MR carotid plaque imaging and contrast-enhanced MR angiography identifies lesions associated with recent ipsilateral thromboembolic symptoms: an in vivo study at 3T.

BACKGROUND AND PURPOSE: Recent research has suggested the importance of plaque composition to identify patients at risk for stroke. This study aims to identify specific plaque features on 3T carotid MR imaging and CE-MRA associated with recent carotid thromboembolic symptoms in patients with mild/moderate versus severe stenosis. MATERIALS AND METHODS: Ninety-seven consecutive patients (symptomatic, 13; asymptomatic, 84) with 50%-99% stenosis by sonography or CT angiography underwent carotid plaque imaging combined with MRA at 3T. The symptomatic carotid artery or the most stenotic asymptomatic carotid artery was chosen as the index vessel to be analyzed. Plaque features were compared by symptomatic status in patients with mild/moderate (30%-70%) versus severe (70%-99%) stenosis on MRA. RESULTS: Ninety (92.8%) patients had sufficient image quality for interpretation. In 50 patients with mild/moderate stenosis, there were significant associations between the presence of the following plaque characteristics and symptoms: thin/ruptured fibrous cap (100% versus 36%, P = .006) and lipid-rich necrotic core (100% versus 39%, P = .022), with marginal association with hemorrhage (86% versus 33%, P = .055). In 40 patients with severe stenosis, only the angiographic presence of ulceration (86% versus 36%, P = .039) was associated with symptoms. CONCLUSIONS: Several plaque components identified on 3T MR imaging are correlated with recent ipsilateral carotid thromboembolic symptoms. These preliminary results also suggest that associations between plaque characteristics and symptom history may vary by degree of stenosis. If confirmed in larger studies, carotid MR imaging may distinguish stable from unstable lesions, particularly in individuals with mild/moderate stenosis in whom the role of surgical intervention is currently unclear.

A noninvasive imaging approach to assess plaque severity: the carotid atherosclerosis score.

BACKGROUND AND PURPOSE: The presence of IPH and/or FCR in the carotid atherosclerotic plaque indicates a high-risk lesion. The aim of this multicenter cross-sectional study was to establish the characteristics of lesions that may precede IPH and/or FCR. We further sought to construct a CAS that stratifies carotid disease severity. MATERIALS AND METHODS: Three hundred forty-four individuals from 4 imaging centers with 16%-99% carotid stenosis by duplex sonography underwent carotid MR imaging. In approximately 60% of the study sample (training group), multivariate analysis was used to determine factors associated with IPH and FCR. Statistically significant parameters identified during multivariate analysis were used to construct CAS. CAS was then applied to the remaining arteries (40%, test group), and the accuracy of classification for determining the presence versus absence of IPH or, separately, FCR was determined by ROC analysis and calculation of the AUC. RESULTS: The maximum proportion of the arterial wall occupied by the LRNC was the strongest predictor of IPH (P < .001) and FCR (P < .001) during multivariate analysis of the training group. The subsequently derived CAS applied to the test group was an accurate classifier of IPH (AUC = 0.91) and FCR (AUC = 0.93). Compared with MRA stenosis, CAS was a stronger classifier of both IPH and FCR. CONCLUSIONS: LRNC quantification may be an effective complementary strategy to stenosis for classifying carotid atherosclerotic disease severity. CAS forms the foundation for a simple imaging-based risk-stratification system in the carotid artery to classify severity of atherosclerotic disease.

Predictors of surface disruption with MR imaging in asymptomatic carotid artery stenosis.

BACKGROUND AND PURPOSE: Surface disruption, either ulceration or fibrous cap rupture, has been identified as a key feature of the unstable atherosclerotic plaque. In this prospective observational study, we sought to determine the characteristics of the carotid lesion that predict the development of new surface disruption. MATERIALS AND METHODS: One hundred eight asymptomatic individuals with 50%-79% carotid stenosis underwent carotid MR imaging at baseline and at 3 years. Multicontrast imaging criteria were used to determine the presence or absence of calcification, LRNC, intraplaque hemorrhage, and surface disruption. Volume measurements of plaque morphology and the LRNC and calcification, when present, were collected. RESULTS: At baseline, 21.3% (23/108) of participants were identified with a surface disruption. After 3 years, 9 (10.6%) of the remaining 85 individuals without disruption at baseline developed a new surface disruption during follow-up. Among all baseline variables associated with new surface disruption during regression analysis, the proportion of wall volume occupied by the LRNC (percentage LRNC volume; OR per 5% increase, 2.6; 95% CI, 1.5-4.6) was the strongest classifier (AUC = 0.95) during ROC analysis. New surface disruption was associated with a significant increase in percentage LRNC volume (1.7 +/- 2.0% per year, P = .035). CONCLUSIONS: This prospective investigation of asymptomatic individuals with 50%-79% stenosis provides compelling evidence that LRNC size may govern the risk of future surface disruption. Identification of carotid plaques in danger of developing new surface disruption may prove clinically valuable for preventing the transition from stable to unstable atherosclerotic disease.

Geometric and compositional appearance of atheroma in an angiographically normal carotid artery in patients with atherosclerosis.

BACKGROUND AND PURPOSE: Arterial remodeling may enable atherosclerotic disease without luminal stenosis. We sought to assess the prevalence and characteristics of atherosclerosis in angiographically normal carotid arteries. MATERIALS AND METHODS: Forty-six arteries with 0% stenosis by MRA were evaluated with multicontrast carotid MR imaging at 3T. For each artery, the percentage wall volume (wall volume/[lumen volume + wall volume] x 100%) and the presence versus absence of an LRNC, calcification, IPH, and fibrous cap rupture were recorded. In addition, the relative size of each plaque component (eg, percentage LRNC = LRNC volume/wall volume x 100%), when present, was calculated. RESULTS: The mean of percentage wall volume in arteries with 0% stenosis was 43.0 +/- 6.9% with a range from 31.6% to 60.1%. An LRNC was present in 67.4% (31/46) of arteries, calcification was present in 65.2% (30/46), IPH was present in 8.7% (4/46), and fibrous cap rupture was present in 4.3% (2/46). In arteries with an LRNC (n = 31), the average percentage LRNC volume was 8.8 +/- 7.3% with a range from 1.0% to 31.5%. For calcification (n = 30), the mean percentage calcification volume was 3.8 +/- 4.2% with a range of 0.1%-17.4%. The mean percentage IPH volume (n = 4) was 2.7 +/- 1.7% with a range of 0.5%-4.1%. CONCLUSIONS: These findings indicate that stenosis by MRA may underestimate the presence of carotid atherosclerosis, and they demonstrate the need for improved methods for accurately identifying carotid atherosclerotic plaque severity.

A controlled evaluation of tuned-aperture computed tomography applied to digital spot mammography.

The purpose of this work was to compare the detection accuracy of 3-dimensional (3D) modalities of tuned-aperture computed tomography (TACT) with that of conventional 2-dimensional (2D) digital spot mammograms. A standardized mammographic phantom was placed beneath cadaveric breast tissues of varying densities. Five radiologists were asked to detect as many objects (specks, fibers, and low-contrast masses) as possible from 90 displays in a controlled and factorially balanced multivariate experiment. Radiographic exposure was varied systematically, and projections were averaged to ensure stochastic comparability. Scores were weighted to eliminate task-specific bias and were analyzed by multivariate analyses of variance. All display modalities based on the linear application of the 3D TACT reconstruction method yielded significantly higher detection scores for all tasks than did conventional 2D digital spot mammography, which served as the scientific control modality. This effect was found to be statistically significant (P < .001) in spite of significant variations between tissues (P < .001), observers (P < .001), and exposures (P < .01). TACT may be a promising alternative or enhancement to conventional 2D digital mammography for tasks well simulated by this experimental design.