Vulnerable Plaque Imaging

The incomplete circle of Willis is associated with vulnerable intracranial plaque features and acute ischemic stroke

BACKGROUND

The circle of Willis (CoW) plays a significant role in intracranial atherosclerosis (ICAS). This study investigated the relationship between different types of CoW, atherosclerosis plaque features, and acute ischemic stroke (AIS).

METHODS

We investigated 97 participants with AIS or transient ischemic attacks (TIA) underwent pre- and post-contrast 3T vessel wall cardiovascular magnetic resonance within 7 days of the onset of symptoms. The culprit plaque characteristics (including enhancement grade, enhancement ratio, high signal in T1, irregularity of plaque surface, and normalized wall index), and vessel remodeling (including arterial remodeling ratio and positive remodeling) for lesions were evaluated. The anatomic structures of the anterior and the posterior sections of the CoW (A-CoW and P-CoW) were also evaluated. The plaque features were compared among them. The plaque features were also compared between AIS and TIA patients. Finally, univariate and multivariate regression analysis was performed to evaluate the independent risk factors for AIS.

RESULT

Patients with incomplete A-CoW showed a higher plaque enhancement ratio (P = 0.002), enhancement grade (P = 0.01), and normalized wall index (NWI) (P = 0.018) compared with the patients with complete A-CoW. A higher proportion of patients with incomplete symptomatic P-CoW demonstrated more culprit plaques with high T1 signals (HT1S) compared with those with complete P-CoW (P = 0.013). Incomplete A-CoW was associated with a higher enhancement grade of the culprit plaques [odds ratio (OR):3.84; 95% CI: 1.36-10.88, P = 0.011], after adjusting for clinical risk factors such as age, sex, smoking, hypertension, hyperlipemia, and diabetes mellitus. Incomplete symptomatic P-CoW was associated with a higher probability of HT1S (OR:3.88; 95% CI: 1.12-13.47, P = 0.033), after adjusting for clinical risk factors such as age, sex, smoking, hypertension, hyperlipemia, and diabetes mellitus. Furthermore, an irregularity of the plaque surface (OR: 6.24; 95% CI: 2.25-17.37, P < 0.001), and incomplete symptomatic P-CoW (OR: 8.03, 95% CI: 2.43-26.55, P = 0.001) were independently associated with AIS.

CONCLUSIONS

This study demonstrated that incomplete A-CoW was associated with enhancement grade of the culprit plaque, and incomplete symptomatic side P-CoW was associated with the presence of HT1S of culprit plaque. Furthermore, an irregularity of plaque surface and incomplete symptomatic side P-CoW were associated with AIS.

Interstudy reproducibility of dark blood high-resolution MRI in evaluating basilar atherosclerotic plaque at 3 Tesla

PURPOSE

We aimed to evaluate the interscan, intraobserver, and interobserver reproducibility of basilar atherosclerotic plaque employing dark blood high-resolution magnetic resonance imaging (HR-MRI) at 3 Tesla.

METHODS

Sixteen patients (14 males and 2 females) with > 30% basilar stenosis as identified by conventional magnetic resonance angiography were prospectively recruited for scan and rescan examinations on a 3 Tesla MRI system using T2-weighted turbo spin-echo protocol. Two observers independently measured the areas of vessels and lumens. Wall area was derived by subtracting the lumen area from the vessel area. Areas of vessels, lumens and walls were compared for the evaluation of interscan variability of basilar plaque. To assess the intraobserver variability, one observer reevaluated all the images of the first scan after a 4-week interval.

RESULTS

Fourteen patients were included in the final analysis. No clinically significant difference was observed for interscan, intraobserver, and interobserver measurements. The intraclass correlations for vessel, lumen, and wall areas were excellent and ranged from 0.973 to 0.981 for the interscan measurements, 0.997 to 0.998 for the intraobserver measurements and 0.979 to 0.985 for the interobserver measurements. The coefficients of variation for quantitative basilar morphology measurements were 4.31%-10.35% for the interscan measurements, 1.41%-4.62% for the intraobserver measurements and 3.79%-8.46% for the interobserver measurements. Compared with the interscan and interobserver measurements, narrow intervals of the scatterplots were observed for the intraobserver measurements by Bland-Altman plots.

CONCLUSION

Basilar atherosclerotic plaque imaging demonstrates excellent reproducibility at 3 Tesla. The study proves that dark blood HR-MRI may serve as a reliable tool for clinical studies focused on the progression and treatment response of basilar atherosclerosis.

Incremental Value of Plaque Enhancement in Patients with Moderate or Severe Basilar Artery Stenosis: 3.0 T High-Resolution Magnetic Resonance Study

Aim

To investigate the clinical relevance of plaque's morphological characteristics and distribution pattern using 3.0 T high-resolution magnetic resonance imaging (HRMRI) in patients with moderate or severe basilar artery (BA) atherosclerosis stenosis.

Materials and Methods

Fifty-seven patients (33 symptomatic patients and 24 asymptomatic patients) were recruited for 3.0 T HRMRI scan; all of them had >50% stenosis on the BA. The intraplaque hemorrhage (IPH), contrast-enhancement pattern, and distribution of BA plaques were compared between the symptomatic and asymptomatic groups. Factors potentially associated with posterior ischemic stroke were calculated by multivariate analyses.

Results

Enhancement of BA plaque was more frequently observed in symptomatic than in asymptomatic patients (27/33, 81.8% versus 11/24, 45.8%; p < 0.01). In multivariate regression analysis, plaque enhancement (OR = 7.193; 95% CI: 1.880–27.517; p = 0.004) and smoking (OR = 4.402; 95% CI: 2.218–15.909; p = 0.024) were found to be independent risk factors of posterior ischemic events in patients with BA stenosis >50%. Plaques were mainly distributed at the ventral site (39.3%) or involved more than two arcs (21.2%) in the symptomatic group but were mainly distributed at left (33.3%) and right (25.0%) sites in the asymptomatic group.

High resolution MRI difference between moyamoya disease and intracranial atherosclerosis

BACKGROUND AND PURPOSE

Along with intracranial atherosclerotic disease (ICAD), moyamoya disease (MMD) is the most common cause of middle cerebral artery (MCA) occlusion in Asians. Although they have differing vascular wall pathologies, conventional angiographic evaluation methods cannot easily differentiate MMD from ICAD in certain situations, such as in young patients with atherosclerotic risk factors. High resolution magnetic resonance imaging (HR-MRI) findings for the diseased segments of MCAs in MMD and symptomatic ICAD were compared to further elucidate differences in arterial wall changes.

METHODS

Angiographically confirmed patients, 12 MMD and 20 ICAD, who suffered a stroke due to MCA occlusion were recruited and underwent HR-MRI. The size of the outer diameter and other stenotic vessel wall characteristics revealed by HR-MRI, including enhancement, eccentricity and other lesion patterns, were analyzed by two independent reviewers in a blind fashion.

RESULTS

MMD patients were younger than ICAD patients (32.92 ± 11.08 years vs. 51.85 ± 11.97 years; mean ± SD) and displayed a smaller outer diameter in the stenotic portion (1.61 ± 0.43 mm for MMD vs. 3.03 ± 0.53 mm for ICAD, P < 0.0001). Eccentric lesions (three of 12 in MMD vs. 19 of 20 in ICAD, P < 0.0001) and focal enhancements in diseased areas (two of seven in MMD vs. 13 of 17 in ICAD, P = 0.061) were less common in MMD cases.

CONCLUSIONS

Our HR-MRI findings show that MMD is associated with smaller, concentric occlusive lesions which are rarely enhanced compared with symptomatic ICAD, consistent with the results of previous pathological reports. HR-MRI may therefore have utility in differentiating MMD from ICAD.

Methods for robust in vivo strain estimation in the carotid artery

A hierarchical block-matching motion tracking algorithm for strain imaging is presented. Displacements are estimated with improved robustness and precision by utilizing a Bayesian regularization algorithm and an unbiased subsample interpolation technique. A modified least-squares strain estimator is proposed to estimate strain images from a noisy displacement input while addressing the motion discontinuity at the wall-lumen boundary. Methods to track deformation over the cardiac cycle incorporate a dynamic frame skip criterion to process data frames with sufficient deformation to produce high signal-to-noise displacement and strain images. Algorithms to accumulate displacement and/or strain on particles in a region of interest over the cardiac cycle are described. New methods to visualize and characterize the deformation measured with the full 2D strain tensor are presented. Initial results from patients imaged prior to carotid endarterectomy suggest that strain imaging detects conditions that are traditionally considered high risk including soft plaque composition, unstable morphology, abnormal hemodynamics and shear of plaque against tethering tissue can be exacerbated by neoangiogenesis. For example, a maximum absolute principal strain exceeding 0.2 is observed near calcified regions adjacent to turbulent flow, protrusion of the plaque into the arterial lumen and regions of low echogenicity associated with soft plaques. Non-invasive carotid strain imaging is therefore a potentially useful tool for detecting unstable carotid plaque.

Imaging of stroke: Part 2, Pathophysiology at the molecular and cellular levels and corresponding imaging changes

OBJECTIVE

Stroke is the third leading cause of death and the leading cause of severe disability. During the "decade of the brain" in the 1990s, the most promising development was the treatment of acute ischemic stroke. It is thought to result from a cascade of events from energy depletion to cell death. In the initial minutes to hour, clinical deficit does not necessarily reflect irreversible damage. The final outcome and residual deficit will be decided by how fast reperfusion is achieved, which in turn depends on how early the diagnosis is made. This article explains the pathophysiology of stroke at the molecular and cellular levels with corresponding changes on various imaging techniques.

CONCLUSION

The pathophysiology of stroke has several complex mechanisms. Understanding these mechanisms is essential to derive neuroprotective agents that limit neuronal damage after ischemia. Imaging and clinical strategies aimed at extending the therapeutic window for reperfusion treatment with mechanical and pharmacologic thrombolysis will add value to existing treatment strategies. Acute ischemic stroke is defined as abrupt neurologic dysfunction due to focal brain ischemia resulting in persistent neurologic deficit accompanied by characteristic abnormalities on brain imaging. Knowledge of the pathophysiologic mechanisms of neuronal injury in stroke is essential to target treatment. Neuroprotective and thrombolytic agents have been shown to improve clinical outcome. Physiologic imaging with diffusion-weighted imaging (DWI) and perfusion CT and MRI provide a pathophysiologic substrate of evolving ischemic stroke.

Coronary computed tomographic angiography (CCTA) in community hospitals: "current and emerging role"

Coronary computed tomographic angiography (CCTA) is a rapidly evolving test for diagnosis of coronary artery disease. Although invasive coronary angiography is the gold standard for coronary artery disease (CAD), CCTA is an excellent noninvasive tool for evaluation of chest pain. There is ample evidence to support the cost-effective use of CCTA in the early triage process of patients presenting with chest pain in the emergency room. CCTA plays a critical role in the diagnosis of chest pain etiology as one of potentially fatal conditions, aortic dissection, pulmonary embolism, and myocardial infarction. This 'triple rule out' protocol is becoming an increasingly practicable and popular diagnostic tool in ERs across the country. In addition to a quick triage of chest pain patients, it may improve quality of care, decrease cost, and prevent medico-legal risk for missing potentially lethal conditions presenting as chest pain. CCTA is also helpful in the detection of subclinical and vulnerable coronary plaques. The major limitations for wide spread acceptance of this test include radiation exposure, motion artifacts, and its suboptimal imaging with increased body mass index.

Identification and quantification of coronary atherosclerotic plaques: a comparison of 64-MDCT and intravascular ultrasound

OBJECTIVE

The purpose of this study was to compare the accuracy of 64-MDCT with that of intravascular ultrasound (IVUS) for the identification and quantitative analysis of coronary atherosclerotic plaques.

MATERIALS AND METHODS

Twenty-six patients (17 men, nine women; mean age, 56 years) with suspected coronary atherosclerotic disease were studied using contrast-enhanced 64-MDCT and IVUS. The coronary arteries were divided into 10-mm segments and vascular cross-sectional area (CSA), luminal CSA, and plaque burden were measured in each segment. Plaque analysis software was used to automatically detect both plaques and vessel walls on CT images. Two investigators who were blinded to IVUS results independently determined the presence, classification, and quantitative measurement of atherosclerotic plaques on the CT images, which were then compared with the IVUS images.

RESULTS

Of 40 coronary arteries, 247 of 263 segments were imaged and analyzed by both contrast-enhanced 64-MDCT and IVUS. Sixteen segments were ruled out because of poor CT image quality. Compared with IVUS, 64-MDCT enabled correct detection in 86 of 89 (96.6%) segments containing noncalcified plaques, 25 of 27 (92.6%) segments containing calcified plaques, and 118 of 131 (90.1%) segments without atherosclerotic plaques. Sensitivity, specificity, positive predictive value, and negative predictive value for the detection of plaques by 64-MDCT were 97.4%, 90.1%, 89.7%, and 97.5%, respectively. Plaque analysis software using predetermined Hounsfield unit ranges for different components of plaque was able to distinguish between fibrous, fibrous-soft, and calcified plaques to a significant degree, but was less able to distinguish between soft and fibrous, and between soft and fibrous-soft plaque. Cohen's kappa coefficient for the sole detection of atherosclerotic segments by observers was 0.91. The correlation coefficients to determine vascular CSA, luminal CSA, and plaque burden were r = 0.85, 0.82, and 0.77, respectively (p < 0.01).

CONCLUSION

Compared with IVUS, contrast-enhanced 64-MDCT has a good ability to identify and quantify coronary atherosclerotic plaques. However, the reliable differentiation of the composition of noncalcified plaques is still limited.

From vulnerable plaque to vulnerable patient--Part III: Executive summary of the Screening for Heart Attack Prevention and Education (SHAPE) Task Force report

Screening for early-stage asymptomatic cancers (eg, cancers of breast and colon) to prevent late-stage malignancies has been widely accepted. However, although atherosclerotic cardiovascular disease (eg, heart attack and stroke) accounts for more death and disability than all cancers combined, there are no national screening guidelines for asymptomatic (subclinical) atherosclerosis, and there is no government- or healthcare-sponsored reimbursement for atherosclerosis screening. Part I and Part II of this consensus statement elaborated on new discoveries in the field of atherosclerosis that led to the concept of the "vulnerable patient." These landmark discoveries, along with new diagnostic and therapeutic options, have set the stage for the next step: translation of this knowledge into a new practice of preventive cardiology. The identification and treatment of the vulnerable patient are the focuses of this consensus statement. In this report, the Screening for Heart Attack Prevention and Education (SHAPE) Task Force presents a new practice guideline for cardiovascular screening in the asymptomatic at-risk population. In summary, the SHAPE Guideline calls for noninvasive screening of all asymptomatic men 45-75 years of age and asymptomatic women 55-75 years of age (except those defined as very low risk) to detect and treat those with subclinical atherosclerosis. A variety of screening tests are available, and the cost-effectiveness of their use in a comprehensive strategy must be validated. Some of these screening tests, such as measurement of coronary artery calcification by computed tomography scanning and carotid artery intima-media thickness and plaque by ultrasonography, have been available longer than others and are capable of providing direct evidence for the presence and extent of atherosclerosis. Both of these imaging methods provide prognostic information of proven value regarding the future risk of heart attack and stroke. Careful and responsible implementation of these tests as part of a comprehensive risk assessment and reduction approach is warranted and outlined by this report. Other tests for the detection of atherosclerosis and abnormal arterial structure and function, such as magnetic resonance imaging of the great arteries, studies of small and large artery stiffness, and assessment of systemic endothelial dysfunction, are emerging and must be further validated. The screening results (severity of subclinical arterial disease) combined with risk factor assessment are used for risk stratification to identify the vulnerable patient and initiate appropriate therapy. The higher the risk, the more vulnerable an individual is to a near-term adverse event. Because <10% of the population who test positive for atherosclerosis will experience a near-term event, additional risk stratification based on reliable markers of disease activity is needed and is expected to further focus the search for the vulnerable patient in the future. All individuals with asymptomatic atherosclerosis should be counseled and treated to prevent progression to overt clinical disease. The aggressiveness of the treatment should be proportional to the level of risk. Individuals with no evidence of subclinical disease may be reassured of the low risk of a future near-term event, yet encouraged to adhere to a healthy lifestyle and maintain appropriate risk factor levels. Early heart attack care education is urged for all individuals with a positive test for atherosclerosis. The SHAPE Task Force reinforces existing guidelines for the screening and treatment of risk factors in younger populations. Cardiovascular healthcare professionals and policymakers are urged to adopt the SHAPE proposal and its attendant cost-effectiveness as a new strategy to contain the epidemic of atherosclerotic cardiovascular disease and the rising cost of therapies associated with this epidemic.