Niranjan Balu

Improved suppression of plaque‐mimicking artifacts in black‐blood carotid atherosclerosis imaging using a multislice motion‐sensitized driven‐equilibrium (MSDE) turbo spin‐echo (TSE) sequence

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 (CNReff) and residual signal‐to‐noise 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 CNReff 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 (CA) imaging. Magn Reson Med 58:973–981, 2007.

Carotid Plaque Assessment using Fast 3D Isotropic-Resolution Black-Blood MRI

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 × 0.7 × 0.7 mm3) 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, 2011.

Carotid plaque morphology and composition: initial comparison between 1.5- and 3.0-T magnetic field strengths.

PURPOSE To prospectively compare the interpretation and quantification of carotid vessel wall morphology and plaque composition at 1.5-T with those at 3.0-T magnetic resonance (MR) imaging. MATERIALS AND METHODS Twenty participants (mean age, 69.8 years [standard deviation] +/- 10.5; 75% men) with 16%-79% carotid stenosis at duplex ultrasonography were imaged with 1.5-T and 3.0-T MR imaging units with bilateral four-element phased-array surface coils. This HIPAA-compliant study was approved by the institutional review board, and all participants gave written informed consent. Protocols designed for similar signal-to-noise ratios across platforms were implemented to acquire axial T1-weighted, T2-weighted, intermediate-weighted, time-of-flight, and contrast material-enhanced T1-weighted images. Lumen area, wall area, total vessel area, wall thickness, and presence or absence and area of plaque components were documented. Continuous variables from different field strengths were compared by using the intraclass correlation coefficient (ICC) and repeated measures analysis. The Cohen kappa was used to evaluate agreement between 1.5 T and 3.0 T on compositional dichotomous variables. RESULTS There was a strong level of agreement between field strengths for all morphologic variables, with ICCs ranging from 0.88 to 0.96. Agreement in the identification of presence or absence of plaque components was very good for calcification (kappa = 0.72), lipid-rich necrotic core (kappa = 0.73), and hemorrhage (kappa = 0.66). However, the visualization of hemorrhage was greater at 1.5 T than at 3.0 T (14.7% vs 7.8%, P < .001). Calcifications measured significantly (P = .03) larger at 3.0 T, while lipid-rich necrotic cores without hemorrhage were similar between field strengths (P = .9). CONCLUSION At higher field strengths, the increased susceptibility of calcification and paramagnetic ferric iron in hemorrhage may alter quantification and/or detection. Nevertheless, imaging criteria at 1.5 T for carotid vessel wall interpretation are applicable at 3.0 T.

Comparison between 2D and 3D high-resolution black-blood techniques for carotid artery wall imaging in clinically significant atherosclerosis

To compare two‐ (2D) and three‐dimensional (3D) black‐blood imaging methods for morphological measurements of the carotid artery wall and atherosclerotic plaque.

Scan-Rescan Reproducibility of Carotid Atherosclerotic Plaque Morphology and Tissue Composition Measurements Using Multicontrast MRI at 3T

To evaluate interscan reproducibility of both vessel morphology and tissue composition measurements of carotid atherosclerosis using a fast, optimized, 3T multicontrast protocol.

Multicontrast High-Resolution Vessel Wall Magnetic Resonance Imaging and Its Value in Differentiating Intracranial Vasculopathic Processes

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 (&kgr;=0.80), pattern of wall thickening (&kgr;=0.87), presence (&kgr;=0.90), pattern (&kgr;=0.73), and intensity (&kgr;=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%. Conclusions— Multicontrast VWI can be a complementary tool for intracranial vasculopathy differentiation, which often leads to more invasive workups when reversible cerebral vasoconstriction syndrome and vasculitis are in the differential diagnosis.

Simultaneous noncontrast angiography and intraPlaque hemorrhage (SNAP) imaging for carotid atherosclerotic disease evaluation

A simultaneous noncontrast angiography and intraplaque hemorrhage (SNAP) MR imaging technique is proposed to detect both luminal stenosis and hemorrhage in atherosclerosis patients in a single scan. Thirteen patients with diagnosed carotid atherosclerotic plaque were admitted after informed consent. All scans were performed on a 3T MR imaging system with SNAP, 2D time‐of‐flight and magnetization‐prepared 3D rapid acquisition gradient echo sequences. The SNAP sequence utilized a phase sensitive acquisition, and was designed to provide positive signals corresponding to intraplaque hemorrhage and negative signals corresponding to lumen. SNAP images were compared to time‐of‐flight images to evaluate lumen size measurements using linear mixed models and the intraclass correlation coefficient. Intraplaque hemorrhage identification accuracy was evaluated by comparing to magnetization‐prepared 3D rapid acquisition gradient echo images using Cohens Kappa. Diagnostic quality SNAP images were generated from all subjects. Quantitatively, the lumen size measurements by SNAP were strongly correlated (intraclass correlation coefficient = 0.96, P < 0.001) with those measured by time‐of‐flight. For intraplaque hemorrhage detection, strong agreement (κ = 0.82, P < 0.001) was also identified between SNAP and magnetization‐prepared 3D rapid acquisition gradient echo images. In conclusion, a SNAP imaging technique was proposed and shows great promise for imaging both lumen size and carotid intraplaque hemorrhage with a single scan. Magn Reson Med, 2013.

Improvements in carotid plaque imaging using a new eight-element phased array coil at 3T.

To design and compare an eight‐channel phased array (PA) coil for carotid imaging to an established four‐channel PA design at 3T.

Improved carotid intraplaque hemorrhage imaging using a slab-selective phase-sensitive inversion-recovery (SPI) sequence

Intraplaque hemorrhage in atherosclerotic plaques has been associated with accelerated plaque growth as well as exacerbation of clinical symptoms. The identification of intraplaque hemorrhage using magnetic resonance imaging primarily relies on the detection of methemoglobin on T1 weighted images. Current techniques are limited by insufficient intraplaque hemorrhage‐wall contrast and poor blood suppression. In this study, a slab‐selective phase‐sensitive inversion‐recovery (SPI) technique is proposed by combining a phase‐sensitive reconstruction with a T1 weighted sequence specifically designed to achieve improved intraplaque hemorrhage imaging. The SPI sequence was optimized and then used on ex vivo plaque specimens for histology based validation and intraplaque hemorrhage‐wall contrast‐to‐noise ratio comparison with magnetization‐prepared 3D rapid acquisition gradient echo MP‐RAGE. SPI and MP‐RAGE were also tested on a group of atherosclerosis patients to compare in vivo intraplaque hemorrhage‐wall contrast‐to‐noise ratio and blood suppression effectiveness. On ex vivo specimens SPI had better intraplaque hemorrhage identification accuracy and a significantly higher intraplaque hemorrhage‐wall contrast‐to‐noise ratio (P = 0.01) than MP‐RAGE. Similar results were found in the in vivo test: Slab‐selective phase‐sensitive inversion‐recovery provided a significantly improved intraplaque hemorrhage‐wall contrast‐to‐noise ratio (P < 0.01) and blood suppression efficiency (P < 0.01). In conclusion, SPI is a novel technique optimized for intraplaque hemorrhage detection and validated against histology. It has demonstrated its capability for improved in vivo intraplaque hemorrhage identification and blood suppression in atherosclerosis patients. Magn Reson Med, 2010.

Subclinical Carotid Atherosclerosis: Short-term Natural History of Lipid-rich Necrotic Core—A Multicenter Study with MR Imaging

PURPOSE To use magnetic resonance (MR) imaging to examine the short-term (6 months) natural history of the lipid-rich necrotic core (LRNC) in carotid artery plaques by examining the placebo group of a multicenter clinical trial. MATERIALS AND METHODS Study procedures and consent forms were approved by the institutional review board for this HIPAA-compliant study. Written informed consent was obtained for all enrolled subjects. Subjects in the placebo group of a multicenter clinical trial who showed LRNC at screening MR imaging had a follow-up MR imaging examination after 6 months. Lumen and wall volumes and LRNC volume and percentage were measured on images from both examinations by readers who were blinded to the time sequence. Plaque progression was calculated as annualized change in common coverage by using the carotid artery bifurcation as a landmark. Associations of clinical and imaging variables with LRNC progression were examined by using linear regression analysis. RESULTS Fifty-nine of 73 (81%) subjects completed the study, with a mean interval ± standard deviation of 6.9 months ± 1.0. The mean progression rates per year ± standard deviation of LRNC volume and percentage were -5.2 mm(3) ± 34.3 (P = .249) and -1.74% ± 6.27% (P = .038), respectively. Of the clinical and imaging variables examined, presence of intraplaque hemorrhage (IPH) was significantly associated with LRNC progression (P = .001). Plaques with IPH had increased LRNC volume per year (62.9 mm(3) ± 46.2 vs -8.8 mm(3) ± 29.9, P < .001) and percentage per year (3.67% ± 1.85% vs -2.03% ± 6.30%, P = .126) compared with those without IPH. Spearman correlation analysis showed that change in LRNC positively correlated with change in wall volume (ρ = 0.60, P < .001), but not with change in lumen volume (ρ = -0.17, P = .201). CONCLUSION Serial MR imaging of the carotid artery allowed observation of changes in LRNC over a short follow-up period and demonstrated the complexity of plaque progression patterns related to tissue composition. LRNC progression may be influenced not only by clinical characteristics, but also and to a large extent by plaque characteristics such as IPH.