial atherosclerotic plaques by using MR imaging sequences. However, dedicated validation of these sequences with histology has not yet been performed. The current study assessed the ability of ultra-high-resolution 7T MR imaging sequences with different image contrast weightings to image plaque components, by using histology as criterion standard.

MATERIALS AND METHODS

Five specimens of the circle of Wills were imaged at 7T with 0.11 × 0.11 mm in-plane-resolution proton attenuation-, T1-, T2-, and T2*-weighted sequences (through-plane resolution, 0.11-1 mm). Tissue samples from 13 fiducial-marked locations (per specimen) on MR imaging underwent histologic processing and atherosclerotic plaque classification. Reconstructed MR images were matched with histologic sections at corresponding locations.

RESULTS

Forty-four samples were available for subsequent evaluation of agreement or disagreement between plaque components and image contrast differences. Of samples, 52.3% (n = 23) showed no image contrast heterogeneity; this group comprised solely no lesions or early lesions. Of samples, 25.0% (n = 11, mostly advanced lesions) showed good correlation between the spatial organization of MR imaging heterogeneities and plaque components. Areas of foamy macrophages were generally seen as proton attenuation-, T2-, and T2*- hypointense areas, while areas of increased collagen content showed more ambiguous signal intensities. Five samples showed image-contrast heterogeneity without corresponding plaque components on histology; 5 other samples showed contrast heterogeneity based on intima-media artifacts.

CONCLUSIONS

MR imaging at 7T has the image contrast capable of identifying both focal intracranial vessel wall thickening and distinguishing areas of different signal intensities spatially corresponding to plaque components within more advanced atherosclerotic plaques.

Systematic reviews and meta-analyses for more profitable strategies in peripheral artery disease

In the peripheral arteries, a thrombus superimposed on atherosclerosis contributes to the progression of peripheral artery disease (PAD), producing intermittent claudication (IC), ischemic necrosis, and, potentially, loss of the limb. PAD with IC is often undiagnosed and, in turn, undertreated. The low percentage of diagnosis (∼30%) in this setting of PAD is of particular concern because of the potential worsening of PAD (amputation) and the high risk of adverse vascular outcomes (vascular death, coronary artery disease, stroke). A Medline literature search of the highest-quality systematic reviews and meta-analyses of randomized controlled trials documents that, due to risk of bias, imprecision, and indirectness, the overall quality of the evidence concerning diagnostic tools and antithrombotic interventions in PAD is generally low. Areas of research emerge from the information collected. Appropriate treatments for PAD patients will only derive from ad-hoc studies. Innovative imaging techniques are needed to identify PAD subjects at the highest vascular risk. Whether IC unresponsive to physical exercise and smoking cessation identifies those with a heritable predisposition to more severe vascular events deserves to be addressed. Devising ways to improve prevention of vascular events in patients with PAD implies a co-ordinated approach in vascular medicine.

Clinical factors associated with high-risk carotid plaque features as assessed by magnetic resonance imaging in patients with established vascular disease (from the AIM-HIGH Study)

Association between clinical factors and high-risk plaque features, such as, thin or ruptured cap, intraplaque hemorrhage, presence of lipid-rich necrotic core (LRNC), and increased LRNC volume as assessed by magnetic resonance imaging (MRI), was examined in patients with established vascular disease in the Atherothrombosis Intervention in Metabolic Syndrome With Low HDL/High Triglycerides (AIM-HIGH) trial. A total of 214 subjects underwent carotid MRI and had acceptable image quality for assessment of plaque burden, tissue contents, and MRI-modified American Heart Association lesion type by a core laboratory. We found that 77% of subjects had carotid plaques, 52% had lipid-containing plaques, and 11% had advanced American Heart Association type-VI lesions with possible surface defect, intraplaque hemorrhage, or mural thrombus. Type-VI lesions were associated with older age (odds ratio [OR] = 2.6 per 5 years increase, p <0.001). After adjusting for age, these lesions were associated with history of cerebrovascular disease (OR = 4.1, p = 0.01), higher levels of lipoprotein(a) (OR = 2.0 per 1 SD increase, p = 0.02), and larger percent wall volume (PWV [OR = 4.6 per 1 SD increase, p <0.001]) but, were negatively associated with metabolic syndrome (OR = 0.2, p = 0.02). Presence of LRNC was associated with the male gender (OR = 3.2, p = 0.02) and PWV (OR = 3.8 per 1 SD, p <0.001); however, it was negatively associated with diabetes (OR = 0.4, p = 0.02) and high-density lipoprotein cholesterol levels (OR = 0.7 per 1 SD, p = 0.02). Increased percent LRNC was associated with PWV (regression coefficient = 0.36, p <0.001) and negatively associated with ApoA1 levels (regression coefficient = -0.20, p = 0.03). In conclusion, older age, male gender, history of cerebrovascular disease, larger plaque burden, higher lipoprotein(a), and lower high-density lipoprotein cholesterol or ApoA1 level have statistically significant associations with high-risk plaque features. Metabolic syndrome and diabetes showed negative associations in this population.

Assessment of carotid artery atherosclerotic disease by using three-dimensional fast black-blood MR imaging: comparison with DSA

PURPOSE

To assess fast three-dimensional (3D) black-blood (BB) magnetic resonance (MR) imaging as a noninvasive alternative to intraarterial digital subtraction angiography (DSA) at quantifying moderate to severe carotid artery atherosclerotic disease.

MATERIALS AND METHODS

Local ethics committee approval and written informed patient consent were obtained for this study. Sixty-five carotid arteries from 52 patients with at least 50% stenosis underwent 3D BB MR imaging and DSA. Quantitative measurements, including stenosis, lesion length, and the presence or absence of plaque ulceration, obtained with the two modalities were independently determined. Sensitivity and specificity, the intraclass correlation coefficient (ICC), Cohen κ, and Bland-Altman analysis were used to assess the agreement.

RESULTS

Excellent agreement in measuring luminal stenosis was found between 3D BB MR imaging and DSA (ICC, 0.96; 95% confidence interval [CI]: 0.93, 0.97). Three-dimensional BB MR imaging was also found to have high sensitivity (91.7%), specificity (96.2%), and agreement (Cohen κ, 0.85; 95% CI: 0.66, 0.99) with DSA for detection of ulcers. Good agreement was found between lesion length measured by using 3D BB MR imaging and DSA (ICC, 0.75; 95% CI: 0.51, 0.84). However, lesion length measurements by using 3D BB MR imaging were, on average, 4.0 mm longer than those measured by using DSA (P < .001).

CONCLUSION

Three-dimensional BB MR imaging is a noninvasive and accurate way to quantify moderate to severe carotid artery atherosclerotic disease. With fast acquisition and large coverage, 3D BB MR imaging has the potential to become an alternative imaging approach in evaluating the severity of atherosclerosis.

The role of imaging in acute ischemic stroke

Neuroimaging has expanded beyond its traditional diagnostic role and become a critical tool in the evaluation and management of stroke. The objectives of imaging include prompt accurate diagnosis, treatment triage, prognosis prediction, and secondary preventative precautions. While capitalizing on the latest treatment options and expanding upon the "time is brain" doctrine, the ultimate goal of imaging is to maximize the number of treated patients and improve the outcome of one the most costly and morbid disease. A broad overview of comprehensive multimodal stroke imaging is presented here to affirm its utilization.

Multi-contrast atherosclerosis characterization (MATCH) of carotid plaque with a single 5-min scan: technical development and clinical feasibility

BACKGROUND

Multi-contrast weighted imaging is a commonly used cardiovascular magnetic resonance (CMR) protocol for characterization of carotid plaque composition. However, this approach is limited in several aspects including low slice resolution, long scan time, image mis-registration, and complex image interpretation. In this work, a 3D CMR technique, named Multi-contrast Atherosclerosis Characterization (MATCH), was developed to mitigate the above limitations.

METHODS

MATCH employs a 3D spoiled segmented fast low angle shot readout to acquire data with three different contrast weightings in an interleaved fashion. The inherently co-registered image sets, hyper T1-weighting, gray blood, and T2-weighting, are used to detect intra-plaque hemorrhage (IPH), calcification (CA), lipid-rich necrotic core (LRNC), and loose-matrix (LM). The MATCH sequence was optimized by computer simulations and testing on four healthy volunteers and then evaluated in a pilot study of six patients with carotid plaque, using the conventional multi-contrast protocol as a reference.

RESULTS

On MATCH images, the major plaque components were easy to identify. Spatial co-registration between the three image sets with MATCH was particularly helpful for the reviewer to discern co-existent components in an image and appreciate their spatial relation. Based on Cohen's kappa tests, moderate to excellent agreement in the image-based or artery-based component detection between the two protocols was obtained for LRNC, IPH, CA, and LM, respectively. Compared with the conventional multi-contrast protocol, the MATCH protocol yield significantly higher signal contrast ratio for IPH (3.1±1.3 vs. 0.4±0.3, p<0.001) and CA (1.6±1.5 vs. 0.7±0.6, p=0.012) with respect to the vessel wall.

CONCLUSIONS

To the best of our knowledge, the proposed MATCH sequence is the first 3D CMR technique that acquires spatially co-registered multi-contrast image sets in a single scan for characterization of carotid plaque composition. Our pilot clinical study suggests that the MATCH-based protocol may outperform the conventional multi-contrast protocol in several respects. With further technical improvements and large-scale clinical validation, MATCH has the potential to become a CMR method for assessing the risk of plaque disruption in a clinical workup.

Non-invasive vulnerable plaque imaging: how do we know that treatment works?

Atherosclerosis is an inflammatory disorder that can evolve into an acute clinical event by plaque development, rupture, and thrombosis. Plaque vulnerability represents the susceptibility of a plaque to rupture and to result in an acute cardiovascular event. Nevertheless, plaque vulnerability is not an established medical diagnosis, but rather an evolving concept that has gained attention to improve risk prediction. The availability of high-resolution imaging modalities has significantly facilitated the possibility of performing in vivo regression studies and documenting serial changes in plaque stability. This review summarizes the currently available non-invasive methods to identify vulnerable plaques and to evaluate the effects of the current cardiovascular treatments on plaque evolution.

Quantifying effect of intraplaque hemorrhage on critical plaque wall stress in human atherosclerotic plaques using three-dimensional fluid-structure interaction models

Recent magnetic resonance studies have indicated that intraplaque hemorrhage (IPH) may accelerate plaque progression and play an important role in plaque destabilization. However, the impact of hemorrhage on critical plaque wall stress (CPWS) and strain (CPWSn) has yet to be determined. The objective of this study was to assess the effect of the presence and size of IPH on wall mechanics. The magnetic resonance image (MRI) of one patient with histology-confirmed IPH was used to build eight 3D fluid-structure interaction (FSI) models by altering the dimensions of the existing IPH. As a secondary end point, the combined effect of IPH and fibrous cap thickness (FCT) was assessed. A volume curve fitting method (VCFM) was applied to generate a mesh that would guarantee numerical convergence. Plaque wall stress (PWS), strain (PWSn), and flow shear stress (FSS) were extracted from all nodal points on the lumen surface for analysis. Keeping other conditions unchanged, the presence of intraplaque hemorrhage caused a significant increase (27.5%) in CPWS; reduced FCT caused an increase of 22.6% of CPWS. Similar results were found for CPWSn. Furthermore, combination of IPH presence, reduced FCT, and increased IPH volume caused an 85% and 75% increase in CPWS and CPWSn, respectively. These results show that intraplaque hemorrhage has considerable impact on plaque stress and strain conditions and accurate quantification of IPH could lead to more accurate assessment of plaque vulnerability. Large-scale studies are needed to further validate our findings.

Iron and atherosclerosis: nailing down a novel target with magnetic resonance

Iron is an essential mineral in many proteins and enzymes in human physiology, with limited means of iron elimination to maintain iron balance. Iron accrual incurs various pathological mechanisms linked to cardiovascular disease. In atherosclerosis, iron catalyzes the creation of reactive oxygen free radicals that contribute to lipid modification, which is essential to atheroma formation. Inflammation further fuels iron-related pathologic processes associated with plaque progression. Given iron's role in atherosclerosis development, in vivo detection techniques sensitive iron are needed for translational studies targeting iron for earlier diagnosis and treatment. Magnetic resonance imaging is uniquely able to quantify iron in human tissues noninvasively and without ionizing radiation, offering appealing for longitudinal and interventional studies. Particularly intriguing is iron's complementary biology vs. calcium, which is readily detectable by computed tomography. This review summarizes the role of iron in atherosclerosis with considerable implications for novel diagnostic and therapeutic approaches.

Clot composition and treatment approach to acute ischemic stroke: The road so far

Recent histological studies of thrombi retrieved from patients with an acute ischemic stroke using the endovascular thrombectomy devices and correlation with early vessel computed tomography (CT) and magnetic resonance imaging (MRI) characteristics have given relevant insights into the pathophysiology of thrombotic lesions and may facilitate the development of improved reperfusion treatment approaches. We present a review of recent studies on the histopathologic analysis of thrombi, studies of MRI, and CT imaging correlation with thrombus histology, and detailed structural analysis of thromboemboli retrieved by thrombectomy devices during an acute ischemic stroke.

Vulnerable atherosclerotic carotid plaque evaluation by ultrasound, computed tomography angiography, and magnetic resonance imaging: an overview

Ischemic syndromes associated with carotid atherosclerotic disease are often related to plaque rupture. The benefit of endarterectomy for high-grade carotid stenosis in symptomatic patients has been established. However, in asymptomatic patients, the benefit of endarterectomy remains equivocal. Current research seeks to risk stratify asymptomatic patients by characterizing vulnerable, rupture-prone atherosclerotic plaques. Plaque composition, biology, and biomechanics are studied by noninvasive imaging techniques such as magnetic resonance imaging, computed tomography, ultrasound, and ultrasound elastography. These techniques are at a developmental stage and have yet to be used in clinical practice. This review will describe noninvasive techniques in ultrasound, magnetic resonance imaging, and computed tomography imaging modalities used to characterize atherosclerotic plaque, and will discuss their potential clinical applications, benefits, and drawbacks.

Numerical simulations of carotid MRI quantify the accuracy in measuring atherosclerotic plaque components in vivo

PURPOSE

Atherosclerotic carotid plaques can be quantified in vivo by MRI. However, the accuracy in segmentation and quantification of components such as the thin fibrous cap (FC) and lipid-rich necrotic core (LRNC) remains unknown due to the lack of a submillimeter scale ground truth.

METHODS

A novel approach was taken by numerically simulating in vivo carotid MRI providing a ground truth comparison. Upon evaluation of a simulated clinical protocol, MR readers segmented simulated images of cross-sectional plaque geometries derived from histological data of 12 patients.

RESULTS

MR readers showed high correlation (R) and intraclass correlation (ICC) in measuring the luminal area (R = 0.996, ICC = 0.99), vessel wall area (R = 0.96, ICC = 0.94) and LRNC area (R = 0.95, ICC = 0.94). LRNC area was underestimated (mean error, -24%). Minimum FC thickness showed a mediocre correlation and intraclass correlation (R = 0.71, ICC = 0.69).

CONCLUSION

Current clinical MRI can quantify carotid plaques but shows limitations for thin FC thickness quantification. These limitations could influence the reliability of carotid MRI for assessing plaque rupture risk associated with FC thickness. Overall, MRI simulations provide a feasible methodology for assessing segmentation and quantification accuracy, as well as for improving scan protocol design.

Enhancement patterns in the fibro cellular tissue in different kinds of plaques of the internal carotid artery

BACKGROUND

The differentiation between stable and vulnerable plaques in the internal carotid artery (ICA) remains a matter of interest. With the implementation of contrast agent in magnetic resonance imaging (MRI) a more detailed plaque characterization is possible. The study at hand focuses on enhancement patterns of fibro cellular tissue in different kinds of plaques in the ICA.

METHODS

Between May 2011 and December 2012, 49 patients (39 male) with >50% stenosis of the ICA were consecutively enrolled. In 10 patients with bilateral ICA stenosis, both plaques were included for analysis. We performed a classification of plaques according to Cai and observed 11 type 4-5 plaques, 15 type 6 plaques and 33 type 8 plaques. MRI was performed on a 3T whole body MR system. The standard 12 channel head coil was combined with the neck extension coil and two bilateral 7 cm loop coils. Post-contrast T1w images were subtracted from pre contrast images to identify late enhancement in fibro cellular tissue. Enhancement patterns were allocated as intraluminal, intraplaque and vasa vasorum enhancement in different types of plaques.

RESULTS

Fibro cellular tissue always exhibited a higher contrast enhancement compared to the sternocleidomastoid muscle. This reflects a higher grade of vascularization of the fibrocellular tissue. Contrast enhancement was present irrespective of the plaque type. In detail, intraluminal, intraplaque and vasa vasorum enhancement were observed in all types of plaques. Even type 8 plaques, according to the classification of Cai, had a significant contrast enhancement, though supposed to be with low inflammatory activity.

CONCLUSION

Type 8 plaques might not be as stable as postulated. Whether the relevant uptake of contrast agent is due to the fibrous tissue or reflects the inflammatory activity of the plaque should be matter of further investigations.

Imaging of the carotid artery vulnerable plaque

Atherosclerosis involving the carotid arteries has a high prevalence in the population worldwide. This condition is significant because accidents of the carotid artery plaque are associated with the development of cerebrovascular events. For this reason, carotid atherosclerotic disease needs to be diagnosed and those determinants that are associated to an increased risk of stroke need to be identified. The degree of stenosis typically has been considered the parameter of choice to determine the therapeutical approach, but several recently published investigations have demonstrated that the degree of luminal stenosis is only an indirect indicator of the atherosclerotic process and that direct assessment of the plaque structure and composition may be key to predict the development of future cerebrovascular ischemic events. The concept of "vulnerable plaque" was born, referring to those plaque's parameters that concur to the instability of the plaque making it more prone to the rupture and distal embolization. The purpose of this review is to describe the imaging characteristics of "vulnerable carotid plaques."