Identification of carotid artery atherosclerosis is conventionally based on measurements of luminal stenosis and surface irregularities using in vivo imaging techniques including sonography, CT and MR angiography, and digital subtraction angiography. However, histopathologic studies demonstrate considerable differences between plaques with identical degrees of stenosis and indicate that certain plaque features are associated with increased risk for ischemic events. The ability to look beyond the lumen using highly developed vessel wall imaging methods to identify plaque vulnerable to disruption has prompted an active debate as to whether a paradigm shift is needed to move away from relying on measurements of luminal stenosis for gauging the risk of ischemic injury. Further evaluation in randomized clinical trials will help to better define the exact role of plaque imaging in clinical decision-making. However, current carotid vessel wall imaging techniques can be informative. The goal of this article is to present the perspective of the ASNR Vessel Wall Imaging Study Group as it relates to the current status of arterial wall imaging in carotid artery disease.

In this study, a turbo spin-echo (TSE) based motion-sensitized driven-equilibrium (MSDE) sequence was used as an alternative black-blood (BB) carotid MRI imaging scheme. The MSDE sequence was first optimized for more efficient residual blood signal suppression in the carotid bulb of healthy volunteers. Effective contrast-to-noise ratio (CNR eff ) and residual signal-tonoise ratio (SNR) in the lumen measured from MSDE images were then compared to those measured from inflow saturation (IS) and double inversion-recovery (DIR) images. Statistically significant higher CNR eff and lower lumen SNR were obtained from MSDE images. To assess MSDE sequence in a clinical carotid protocol, 42 locations from six subjects with 50% to 79% carotid stenosis by duplex ultrasound were scanned with both MSDE and multislice DIR. The comparison showed that MSDE images present significantly higher CNR and lower lumen SNR compared to corresponding multislice DIR images. The vessel wall area and mean wall thickness measurements in MSDE images were slightly but significantly lower than those obtained with other blood suppression techniques. In conclusion, in vivo comparisons demonstrated that MSDE sequence can achieve better blood suppression and provide a more accurate depiction of the lumen boundaries by eliminating plaque mimicking artifacts in carotid artery ( The carotid bifurcation is a frequent site of the atherosclerotic plaque formation that has drawn specific attention in numerous MRI studies of atherosclerosis intended for prediction of plaque vulnerability and the tracking of the disease progression and therapeutic response (1-3). Bloodsuppressed (black-blood [BB]) MRI methods are widely used in various cardiovascular applications and particularly for vessel wall imaging. In BB imaging of carotid arteries, efficient suppression of the signal from flowing blood is critical for precise delineation of the lumen-wall interface, and therefore plays an important role in assessing the morphology and tissue composition of the atherosclerotic plaque (1-3). However, due to complicated flow patterns in the carotid bifurcation representing recirculation, slow, and stagnant flow, BB images of the carotid artery (CA) are frequently compromised by plaque-mimicking artifacts (4), which may result in incorrect measurements of the vessel wall and plaque size.Several techniques have been proposed for suppression of the signal from flowing blood (5,6). The most widely used solutions for BB imaging are based on presaturation of the inflowing blood by a slab-selective RF pulse (5) and the double inversion-recovery (DIR) preparative sequence (6). The inflow saturation (IS) method usually does not allow for complete elimination of the signal from blood and may be ineffective in the presence of complicated flow patterns (4), especially those observed in the carotid bifurcation. The DIR technique is known to suppress blood signal more effectively, but it is limited by its long scan time due to the requirement of single-slice sequential acquisition. To ...

Background and Purpose-Although studies have attempted to differentiate intracranial vascular disease using vessel wall magnetic resonance imaging (VWI), none have incorporated multicontrast imaging. This study uses T1-and T2-weighted VWI to differentiate intracranial vasculopathies. Methods-We retrospectively reviewed patients with clinically defined intracranial vasculopathies causing luminal stenosis/ irregularity who underwent VWI studies. Two blinded experts evaluated T1 precontrast and postcontrast and T2-weighted VWI characteristics, including the pattern of wall thickening; presence, pattern, and intensity of postcontrast enhancement; and T2 signal characteristics. Results-Twenty-one cases of atherosclerosis (intracranial atherosclerotic disease [ICAD]), 4 of reversible cerebral vasoconstriction syndrome, and 4 of vasculitis were identified, with a total of 118 stenotic lesions (81 ICAD, 22 reversible cerebral vasoconstriction syndrome, and 15 vasculitic lesions). There was substantial to excellent inter-reader agreement for the assessment of lesional T2 hyperintensity (κ=0.80), pattern of wall thickening (κ=0.87), presence (κ=0.90), pattern (κ=0.73), and intensity (κ=0.77) of enhancement. ICAD lesions were significantly more likely to have eccentric wall involvement (90.1%) than reversible cerebral vasoconstriction syndrome (8.2%; P<0.001) and vasculitic lesions (6.7%; P<0.001) and were also more likely to have T2 hyperintensity present than the other 2 vasculopathies (79% versus 0%; P<0.001). There were also significant differences in the presence, intensity, and pattern of enhancement between all lesion types. Combining T1 and T2 VWI increased the sensitivity of VWI in differentiating ICAD from other vasculopathies from 90.1% to 96.3%. on VWI has been described and shown to correspond to the fibrous cap on histology. 15 In contrast, the T2 hypointense outer component of the plaque corresponds to areas rich in foamy macrophages and proteoglycans, and lipid rich necrotic core on T2-weighted VWI. 16 To our knowledge, no reports have used T2-weighted high-resolution VWI and multicontrast protocols as a technique to discriminate between vasculopathies. In this study, we evaluated the imaging findings of different vasculopathies on T2 and T1 pre and postcontrast imaging to identify unique features and test their ability to correctly identify disease and develop an algorithm to differentiate intracranial vasculopathies. We also investigate the additional benefit of using multicontrast VWI over pre and postcontrast T1 alone to differentiate disease. Conclusions-Multicontrast Methods Patient Population and Clinical DiagnosisAfter institutional review board approval, we reviewed consecutive patients from January 2011 to April 2014 with suspicion of intracranial vasculopathy who had VWI and, on luminal imaging, had appreciable intracranial arterial stenosis or irregularity. There were a total of 68 patients, who had 77 high-resolution VWI studies performed. Patients were further stratified into diagnostic vascu...

A Simultaneous Non-contrast Angiography and intraPlaque hemorrhage (SNAP) MR imaging technique is proposed to detect both luminal stenosis and hemorrhage in atherosclerosis patients in a single scan. 13 patients with diagnosed carotid atherosclerotic plaque were recruited after informed consent. All scans were performed on a 3T MR imaging system with SNAP, 2D time-of-flight (TOF) and magnetization-prepared 3D rapid acquisition gradient echo (MP-RAGE) sequences. The SNAP sequence utilized a phase sensitive acquisition, and was designed to provide positive signals corresponding to intraplaque hemorrhage (IPH) and negative signals corresponding to lumen. SNAP images were compared to TOF images to evaluate lumen size measurements using linear mixed models and the intraclass correlation coefficient (ICC). IPH identification accuracy was evaluated by comparing to MP-RAGE images using Cohen’s Kappa. Diagnostic quality SNAP images were generated from all subjects. Quantitatively, the lumen size measurements by SNAP were strongly correlated (ICC=0.96, p<0.001) with those measured by TOF. For IPH detection, strong agreement (κ=0.82, p<0.001) was also identified between SNAP and MP-RAGE images. In conclusion, a Simultaneous Non-contrast Angiography and intraPlaque hemorrhage (SNAP) imaging technique was proposed and shows great promise for imaging both lumen size and carotid intraplaque hemorrhage with a single scan.

Black-blood MRI is a promising tool for carotid atherosclerotic plaque burden assessment and compositional analysis. However, current sequences are limited by large slice thickness. Accuracy of measurement can be improved by moving to isotropic imaging but can be challenging for patient compliance due to long scan times. We present a fast isotropic high spatial resolution (0.7 3 0.7 3 0.7 mm 3 ) three-dimensional black-blood sequence (3D-MERGE) covering the entire cervical carotid arteries within 2 min thus ensuring patient compliance and diagnostic image quality. The sequence is optimized for vessel wall imaging of the carotid bifurcation based on its signal properties. The optimized sequence is validated on patients with significant carotid plaque. Quantitative plaque morphology measurements and signal-to-noise ratio measures show that 3D-MERGE provides good blood suppression and comparable plaque burden measurements to existing MRI protocols. 3D-MERGE is a promising new tool for fast and accurate plaque burden assessment in patients with atherosclerotic plaque. Magn Reson Med 65:627-637, 2011. V C 2010 Wiley-Liss, Inc. Key words: three dimensional black-blood; carotid atherosclerotic plaque; 3D-MERGE; approach to spoiled steady state; MSDE; SPACE; snapshot FLASH; diffusion preparation; vessel wall imaging High-resolution black-blood MRI can quantitatively measure carotid atherosclerotic plaque morphology and tissue composition (1,2). Measurements of plaque burden using black-blood MRI are widely used as primary endpoints in clinical trials (3,4) to serially monitor response to therapy and/or disease progression. Plaque burden measurement can provide an independent assessment of atherosclerotic burden analogous to stenosis assessment by angiography. Accurate measurement of plaque morphology requires high isotropic resolution in all three spatial directions (5). However, the slice resolution is limited compared with in-plane resolution (2-3 mm vs. 0.6-0.7 mm) in current two-dimensional (2D) blackblood sequences (1-5) used in carotid imaging studies. With large slice thickness, reliable detection and reproducible measurements of plaque components can also be hampered due to the partial volume effect (6), and morphological measurements in serial studies become more prone to errors caused by variations in the slice position and alignment (7).Three-dimensional (3D) black-blood imaging can provide increased resolution in the slice-select direction. Isotropic voxels can potentially improve measurement accuracy and reproducibility of carotid MRI by minimizing slice-positioning error allowing registration of images in serial studies (5,7). However, blood flow suppression and motion artifacts secondary to long scan times are challenging for 3D black-blood carotid MRI implementations. Traditional black-blood preparations such as inflow suppression and double inversion recovery developed for 2D MRI do not provide adequate flow suppression for 3D MRI. While double inversion recovery blackblood preparation in 3D carotid MRI...

Purpose: To compare two-(2D) and three-dimensional (3D) black-blood imaging methods for morphological measurements of the carotid artery wall and atherosclerotic plaque. Materials and Methods:A total of 18 subjects with 50% to 79% carotid stenosis were scanned with 2D (2-mm slice thickness) and 3D (1-mm/0.5-mm actual/interpolated slice thickness) T1-weighted fast spin-echo (FSE) blackblood imaging sequences with double inversion-recovery (DIR) blood suppression. Morphological measurements (lumen area, wall area, vessel area, mean wall thickness, and maximal wall thickness), signal-to-noise ratio (SNR) in the wall and lumen, and wall-lumen contrast-to-noise ratio (CNR) were compared between 2D and 3D images. The effect of improved slice resolution in 3D imaging was evaluated for visualization of small plaque components.Results: Lumen SNR (P ϭ 0.16), wall SNR (P ϭ 0.65), and CNR (P ϭ 0.94) were comparable between 2D/3D. There was no difference in average lumen area (P ϭ 0.16), average wall area (P ϭ 0.99), average vessel area (P ϭ 0.0.58), mean wall thickness (P ϭ 0.09), and maximum wall thickness (P ϭ 0.06) between 2D/3D. Distributions of small plaque components such as calcification were better characterized by the 3D acquisition. There was a higher sensitivity to motion artifacts with 3D imaging, resulting in three examinations with low image quality.Conclusion: 2D and 3D protocols provided comparable morphometric measurements of the carotid artery. The major advantage of 3D imaging is improved small plaque component visualization, while the 2D technique provides higher reliability for image quality.

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] Ϯ 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 was used to evaluate agreement between 1.5 T and 3.0 T on compositional dichotomous variables.

A semiautomated quantitative method to trace, label, and measure intracranial arteries from 3D-MRA was developed and validated. This technique can be used to facilitate quantitative intracranial vascular research, such as studying cerebrovascular adaptation to aging and disease conditions. Magn Reson Med 79:3229-3238, 2018. © 2017 International Society for Magnetic Resonance in Medicine.