Background-Previous studies with contrast-enhanced magnetic resonance imaging (CEMRI) have shown that the fibrous cap (FC) in atherosclerotic carotid plaques enhances with gadolinium-based contrast agents. Conversely, the lipid-rich necrotic core (LR-NC), lacking both vasculature and matrix, shows no or only slight enhancement. The goal of this study was to assess whether CEMRI can be used to accurately measure the dimensions of the intact FC and LR-NC. Methods and Results-Twenty-one patients scheduled for carotid endarterectomy were imaged with a 1.5-T scanner.Precontrast images and CEMRI were obtained. One hundred eight locations with an intact FC were matched between MRI and the excised histology specimens. Quantitative measurements of FC length along the lumen circumference, FC area, and LR-NC area were collected from CEMRI images and histology sections.

Background and Purpose-MRI is able to quantify carotid plaque size and composition with good accuracy and reproducibility and provides an opportunity to prospectively examine the relationship between plaque features and subsequent cerebrovascular events. We tested the hypothesis that the characteristics of carotid plaque, as assessed by MRI, are possible predictors of future ipsilateral cerebrovascular events. Methods-A total of 154 consecutive subjects who initially had an asymptomatic 50% to 79% carotid stenosis by ultrasound with Ն12 months of follow-up were included in this study. Multicontrast-weighted carotid MRIs were performed at baseline, and participants were followed clinically every 3 months to identify symptoms of cerebrovascular events. Results-Over a mean follow-up period of 38.2 months, 12 carotid cerebrovascular events occurred ipsilateral to the index carotid artery. Cox regression analysis demonstrated a significant association between baseline MRI identification of the following plaque characteristics and subsequent symptoms during follow-up: presence of a thin or ruptured fibrous cap (hazard ratio, 17.0; PՅ0.001), intraplaque hemorrhage (hazard ratio, 5.2; Pϭ0.005), larger mean intraplaque hemorrhage area (hazard ratio for 10 mm 2 increase, 2.6; Pϭ0.006), larger maximum %lipid-rich/necrotic core (hazard ratio for 10% increase, 1.6; Pϭ0.004), and larger maximum wall thickness (hazard ratio for a 1-mm increase, 1.6; Pϭ0.008). Conclusions-Among patients who initially had an asymptomatic 50% to 79% carotid stenosis, arteries with thinned or ruptured fibrous caps, intraplaque hemorrhage, larger maximum %lipid-rich/necrotic cores, and larger maximum wall thickness by MRI were associated with the occurrence of subsequent cerebrovascular events. Findings from this prospective study provide a basis for larger multicenter studies to assess the risk of plaque features for subsequent ischemic events. (Stroke. 2006;37:818-823.)

Purpose:To determine if a gadolinium-based contrast agent provides additional information for characterization of human plaque tissues, particularly neovasculature. Although high-resolution magnetic resonance imaging (MRI) has been used to identify plaque constituents in advanced atherosclerosis, some constituents, such as neovascularized tissue, defy detection. Materials and Methods:Non-contrast-enhanced carotid artery images from 18 patients scheduled for carotid endarterectomy and two normal volunteers were used to identify regions of fibrous tissue, necrotic core, or calcification, using established criteria. Then, the percent change in T1-weighted images after contrast enhancement was calculated for each region.Results: There were statistically significant differences in mean intensity change between tissues, with the largest increase for fibrous tissue (79.5%) and the smallest for necrotic core (28.6%). Additionally, histological analysis showed that a subset of fibrous regions rich in plaque neovascularization could be identified using a threshold of 80% enhancement (sensitivity ϭ 76%, specificity ϭ 79%). Conclusion:The ability of contrast-enhanced MRI to identify neovascularization and potentially improve differentiation of necrotic core from fibrous tissue further establishes MRI as a viable tool for in vivo study of atherosclerotic plaque.

"Vulnerable" plaques are atherosclerotic plaques that have a high likelihood to cause thrombotic complications, such as myocardial infarction or stroke. Plaques that tend to progress rapidly are also considered to be vulnerable. Besides luminal stenosis, plaque composition and morphology are key determinants of the likelihood that a plaque will cause cardiovascular events. Noninvasive magnetic resonance (MR) imaging has great potential to enable characterization of atherosclerotic plaque composition and morphology and thus to help assess plaque vulnerability. A classification for clinical, as well as pathologic, evaluation of vulnerable plaques was recently put forward in which five major and five minor criteria to define vulnerable plaques were proposed. The purpose of this review is to summarize the status of MR imaging with regard to depiction of the criteria that define vulnerable plaques by using existing MR techniques. The use of MR imaging in animal models and in human disease in various vascular beds, particularly the carotid arteries, is presented.

This study revealed significant differences between symptomatic and asymptomatic plaques in the same patient.

Purpose: To evaluate the in vivo accuracy of a multisequence MRI technique for prospectively identifying one feature of the vulnerable plaque-an unstable fibrous cap-in human carotid atherosclerosis. Materials and Methods:The carotid arteries of 18 endarterectomy patients were preoperatively imaged in a 1.5T scanner using a multisequence protocol that generated four contrast weightings (3D time of flight (ToF), T1, proton density (PD), and T2) at each slice location. With the use of previously published MR criteria, the images of the vessel wall were first examined for evidence of an unstable fibrous cap. The imaging findings were then correlated with the histology from the surgical specimens.Results: A blinded review of the MR findings with the histologic state of the fibrous cap revealed that 1) assessing the preoperative appearance of the fibrous cap has a high test sensitivity (0.81) and specificity (0.90) for identifying an unstable cap in vivo; and 2) the availability of different contrast weightings facilitated image interpretation when intimal calcifications or flow artifacts obscured the lumen surface. A growing body of research is also demonstrating that magnetic resonance imaging (MRI) can be used to characterize human atherosclerotic plaque morphology and identify important intraplaque structures such as the fibrous cap. Although early investigations noted anecdotally that T2-weighted images could differentiate fibrous from lipid-rich regions of plaque (4,5), the accuracy of identifying unstable fibrous caps based on a single T2-weighted sequence tested with ex vivo specimens was only marginal (sensitivity ϭ 0.12, specificity ϭ 0.98) (6). Improved characterization of the cap was achieved in a subsequent study (7) that showed that the axial source images from a 3D multiple-overlapping thin slab carotid angiogram (MOTSA) could be used to distinguish intact thick fibrous caps from unstable caps. Together, these studies provided the basis for recent work (8) that revealed that the in vivo detection of an unstable fibrous cap by MRI was highly associated with the history of a recent TIA or stroke (odds ratio Ͼ 10). This important result suggests that MRI can enable detection of a vulnerable plaque prior to the development of an acute ischemic event. ConclusionWhile the development of a noninvasive means of assessing plaque stability could have a tremendous impact on the management of atherosclerotic vascular disease, the accuracy of these MRI techniques for plaque characterization in vivo must be determined before they can be applied clinically (9). Given the important relationship between the state of the fibrous cap and plaque rupture risk, the following investigation was performed to assess the diagnostic performance of a multisequence MR technique in noninvasively detecting unstable fibrous caps in human carotid plaques.

In vivo MRI is capable of quantifying plaque volume and plaque composition, such as %lipid-rich/necrotic core and %calcification, in the clinical setting of a multi-center trial with low inter-scan variability. This study provides the basis for sample size calculation of future MRI trials.

It has been demonstrated that hydrogen can selectively reduce hydroxyl and peroxynitrite in vitro. Since most of the ionizing radiation-induced cellular damage is caused by hydroxyl radicals, this study was designed to test the hypothesis that hydrogen may be an effective radioprotective agent. This paper demonstrates that treating cells with hydrogen before irradiation could significantly inhibit ionizing irradiation(IR)-induced Human Lymphocyte AHH-1 cells apoptosis and increase cells viability in vitro. This paper also shows that hydrogen can protect gastrointestinal endothelia from radiation-induced injury, decrease plasma malondialdehyde (MDA) intestinal 8-hydroxydeoxyguanosine (8-OHDG) levels and increase plasma endogenous antioxidants in vivo. It is suggested that hydrogen has a potential as an effective and safe radioprotective agent.