Minako Oikawa

MR imaging of adventitial vasa vasorum in carotid atherosclerosis

Vasa vasorum in the adventitia of atherosclerotic arteries may play a role in plaque progression. In this investigation, a method for characterizing vasa vasorum in the carotid artery is proposed, in which the perfusion properties of the adventitia are probed via dynamic contrast‐enhanced (DCE) MRI. A parametric “vasa vasorum image” is automatically generated that depicts the plasma volume (vp) and transfer constant (Ktrans). The average Ktrans within the adventitia is proposed as a quantitative measurement related to the extent of the vasa vasorum. In 25 subjects with lesions meeting the requirements for carotid endarterectomy (CEA) significantly higher adventitial Ktrans of 0.155 ± 0.045 min–1 was observed, compared to 0.122 ± 0.029 min–1 in the remaining 20 subjects with moderate disease (P < 0.01). In the 25 subjects with endarterectomy specimens, histological evaluation showed that adventitial Ktrans was significantly correlated with the amount of neovasculature (R = 0.41; P = 0.04) and macrophages (R = 0.49; P = 0.01) in the excised plaque. In the remaining 20 subjects without histology, elevated adventitial Ktrans was significantly correlated with the log of C‐reactive protein (CRP) levels (R = 0.57; P = 0.01) and was elevated in active smokers compared to nonsmokers (0.141 ± 0.036 vs. 0.111 ± 0.017 min–1; P = 0.02). Because these factors are all associated with higher risk of atherosclerotic complications, these results suggest that adventitial Ktrans may be a marker of risk as well. Magn Reson Med 59:507–514, 2008.

Carotid intraplaque hemorrhage imaging at 3.0-T MR imaging: comparison of the diagnostic performance of three T1-weighted sequences.

PURPOSE To compare the diagnostic performances of three T1-weighted 3.0-T magnetic resonance (MR) sequences at carotid intraplaque hemorrhage (IPH) imaging, with histo logic analysis as the reference standard. MATERIALS AND METHODS Institutional review board approval and informed consent were obtained for this HIPAA-compliant study. Twenty patients scheduled for carotid endarterectomy underwent 3.0-T carotid MR imaging, including two-dimensional fast spin-echo, three-dimensional time-of-flight (TOF), and three-dimensional magnetization-prepared rapid acquisition gradient-echo (RAGE) sequences. Two reviewers blinded to the histologic findings assessed the presence, area, and signal intensity of IPH with each sequence. Detection statistics (sensitivity, specificity, and Cohen kappa values) and agreement between area measurements (Pearson correlation coefficient [r] values) were calculated for each sequence. RESULTS When all 231 available MR sections were included for analysis, the magnetization-prepared RAGE (kappa = 0.53) and fast spin-echo (kappa = 0.42) sequences yielded moderate agreement between MR and histologic measurements, while the TOF sequence yielded fair agreement (k = 0.33). However, when 47 sections with either small IPHs or heavily calcified IPHs were excluded, sensitivity, specificity, and kappa values, respectively, were 80%, 97%, and 0.80 for magnetization-prepared RAGE imaging; 70%, 92%, and 0.63 for fast spin-echo imaging; and 56%, 96%, and 0.57 for TOF imaging. MR imaging-histologic analysis correlation for IPH area was highest with magnetization-prepared RAGE imaging (r = 0.813), followed by TOF (r = 0.745) and fast spin-echo (r = 0.497) imaging. The capability of these three sequences for IPH detection appeared to be in good agreement with the quantitative contrast of IPH versus background plaque tissue. CONCLUSION The magnetization-prepared RAGE sequence, as compared with the fast spin-echo and TOF sequences, demonstrated higher diagnostic capability for the detection and quantification of IPH. Potential limitations of 3.0-T IPH MR imaging are related to hemorrhage size and coexisting calcification.

Carotid plaque morphology and composition: initial comparison between 1.5- and 3.0-T magnetic field strengths.

PURPOSE To prospectively compare the interpretation and quantification of carotid vessel wall morphology and plaque composition at 1.5-T with those at 3.0-T magnetic resonance (MR) imaging. MATERIALS AND METHODS Twenty participants (mean age, 69.8 years [standard deviation] +/- 10.5; 75% men) with 16%-79% carotid stenosis at duplex ultrasonography were imaged with 1.5-T and 3.0-T MR imaging units with bilateral four-element phased-array surface coils. This HIPAA-compliant study was approved by the institutional review board, and all participants gave written informed consent. Protocols designed for similar signal-to-noise ratios across platforms were implemented to acquire axial T1-weighted, T2-weighted, intermediate-weighted, time-of-flight, and contrast material-enhanced T1-weighted images. Lumen area, wall area, total vessel area, wall thickness, and presence or absence and area of plaque components were documented. Continuous variables from different field strengths were compared by using the intraclass correlation coefficient (ICC) and repeated measures analysis. The Cohen kappa was used to evaluate agreement between 1.5 T and 3.0 T on compositional dichotomous variables. RESULTS There was a strong level of agreement between field strengths for all morphologic variables, with ICCs ranging from 0.88 to 0.96. Agreement in the identification of presence or absence of plaque components was very good for calcification (kappa = 0.72), lipid-rich necrotic core (kappa = 0.73), and hemorrhage (kappa = 0.66). However, the visualization of hemorrhage was greater at 1.5 T than at 3.0 T (14.7% vs 7.8%, P < .001). Calcifications measured significantly (P = .03) larger at 3.0 T, while lipid-rich necrotic cores without hemorrhage were similar between field strengths (P = .9). CONCLUSION At higher field strengths, the increased susceptibility of calcification and paramagnetic ferric iron in hemorrhage may alter quantification and/or detection. Nevertheless, imaging criteria at 1.5 T for carotid vessel wall interpretation are applicable at 3.0 T.

MRI of Cardiac Sarcoidosis: Basal and Subepicardial Localization of Myocardial Lesions and Their Effect on Left Ventricular Function

OBJECTIVE The objective of our study was to use MRI to analyze the topographic localization of myocardial lesions and their relationship to plasma brain natriuretic peptide (BNP) levels and several cardiac function parameters in patients with cardiac sarcoidosis. MATERIALS AND METHODS Delayed contrast-enhanced MRI was performed in 40 patients with sarcoidosis (11 cardiac, 29 extracardiac cases). Using a 29-segment model of the left ventricle (LV), the extent of myocardial hyperenhancement was visually scored (0 = no hyperenhancement, 1 = 1-25%, 2 = 26-50%, 3 = 51-75%, 4 = 76-100% hyperenhancement) and was compared with plasma BNP level and several parameters of cardiac function. RESULTS Ten of the 11 patients with cardiac sarcoidosis showed myocardial hyperenhancement, whereas none of the 29 patients without cardiac sarcoidosis did. In patients with cardiac sarcoidosis, hyperenhancement was significantly more extensive in basal short axis slices than in apical short axis slices (p < 0.0005). Myocardial hyperenhancement was significantly more frequent in subepicardial layers than in subendocardial layers. The global extent of myocardial hyperenhancement was significantly correlated with plasma BNP levels and the LV end-diastolic volume index and was negatively correlated with the LV ejection fraction. CONCLUSION In patients with cardiac sarcoidosis, myocardial lesions detected on delayed contrast-enhanced MRI were predominantly localized in the basal and subepicardial myocardium. The extent of myocardial lesions may be related to LV dysfunction and plasma BNP level in patients with cardiac sarcoidosis.

Arterial Remodeling in the Subclinical Carotid Artery Disease

OBJECTIVES We sought to identify clinical and/or plaque characteristics that affect atherosclerotic disease progression and arterial remodeling in the carotid artery with subclinical stenosis. BACKGROUND Increasing severity of stenosis has been associated with a higher risk of stroke. Factors that drive subclinical lesions to become stenotic plaques remain ambiguous. Carotid magnetic resonance imaging (MRI) has been validated with histology to accurately quantify in vivo arterial morphology and plaque composition. METHODS A total of 67 asymptomatic participants with 16% to 49% carotid stenosis as demonstrated by duplex ultrasonography were imaged at 1.5-T with a carotid MRI protocol at baseline and at 18-month follow-up. Clinical and/or intra-arterial metrics with a significant association with change in plaque burden during multivariate analysis were evaluated for effects on lumen, wall, and total vessel volume. RESULTS From multiple regression analysis, intraplaque hemorrhage (IPH) (p < 0.001) and statin therapy (p = 0.015) were identified as key determinants of change in plaque burden. The group with IPH compared with the group without IPH demonstrated luminal narrowing, with a mean +/- SD decrease in lumen volume (-24.9 +/- 21.1 mm(3)/year vs. -0.5 +/- 26.9 mm(3)/year; p = 0.005), a larger increase in wall volume (44.1 +/- 36.1 mm(3)/year vs. 0.8 +/- 34.5 mm(3)/year; p < 0.001), and no difference in total vessel volume (19.3 +/- 27.4 mm(3)/year vs. 0.4 +/- 42.4 mm(3)/year; p = 0.15). The nonstatin group compared with the statin group demonstrated outward remodeling, with an increase in wall volume (22.4 +/- 35.6 mm(3)/year(3)/year vs. 0.9 +/- 38.0 mm(3)/year; p = 0.026) and total vessel volume (19.2 +/- 36.9 mm(3)/year vs. -4.9 +/- 40.4 mm(3)/year; p = 0.019) and no difference in lumen volume (-5.8 +/- 26.6 mm(3)/year vs. -3.2 +/- 29.5 mm(3)/year; p = 0.72). CONCLUSIONS IPH may represent an indication of accelerated plaque growth and impending luminal compromise in the subclinical carotid artery. Statin therapy may stabilize lesions by slowing or halting lesion progression. This phase of plaque stenosis (16% to 49%) may be a critical stage for intrinsic and extrinsic factors to affect the atherosclerotic disease process.

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.

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.

Discriminating Carotid Atherosclerotic Lesion Severity by Luminal Stenosis and Plaque Burden: A Comparison Utilizing High-Resolution Magnetic Resonance Imaging at 3.0 Tesla

Background and Purpose— To determine associations between stenosis, measures of plaque burden, and compositional features of carotid atherosclerosis, including high-risk features of intraplaque hemorrhage (IPH) and surface disruption. Methods— Institutional Review Board approval and informed consent for all participants were obtained before study initiation. Patients with either carotid stenosis >50% by duplex ultrasound or suspected coronary artery disease underwent multi-contrast carotid MRI at 3.0 T. For each artery, stenosis, percent wall volume (PWV=100%×wall volume/total vessel volume), and mean wall thickness (MWT) were measured. Presence or absence of a lipid-rich necrotic core, calcification, IPH, and surface disruption were recorded. Results— One hundred eighty-one patients were included in the final analysis. The area under the curve (AUC) calculated from receiver-operating-characteristics analysis found the presence of IPH was similarly classified by stenosis (AUC=0.82), PWV (AUC=0.88), and MWT (AUC=0.88). Notably, IPH was present in the lowest category of each parameter. Prevalence of IPH in arteries with 0% stenosis was 4.4%. In arteries with PWV <40%, prevalence was 3.2%; in arteries with MWT <1.0 mm, prevalence was 2.3%. Strength of classification for surface disruption was similarly classified by stenosis (AUC=0.87), PWV (AUC=0.93), and MWT (AUC=0.94). Conclusions— Measures of plaque burden do not substantially improve disease assessment compared to stenosis. The finding of IPH in all categories of stenosis and plaque burden suggests that direct characterization of plaque composition and surface status is necessary to fully discriminate disease severity.

MRI of Carotid Atherosclerosis

SummaryMRI of carotid atherosclerosis provides a unique method to characterize plaque morphology and tissue composition, as well as, to a certain extent, plaque inflammation. Because of its noninvasiveness, it has many current and potential applications: the fact that it is the only technique that can examine the fibrous cap status in vivo makes it a powerful tool to identify high-risk plaques. With quantitative measurement achievable on a series of plaque compositional and morphologic features, this technique is also well suited for studying atherosclerosis progression and regression. This technique can also be combined with other imaging modalities such as ultrasound and nuclear medicine to create a comprehensive evaluation of carotid atherosclerosis from tissue compliance and composition to inflammation.

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] × 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 × 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.