Background-High-resolution MRI has been shown to be capable of identifying plaque constituents, such as the necrotic core and intraplaque hemorrhage, in human carotid atherosclerosis. The purpose of this study was to evaluate differential contrast-weighted images, specifically a multispectral MR technique, to improve the accuracy of identifying the lipid-rich necrotic core and acute intraplaque hemorrhage in vivo. Methods and Results-Eighteen patients scheduled for carotid endarterectomy underwent a preoperative carotid MRI examination in a 1.5-T GE Signa scanner using a protocol that generated 4 contrast weightings (T1, T2, proton density, and 3D time of flight). MR images of the vessel wall were examined for the presence of a lipid-rich necrotic core and/or intraplaque hemorrhage. Ninety cross sections were compared with matched histological sections of the excised specimen in a double-blinded fashion. Overall accuracy (95% CI) of multispectral MRI was 87% (80% to 94%), sensitivity was 85% (78% to 92%), and specificity was 92% (86% to 98%). There was good agreement between MRI and histological findings, with a value of ϭ0.69 (0.53 to 0.85). Conclusions-Multispectral MRI can identify the lipid-rich necrotic core in human carotid atherosclerosis in vivo with high sensitivity and specificity. This MRI technique provides a noninvasive tool to study the pathogenesis and natural history of carotid atherosclerosis. Furthermore, it will permit a direct assessment of the effect of pharmacological therapy, such as aggressive lipid lowering, on plaque lipid composition.

This article introduces a new image processing technique for rapid analysis of tagged cardiac magnetic resonance image sequences. The method uses isolated spectral peaks in SPAMMtagged magnetic resonance images, which contain information about cardiac motion. The inverse Fourier transform of a spectral peak is a complex image whose calculated angle is called a harmonic phase (HARP) image. It is shown how two HARP image sequences can be used to automatically and accurately track material points through time. A rapid, semiautomated procedure to calculate circumferential and radial Lagrangian strain from tracked points is described. This new computational approach permits rapid analysis and visualization of myocardial strain within 5-10 min after the scan is complete. Its performance is demonstrated on MR image sequences reflecting both normal and abnormal cardiac motion. Results from the new method are shown to compare very well with a previously validated tracking algorithm. Magn Reson Med 42:1048-1060,

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-High-resolution, multicontrast magnetic resonance imaging (MRI) has developed into an effective tool for the identification of carotid atherosclerotic plaque components, such as necrotic core, fibrous matrix, and hemorrhage/thrombus. Factors that may lead to plaque instability are lipid content, thin fibrous cap, and intraplaque hemorrhage. Determining the age of intraplaque hemorrhage can give insight to the history and current condition of the biologically active plaque. The aim of this study was to develop criteria for the identification of the stages of intraplaque hemorrhage using high-resolution MRI. Methods-Twenty-seven patients, scheduled for carotid endarterectomy (CEA), were imaged on a 1.5-T GE SIGNA scanner (sequences: 3-dimensional time of flight, double-inversion recovery, T1-weighted (T1W), PDW and T2W). Two readers, blinded to histology, reviewed MR images and grouped hemorrhage into fresh, recent, and old categories using a modified cerebral hemorrhage criteria. The CEA specimens were serially sectioned and graded as to presence and stage of hemorrhage. Results-Hemorrhage was histologically identified and staged in 145/189 (77%) of carotid artery plaque locations. MRI detected intraplaque hemorrhage with high sensitivity (90%) but moderate specificity (74%). Moderate agreement in classifying stages occurred between MRI and histology (Cohen ϭ0.7, 95% CI: 0.5 to 0.8 for reviewer 1 and 0.4, 95% CI: 0.2 to 0.6 for reviewer 2), with moderate agreement between the 2 MRI readers (ϭ0.4, 95% CI: 0.3 to 0.6). Conclusion-Multicontrast MRI can detect and classify carotid intraplaque hemorrhage with high sensitivity and moderate specificity.

Background-Neovasculature within atherosclerotic plaques is believed to be associated with infiltration of inflammatory cells and plaque destabilization. The aim of the present investigation was to determine whether the amount of neovasculature present in advanced carotid plaques can be noninvasively measured by dynamic, contrast-enhanced MRI. Methods and Results-A total of 20 consecutive patients scheduled for carotid endarterectomy were recruited to participate in an MRI study. Images were obtained at 15-second intervals, and a gadolinium contrast agent was injected coincident with the second of 10 images in the sequence. The resulting image intensity within the plaque was tracked over time, and a kinetic model was used to estimate the fractional blood volume. For validation, matched sections from subsequent endarterectomy were stained with ULEX and CD-31 antibody to highlight microvessels. Finally, all microvessels within the matched sections were identified, and their total area was computed as a fraction of the plaque area. Results were obtained from 16 participants, which showed fractional blood volumes ranging from 2% to 41%. These levels were significantly higher than the histological measurements of fractional vascular area. Nevertheless, the 2 measurements were highly correlated, with a correlation coefficient of 0.80 (PϽ0.001). Conclusions-Dynamic contrast-enhanced MRI provides an indication of the extent of neovasculature within carotid atherosclerotic plaque. MRI therefore provides a means for prospectively studying the link between neovasculature and plaque vulnerability. Key Words: magnetic resonance imaging Ⅲ contrast media Ⅲ carotid arteries Ⅲ atherosclerosis R ecent investigations have targeted neovasculature as an important factor contributing to atherosclerotic plaque vulnerability. Zamir and Silver 1 speculated that the presence of neovasculature within coronary artery walls may play a role in the pathogenesis of vascular disease. Kumamoto et al 2 showed that intimal neovasculature arising from the adventitial vasa vasorum was associated with inflammatory infiltrate. A role for neovasculature in the recruitment of leukocytes to the shoulder regions of lipid-rich plaques was proposed by de Boer et al. 3 Because such inflammatory cells are present at the sites of plaque rupture, 4 neovasculature may be a contributor to or a marker for vulnerable plaque. Support for this claim is provided by Mofidi et al, 5 who found higher microvessel counts in carotid endarterectomy specimens from symptomatic patients than from asymptomatic ones. Similarly, McCarthy et al 6 found microvessels in symptomatic patients were larger and more irregular in shape.These studies suggest that an imaging tool capable of measuring the extent of plaque neovasculature could be invaluable for identifying high-risk plaques or assessing the response to plaque-stabilizing therapies. A strong contender for measuring plaque neovasculature is MRI using an intravenously injected contrast-enhancing agent. Contrastenhanced (CE) MRI h...

Purpose-To prospectively evaluate if there is an association between plaque enhancement at magnetic resonance (MR) imaging and proinflammatory cardiovascular risk factors and plaque content.Materials and Methods-This study was performed with informed consent, HIPAA compliance, and institutional review board approval. Contrast agent dynamics within carotid plaques were measured in 30 patients (29 men, one woman; mean age, 67.7 years ± 10.7 [standard deviation]) who were scheduled to undergo carotid endarterectomy. Measurements were based on kinetic modeling of images obtained at 15-second intervals during which a gadolinium-based contrast agent was injected. The time-varying signal intensities within the plaques were used to estimate the fractional plasma volume (v p ) and transfer constant (K trans ) of contrast material into the extracellular space. Pearson correlation coefficients were computed between blinded MR measurements and histologic measurements of plaque composition, including macrophages, neovasculature, necrotic core, calcification, loose matrix, and dense fibrous tissue. Correlation coefficients or mean differences were computed regarding clinical markers of cardiovascular risk.Results-Analyzable MR images and histologic results were obtained in 27 patients. Measurements of K trans correlated with macrophage (r = 0.75, P < .001), neovasculature (r = 0.71, P <.001), and loose matrix (r = 0.50, P = .01) content. Measurements of v p correlated with macrophage (r = 0.54, P = .004), neovasculature (r = 0.68, P <.001), and loose matrix (r = 0.42, P = .03) content. For clinical parameters, significant associations were correlated with K trans only, with decreased high-density lipoprotein levels (r = −0.66, P <.001) and elevated K trans measurements in smokers compared with nonsmokers (mean, 0.134 min −1 vs 0.074 min −1 , respectively; P = .01). Conclusion-The correlations between K trans and histologic markers of inflammation suggest thatK trans is a quantitative and non-invasive marker of plaque inflammation, which is further supported by the correlation of K trans with proinflammatory cardiovascular risk factors, decreased high-density lipoprotein levels, and smoking.Address correspondence to W.S.K. (e-mail: bkerwin@u.washington.edu).. Author contributions: Guarantor of integrity of entire study, W.S.K.; study concepts/study design or data acquisition or data analysis/ interpretation, all authors; manuscript drafting or manuscript revision for important intellectual content, all authors; manuscript final version approval, all authors; literature research, W. Contrast material enhancement in carotid atherosclerotic plaques has been observed in several recent investigations with magnetic resonance (MR) imaging after the injection of clinically available gadolinium-based contrast agents (1-5). Strong contrast enhancement suggests the presence of a vascular supply to the plaque and increased endothelial permeability that facilitates the entry of the contrast agent from the blood plasma. Because neov...

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.

This article introduces a new image processing technique for rapid analysis of tagged cardiac magnetic resonance image sequences. The method uses isolated spectral peaks in SPAMM-tagged magnetic resonance images, which contain information about cardiac motion. The inverse Fourier transform of a spectral peak is a complex image whose calculated angle is called a harmonic phase (HARP) image. It is shown how two HARP image sequences can be used to automatically and accurately track material points through time. A rapid, semiautomated procedure to calculate circumferential and radial Lagrangian strain from tracked points is described. This new computational approach permits rapid analysis and visualization of myocardial strain within 5-10 min after the scan is complete. Its performance is demonstrated on MR image sequences reflecting both normal and abnormal cardiac motion. Results from the new method are shown to compare very well with a previously validated tracking algorithm. Keywords cardiac motion; harmonic phase; magnetic resonance tagging; myocardial strain Major developments over the past decade in tagged cardiac magnetic resonance imaging (1-6) have made it possible to measure the detailed strain patterns of the myocardium in vivo (7-11). MR tagging uses a special pulse sequence to spatially modulate the longitudinal magnetization of the subject to create temporary features, called tags, in the myocardium. Fast spoiled gradient echo imaging techniques are used to create CINE sequences that show the motion of both the anatomy of the heart and the tag features that move with the heart. Analysis of the motion of the tag features in many images taken from different orientations and at different times can be used to track material points in 3D, leading to detailed maps of the strain patterns within the myocardium (11,12). Tagged MRI has figured prominently in many recent medical research and scientific investigations. It has been used to develop and refine models of normal and abnormal myocardial motion (7,8,12-14) to better understand the correlation of coronary artery disease with myocardial motion abnormalities (15), to analyze cardiac activation patterns using pacemakers (16), to understand the effects of treatment after myocardial infarction (17), and in combination with stress testing for the early detection of myocardial ischemia (18). Despite