CMR, a non-invasive, non-radiating technique can detect myocardial oedema and fibrosis.

CMR imaging, using T2-weighted and T1-weighted gadolinium enhanced images, has been successfully used in Cardiology to detect myocarditis, myocardial infarction and various cardiomyopathies.

Transmitting this experience from Cardiology into Rheumatology may be of important value because: (a) heart involvement with atypical clinical presentation is common in autoimmune connective tissue diseases (CTDs). (b) CMR can reliably and reproducibly detect early myocardial tissue changes. (c) CMR can identify disease acuity and detect various patterns of heart involvement in CTDs, including myocarditis, myocardial infarction and diffuse vasculitis. (d) CMR can assess heart lesion severity and aid therapeutic decisions in CTDs.

The CMR experience, transferred from Cardiology into Rheumatology, may facilitate early and accurate diagnosis of heart involvement in these diseases and potentially targeted heart treatment.

Calcium can potentially shorten T1, generating high signal intensity in GREs. Because IPH appears as high signal intensity in MRIPH and the surface effects of calcium can potentially shorten T1 of surrounding water protons, the purpose of this study was to evaluate whether the high signal intensity seen on MRIPH could be attributed solely to IPH and not calcification.

Eleven patients undergoing carotid endarterectomy were imaged by using MRIPH. Calcification was assessed by scanning respective endarterectomy specimens with a tabletop MicroCT. MRIPH/MicroCT correlation used an 8-segment template. Two readers evaluated images from both modalities. Agreement between MRIPH/MicroCT was measured by calculating Cohen κ.

High signal intensity was seen in 58.8% and 68.9% (readers 1 and 2, respectively) of MRIPH segments, whereas calcification was seen in 44.7% and 32.1% (readers 1 and 2, respectively) of MicroCT segments. High signal intensity seen by MRIPH showed very good but inverse agreement to calcification (κ = -0.90; P < .0001, 95% CI, -0.93 to -0.86, reader 1; and κ = -0.74; P < .0001; 95% CI, -0.81 to -0.69, reader 2). Most interesting, high signal intensity demonstrated excellent agreement with lack of calcification on MicroCT (κ = 0.92; P < .0001; 95% CI, 0.89-0.94, reader 1; and κ = 0.97; P < .0001; 95% CI, 0.96-0.99, reader 2). In a very small number of segments, high signal intensity was seen in MRIPH, and calcification was seen on MicroCT; however, these represented a very small proportion of segments with high signal intensity (5.9% and 1.6%, readers 1 and 2, respectively).

High signal intensity, therefore, reliably identified IPH, known to describe complicated plaque, rather than calcification, which is increasingly recognized as identifying more stable vascular disease.

Atherosclerosis affects all vascular beds, including the coronary, carotid, intracerebral, peripheral and aortic vascular beds, and is responsible for tremendous morbidity and mortality, with the most serious outcomes being myocardial infarction, stroke and death. Historically the effects of vascular narrowing and associated thrombosis have been key indicators of disease in the coronary and carotid territories, with degrees of vascular stenosis being of profound importance in carotid surgery trials. Our improving understanding of the biology of atheromatous lesions and the development of alternative therapeutic agents which can initiate actual plaque regression have created a need to attempt to image plaque itself, with the carotid artery being an achievable target. This article reviews current strategies for assessing carotid atherosclerotic disease, particularly with reference to identifying plaque components and risk of rupture, the so-called vulnerable plaque.

The goal of this article is to illustrate the main invasive and noninvasive diagnostic modalities to image the vulnerable coronary plaque, which is responsible for acute coronary syndrome. The main epidemiologic and histological issues are briefly discussed in order to provide an adequate background. Comprehensive coronary atherosclerosis imaging should involve visualization of the entire coronary artery tree and plaque characterization, including three-dimensional morphology, relationship with the lumen, composition, vascular remodelling and presence of inflammation. No single technique provides such a comprehensive description, and no available modality extensively identifies the vulnerable plaque. In particular, we describe multislice computed tomography, which at present seems to be the most promising noninvasive tool for an exhaustive image-based quantification of coronary atherosclerosis.

To evaluate the ability of a custom-built coil design to provide improved signal-to-noise ratio (SNR) and less signal drop with increasing depth at the carotid artery.

Phased-array surface coils can provide a high SNR to image the carotid vessel wall. However, given the required field-of-view (FOV) and penetration depth, these coils show either a fast signal drop with increasing depth or a moderate SNR at increased coil size. A quadrature surface coil (a butterfly coil in conjunction with a linear single-loop coil) was compared with a phased-array coil in phantom and human studies.

The phantom studies showed that the quadrature coil has better SNR over the required FOV than a standard phased-array coil (26% at 3 cm depth).

The quadrature coil enables better image quality to be achieved.

Multicontrast-weighted MRI has the potential to become a powerful tool for assessment of atherosclerotic plaque. However, similarities in MR properties across plaque components limit the certainty with which these components can be differentiated. An understanding of MRI's underlying limitations in distinguishing atherosclerotic plaque components, and optimization of key parameters (including the set of components investigated and contrast weightings used) are required. In this study we analyzed endarterectomy specimens using multicontrast MRI and compared the results with matching histological findings to determine the probability of error, an unbiased measure of the underlying error caused by similarity in the spectral characteristics of components. The total error was >40% when five distinct components were investigated, but this was halved when components with similar functions and intensities were grouped together. When three contrast weightings were used to view plaque, diffusion-weighted imaging (DWI) proved valuable for separating hemorrhage from necrotic core, and "hemorrhage + necrotic" from "loose connective tissue + fibrous tissue." A two-way interaction between contrast weightings and components demonstrated that the value of a contrast can be exploited or marginalized depending on the choice of contrast weightings used.

This HIPAA-compliant study had institutional review board approval. Informed consent was obtained. The purpose was to prospectively evaluate a segmented three-dimensional (3D) double inversion recovery (DIR)-prepared steady-state free precession (SSFP) magnetic resonance (MR) imaging sequence for fast high-spatial-resolution black-blood carotid arterial wall imaging. Carotid wall-lumen contrast-to-noise ratio (CNR) obtained with this sequence was compared with those obtained with two-dimensional (2D) single- and multisection black-blood fast spin-echo (SE) sequences. MR imaging of both carotid artery bifurcations over 3 cm of transverse coverage was performed in eight volunteers (seven men, one woman; age range, 26-56 years) with no known history of carotid artery disease. Adjusted for section thickness and imaging time per section, higher effective mean CNR was achieved with segmented 3D DIR-prepared SSFP than with single-section 2D DIR-prepared fast SE or multisection 2D saturation-band fast SE (P < .05). Segmented 3D DIR-prepared SSFP enables black-blood carotid arterial wall MR imaging with contiguous thin-section coverage and greater imaging speed and effective CNR than conventional 2D fast SE techniques.

To compare two multislice turbo spin-echo (TSE) carotid artery wall imaging techniques at 1.5 T and 3.0 T, and to investigate the feasibility of higher spatial resolution carotid artery wall imaging at 3.0 T.

Multislice proton density-weighted (PDW), T2-weighted (T2W), and T1-weighted (T1W) inflow/outflow saturation band (IOSB) and rapid extended coverage double inversion-recovery (REX-DIR) TSE carotid artery wall imaging was performed on six healthy volunteers at 1.5 T and 3.0 T using time-, coverage-, and spatial resolution-matched (0.47 x 0.47 x 3 mm3) imaging protocols. To investigate whether improved signal-to-noise ratio (SNR) at 3.0 T could allow for improved spatial resolution, higher spatial resolution imaging (0.31 x 0.31 x 3 mm3) was performed at 3.0 T. Carotid artery wall SNR, carotid lumen SNR, and wall-lumen contrast-to-noise ratio (CNR) were measured.

Signal gain at 3.0 T relative to 1.5 T was observed for carotid artery wall SNR (223%) and wall-lumen CNR (255%) in all acquisitions (P < 0.025). IOSB and REX-DIR images were found to have different levels of SNR and CNR (P < 0.05) with IOSB values observed to be larger. Normalized to a common imaging time, the higher spatial resolution imaging at 3.0 T and the lower spatial resolution imaging at 1.5 T provided similar levels of wall-lumen CNR (P = NS).

Multislice carotid wall imaging at 3.0 T with IOSB and REX-DIR benefits from improved SNR and CNR relative to 1.5 T, and allows for higher spatial resolution carotid artery wall imaging.

The accuracy of a two-step interventional MRI protocol to quantify coronary artery disease was compared to the clinical gold standard, X-ray angiography. Studies were conducted in nine swine with a surgically induced stenosis in the proximal left circumflex coronary artery. The two-step protocol consisted of catheter-directed magnetic resonance angiography (MRA), which was first used to localize the stenosis, followed by MRI cross-sectional images to quantify the degree of stenosis without the use of contrast agent. Line signal intensity profiles were drawn across the vessel diameter at the stenosis site and proximal to the stenosis for each data set to measure percentage stenosis for each animal. Catheter-directed MRA successfully detected eight of nine stenoses. Cross-sectional MRI accurately quantified each stenosis, with strong agreement to the measurements made using X-ray fluoroscopy (intraclass correlation coefficient = 0.955; P < 0.05). This study demonstrates that in the future interventional MRI may be an alternative to X-ray angiography for the detection and quantification of coronary artery disease.

Multicontrast-weighted MRI, which is increasingly being used in combination with automatic classification algorithms, has the potential to become a powerful tool for assessing plaque composition. The current literature, however, does not address the relationship between imaging conditions and segmentation viability well. In this study 13 carotid endarterectomy samples were imaged with a 156-microm in-plane resolution and high signal-to-noise ratio (SNR) using proton density (PD), T1, T2, and diffusion weightings. The maximum likelihood (ML) algorithm was used to classify plaque components, with sets of three contrast weighting intensities used as features. The resolution and SNR of the images were then degraded. Classification accuracy was found to be independent of in-plane resolution between 156 microm and 1250 microm, but dependent on SNR. Accuracy decreased less than 10% for degradation in SNR down to 25% of original values, and decreased sharply thereafter. The robustness of automatic classifiers makes them applicable to a wide range of imaging conditions, including standard in vivo carotid imaging scenarios.

To evaluate the potential role of carotid artery atherosclerosis plaque magnetic resonance (MR) microimaging as magnetic resonance imaging (MRI) marker, ex vivo MR images were acquired at optimized parameters on 9.4T Bruker animal imager for occluded tissue resected by carotid endarterectomy (CEA) and corresponding histopathological analysis was made.

For imaging, CEA tissues of size 2-6 cm long and 0.5-1.5 cm wide, were transferred to 15 ml co-polymer laboratory culture tubes containing either 10% formalin in phosphate buffered saline (PBS) or in 50% glycerol in PBS. Imaging protocol was set at TE=30 ms, TR=1.5 s, matrix size=265 x 512, NEX=128, slice thickness=1 mm and in-plane resolution=0.1 mm for total sample size 2.5 cm. Soon after imaging done, carotid artery tissues were cut into 5-mm segments and processed for histological section for successive 5-micrometer slices. To compare morphology of 5 mum thin CEA section with that of 1 mm MR slices, registration was obtained between histologic sections and MR slices. Contrast and magnetic resonance relaxation characteristics were analyzed.

Total carotid artery area computed by MR imaging was correlated with areas determined from histologic sections (r(2)=0.989, p=0.0001). For the lumen area, the correlation between MR images and histologic area was (r(2)=0.942, p=0.0001). Relaxation times and T(2) parametric images of different plaque components were determinant for contrast resolution. Scan parameters were optimized for fibrous cap and atheroma. Scan parameters were characteristic for comparison at 1.5T and 9.4T MR imagers.

The observed correlation validated MR microimaging to assess morphological features of carotid artery plaques and contrast resolution highlighted the potential of in vivo MR imaging as non-invasive MRI marker to monitor carotid artery plaque morphometry and plaque composition.

High-resolution MRI methods have been used to evaluate carotid artery atherosclerotic plaque content. The purpose of this study was to assess the performance of high-resolution MRI in evaluation of the quantity and pattern of mineral deposition in carotid endarterectomy (CEA) specimens, with quantitative micro-CT as the gold standard.

High-resolution MRI and CT were compared in 20 CEA specimens. Linear regression comparing mineral volumes generated from CT (VCT) and MRI (VMRI) data demonstrated good correlation using simple thresholding (VMRI=-0.01+0.98VCT; R2=0.90; threshold=4xnoise) and k-means clustering methods (VMRI=-0.005+1.38VCT; R2=0.93). Bone mineral density (BMD) and bone mineral content (BMC [mineral mass]) were calculated for CT data and BMC verified with ash weight. Patterns of mineralization like particles, granules, and sheets were more clearly depicted on CT.

Mineral volumes generated from MRI or CT data were highly correlated. CT provided a more detailed depiction of mineralization patterns and provided BMD and BMC in addition to mineral volume. The extent of mineralization as well as the morphology may ultimately be useful in assessing plaque stability.

Computer simulations and measurements on human volunteers were used to test the extent to which the quality of carotid imaging might be improved by coil arrays that are not limited by a constraint on the number of RF coil receiver ports.

Analytic near-field equations for the magnetic and electric fields of a rectangular loop resonator were used to estimate the relative signal-to-noise ratio (rSNR) along the length of a simulated carotid artery as a function of loop size, loop position and vessel depth. The sizes, positions and number of elements in a linear coil array that resulted in the maximum composite SNR along the length of a simulated carotid artery were then estimated. The linear array results were used to predict the total number of elements needed for optimal imaging of the carotid arteries. Also, three normal volunteers were imaged with a variety of RF coils, and the rSNR measurements along the lengths of the carotid artery were evaluated for each coil combination.

The analytic simulation and the human volunteer measurements both show that improved SNR (e.g., >300% at the bifurcation) can be obtained with coils tailored to each specific region of the carotid artery in comparison to that obtained with four-element arrays designed and used to image the entire carotid artery.

The resulting number of coil ports, 16 to 24, required for full coverage of the carotid arteries is consistent with the number of channels just becoming available on recently developed clinical scanners.

The two most promising noninvasive imaging modalities for the study of atherosclerosis are magnetic resonance imaging (MRI) and computed tomography (CT). Both have been shown to be capable of imaging vessel wall structures and differentiating various stages of atherosclerotic wall changes. MRI has been applied in various in vivo human studies to image atherosclerotic plaques in coronary arteries, carotid arteries, and aorta. The latest generation of multidetector row computed tomography (MDCT) systems allows for the noninvasive characterization of different plaque components in various vascular structures. MDCT allows evaluation of the whole arterial vasculature. In addition, MDCT has the ability to visualize the vessel wall and to give a quantitative measurement of calcified and noncalcified plaque. Using either technique, the repeatable, noninvasive study of atherosclerotic disease during its natural history and after therapeutic intervention will enhance our understanding of disease progression and regression. MDCT and MRI, therefore, may help in selecting appropriate treatments.

This work reports on the development of a pulse sequence to simultaneously acquire proton density, T(1), and T(2) weighted images in a single magnetization prepared fast spin echo acquisition. The technique is based upon the application of a magnetization preparation consisting of a global inversion followed by slice-selective 180 degrees and 90 degrees pulses to prepare the signal of specific slices. Slices are acquired in an interleaved manner with time delays appropriate for the desired image contrasts. Data acquisition is repeated for all combinations of slice interleaving covering the region of interest until images from all slice locations have been acquired with all desired image contrasts. The multiple image contrasts obtained with this technique should be useful in applications where discrimination between different types of tissue components is desired, such as in the analysis of plaque in cervical carotid artery disease.

To prospectively compare dynamic three-dimensional (3D) gadolinium-enhanced magnetic resonance (MR) angiography and digital subtraction angiography (DSA) for the detection of ostial stenosis of the craniocervical vessels.

Thirty-three patients with carotid stenosis of more than 50% at sonography prospectively underwent both MR angiography and DSA. The overall quality of each DSA and MR angiographic study was analyzed. For each craniocervical vessel (brachiocephalic, common carotid, subclavian, and vertebral arteries) (n = 231), ostial stenosis was graded as follows: normal, mild (<50%), moderate to severe (>50%), or occlusion. MR angiographic and DSA results were compared by means of the Spearman rank correlation coefficient (Rs).

The overall diagnostic quality of MR angiography was excellent or adequate. Three studies were inadequate because of a poor signal-to-noise ratio (13 of 231 arteries) or a coverage error (five of 231 arteries). Findings at MR angiography and DSA agreed on the degree of stenosis (Rs = 0.82, P <.001). No cases of stenosis of more than 50% were missed at MR angiography. However, some discrepancies were noted between vertebral arteries and the other craniocervical vessels. The sensitivity and specificity for stenosis of more than 50% in other craniocervical vessels were 100% and 98%, respectively. The sensitivity and specificity for stenosis of more than 50% in the vertebral arteries were 100% and 85%, respectively. Findings at MR angiography tended to result in overestimation of the degree of ostial stenosis, especially in vertebral arteries (10 [15%] of 66 arteries).

MR angiography is useful to rule out ostial stenosis of the craniocervical vessels. MR angiography is an adequate diagnostic tool for ostial stenosis, except in the vertebral artery.

There have been tremendous advances in our ability to image atheromatous disease, particularly in the carotid artery, which is accessible and large enough to image. The repertoire of methodology available is growing, giving anatomical information on luminal narrowing which is approaching the level at which conventional carotid angiography will become very uncommon as CT and contrast-enhanced MR angiographic techniques become the norm. More exciting is the tentative ability to perform functional plaque imaging addressing enhancement patterns and macrophage activity using MR or positron-emission tomography techniques. These techniques, once rigorously evaluated, may, in addition to complex mathematical modelling of plaque, eventually allow us to assess true plaque risk. Time will best judge whether we will be able to move from the use of simple luminology to assessment of plaque function.

The geometry of an RF phased-array receiving coil for high-resolution MRI of the carotid artery, particularly the bifurcation, was optimized with respect to signal-to-noise ratio (SNR). A simulation tool was developed to determine homogeneity, sensitivity, and SNR for a given imaging situation. The algorithm takes into account the coil geometry, the parameters of the measured object, and the imaging parameters of the pulse sequence. The coil with the optimum geometry was implemented as a receive-only coil for 1.5 T and comparative SNR measurements with different coils were performed. The experimental SNR measurements verified the simulations. The optimized carotid artery phased array offered the best SNR over the desired field of view. In vivo high-resolution MRI of the carotid arteries of healthy volunteers and patients with known stenosis was conducted with the optimized phased array coil. The capability of the phased array coil for resolving components within the carotid artery walls is demonstrated. Magn Reson Med 50:439-443, 2003.

The interaction between the vulnerable atherosclerotic plaque prone to disruption and thrombus formation is the cornerstone of acute coronary syndrome (ACS). Although distinct from one another, the atherosclerotic and thrombotic processes appear to be interdependent, hence the term atherothrombosis. Inflammation is a crucial common pathophysiological mechanism. Overall, the association of plaque vulnerability and ACS has been well documented. Given the multifactorial origin of atherothrombosis the best preventive approach should be aggressive management of all the risk factors. New interventions should be directed toward decreasing vulnerability of the lesions thereby decreasing the risk of ACS.

To use a volume-selective 3D turbo spin echo (TSE) technique to image the carotid artery wall and measure distensibility.

A high-resolution volume-selective 3D TSE sequence has been developed. Volume selection is accomplished by orthogonal gradients for the 90 degrees and 180 degrees excitations and allows a 3D volume of vessel wall to be imaged in a relatively short time. The technique has been developed to allow imaging at any defined phase of the cardiac cycle so that the vascular function and distensibility can be studied.

Scan efficiency is increased by the reduced phase encode field of view (FOV) (k(y) steps) by the use of selective volume excitation. Significantly more slices (k(z) phase encode steps) for vessel coverage can be acquired with the same scan time as that of the conventional sequence while maintaining signal-to-noise ratio (SNR) levels. The practical value of the technique was demonstrated on 10 normal subjects with high-resolution vessel distensibility measurements of the carotid arteries.

A volume-selective TSE method has been used for carotid artery wall imaging and measurement of distensibility in normal subjects. Larger coverage of the vessel, and therefore more information for clinical diagnostics, was achieved with the same overall scan time with an SNR comparable to that of 2D full FOV images.

Imaging methods to quantify the progression and regression of atherosclerosis could play a strong role in the management of patients. High-resolution, noninvasive MR imaging may provide exhaustive 3D anatomical information about the lumen and the vessel wall. Furthermore, MR imaging has the ability to characterize plaque composition and microanatomy and therefore to identify lesions vulnerable to rupture or erosion. The high resolution of MR imaging and the development of sophisticated contrast agents offer the promise of molecular in vivo molecular imaging of the plaque. This may aid early intervention (eg, lipid-lowering drug regiments) in both primary and secondary treatment of vascular disease in all arterial beds.

In order to study human atherosclerotic plaque burden and composition in vivo, an imaging technique is needed that can directly measure volume and characterize the cross-sectional morphologic components of the atherosclerotic arterial wall. High-resolution magnetic resonance imaging (MRI), which is noninvasive and nonirradiative, has been described as one promising modality to achieve these purposes. MRI allows direct visualization of the diseased vessel wall and is capable of characterizing the morphology of individual atherosclerotic carotid plaques.

High spatial resolution magnetic resonance imaging (MRI) is one of the most promising modalities for visualizing the carotid atherosclerotic plaque. MR allows direct visualization of the diseased vessel wall, is capable of characterizing plaque morphology, and can potentially monitor progression of the disease. Though ultrasound and angiography have been the principal methods for determining the severity of carotid atherosclerosis and the need for endarterectomy, these methods only measure percentage of vessel stenosis. There is strong evidence that this is not the best indicator for assessing clinical risk. Improved imaging techniques are therefore needed to reliably identify the high-risk plaques that lead to cerebrovascular events. This article focuses on the current state-of-the-art in MR carotid atherosclerotic plaque imaging to evaluate plaque morphology and composition.

In the future, the use of imaging methods to quantify the progression and regression of atherosclerosis could play a strong role in the management of patients. High-resolution, noninvasive MRI may provide exhaustive 3-D anatomic information about the lumen and the vessel wall. Furthermore, MRI has the ability to characterize plaque composition and microanatomy and therefore to identify lesions vulnerable to rupture or erosion. The high resolution of MRI and the development of sophisticated contrast agents offer the promise of molecular in vivo molecular imaging of the plaque. This may aid early intervention (e.g., lipid lowering drug regiments) in both primary and secondary treatment of vascular disease in all arterial beds.

Double-inversion fast spin-echo (FSE) pulse sequences can be designed to provide excellent suppression of blood signal in black-blood MRI. However, because a nonselective inversion is used, these sequences typically have been highly inefficient. In this work it is demonstrated that the efficiency of double-inversion sequences can be greatly improved by a form of interleaving in which all of the slices to be imaged in a single pass are reinverted each time a signal is obtained from any single slice. To date, several studies have demonstrated a high level of blood suppression with these more efficient techniques.

To investigate the ability of magnetic resonance imaging (MRI) to visualize the carotid vessel wall using a phased-array coil and a black-blood (BB) fast spin-echo (FSE) sequence.

The phased-array coil was compared with a three-inch coil. Images from volunteers were evaluated for artifacts, wall layers, and wall signal intensity. Signal intensity and homogeneity of atherosclerosis were assessed. Lumen diameter and vessel area were measured.

Comparison between the phased-array coil and the three-inch coil showed a 100% increase in signal-to-noise ratio. BB-FSE imaging resulted in good delineation between blood and vessel wall. Most volunteers had a two-layered vessel wall with a hyperintense inner layer. MRI showed both homogeneous hyperintense and heterogeneous plaques, which consisted of a main hyperintense part with hypointense spots and/or intermediate regions. MRI lumen and area measurements were performed easily.

High resolution MRI of carotid atherosclerosis is feasible with a phased-array coil and a BB-FSE sequence.

Noninvasive detection of plaque lipid and calcium in human atherosclerosis may have clinical utility, because the presence of each may be associated with increased risk of plaque disruption. Magnetic resonance imaging (MRI) has the potential to detect both plaque lipid and calcium. However, no previous studies have: 1) used an MR coil with sufficient resolution to image the components of human coronary arteries, 2) evaluated the utility of a combination of different MR contrast weightings in discriminating plaque components in human coronary arteries, or 3) used sensitive and specific histological stains for lipid and calcium to determine their MR image characteristics in human atherosclerosis.

Using a custom-made surface coil on a whole-body, 1.5T MRI scanner, high resolution MR images were obtained from 22 nonatherosclerotic and atherosclerotic human coronary artery segments and then compared with histological sections stained for neutral lipid, calcium, and ribrous and cellular components.

With a multicontrast protocol using T1-, proton density-, and T2-weighted images, statistically significant differences were found among MR image contrast values for regions identified by histological stains as containing lipid only, calcium only, mixed lipid and calcium, or fibrous tissue. All four of these histologically defined region types could be differentiated from one another by a multicontrast MRI protocol. Of the 22 segments, 10 (45%) contained areas with combined plaque lipid and calcium; calcium would not have been recognized histologically in these regions without the use of a specific calcium stain.

These results demonstrate that multicontrast MRI can produce remarkably high-resolution images and can discriminate between clinically relevant components of the atherosclerotic vessel wall.

Measurement of vessel stenosis by using ultrasonography or angiography remains the principal method for determining the severity of carotid atherosclerosis and the need for endarterectomy. The ipsilateral stroke rate, however--even in patients with severely stenotic vessels--is relatively low, which suggests that the amount of luminal narrowing may not represent the optimal means of assessing clinical risk. As a result, some patients may undergo unnecessary surgery. Improved imaging techniques are, therefore, needed to enable reliable identification of high-risk plaques that lead to cerebrovascular events. High-spatial-resolution magnetic resonance (MR) imaging has been described as one promising modality for this purpose, because the technique allows direct visualization of diseased vessel wall and can be used to characterize the morphology of individual atherosclerotic carotid plaques. The purpose of this report is to review the current state of carotid plaque MR imaging and the use of carotid MR to evaluate plaque morphology and composition.

High-resolution magnetic resonance imaging (MRI) with flow suppression not only provides useful information on luminal and wall areas of the carotid artery but also can identify the principal tissue components of the carotid atherosclerotic plaque. The effects of intensive lipid-lowering therapy on these MRI tissue characteristics were examined in patients with coronary disease (CAD). Eight CAD patients who have been receiving intensive lipid-lowering treatment (niacin 2.5 g/d, lovastatin 40 mg/d, and colestipol 20 g/d) for 10 years in the Familial Atherosclerosis Treatment Study (FATS) follow-up were randomly selected from among 60 such treated patients. Eight CAD patients who were matched to the treated patients for age (+/-3 years), baseline low density lipoprotein (+/-5 mg/dL), and triglycerides (+/-50 mg/dL) but who had never been treated with lipid-lowering drugs were selected as controls. For each of these 32 carotid arteries, luminal and plaque areas were measured by planimetry, in a blinded protocol, from the magnetic resonance image that showed most plaque. Fibrous tissue, calcium, and lipid deposits were identified on the basis of established criteria. Plaque composition was estimated as a fraction of total planimetered area. Patients treated with 10-year intensive lipid-lowering therapy, compared with control subjects, had significantly lower low density lipoprotein cholesterol levels (84 versus 158 mg/dL, respectively; P<0.001) and higher high density lipoprotein cholesterol levels (51 versus 37 mg/dL, respectively; P<0.001). As a group, treated patients, compared with untreated control subjects, had a smaller core lipid area (0.7 versus 10.2 mm(2), respectively; P=0.01) and lipid composition (1% versus 17%, respectively). Group differences in luminal area (55 [treated] versus 44 [control] mm(2), P=NS) and plaque area (58 [treated] versus 64 [control] mm(2), P=NS) tended to favor treatment. MRI appears useful for estimating carotid plaque size and composition. Hyperlipidemic CAD patients frequently (97%) have at least moderate (>/=40% area stenosis) carotid plaque. In this case-control study, prolonged intensive lipid-lowering therapy is associated with a markedly decreased lipid content, a characteristic of clinically stable plaques.

Measuring carotid artery plaque burden from MRI is a reliable method for monitoring regression and progression of atherosclerosis. However, to measure all available images would be very time consuming, and in practice the image quality (IQ) of these images may be inconsistent, which can directly impact the quality of measurement. It is hypothesized that if IQ is comparable among different contrast weighted images, then carotid artery area measurements obtained from different contrast images of the same location will produce identical results. To test this, T1, proton density and T2 weighted images were acquired from ten patients (51 +/- 7 years old). Carotid lumen and vessel wall area was measured using a custom designed software program. The results showed strong agreement evidenced with only small differences on both lumen (mean: 40.5 mm(2)) and wall (mean: 52.6 mm(2)) area measurement among different weighted images. The maximum absolute mean differences are less than 2.7 mm(2) and 4.4 mm(2), and 90(th) percentile of the absolute differences are 5.6 mm(2) and 8.2 mm(2) respectively. In conclusion, different contrast weighted images with high and comparable IQ will yield similar results in lumen and vessel wall area measurement. At each matched location, it is recommended that the image with the highest IQ be used for area measurement.

The study of atherosclerotic disease during its natural history and after therapeutic intervention may enhance our understanding of the progression and regression of this disease and will aid in selecting the appropriate medical treatments or surgical interventions. Several invasive and non-invasive imaging techniques are available to assess atherosclerotic disease vessels. Most of these techniques are strong in identifying the morphological features of the disease such as lumenal diameter and stenosis or wall thickness, and in some cases provide an assessment of the relative risk associated with the atherosclerotic disease. However, none of these techniques can fully characterize the composition of the atherosclerotic plaque in the vessel wall and therefore are incapable of identifying the vulnerable plaques. High-resolution, multi-contrast, magnetic resonance (MR) can non-invasively image vulnerable plaques and characterize plaques in terms of lipid and fibrous content and identify the presence of thrombus or calcium. Application of MR imaging opens up whole new areas for diagnosis, prevention, and treatment of atherosclerosis.

To evaluate if T2-weighted high-spatial-resolution magnetic resonance (MR) imaging (117 microm per pixel) can help accurate classification of atherosclerotic plaques.

Thirty human arteries and 11 carotid endarterectomy specimens from 31 patients underwent T2-weighted MR imaging (2-T magnet; repetition time, 2,000 msec; echo time, 50 msec) at room temperature. After imaging, Bouin fixative was used to fix 26 arteries, and the other 15 arteries were fixed by means of freezing. Specimens were stained with hematoxylin-eosin and safranin or Sudan lipid stain. MR images and histologic slices were classified independently by two radiologists and a pathologist, respectively, on the basis of the American Heart Association classification.

Results with MR imaging were the following: type I-II plaques, sensitivity of 67% and specificity of 100%; type IV-Va plaques, sensitivity of 74% and specificity of 85%; type Vb plaques, sensitivity of 90% and specificity of 100%; type Vc plaques, sensitivity of 80% and specificity of 90%. No type III plaque was diagnosed in the study. The overall kappa value was 0.68.

High-spatial-resolution MR imaging with T2 weighting alone can help accurate classification of fibrocalcic plaques (type Vb), but it is subject to limitations for the classification and analysis of other types of atherosclerotic plaques.

High-resolution MRI may be used to monitor the progression of human carotid atherosclerosis by measuring the lumen and wall area changes over time. The purpose of this study was to analyze the precision of quantitative measurements of lumen and wall areas. Two independent MR scans near the carotid bifurcation were conducted on eight patients within 2 weeks. The error of lumen area measurement was 6. 2%, 9.2%, and 9.7% for T(1), proton density, and T(2)-weighted images, respectively, and the error of wall area measurement was 10. 8%, 10.9%, and 12.0%. The precision of area measurement correlates strongly with image quality.

In clinical MR imaging the design and selection of receiver coil is an important step in ensuring the highest image quality. Often this choice is based on selecting a receiver coil characterized by high spatial uniformity such as the body and head volume receiver coils or a surface coil (or array of coils) that provide high signal-to-noise ratio (SNR). In the past, it has been difficult to accomplish both high SNR and spatial uniformity as both coil types achieve one of these characteristics at the expense of the other. The purpose of this study was to achieve both high SNR and spatial uniformity through the simultaneous acquisition of the MR signal using the body and a surface coil array. Results indicate that this hybrid system can provide uniformity and SNR values comparable to those achieved by the body and surface coil arrays, respectively.

High-resolution MRI has the potential to noninvasively image the human coronary artery wall and define the degree and nature of coronary artery disease. Coronary artery imaging by MR has been limited by artifacts related to blood flow and motion and by low spatial resolution.

We used a noninvasive black-blood (BB) MRI (BB-MR) method, free of motion and blood-flow artifacts, for high-resolution (down to 0.46 mm in-plane resolution and 3-mm slice thickness) imaging of the coronary artery lumen and wall. In vivo BB-MR of both normal and atherosclerotic human coronary arteries was performed in 13 subjects: 8 normal subjects and 5 patients with coronary artery disease. The average coronary wall thickness for each cross-sectional image was 0.75+/-0.17 mm (range, 0.55 to 1.0 mm) in the normal subjects. MR images of coronary arteries in patients with >/=40% stenosis as assessed by x-ray angiography showed localized wall thickness of 4.38+/-0.71 mm (range, 3.30 to 5.73 mm). The difference in maximum wall thickness between the normal subjects and patients was statistically significant (P<0.0001).

In vivo high-spatial-resolution BB-MR provides a unique new method to noninvasively image and assess the morphological features of human coronary arteries. This may allow the identification of atherosclerotic disease before it is symptomatic. Further studies are necessary to identify the different plaque components and to assess lesions in asymptomatic patients and their outcomes.

The purpose of this work was to compare intracranial magnetic resonance angiography (MRA) image quality using three different radiofrequency coils. The three coil types included a reduced volume quadrature birdcage coil with endcap, a commercially available quadrature birdcage head coil, and a four-element phased-array coil. Signal-to-noise ratio (SNR) measurements were obtained from comparison studies performed on a uniform cylindrical phantom. MRA comparisons were performed using data acquired from 15 volunteers and applying a thick-slab three-dimensional time-of-flight sequence. Analysis was performed using the signal difference-to-noise ratio, a quantitative measure of the relative vascular signal. The reduced-volume endcap and phased-array coils, which were designed specifically for imaging the intracranial volume of the head, improved the image SNR and vascular detail considerably over that obtained using the commercially available head coil. The endcap coil configuration provided the best vascular signal overall, while the phased-array coil provided the best results for arteries close to the coil elements.

The internal structure of atherosclerotic-plaque lesions may be a useful predictor of which lesions will rupture and cause sudden events such as heart attack or stroke. With lipid and flow suppression, we obtained high-resolution, three-dimensional (3D) images of atherosclerotic plaque in vivo that show the cap thickness and core size of the lesions. 3D GRASE was used because it provides flexible T(2) contrast and good resistance to off-resonance artifacts. While 2D RARE has similar properties, its resolution in the slice-select direction, which is important because of the irregular geometry of atherosclerotic lesions, is limited by achievable slice-excitation profiles. Also, 2D imaging generally achieves lower SNR than 3D imaging because, for SNR purposes, 3D image data is averaged over all the slices of a corresponding multislice 2D dataset. Although 3D RARE has many of the advantages of 3D GRASE, it requires a longer scan time because it uses more refocusing pulses to acquire the same amount of data. Finally, cardiac gating is an important part of our imaging sequence, but can make the imaging time quite long. To obtain reasonable scan times, a 2D excitation pulse was used to restrict the field of view. Magn Reson Med 42:762-771, 1999.

The purpose of this study was to clarify temporal changes of carotid wall enhancement using dynamic magnetic resonance (MR) and to correlate its findings with pathological conditions. Cervical carotid arteries of 84 consecutive patients were studied with a 1.5 T MR imager using phased array coils. Axial spoiled gradient-echo (SPGR) images (30-58 second scan time) with fat saturation were repeated 4-8 times after the injection of contrast material. We evaluated the presence and thickness of hypointense inner rims and hyperintense outer rims of the carotid wall, temporal changes of outer rim enhancement, and their changes in relation to pathological conditions. Hypointense inner rims and enhanced outer rims were clearly visualized in 87% (73/84) of our subjects. Enhancement of the outer rim was minimal in early phases and gradually increased. Patient age had a significant correlation with outer rim thickness. In the portions with large atheromatous plaques, inner rims were disrupted or thickened. A marked thickening of the outer rim was observed in one patient with arteritis. The outer rims adjacent to malignant tumors were often obscured. Our study suggests that dynamic MR images of the cervical carotid artery can uniquely demonstrate angiogenesis of the wall itself. The outer rim of the artery shows relatively rapid enhancement, and its thickness correlates with age.

Current imaging modalities, such as contrast angiography, accurately determine the degree of luminal narrowing but provide no direct information on plaque size. Magnetic resonance imaging (MRI), however, has potential for noninvasively determining arterial wall area (WA). This study was conducted to determine the accuracy of in vivo MRI for measuring the cross-sectional maximum wall area (MaxWA) of atherosclerotic carotid arteries in a group of patients undergoing carotid endarterectomy.

Fourteen patients scheduled for carotid endarterectomy underwent preoperative carotid MRI using a custom-made phased-array coil. The plaques were excised en bloc and scanned using similar imaging parameters. MaxWA measurements from the ex vivo MRI were used as the reference standard and compared with MaxWA measurements from the corresponding in vivo MR study. Agreement between the in vivo and ex vivo measurement was analyzed using the Bland-Altman method. The paired in vivo and ex vivo MaxWA measurements strongly agreed: the mean difference (in vivo minus ex vivo) in MaxWA was 13.1+/-6.5 mm2 for T1-weighted (T1W) imaging (mean MaxWA in vivo=94.7 mm2, ex vivo=81.6 mm2) and 14.1+/-11.7 mm2 for proton density-weighted (PDW) imaging (mean MaxWA in vivo=93.4 mm2, ex vivo=79.3 mm2). Intraobserver and interobserver variability was small, with intraclass correlation coefficients ranging from 0.90 to 0.98.

MRI is highly accurate for in vivo measurement of artery WA in atherosclerotic carotid lesions. This imaging technique has potential application monitoring lesion size in studies examining plaque progression and/or regression.

To apply a new, automatic and non-invasive method for quantification of blood flow, dynamic cross-sectional vessel area, and wall shear stress (WSS) by in vivo magnetic resonance velocity mapping of normal subjects.

Prospective, open study.

Six young volunteers.

A three-dimensional paraboloid model enabling automatic determination of blood flow, vessel distensibility and WSS was applied to blood velocity determinations in the common carotid artery. Blood flow was also determined by a manual edge detection method.

Using the new method, the common carotid mean blood flow was 7.28 (5.61-9.63) (mean (range)) ml/s. By the manual-method blood flow was 7.21 (5.55-9.60) ml/s. Mean luminal vessel area was 26% larger in peak systole than in diastole. Mean/peak WSS was 0.82/2.28 N/m2. Manually and automatically determined flows correlated (r2 = 0.998, p < 0.0001). WSS and peak centre velocity were associated (r2 = 0.805, p < 0.0001).

Blood flow, luminal vessel area dilatation, and WSS can be determined by the automatic three-dimensional paraboloid method. The hypothesis of association between peak centre velocity and WSS was not contradicted by the results of the present study.

Methods are lacking for accurate, noninvasive circumferential edge detection and wall shear stress calculation. Using standard MR phase contrast sequences, parts of the velocity profiles were fitted to a multiple sectored three-dimensional paraboloid model enabling exact calculation of vessel wall position and wall shear stress in 24 locations evenly distributed around the luminal vessel wall. The model was evaluated by in vitro scans and computer simulations and applied to the common carotid artery of humans. In vitro, the luminal area of a glass tube was assessed with an error of 0.9%. Computer simulations of peak systolic data revealed errors of +/-0.9% (vessel area) and +/-3.25% (wall shear stress). The in vivo results showed substantial difference between anterior and posterior wall shear stress values due to skewed velocity profiles. A new noninvasive method for highly accurate measurement of circumferential subpixel vessel wall position and wall shear stress has been developed.

The precise role played by hemodynamics, particularly wall shear stress, in the development and progression of vascular disease remains unclear, in large part because of a lack of in vivo studies with humans. Although technical challenges remain for noninvasively imaging wall shear stresses in humans, vascular anatomy can be imaged with sufficiently high resolution to allow reconstruction of three-dimensional models for computational hemodynamic studies. In this paper we present an entirely noninvasive magnetic resonance imaging (MRI) protocol that provides carotid bifurcation geometry and flow rates from which the in vivo hemodynamics can be computed. Maps of average, oscillatory, and gradients of wall shear stress are presented for two normal human subjects, and their data are compared with those computed for an idealized carotid bifurcation model.

An MRI protocol was developed to acquire all necessary image data in scan times suitable for patient studies. Three-dimensional models of the carotid bifurcation lumen were reconstructed from serial black blood MR images of two normal volunteers. Common and internal carotid artery flow rate waveforms were determined from MRI phase-contrast velocity imaging in the same subjects and were used to impose fully developed velocity boundary conditions for the computational model. Subject-specific time-resolved velocities and wall shear stresses were then computed with a finite element-based Navier-Stokes equation solver.

Models reconstructed from in vivo MRI of two subjects showed obvious differences in branch angle, bulb size and extent, and three-dimensional curvature. Maps of a variety of wall shear stress indices showed obvious qualitative differences in patterns between the in vivo models and between the in vivo models and the idealized model. Secondary, helical flow patterns, induced primarily by the asymmetric and curved in vivo geometries, were found to play a key role in determining the resulting wall shear stress patterns. The use of in vivo flow rate waveforms was found to play a minor but noticeable role in some of the wall shear stress behavior observed.

Conventional "averaged" carotid bifurcation models mask interesting hemodynamic features observed in realistic models derived from noninvasive imaging of normal human subjects. Observation of intersubject variations in the in vivo wall shear stress patterns supports the notion that more conclusive evidence regarding the role of hemodynamics in vascular disease may be derived from such individual studies. The techniques presented here, when combined with subject-specific MRI measurements of carotid artery plaque thickness and composition, provide the tools necessary for entirely noninvasive, prospective, in vivo human studies of hemodynamics and the relationship of hemodynamics to vascular disease.

We present a new method in which a priori knowledge of the blood velocity fields within the boundary layer at the vessel wall, combined with acquisition of high resolution magnetic resonance imaging (MRI) blood velocity data, allow exact modeling at the subpixel level.

Methods are lacking for accurate, noninvasive estimation of blood flow, dynamic cross-sectional lumen vessel area and wall shear stress.

Using standard acquisition of MRI blood flow velocity data, we fitted all data points (n = 69) within the boundary layer of the velocity profile to a three-dimensional paraboloid, which enabled calculation of absolute volume blood flow, circumferential vessel wall position, lumen vessel area and wall shear stress. The method was tested in a 8.00 +/ 0.01-mm diameter glass tube model and applied in vivo to the common carotid artery of seven volunteers.

In vitro the lumen area was assessed with a mean error of 0.6%. The 95% confidence interval included the specified tube dimensions. Common carotid mean blood flow was 7.42 ml/s, and mean (standard error) diastolic/systolic vessel area was 33.25 (0.72 [2.2%])/43.46 (0.65 [1.5%]) mm2. Mean/peak wall shear stress was 0.95 (0.04 [4.2%])/2.56 (0.08 [3.1%]) N/m2.

We describe a new noninvasive method for highly accurate estimation of blood flow, cross-sectional lumen vessel area and wall shear stress. In vitro results and statistical analysis demonstrate the feasibility of the method, and the first in vivo results are comparable to published data.

We measured hippocampal volumes and cognitive functioning in crack-cocaine and crack-cocaine/alcoholdependent subjects (abstinent approximately 10-12 weeks) compared to age-matched controls. Cognitive function was evaluated using the computerized MicroCog Assessment of Cognitive Functioning (which includes tests of explicit, declarative memory subserved by the hippocampus). The hippocampal volumes were quantified on T1-weighted MRIs and were expressed as a proportion of intracranial vault volume. Both subjects and controls showed the larger right versus left hippocampal volume expected in normal anatomy, but we found no differences in hippocampal volume between any of the groups. However, both abstinent cocaine-dependent subjects and abstinent cocaine/alcohol-dependent subjects showed persistent cognitive impairments, including deficits in explicit memory. Our results suggest that either: (1) the hippocampus is resistant to structural volume loss in young and middle-aged cocaine or cocaine/alcohol-dependent subjects, (2) the hippocampal volume loss suffered by young and middle-aged cocaine or cocaine/alcohol-dependent subjects resolves after approximately 3 months of abstinence, or (3) hippocampal atrophy is obscured by the process of gliosis. Further, the cognitive impairments persisting in these abstinent cocaine and cocaine/alcohol-dependent samples may (1) be unrelated to hippocampal function or (2) be associated with abnormal hippocampal function that is not reflected in MRI measures of overall hippocampal atrophy.

Cardiac-gated black blood MRI of the carotid artery bifurcation in normal human subjects shows signal within the lumen suggesting wall thickening or atherosclerotic plaque. This signal was believed to be artifactual, arising from complex flow patterns present at the carotid bifurcation. Computer simulation of the hemodynamics and black blood multislice image acquisition in a model of the carotid bifurcation showed that these artifacts arise from spins recovering their signal within the slow, recirculating flow of the carotid bulb. The computed hemodynamics also suggested that these artifacts could be minimized or eliminated entirely by gating the acquisition of slices in the most artifact-prone region of the carotid bulb within a 250-ms window after peak systole. Application of these predictions to studies of normal volunteers showed that, in most cases, these flow artifacts in black blood MRI can be eliminated simply by altering the phase of the cardiac cycle to which the image acquisition is gated. The observation that the size and placement of the saturation slabs had little effect on these artifacts suggested that, in those cases in which recirculation persists throughout the cardiac cycle, either inversion-recovery or presaturation within the bulb itself would be required to suppress them.