Xihai Zhao

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.

Discriminating Carotid Atherosclerotic Lesion Severity by Luminal Stenosis and Plaque Burden: A Comparison Utilizing High-Resolution Magnetic Resonance Imaging at 3.0 Tesla

Background and Purpose— To determine associations between stenosis, measures of plaque burden, and compositional features of carotid atherosclerosis, including high-risk features of intraplaque hemorrhage (IPH) and surface disruption. Methods— Institutional Review Board approval and informed consent for all participants were obtained before study initiation. Patients with either carotid stenosis >50% by duplex ultrasound or suspected coronary artery disease underwent multi-contrast carotid MRI at 3.0 T. For each artery, stenosis, percent wall volume (PWV=100%×wall volume/total vessel volume), and mean wall thickness (MWT) were measured. Presence or absence of a lipid-rich necrotic core, calcification, IPH, and surface disruption were recorded. Results— One hundred eighty-one patients were included in the final analysis. The area under the curve (AUC) calculated from receiver-operating-characteristics analysis found the presence of IPH was similarly classified by stenosis (AUC=0.82), PWV (AUC=0.88), and MWT (AUC=0.88). Notably, IPH was present in the lowest category of each parameter. Prevalence of IPH in arteries with 0% stenosis was 4.4%. In arteries with PWV <40%, prevalence was 3.2%; in arteries with MWT <1.0 mm, prevalence was 2.3%. Strength of classification for surface disruption was similarly classified by stenosis (AUC=0.87), PWV (AUC=0.93), and MWT (AUC=0.94). Conclusions— Measures of plaque burden do not substantially improve disease assessment compared to stenosis. The finding of IPH in all categories of stenosis and plaque burden suggests that direct characterization of plaque composition and surface status is necessary to fully discriminate disease severity.

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.

Association of carotid atherosclerotic plaque features with acute ischemic stroke: A magnetic resonance imaging study

BACKGROUND AND PURPOSE It remains unclear whether direct vessel wall imaging can identify carotid high-risk lesions in symptomatic subjects and whether carotid plaque characteristics are more effective indicators for cerebral infarct severity than stenosis. This study sought to determine the associations of carotid plaque characteristics by MR imaging with stenosis and acute cerebral infarct (ACI) sizes on diffusion weighted imaging (DWI). MATERIALS AND METHODS One hundred and fourteen symptomatic patients underwent carotid and brain MRI. ACI volume was determined from symptomatic internal carotid artery territory on DWI images. Ipsilateral carotid plaque morphological and compositional characteristics, and stenosis were also determined. The relationships between carotid plaque characteristics, stenosis and ACIs size were then evaluated. RESULTS In carotid arteries with 30-49% stenosis, 86.7% and 26.7% were found to have lipid-rich necrotic core (LRNC) and intraplaque hemorrhage, respectively. Furthermore, 45.8% of carotid arteries with 0-29% stenosis developed LRNCs. Carotid morphological measurements, such as % wall volume, and the LRNC size were significantly associated with ipsilateral ACIs volume before and after adjustment for significant demographic factors (age and LDL) or stenosis in patients with carotid plaque (all p<0.05). CONCLUSIONS A substantial number of high-risk plaques characterized by vessel wall imaging exist in carotid arteries with lower grade stenosis. In addition, carotid plaque characteristics, particularly the % wall volume and LRNC size, are independently associated with cerebral infarction as measured by DWI lesions. Our findings indicate that characterizing atherosclerotic plaque by MR vessel wall imaging might be useful for stratification of plaque risk and infarction severity.

Ultrasound-Based Carotid Elastography for Detection of Vulnerable Atherosclerotic Plaques Validated by Magnetic Resonance Imaging

Ultrasound-based carotid elastography has been developed to estimate the mechanical properties of atherosclerotic plaques. The objective of this study was to evaluate the in vivo capability of carotid elastography in vulnerable plaque detection using high-resolution magnetic resonance imaging as reference. Ultrasound radiofrequency data of 46 carotid plaques from 29 patients (74 ± 5 y old) were acquired and inter-frame axial strain was estimated with an optical flow method. The maximum value of absolute strain rate for each plaque was derived as an indicator for plaque classification. Magnetic resonance imaging of carotid arteries was performed on the same patients to classify the plaques into stable and vulnerable groups for carotid elastography validation. The maximum value of absolute strain rate was found to be significantly higher in vulnerable plaques (2.15 ± 0.79 s(-1), n = 27) than in stable plaques (1.21 ± 0.37 s(-1), n = 19) (p < 0.0001). Receiver operating characteristic curve analysis was performed, and the area under the curve was 0.848. Therefore, the in vivo capability of carotid elastography to detect vulnerable plaques, validated by magnetic resonance imaging, was proven, revealing the potential of carotid elastography as an important tool in atherosclerosis assessment and stroke prevention.

Segmentation of carotid plaque using multicontrast 3D gradient echo MRI.

To evaluate the performance of automatic segmentation of atherosclerotic plaque components using solely multicontrast 3D gradient echo (GRE) magnetic resonance imaging (MRI).

Magnetic Resonance Lymphography at 3T: A Promising Noninvasive Approach to Characterise Inguinal Lymphatic Vessel Leakage

PURPOSE To explore the feasibility of using 3T high-resolution MR lymphangiography to characterize inguinal lymphatic vessel leakage (LVL). MATERIALS AND METHODS Sixteen patients with known inguinal LVL underwent 3T MR lymphangiography and T(2)-weighted imaging. The presence or absence of inguinal LVL and the responsible lymphatic vessels were determined using the above imaging modalities and confirmed by surgical procedure. Afterwards, fifteen patients with recurring LVL following conservative treatment were referred to surgical intervention. RESULTS Specific inguinal LVL enhancement patterns and leaking lymphatic vessels were detected in 15 of 16 patients. Compared to the SNR of enhanced lymph nodes, that of the enhanced LVL was significantly greater (t = 7.149, p < 0.01), thereby making it possible to differentiate between LVL sites and enhancing inguinal lymph nodes. Furthermore, the steepest contrast enhancement curve slope of enhanced LVL was lower than that of enhanced lymph nodes (t = -2.860, p = 0.02). After MR diagnosis, 15 patients successfully underwent open exploration and ligation of the leaking lymphatic vessel. Clinical follow-up did not demonstrate recurrence of lymphatic fluid in the groin. CONCLUSIONS High-resolution MR lymphangiography combined with T(2)-weighted imaging is a promising approach to identifying specific features of lymphatic vessel leakage in the groin.

Varying Correlation Between 18F-Fluorodeoxyglucose Positron Emission Tomography and Dynamic Contrast-Enhanced MRI in Carotid Atherosclerosis Implications for Plaque Inflammation

Background and Purpose— 18F-fluorodeoxyglucose positron emission tomography and dynamic contrast-enhanced MRI have been proposed to quantitatively assess plaque inflammation by probing macrophages and neovessels, respectively. We examined their correlation to study the in vivo relationship between macrophage and neovessel activities in atherogenesis. Methods— Forty-one patients (34 men; aged 65±12 years) with a total of 68 carotid plaques (thickness ≥2 mm on ultrasound; 20 symptomatic) were assessed by both 18F-fluorodeoxyglucose positron emission tomography/computed tomography and dynamic contrast-enhanced MRI within 2 weeks, measured as target-to-background ratio and transfer constant (Ktrans), respectively. Results— Overall, the correlation between target-to-background ratio and Ktrans was weak and marginal (r=0.22; P=0.068). They were correlated in the symptomatic plaques (r=0.59; P=0.006) but not in the asymptomatic plaques (r=0.07; P=0.625; P=0.033 for difference in r). Neither target-to-background ratio nor Ktrans was significantly higher in the symptomatic plaques, but both showed an inverse relationship with time since last neurological event (r=−0.94 and −0.69 for target-to-background ratio and Ktrans, respectively). Conclusions— The correlation between 18F-fluorodeoxyglucose positron emission tomography and dynamic contrast-enhanced MRI measurements varied with clinical conditions, pointing to a complex interplay between macrophages and neovessels under different pathophysiological conditions. The moderate correlation shown only in symptomatic plaques indicates the presence of acute plaque inflammation with increased metabolic activity and cytokine production by inflammatory cells.

Correlation of Coronary Plaque Phenotype and Carotid Atherosclerotic Plaque Composition

Introduction:Studies have shown that atherosclerosis in coronary arteries is closely related to that in carotid arteries, but there are few investigations on the correlation between unstable plaques in these 2 vascular beds. The authors aim to investigate the correlation between coronary plaque phenotype and carotid plaque composition. Methods:Patients (n = 123) with suspected coronary artery disease underwent computed tomography angiography of coronary arteries. Magnetic resonance imaging of bilateral carotid arteries was performed within 2 weeks after computed tomography angiography. The plaque type in each coronary segment was analyzed. Coronary plaques were classified into 3 types: noncalcified, calcified and mixed. The total number of each plaque type was scored. Carotid plaque with calcification, lipid-rich necrotic core (LRNC) or intraplaque hemorrhage (IPH) in either carotid artery was defined as positive. Logistic regression analysis was used to determine the correlation between coronary plaque phenotype and carotid plaque composition. The area under the receiver-operating characteristic curve (AUC) was calculated. Results:There was a significant correlation between the mixed coronary plaque score and carotid IPH (odds ratio = 1.50, P < 0.05). The scores for all 3 types of the coronary plaque were significantly correlated with carotid LRNC and calcification. The mixed coronary plaque score had the highest value in predicting carotid IPH (AUC = 0.74). The calcified coronary plaque score showed the highest value in predicting carotid LRNC (AUC = 0.75) and calcification (AUC = 0.75). Conclusion:There was significant correlation between coronary plaque phenotype and carotid plaque composition. A mixed coronary plaque may be suggestive of a high-risk carotid plaque.

Measuring the labeling efficiency of pseudocontinuous arterial spin labeling.

Optimization and validation of a sequence for measuring the labeling efficiency of pseudocontinuous arterial spin labeling (pCASL) perfusion MRI.