Characterisation of carotid atherosclerotic plaque: comparison between magnetic resonance imaging and histology

Assessment for Carotid Atherosclerotic Plaque Using Vessel Wall Magnetic Resonance Imaging: A Multireader ROC Study to Determine Optimal Sequence for Detecting Vessel Wall Calcification

INTRODUCTION

We aimed to compare conventional vessel wall MR imaging techniques and quantitative susceptibility mapping (QSM) to determine the optimal sequence for detecting carotid artery calcification.

METHODS

Twenty-two patients who underwent carotid vessel wall MR imaging and neck CT were enrolled. Four slices of 6-mm sections from the bilateral internal carotid bifurcation were subdivided into 4 segments according to clock position (0-3, 3-6, 6-9, and 9-12) and assessed for calcification. Two blinded radiologists independently reviewed a total of 704 segments and scored the likelihood of calcification using a 5-point scale on spin-echo imaging, FLASH, and QSM. The observer performance for detecting calcification was evaluated by a multireader, multiple-case receiver operating characteristic study. Weighted κ statistics were calculated to assess interobserver agreement.

RESULTS

QSM had a mean area under the receiver operating characteristic curve of 0.85, which was significantly higher than that of any other sequence (p < 0.01) and showed substantial interreader agreement (κ = 0.68). A segment with a score of 3-5 was defined as positive, and a segment with a score of 1-2 was defined as negative; the sensitivity and specificity of QSM were 0.75 and 0.87, respectively.

CONCLUSION

QSM was the most reliable MR sequence for the detection of plaque calcification.

Novel Imaging-Based Biomarkers for Identifying Carotid Plaque Vulnerability

Carotid artery disease has traditionally been assessed based on the degree of luminal narrowing. However, this approach, which solely relies on carotid stenosis, is currently being questioned with regard to modern risk stratification approaches. Recent guidelines have introduced the concept of the "vulnerable plaque," emphasizing specific features such as thin fibrous caps, large lipid cores, intraplaque hemorrhage, plaque rupture, macrophage infiltration, and neovascularization. In this context, imaging-based biomarkers have emerged as valuable tools for identifying higher-risk patients. Non-invasive imaging modalities and intravascular techniques, including ultrasound, computed tomography, magnetic resonance imaging, intravascular ultrasound, optical coherence tomography, and near-infrared spectroscopy, have played pivotal roles in characterizing and detecting unstable carotid plaques. The aim of this review is to provide an overview of the evolving understanding of carotid artery disease and highlight the significance of imaging techniques in assessing plaque vulnerability and informing clinical decision-making.

Vessel wall MR imaging of aortic arch, cervical carotid and intracranial arteries in patients with embolic stroke of undetermined source: A narrative review

Despite advancements in multi-modal imaging techniques, a substantial portion of ischemic stroke patients today remain without a diagnosed etiology after conventional workup. Based on existing diagnostic criteria, these ischemic stroke patients are subcategorized into having cryptogenic stroke (CS) or embolic stroke of undetermined source (ESUS). There is growing evidence that in these patients, non-cardiogenic embolic sources, in particular non-stenosing atherosclerotic plaque, may have significant contributory roles in their ischemic strokes. Recent advancements in vessel wall MRI (VW-MRI) have enabled imaging of vessel walls beyond the degree of luminal stenosis, and allows further characterization of atherosclerotic plaque components. Using this imaging technique, we are able to identify potential imaging biomarkers of vulnerable atherosclerotic plaques such as intraplaque hemorrhage, lipid rich necrotic core, and thin or ruptured fibrous caps. This review focuses on the existing evidence on the advantages of utilizing VW-MRI in ischemic stroke patients to identify culprit plaques in key anatomical areas, namely the cervical carotid arteries, intracranial arteries, and the aortic arch. For each anatomical area, the literature on potential imaging biomarkers of vulnerable plaques on VW-MRI as well as the VW-MRI literature in ESUS and CS patients are reviewed. Future directions on further elucidating ESUS and CS by the use of VW-MRI as well as exciting emerging techniques are reviewed.

A preliminary study of relationship among the degree of internal carotid artery stenosis, wall shear stress on MR angiography and 18F-FDG uptake on PET/CT

BACKGROUND

This preliminary study was undertaken to evaluate relationship among the degree of internal carotid artery (ICA) stenosis, wall shear stress (WSS) by computational fluid dynamics (CFD) on magnetic resonance angiography (MRA) and 18F-FDG uptake of ICA on PET/CT.

METHODS

A total of 40 carotid arteries in 20 patients with carotid atherosclerotic disease were examined with MRA and 18F-FDG PET/CT. Atherosclerotic risk factors were assessed in all patients. Degree of ICA stenosis was calculated according to NASCET method. CFD analysis was performed and maximum WSS (WSSmax) was measured. 18F-FDG uptake in ICA was quantified using maximum target-to-blood pool ratio (TBRmax).

RESULTS

Atherosclerotic risk factors did not affect imaging findings. There were significant correlations between WSSmax and degree of ICA stenosis (ρ = .81, P < .001), WSSmax and TBRmax (ρ = .64, P < .001), and TBRmax and degree of ICA stenosis (ρ = .50, P = .001).

CONCLUSIONS

These preliminary results indicate that there may be significant correlations among the degree of ICA stenosis, WSSmax and TBRmax in patients with carotid artery stenosis.

Cervical Carotid Plaque MRI : Review of Atherosclerosis Imaging Features and their Histologic Underpinnings

Magnetic resonance (MR) imaging is considered the gold standard for non-invasive evaluation of carotid artery plaque morphology and composition. A number of studies have demonstrated the clinical utility of MR plaque imaging in the risk stratification of carotid atherosclerotic disease, determination of stroke etiology, and identification of surgical and endovascular candidates for carotid revascularization procedures. The MR plaque imaging also provides researchers and clinicians with valuable insights into the pathogenesis, natural history and composition of carotid atherosclerotic disease. Nevertheless, the field of MR plaque imaging is complex, and requires a thorough knowledge of the histologic basis for how various plaque features appear on imaging. This article details the pathogenesis and histology of atherosclerosis, reviews the expected appearance of different plaque components, and describes how MR imaging features may be related to symptomatology or predict future ischemic events.

Carotid intraplaque haemorrhage: pathogenesis, histological classification, imaging methods and clinical value

Vulnerable carotid atherosclerotic plaques are characterised by several risk factors, such as inflammation, neovascularization and intraplaque haemorrhage (IPH). Vulnerable plaques can lead to ischemic events such as stroke. Many studies reported a relationship between IPH, plaque rupture, and ischemic stroke. Histology is the gold standard to evaluate IPH, but it required carotid endarterectomy (CEA) surgery to collect the tissue sample. In this context, several imaging methods can be used as a non-invasive way to evaluate plaque vulnerability and detect IPH. Most imaging studies showed that IPH is associated with plaque vulnerability and stroke, with magnetic resonance imaging (MRI) being the most sensitive and specific to detect IPH as a predictor of ischemic events. These conclusions are however still debated because of the limited number of patients included in these studies; further studies are required to better assess risks associated with different IPH stages. Moreover, IPH is implicated in plaque vulnerability with other risk factors which need to be considered to predict ischemic risk. In addition, MRI sequences standardization is required to compare results from different studies and agree on biomarkers that need to be considered to predict plaque rupture. In these circumstances, IPH detection by MRI could be an efficient clinical method to predict stroke. The goal of this review article is to first describe the pathophysiological process responsible for IPH, its histological detection in carotid plaques and its correlation with plaque rupture. The second part will discuss the benefits and limitations of imaging the carotid plaque, and finally the clinical interest of imaging IPH to predict plaque rupture, focusing on MRI-IPH.

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.

Embolic Stroke of Undetermined Source and Carotid Intraplaque Hemorrhage on MRI : A Systemic Review and Meta-Analysis

BACKGROUND

Embolic stroke of undetermined source (ESUS) has traditionally discounted the significance of internal carotid artery stenosis of <50%; however, recent studies have examined the role of carotid artery intraplaque hemorrhage (IPH) as an etiology in nonstenotic carotid arteries. We performed a systemic review of the literature to determine the prevalence of carotid artery IPH on magnetic resonance imaging (MRI) of the vessel wall in patients with ESUS.

METHODS

We used PubMed, Epub ahead of print, Ovid MEDLINE in-process and other non-indexed citations, Ovid MEDLINE, Ovid EMBASE, Ovid Cochrane central register of controlled trials, Ovid Cochrane database of systematic reviews and Scopus. Our study consisted of all case series with >10 patients with IPH and ESUS published through October 2018. Additionally, we included 123 patients from an institutional database from 2015-2019. Random effects meta-analysis was used for pooling across studies. Meta-analysis results were expressed as odds ratio (OR) with respective 95% confidence intervals (CI).

RESULTS

A total of 7 studies with 354 patients were included. The mean age was 67.5 years old. The overall prevalence estimate for prevalence of IPH ipsilateral to the ischemic lesion was 25.8% (95% CI 13.1-38.5). The odds of having IPH on the ipsilateral side versus the contralateral side was 6.92 (95% CI 3.04-15.79).

CONCLUSION

Patients with ESUS have IPH in the carotid artery ipsilateral to the ischemic stroke in 25.8% of cases. Carotid artery vessel wall MRI should be considered as part of the standard work-up in patients with ESUS.

Diabetes-specific characteristics of atherosclerotic plaques in femoral arteries determined by three-dimensional magnetic resonance vessel wall imaging

OBJECTIVES

This study aimed to investigate the characteristics of femoral atherosclerotic plaques in patients with diabetes mellitus (DM) compared with those without DM using three-dimensional magnetic resonance vessel wall imaging.

METHODS

Lower extremity atherosclerotic disease patients with and without DM (age ≥ 50 year-old) were recruited and underwent three-dimensional magnetic resonance imaging for femoral arteries. The femoral arteries were divided into common femoral artery (CFA), proximal of superficial femoral artery (pSFA), adductor canal (AC), and popliteal artery (PA) segments. The characteristics of femoral artery atherosclerotic plaques were compared between patients with and without DM.

RESULTS

Forty-eight patients with DM (69.5 ± 8.2 years; 26 males) and 50 patients without DM (71.9 ± 5.7 years; 28 males) were included. Significant differences were found in maximum wall thickness in CFA and AC segments, eccentricity index in AC segment, prevalence of plaque in CFA, pSFA and AC segments, stenosis and prevalence of calcification in pSFA, AC and PA segments, prevalence of lipid-rich necrotic core (LRNC) in all segments, and prevalence of intraplaque haemorrhage in PA segment between patients with and without DM (all P < .05). After adjusted for confounding factors of age, gender, hyperlipidemia, coronary artery disease, and statin use, the differences in eccentricity index, stenosis and prevalence of plaque, calcification and LRNC in pSFA and AC segments, and stenosis and prevalence of LRNC in PA segment remained statistically significant between patients with and without DM (all P < .05).

CONCLUSIONS

Patients with DM have significantly larger plaque burden, higher prevalence of plaques, and more complex plaque compositions in femoral arteries than those without DM.

Associations between local haemodynamics and carotid intraplaque haemorrhage with different stenosis severities: A preliminary study based on MRI and CFD

The relationship between carotid blood flow and carotid intraplaque haemorrhage (IPH) is not fully understood. This study was to investigate the relationship between local haemodynamics and carotid plaques with IPH associated with severe artery stenosis. Fifty-nine patients with carotid atherosclerosis were enrolled in this study and underwent magnetic resonance imaging (MRI) measurement. IPH and non-IPH compositions were differentiated based on plaque sequences. Haemodynamic simulations were performed by using computational fluid dynamics (CFD). All the carotids were categorised into IPH and non-IPH groups. In each group, the artery stenosis was divided into mild (<50%), moderate (50-70%) and severe (>70%) subgroups. Maximum wall shear stress (mWSS) was calculated and comparisons made between IPH and non-IPH groups using independent t-test. Furthermore, the relationship between mWSS and IPH volume was examined using Pearson's correlation. The mWSS result calculated from the IPH group was significantly higher than that of the non-IPH group; at mild stenosis (P = 0.001) and moderate stenosis (P = 0.002) respectively. However, there was no significant difference in cases of severe stenosis (P = 0.42). Furthermore, the results showed a positive correlation between mWSS and IPH volume (r = 0.763, P < 0.001) in the cases of stenosis of less than 70%. mWSS was found to be significantly associated with IPH for carotids with stenosis of less than 70%. This highlights that mWSS is a potential quantitative parameter for the risk diagnosis of the carotid atherosclerosis.

Calcifications in atherosclerotic plaques and impact on plaque biomechanics

The catastrophic mechanical rupture of an atherosclerotic plaque is the underlying cause of the majority of cardiovascular events. The infestation of vascular calcification in the plaques creates a mechanically complex tissue composite. Local stress concentrations and plaque tissue strength properties are the governing parameters required to predict plaque ruptures. Advanced imaging techniques have permitted insight into fundamental mechanisms driving the initiating inflammatory-driven vascular calcification of the diseased intima at the (sub-) micron scale and up to the macroscale. Clinical studies have potentiated the biomechanical relevance of calcification through the derivation of links between local plaque rupture and specific macrocalcification geometrical features. The clinical implications of the data presented in this review indicate that the combination of imaging, experimental testing, and computational modelling efforts are crucial to predict the rupture risk for atherosclerotic plaques. Specialised experimental tests and modelling efforts have further enhanced the knowledge base for calcified plaque tissue mechanical properties. However, capturing the temporal instability and rupture causality in the plaque fibrous caps remains elusive. Is it necessary to move our experimental efforts down in scale towards the fundamental (sub-) micron scales in order to interpret the true mechanical behaviour of calcified plaque tissue interactions that is presented on a macroscale in the clinic and to further optimally assess calcified plaques in the context of biomechanical modelling.

Diagnostic performance of MRI for detecting intraplaque hemorrhage in the carotid arteries: a meta-analysis

OBJECTIVES

To investigate the diagnostic performance of MRI in diagnosing carotid atherosclerotic intraplaque hemorrhage (IPH) and to provide a clinical guide for MRI application.

METHODS

We searched MEDLINE, Embase, and Cochrane library from the earliest available date of indexing through November 30, 2017. All investigators screened and selected studies comparing the use of MRI with histology. The accuracy to diagnose pathological IPH was expressed by sensitivity, specificity, negative likelihood ratios (LRs), positive LRs, and the area under summary receiver-operating characteristic (SROC) curve. We calculated the post-test probability to assess the clinical utility of MRI.

RESULTS

We analyzed 696 patients from 20 articles. The sensitivity and specificity were 87% (95% CI, 81-91%) and 92% (95% CI, 87-95%), respectively. The positive and negative LRs were 10.27 (95% CI, 6.76-15.59) and 0.15 (95% CI, 0.10-0.21), respectively. The area under SROC curve was 0.95 (95% CI, 0.93-0.97). MRI was accurate in confirming or in ruling out disease over a wide range of pre-test probabilities of IPH: MRI could increase the post-test probability to > 80% in patients with a pre-test probability > 27% and could decrease the post-test probability to < 20% in patients with a pre-test probability < 64%.

CONCLUSION

Non-invasive MRI has excellent specificity and good sensitivity for diagnosing IPH. MRI is a tool for confirming or ruling out carotid atherosclerotic IPH.

KEY POINTS

• Non-invasive MRI has excellent performance for diagnosing IPH, which is a component of vulnerable plaque. • The high accuracy of MRI for IPH helps clinicians analyze the prognosis of clinical events and plan personalized treatment.

Negative Carotid Artery Remodeling in Early Type 2 Diabetes Mellitus and Increased Carotid Plaque Vulnerability in Obesity as Assessed by Magnetic Resonance Imaging

Background Ischemic stroke from carotid plaque embolism remains a major cause of morbidity in patients with type 2 diabetes mellitus (T2 DM ). However, the effect of early T2 DM and obesity on carotid remodeling and plaque burden remains elusive. We assessed carotid remodeling and plaque composition by carotid magnetic resonance imaging in patients with short-duration T2 DM compared with a sex- and age-matched control group. Methods and Results One hundred patients with T2 DM (duration <5 years) and 100 sex- and age-matched controls underwent bilateral carotid artery magnetic resonance imaging in a 1.5-T magnetic resonance imaging scanner. Plaque burden was quantified by normalized wall index, maximum wall thickness, maximum wall area, and minimum lumen size. Plaque morphology was quantified by calcified plaque volume, necrotic core volume, and loose matrix volume. Magnetic resonance imaging data were available for 149 and 177 carotid arteries from T2 DM patients and controls, respectively. Adjusted for age and sex, T2 DM was associated with increased plaque burden indicated by a higher normalized wall index (ratio 1.03 [95% confidence interval, 1.002; 1.06], P=0.03), and negative remodeling indicated by a lower minimum lumen area (ratio 0.81 [0.74; 0.89], P<0.001), and lower maximum wall area (ratio 0.94 [0.88; 1.00], P=0.048) compared with controls. In both T2 DM and controls, body mass index ≥30.0 kg/m2 was associated with an 80% increase in total calcified plaque volume, and a 44% increase in necrotic core volume compared with body mass index <25.0 kg/m2. Conclusions Short-duration T2 DM was associated with increased carotid plaque burden and negative remodeling. Obesity was associated with increased carotid artery necrotic core volume and calcification independently of diabetes mellitus status. Clinical Trial Registration URL : https://www.clinicaltrials.gov . Unique identifier: NCT 00674271.

Pathological Roles of Iron in Cardiovascular Disease

Iron is an essential mineral required for a variety of vital biological functions. Despite being vital for life, iron also has potentially toxic aspects. Iron has been investigated as a risk factor for coronary artery disease (CAD), however, iron's toxicity in CAD patients still remains controversial. One possible mechanism behind the toxicity of iron is "ferroptosis", a newly described form of irondependent cell death. Ferroptosis is an iron-dependent form of regulated cell death that is distinct from apoptosis, necroptosis, and other types of cell death. Ferroptosis has been reported in ischemiareperfusion (I/R) injury and several other diseases. Recently, we reported that ferroptosis is a significant form of cell death in cardiomyocytes. Moreover, myocardial hemorrhage, a major event in the pathogenesis of heart failure, could trigger the release of free iron into cardiac muscle and is an independent predictor of adverse left ventricular remodeling after myocardial infarction. Iron deposition in the heart can now be detected with advanced imaging methods, such as T2 star (T2*) cardiac magnetic resonance imaging, which can non-invasively predict iron levels in the myocardium and detect myocardial hemorrhage, thus existing technology could be used to assess myocardial iron. We will discuss the role of iron in cardiovascular diseases and especially with regard to myocardial I/R injury.

The association between carotid intraplaque hemorrhage and outcomes of carotid stenting: a systematic review and meta-analysis

BACKGROUND AND PURPOSE

The purpose of this systematic review and meta-analysis was to determine whether carotid stenting patients with intraplaque hemorrhage (IPH) identified on preoperative MRI were more likely to suffer perioperative ischemic complications compared with patients without IPH.

METHODS

We conducted a comprehensive literature search of studies published between January 1, 2005 and December 31, 2015 reporting perioperative outcomes of carotid stenting among patients with and without IPH on hemorrhage sensitive carotid MRI sequences. Clinical outcomes included perioperative (≤30 days post-stenting) minor stroke, major stroke, death, and a composite outcome combining stroke, death, and myocardial infarction (MI). We also compared the rate of silent ischemia on diffusion weighted imaging (DWI) between groups. Statistical analysis was performed using a random effects meta-analysis.

RESULTS

9 studies with 491 unique patients (198 in the IPH group and 293 in the non-IPH group) were included. The rate of the composite outcome of any stroke, death, or MI within 30 days was 8.1% (13/160) in the IPH group and 2.1% (5/239) in the non-IPH group (OR=4.45, 95% CI 1.61 to 12.30, p<0.01). There were no significant differences between groups in the rates of minor stroke, major stroke, or death when considered individually. The rate of postoperative infarct on DWI was 49.7% (75/161) for the IPH group and 33.6% (81/241) for the non-IPH group (OR=2.01, 95% CI 1.31 to 3.09, p<0.01).

CONCLUSIONS

Our systematic review and meta-analysis demonstrated that patients with IPH on pre-carotid stenting MRI had higher rates of silent ischemia as well as of a composite outcome of perioperative stroke, death, and MI compared with those without IPH.

Evaluation of Fibrous Cap Rupture of Atherosclerotic Carotid Plaque with Thin-Slice Source Images of Time-of-Flight MR Angiography

OBJECTIVE

To investigate the ability of source image of time-of-flight magnetic resonance angiography (TOF-MRA) in the detection of fibrous cap rupture of atherosclerotic carotid plaques.

MATERIALS AND METHODS

From the database of radiological information in our hospital, 35 patients who underwent carotid MR imaging and subsequent carotid endoarterectomy within 2 weeks were included in this retrospective study. MR imaging included thin-slice time-of-flight MR angiography, black-blood T1- and T2-weighted imaging. Sensitivity, specificity and accuracy were calculated for the detection of fibrous cap rupture with source image of TOF-MRA. The Cohen k coefficient was also calculated to quantify the degree of concordance of source image of TOF-MRA with histopathological data.

RESULTS

Sensitivity, specificity and accuracy in the detection of fibrous cap rupture were 90% (95%CI: 81-98), 69% (95%CI: 56-82) and 79% (95%CI: 71-87) with a k value of 0.59. The false positives (n = 15) were caused by partial-volume averaging between fibrous cap and lumen at the shoulder of carotid plaque. The false negatives (n = 5) were underestimated as partial thinning of fibrous cap.

CONCLUSION

Source image of TOF-MRA can be useful in the detection of fibrous cap rupture with high sensitivity, but further technical improvement should be necessary to overcome shortcomings causing image degradation.

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.

Grading of carotid artery stenosis in the presence of extensive calcifications: dual-energy CT angiography in comparison with contrast-enhanced MR angiography

PURPOSE

We investigated the agreement of dual-energy computed tomography angiography (DE-CTA) and contrast-enhanced magnetic resonance angiography (CE-MRA)in the quantitative measurement of stenoses of the internal carotid artery in comparison with digital subtraction angiography (DSA).

METHODS

A total of 21 patients with stenoses of the external carotid artery were investigated with a DE-CTA and CE-MRA before undergoing carotid angioplasty. The grade of the stenoses was assessed in axial multiplanar reformations (MPR) before and multi-intensity projections (MIP) after plaque subtraction (PS) and compared with results from CE-MRA and DSA according to the North American Symptomatic Carotid Endarterectomy Trial.

RESULTS

Average grades of stenoses were 80.7 ± 16.1 % (DSA), 81.4 ± 15.3 % (MRA), 80.0 ± 16.7 % (DE-CTA-MPR), and 85.2 ± 14.7 % (DE-CTA-PS-MIP). Of 21 stenoses, 6 were filiform (stenosis grade, 99 %) in the DSA examination. Five of these cases were identified as pseudo-occlusions in MRA, while four were considered as occlusions in DE-CTA-PS-MIP. Another four cases were identified as pseudo-occlusion in DE-CTA-PS-MIP, which were identified as 90 % stenosis in the DSA examination.

CONCLUSIONS

In comparison with the gold standard DSA, DE-CTA-MPR had a slightly better agreement in measuring the degree of stenosis of the internal carotid arteries than CE-MRA. In DE-CTA-PS-MIP images, a systematic overestimation has to be taken into account due to partial extinction of the lumen by the PS algorithm. Nevertheless, DE-CTA should be preferred in imaging patients with carotid artery stenosis in the presence of extensive calcifications.

Comparison of carotid arterial morphology and plaque composition between patients with acute coronary syndrome and stable coronary artery disease: a high-resolution magnetic resonance imaging study

The purpose of this study was to evaluate the differences in carotid arterial morphology and plaque composition between patients with acute coronary syndrome (ACS) and patients with stable coronary artery disease (SCAD). Twenty-eight patients (12 ACS patients and 16 SCAD patients) underwent carotid high-resolution MRI examination using a 3.0-Tesla (3.0T) MRI scanner. The indicators of carotid arterial morphology included the maximum total vessel area (Max-TVA), mean TVA, minimum lumen area (Min-LA), mean LA, maximum wall area (Max-WA), mean WA, maximum wall thickness (Max-WT), mean WT, maximum normalized wall index (Max-NWI), mean NWI, and maximum stenosis (Max-stenosis). The indicators of plaque composition included the prevalence and mean area percentage (%) of lipid-rich necrotic core (LRNC), calcification (Ca), intraplaque hemorrhage (IPH), and fibrous cap rupture (FCR). None of the indicators of carotid arterial morphology had significant differences (all P > 0.05) between the ACS and SCAD patients. The prevalence and plaque composition area percentage of LRNC, Ca, and IPH did not exhibit significant differences between the two groups. However, carotid plaques in the ACS patients presented a higher prevalence of FCR than SCAD patients (P < 0.05). This study revealed a similar carotid arterial morphology between ACS and SCAD patients. However, FCR is more common in carotid plaques with ACS than in those with SCAD. Ruptured carotid plaques may be a forewarning factor for those patients who are at high risk of ACS.

Carotid MRI: a tool for monitoring individual response to cardiovascular therapy?

Stroke remains a leading cause of morbidity and mortality. While stroke-related mortality has declined over the past four decades, data indicate that the mortality rate has begun to plateau. This change in trend may be attributable to variation in individual response to therapies that were derived from population-based studies. Further reductions in stroke mortality may require individualized care governed by directly monitoring the effects of cardiovascular therapy. In this article, carotid MRI is considered as a tool for monitoring in vivo carotid atherosclerotic disease, a principal etiology of stroke. Carotid MRI has been previously utilized to identify specific plaque features beyond luminal stenosis that are predictive of transient ischemic attack and stroke. To gain perspective on the possibility of monitoring plaque change within the individual, clinical trials and natural history studies that have used serial carotid MRI are considered. Data from these studies indicate that patients with a lipid-rich necrotic core with or without intraplaque hemorrhage may represent the desired phenotype for monitoring treatment effects in the individual. Advances in tissue-specific sequences, acquisition resolution, scan time, and techniques for monitoring inflammation and mechanical forces are expected to enable earlier detection of response to therapy. In so doing, cost-effective multicenter studies can be conducted to confirm the anticipated positive effects on outcomes of using carotid MRI for individualized care in patients with carotid atherosclerosis. In accordance, carotid MRI is poised to emerge as a powerful clinical tool for individualized management of carotid atherosclerotic disease to prevent stroke.

Noninvasive imaging of the vulnerable atherosclerotic plaque

Atherosclerosis is an inflammatory disease, complicated by progressively increasing atherosclerotic plaques that eventually may rupture. Plaque rupture is a major cause of cardiovascular events, such as unstable angina, myocardial infarction, and stroke. A number of noninvasive imaging techniques have been developed to evaluate the vascular wall in an attempt to identify so-called vulnerable atherosclerotic plaques that are prone to rupture. The purpose of the present review is to systematically investigate the accuracy of noninvasive imaging techniques in the identification of plaque components and morphologic characteristics associated with plaque vulnerability, assessing their clinical and diagnostic value.

Imaging of the fibrous cap in atherosclerotic carotid plaque

In the last two decades, a substantial number of articles have been published to provide diagnostic solutions for patients with carotid atherosclerotic disease. These articles have resulted in a shift of opinion regarding the identification of stroke risk in patients with carotid atherosclerotic disease. In the recent past, the degree of carotid artery stenosis was the sole determinant for performing carotid intervention (carotid endarterectomy or carotid stenting) in these patients. We now know that the degree of stenosis is only one marker for future cerebrovascular events. If one wants to determine the risk of these events more accurately, other parameters must be taken into account; among these parameters are plaque composition, presence and state of the fibrous cap (FC), intraplaque haemorrhage, plaque ulceration, and plaque location. In particular, the FC is an important structure for the stability of the plaque, and its rupture is highly associated with a recent history of transient ischaemic attack or stroke. The subject of this review is imaging of the FC.

Vulnerable plaque: definition, diagnosis, and treatment

This article provides a systematic approach to vulnerable plaques. It is divided into 4 sections. The first section is devoted to definition, incidence, anatomic distribution, and clinical presentation. The second section is devoted to plaque composition, setting up the foundations to understand plaque vulnerability. The third section relates to invasive plaque imaging. The fourth section is devoted to therapy, from conservative pharmacologic options to aggressive percutaneous coronary intervention alternatives.

Minimization of MR contrast weightings for the comprehensive evaluation of carotid atherosclerotic disease

OBJECTIVE

Multicontrast, high-resolution carotid magnetic resonance imaging (MRI) has been validated with histology to quantify atherosclerotic plaque morphology and composition. For evaluating the lipid-rich necrotic core (LRNC) and fibrous cap, both of which are key elements in determining plaque stability, the combined pre- and postcontrast T1-weighted (T1W) sequences have been recently shown to have a higher reproducibility than other contrast weightings. In this study, we sought to determine whether contrast weightings beyond T1W (pre- and postcontrast) are necessary for comprehensive, quantitative, carotid plaque interpretation.

MATERIALS AND METHODS

Our HIPAA compliant study protocol was approved by the IRB and all participants gave written, informed consent. Sixty-five participants with carotid stenosis >50% detected by ultrasound underwent carotid MRI with a standard multicontrast protocol (time-of-flight [TOF], T1W, contrast-enhanced [CE]-T1W, proton density [PD], and T2W). For each subject, images were partitioned into 3 combinations of contrast weightings (CW): (1) 2CW: T1W and CE-T1W; (2) 3CW: T1W, CE-T1W, and TOF; and (3) 5CW: T1W, CE-T1W, TOF, PD, and T2W. Each CW set was interpreted by 2 reviewers, blinded to results of each of the other CW combinations, via consensus opinion. Wall, lumen, and total vessel volumes, along with mean wall thickness were recorded. The presence or absence of calcification, LRNC, intraplaque hemorrhage (IPH), and surface disruption was also documented.

RESULTS

Compared with 5CW, there was strong agreement in the parameters of plaque morphology for 2CW (intraclass correlation coefficient, 0.96-0.99) and 3CW (intraclass correlation coefficient, 0.97-1.00). Agreement with 5CW for the detection of plaque composition was stronger for 3CW compared with 2CW: Cohen's kappa, 0.59 versus 0.42 for calcification; 0.75 versus 0.47 for LRNC; 0.91 versus 0.88 for IPH; and 0.74 versus 0.34 for surface disruption. Using 5CW as the reference standard during receive-operating-characteristics analysis, 3CW compared with 2CW showed a larger area-under-the-curve for classifying the presence or absence of calcification (0.78 vs. 0.69), LRNC (0.98 vs. 0.69), and surface disruption (0.87 vs. 0.65), and similar area-under-the-curve in classifying IPH (0.96 vs. 0.94).

CONCLUSION

Comprehensive, quantitative carotid plaque interpretation can be performed with T1W, CE-T1W, and TOF sequences. Elimination of PD and T2W sequences from the carotid MRI protocol may result in a substantial reduction in scan time. The ability to perform plaque interpretation on images acquired within a clinically acceptable scan time may broaden the research utility of carotid MRI and increase translatability to clinical applications.

Window settings for the study of calcified carotid plaques with multidetector CT angiography

SUMMARY

CT angiography (CTA) shows high sensitivity in detecting calcified plaques, but sometimes a bias in the exact quantification of stenosis degree occurs, mainly caused by the high linear attenuation coefficient of the calcified plaques. The purpose of this technical study was to evaluate the most appropriate CT window parameters for the assessment of calcified plaques stating which of them can provide the best inter-observer agreement. Scatter-plots and regression results showed the correlation between both width and level respectively depending on intraluminal Hounsfield units (HU) value (width = intraluminal HU x 2.07; level = intraluminal HU x 0.72). Obtained data indicated that the presence of different stenosis degrees did not modify visualization parameters.

Variability of carotid artery measurements on 3-Tesla MRI and its impact on sample size calculation for clinical research

Carotid MRI measurements are increasingly being employed in research studies for atherosclerosis imaging. The majority of carotid imaging studies use 1.5 T MRI. Our objective was to investigate intra-observer and inter-observer variability in carotid measurements using high resolution 3 T MRI. We performed 3 T carotid MRI on 10 patients (age 56 +/- 8 years, 7 male) with atherosclerosis risk factors and ultrasound intima-media thickness > or =0.6 mm. A total of 20 transverse images of both right and left carotid arteries were acquired using T2 weighted black-blood sequence. The lumen and outer wall of the common carotid and internal carotid arteries were manually traced; vessel wall area, vessel wall volume, and average wall thickness measurements were then assessed for intra-observer and inter-observer variability. Pearson and intraclass correlations were used in these assessments, along with Bland-Altman plots. For inter-observer variability, Pearson correlations ranged from 0.936 to 0.996 and intraclass correlations from 0.927 to 0.991. For intra-observer variability, Pearson correlations ranged from 0.934 to 0.954 and intraclass correlations from 0.831 to 0.948. Calculations showed that inter-observer variability and other sources of error would inflate sample size requirements for a clinical trial by no more than 7.9%, indicating that 3 T MRI is nearly optimal in this respect. In patients with subclinical atherosclerosis, 3 T carotid MRI measurements are highly reproducible and have important implications for clinical trial design.

Detection of unstable carotid artery stenosis using MRI

BACKGROUND AND PURPOSE

Carotid artery stenosis can be classified by magnetic resonance imaging (MRI) as lesion types I-VIII according to a modified histological scheme based on American Heart Association (AHA) guidelines. Lesion types IV-V and VI are regarded as high-risk plaques.We aimed to evaluate the clinical relevance of this classification for identifying unstable plaques.

METHODS

Eighty-five patients (29 female) with severe carotid artery stenosis (diagnosed by Doppler and duplex ultrasonography) were imaged using a 1.5 T scanner with bilateral phased-array carotid coils. T1-, T2-, time-offlight (TOF) and proton-density (PD)-weighted studies were obtained. The carotid plaques were classified as lesion types III-VIII according to the MRI-modified AHA criteria.

RESULTS

Thirty-five patients presented with a recently symptomatic stenosis; 50 patients were asymptomatic. Lesion types IV-V (51.4 % vs. 22 %) and VI (20 % vs. 4%; P < 0.0001) were found significantly more often in symptomatic patients compared to those without a history of cerebral ischemia.

CONCLUSIONS

The distribution of lesion types differs significantly between symptomatic and asymptomatic carotid artery stenosis. High-risk lesion types IV-V and VI were overrepresented in recently symptomatic patients. MRI according to the modified AHA-criteria may be a suitable tool for detection of unstable carotid lesions.

From vulnerable plaque to vulnerable patient: the search for biomarkers of plaque destabilization

There is a strong need for biomarkers to identify patients at risk for future cardiovascular events related with progressive atherosclerotic disease. Ideally, increasing knowledge of the mechanisms of atherosclerotic plaque destabilization should be translated in clinical practice. Currently, the following commonly followed strategies can be identified with the objective to detect either the local vulnerable plaque that is prone to rupture and gives rise to a thrombotic occlusion, or the systemic vulnerable patient, who has a high probability to suffer from an adverse clinical event. On the one hand, studies are ongoing to determine local atherosclerotic plaque characteristics to predict future local plaque rupture and subsequent vascular thrombosis. Newly developed imaging modalities are being developed and validated to detect these plaques in vivo. On the other hand, systemic approaches are pursued to discover serum biomarkers that are applicable to define patients at risk for future cardiovascular events. We propose a third original approach that is optional but yet unexplored, that is, to use local plaque characteristics as a biomarker not just for local plaque destabilization but for future cardiovascular events due to plaque progression in any vascular system. This review aims to provide an overview of the current standings of the identification of the vulnerable plaque and the vulnerable patient.