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.

Prognostic impact of myocardial interstitial fibrosis in non-ischemic heart failure. -Comparison between preserved and reduced ejection fraction heart failure.-.

BACKGROUND: Although myocardial fibrosis plays an important role in the progression of heart failure (HF), its prognostic impact still remains to be clarified. METHODS AND RESULTS: A total of 172 consecutive patients with chronic HF, who underwent cardiac catheterization and endomyocardial biopsy between January 2001 and September 2008, were examined. They were divided into 2 groups: HF with preserved ejection fraction (HFPEF; left ventricular ejection fraction [LVEF] ≥ 50%, n=81); and HF with reduced LVEF (HFREF; LVEF < 50%, n=91). The collagen volume fraction (CVF) in biopsy samples was calculated and its prognostic impact examined. Mean follow-up in the HFPEF and the HFREF groups was 41 ± 33 months and 41 ± 26 months, respectively. Although CVF was similar between the 2 groups (1.83 ± 1.54% vs. 2.07 ± 2.35%), CVF was significantly correlated with LV end-diastolic pressure in the HFREF group but not in the HFPEF group. When HF stage was adjusted, the long-term prognosis was comparable between the 2 groups. When the patients were divided into 2 groups according to median CVF, however, severe fibrosis was a significant predictor for all-cause death (P=0.014) and cardiac events (P=0.02) in the HFREF, but not in the HFPEF group. CONCLUSIONS: Myocardial fibrosis evaluated on biopsy samples is a useful indicator for long-term survival, suggesting that it may be an important therapeutic target as well.

Longitudinal distribution of mechanical stresses in carotid plaques of symptomatic patients.

BACKGROUND AND PURPOSE: Mechanical stress may contribute to plaque rupture in patients with carotid atherosclerosis. We determined longitudinal mechanical stresses in carotid atherosclerotic plaques and compared them with known markers of plaque vulnerability. METHODS: Nineteen symptomatic patients scheduled for carotid endarterectomy underwent carotid MRI with a multicontrast protocol to characterize plaque morphology and geometry. Longitudinal 2-dimensional computational models were generated from the MRI data, and the mechanical stresses were calculated. RESULTS: Peak longitudinal mechanical stresses occurred predominantly in the shoulder regions of the carotid plaque and correlated inversely with fibrous cap thickness (r(s)=-0.61; P=0.01), and increasing degrees of stenosis (r(s)=0.71; P=0.003). Peak stress levels were asymmetrically distributed longitudinally, with 50% occurring proximal to the maximal stenosis, 25% at the point of maximal stenosis, and 25% distal to the maximal stenosis. CONCLUSIONS: The peak longitudinal mechanical stresses in the fibrous caps of symptomatic patients with carotid atherosclerotic stenosis were located at known predilection sites for plaque rupture, suggesting that mechanical stresses may play a role in plaque destabilization.

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.

Localized measurement of atherosclerotic plaque inflammatory burden with dynamic contrast-enhanced MRI.

Inflammation plays an important role in progression and rupture of atherosclerotic plaque. Dynamic contrast-enhanced MRI has been proposed as a tool to evaluate inflammation in vivo by measuring the transfer constant and partial plasma volume, which are influenced by inflammation. This study sought to demonstrate the ability of dynamic contrast-enhanced MRI to provide localized measurements of transfer constant and partial plasma volume within plaque regions of different compositions. In order to do that, a highly automatic procedure for localized measurement of dynamic contrast-enhanced MRI parameters was developed. In 47 subjects, the average transfer constant and partial plasma volume were highest in loose matrix and fibrous tissue and substantially lower in intraplaque hemorrhage, lipid rich/necrotic core, and calcification. In addition, except for hemorrhage and calcification, statistically significant differences of transfer constant and partial plasma volume were observed for any pair of these components. This suggests that transfer constant and partial plasma volume could be helpful to differentiate different plaque components and that dynamic contrast-enhanced MRI has the potential to assess inflammatory burden in specific regions.

Hemorrhage and large lipid-rich necrotic cores are independently associated with thin or ruptured fibrous caps: an in vivo 3T MRI study.

OBJECTIVE: Histological studies suggest associations between hemorrhage and large lipid-rich/necrotic cores with thin or ruptured fibrous caps in advanced atherosclerosis. We investigated these associations in carotid arteries with mild to severe stenosis by in vivo 3T MRI. METHODS AND RESULTS: Seventy-seven patients with >or=50% carotid stenosis in at least one side by duplex ultrasound underwent bilateral multi-contrast carotid MRI scans. Measurements for wall and lipid-rich/necrotic core sizes, presence of hemorrhage, and fibrous cap status (classified as intact thick, intact thin or ruptured) were recorded. Arteries with poor image quality, occlusion, or no detectable lipid-rich/necrotic core were excluded. For the 798 MRI slices included, multivariate ordinal regression analysis demonstrated larger %lipid-rich/necrotic core (odds ratio for 10% increase, 1.49; P=0.02) and presence of hemorrhage (odds ratio, 5.91; P<0.001) were independently associated with a worse (intact thin or ruptured) stage of fibrous cap status. For artery-based multivariate analysis, a larger maximum %lipid-rich/necrotic core and presence of hemorrhage independently associated with worse fibrous cap status (P<0.001, for both). No hemorrhage was detected in arteries with thick fibrous caps. CONCLUSIONS: Hemorrhage and larger %lipid-rich/necrotic core were independently associated with a thin or ruptured fibrous cap status at an early to advanced stage of carotid atherosclerosis.

Identification of new prognostic factors of pulmonary hypertension.

BACKGROUND: Pulmonary hypertension (PH) still remains a serious disease, for which the plasma level of brain natriuretic peptide (BNP) and hemodynamic variables (eg, cardiac index: CI) are established prognostic factors. The aim of the present study was to identify new additional prognostic factors of the disorder to improve the management of PH. METHODS AND RESULTS: The study cohort comprised 136 consecutive PH patients admitted to hospital from 1974 to 2008, all of whom were closely followed every 6-12 months. During the follow-up period of 53.5+/-4.5 [SEM] months, 47 patients died of cardiopulmonary causes. The patients who were initially treated with monotherapy showed improved pulmonary hemodynamics when subsequently treated with combination therapy. Multivariate analysis showed that BNP and CI were significant and independent prognostic factors in all PH patients. However, in PH patients with low CI at diagnosis, only CI improvement by PH therapy was a significant and independent prognostic factor. Indeed, the patients with low CI at diagnosis (CI <2.5) followed by subsequent normalization in response to therapy (CI > or =2.5) showed a significantly better survival compared with those without such normalization. CONCLUSIONS: CI normalization in response to treatment is an independent new prognostic factor of PH in patients with low CI at diagnosis, suggesting the importance of intensive therapy to achieve CI normalization.

Carotid magnetic resonance imaging. A window to study atherosclerosis and identify high-risk plaques.

Despite recent advances in the understanding and etiology of cardiovascular disease, it remains the leading cause of morbidity and mortality worldwide. A great deal of research has been dedicated to investigating and identifying plaque instability: the so-called "vulnerable plaque". A reliable, in vivo, imaging method capable of identifying plaque characteristics associated with high-risk plaque will be immensely useful for evaluating plaque status and predicting future events. With excellent soft-tissue contrast and resolution, magnetic resonance imaging (MRI) has the ability to visualize features of vulnerable plaques, as well as perform longitudinal studies on the etiology, progression, and regression of atherosclerotic plaque. This review will cover the current state-of-the-art and new developments in carotid MRI to characterize atherosclerosis and its use in clinical diagnoses and longitudinal studies to understand mechanisms of lesion progression and regression.

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.

Differences in carotid arterial morphology and composition between individuals with and without obstructive coronary artery disease: a cardiovascular magnetic resonance study.

OBJECTIVE: We sought to determine differences with cardiovascular magnetic resonance (CMR) in the morphology and composition of the carotid arteries between individuals with angiographically-defined obstructive coronary artery disease (CAD, > or = 50% stenosis, cases) and those with angiographically normal coronaries (no lumen irregularities, controls). METHODS AND RESULTS: 191 participants (50.3% female; 50.8% CAD cases) were imaged with a multi-sequence, carotid CMR protocol at 1.5T. For each segment of the carotid, lumen area, wall area, total vessel area (lumen area + wall area), mean wall thickness and the presence or absence of calcification and lipid-rich necrotic core were recorded bilaterally. In male CAD cases compared to male controls, the distal bulb had a significantly smaller lumen area (60.0 +/- 3.1 vs. 79.7 +/- 3.2 mm2, p < 0.001) and total vessel area (99.6 +/- 4.0 vs. 119.8 +/- 4.1 mm2; p < 0.001), and larger mean wall thickness (1.25 +/- 0.03 vs. 1.11 +/- 0.03 mm; p = 0.002). Similarly, the internal carotid had a smaller lumen area (37.5 +/- 1.8 vs. 44.6 +/- 1.8 mm2; p = 0.006) and smaller total vessel area (64.0 +/- 2.3 vs. 70.9 +/- 2.4 mm2; p = 0.04). These metrics were not significantly different between female groups in the distal bulb and internal carotid or for either gender in the common carotid. Male CAD cases had an increased prevalence of lipid-rich necrotic core (49.0% vs. 19.6%; p = 0.003), while calcification was more prevalent in both male (46.9% vs. 17.4%; p = 0.002) and female (33.3% vs. 14.6%; p = 0.031) CAD cases compared to controls. CONCLUSION: Males with obstructive CAD compared to male controls had carotid bulbs and internal carotid arteries with smaller total vessel and lumen areas, and an increased prevalence of lipid-rich necrotic core. Carotid calcification was related to CAD status in both males and females. Carotid CMR identifies distinct morphological and compositional differences in the carotid arteries between individuals with and without angiographically-defined obstructive CAD.

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.

Temporal change in brain natriuretic Peptide after radiotherapy for thoracic esophageal cancer.

PURPOSE: To investigate the relationships of plasma levels of brain natriuretic peptide (BNP) with abnormal (18)F-fluorodeoxyglucose (FDG) accumulation in the myocardium corresponding to irradiated fields and temporal changes in BNP, which is used as an index of heart remodeling, after radiotherapy for the mediastinum. MATERIALS AND METHODS: Brain natriuretic peptide concentrations were measured before and after radiotherapy for thoracic esophageal cancer, and the change in BNP concentration after radiotherapy was investigated. Moreover, FDG accumulation in the myocardium was investigated in patients who had undergone FDG positron emission tomography less than 14 days before or after measurement of BNP concentration, and the Mann-Whitney U test was used to detect significant difference between BNP concentrations in patients with and without abnormal FDG accumulation corresponding to the irradiated field. RESULTS: There was significant difference between the levels of BNP in patients without abnormal FDG accumulation in the irradiated myocardium and in patients with abnormal FDG accumulation (p < 0.001). The levels of BNP in the 9-24 months after radiotherapy group and in the >24 months after radiotherapy group were significantly higher than the levels in the before radiotherapy group, immediately after radiotherapy group, 1-2 months after radiotherapy group, and control group. CONCLUSIONS: The level of BNP was significantly increased more than 9 months after the start of radiotherapy and was significantly higher in patients who had high FDG accumulation corresponding to the irradiated field. The results of this study indicate that BNP concentration might be an early indicator of radiation-induced myocardial damage.

Increased [18F]fluorodeoxyglucose accumulation in right ventricular free wall in patients with pulmonary hypertension and the effect of epoprostenol.

OBJECTIVES: We examined whether right ventricular (RV) [(18)F]fluorodeoxyglucose (FDG) accumulation is increased in patients with pulmonary hypertension using gated positron emission tomography (PET) and whether RV FDG accumulation changes after therapy with epoprostenol. BACKGROUND: Myocardial glucose utilization is increased in animal models with ventricular pressure overload. METHODS: We performed gated FDG-PET in 24 patients with pulmonary hypertension. The RV standardized uptake value (SUV) of FDG was corrected for the partial volume effect based on the wall thickness measured by electron-beam computed tomography or magnetic resonance imaging. RESULTS: The corrected RV SUV of FDG was significantly correlated with the pulmonary vascular resistance, mean pulmonary artery pressure, right atrial pressure, RV wall stress, and plasma brain natriuretic peptide levels, but not with the RV wall thickness and mass. After pulmonary vasodilator therapy with epoprostenol for three months, the corrected RV SUV of FDG significantly decreased in the responders, but not in the non-responders, and the percentage change of the corrected RV SUV of FDG was significantly correlated with the percentage change of the pulmonary vascular resistance (r = 0.78; p < 0.01) and RV systolic wall stress (r = 0.76; p < 0.05). CONCLUSIONS: The RV FDG accumulation corrected for the partial volume effect was significantly increased in accordance with the severity of the RV pressure overload (i.e., the RV peak-systolic wall stress) in patients with pulmonary hypertension. Furthermore, the corrected RV FDG accumulation was decreased after the treatment with epoprostenol in accordance with the degree of reduction in the pulmonary vascular resistance and RV peak-systolic wall stress.

The utility of 18F-fluorodeoxyglucose positron emission tomography for early diagnosis of radiation-induced myocardial damage.

PURPOSE: We evaluated the clinical significance of focal increased uptake in the basal myocardium on F-fluorodeoxyglucose positron emission tomography (FDG-PET) in patients with esophageal cancer after radiotherapy. METHODS AND MATERIALS: Between August 2004 and July 2005, a total of 64 patients who had been irradiated for thoracic esophageal cancer underwent FDG-PET at least three months after the completion of chemoradiotherapy. Some patients showed increased FDG uptake in the basal portion of the myocardium. To clarify the clinical significance of these findings, further examinations of hearts were performed. The dose distribution in the myocardium with high FDG uptake was also analyzed retrospectively. RESULTS: Thirteen (20.3%) of the 64 patients showed high FDG uptake in the basal myocardium corresponding to the irradiated fields compared with FDG uptake in the myocardium outside the irradiated fields. Eight of the 13 patients consented to undergo examinations of the heart. Five of those eight patients showed low 123I-BMIPP uptake and four showed low 201TlCl uptake in the myocardium corresponding with high FDG uptake regions. In two patients, delayed enhancement was found in some parts of the area with high FDG uptake on Gd-DTPA magnetic resonance imaging (MRI), and the delay-enhanced lesion showed hypokinesia on cine-MRI in one patient. CONCLUSIONS: FDG-PET often shows focal increased uptake in the basal myocardium after radiotherapy for esophageal cancer. This finding indicates the possibility of radiation-induced cardiac damage, and cardiac function and symptoms of such patients should be followed carefully.

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.

Arterial remodeling in [corrected] 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.

Signal features of the atherosclerotic plaque at 3.0 Tesla versus 1.5 Tesla: impact on automatic classification.

PURPOSE: To investigate the impact of different field strengths on determining plaque composition with an automatic classifier. MATERIALS AND METHODS: We applied a previously developed automatic classifier-the morphology enhanced probabilistic plaque segmentation (MEPPS) algorithm-to images from 20 subjects scanned at both 1.5 Tesla (T) and 3T. Average areas per slice of lipid-rich core, intraplaque hemorrhage, calcification, and fibrous tissue were recorded for each subject and field strength. RESULTS: All measurements showed close agreement at the two field strengths, with correlation coefficients of 0.91, 0.93, 0.95, and 0.93, respectively. None of these measurements showed a statistically significant difference between field strengths in the average area per slice by a paired t-test, although calcification tended to be measured larger at 3T (P = 0.09). CONCLUSION: Automated classification results using an identical algorithm at 1.5T and 3T produced highly similar results, suggesting that with this acquisition protocol, 3T signal characteristics of the atherosclerotic plaque are sufficiently similar to 1.5T characteristics for MEPPS to provide equivalent performance.