MR Imaging Measures of Intracranial Atherosclerosis in a Population-based Study

Purpose To implement a magnetic resonance (MR) imaging protocol to measure intracranial atherosclerotic disease (ICAD) in a population-based multicenter study and report examination and reader reliability of these MR imaging measurements and descriptive statistics representative of the general population. Materials and Methods This prospective study was approved by the institutional review boards and compliant with HIPAA. Atherosclerosis Risk in Communities (ARIC) study participants (n = 1980) underwent brain MR imaging from 2011 to 2013 at four ARIC sites. Imaging included three-dimensional black-blood MR imaging and time-of-flight MR angiography. One hundred two participants returned for repeat MR imaging to estimate examination and reader variability. Plaque presence according to vessel segment was recorded. Quantitative measurements included lumen size and degree of stenosis, wall and/or plaque thickness, area and volume, and normalized wall index for each vessel segment. Reliability was assessed with percentage agreement, κ statistics, and intraclass correlation coefficients. Results Of the 1980 participants, 1755 (mean age, 77.6 years; 1026 women [59%]; 1234 white [70%]) completed examinations with adequate to excellent image quality. The weighted ICAD prevalence was 34.4% (637 of 1755 participants) and was higher in men than women (38.5% [302 of 729 participants] vs 31.7% [335 of 1026 participants], respectively; P = .012) and in African Americans compared with whites (41.1% [215 of 518 participants] vs 32.4% [422 of 1234 participants], respectively; P = .002). Percentage agreement of plaque identification per participant was 87.0% (interreader estimate), 89.2% (intrareader estimate), and 89.9% (examination estimate). Examination and reader reliability ranged from fair to good (κ, 0.50-0.78) for plaque presence and from good to excellent (intraclass correlation coefficient, 0.69-0.99) for quantitative vessel wall measurements. Conclusion Vessel wall MR imaging is a reliable tool for identifying and measuring ICAD and provided insight into ICAD distribution across a U.S. community-based population. (©) RSNA, 2016 Online supplemental material is available for this article.

Severe Cerebral Vasospasm and Childhood Arterial Ischemic Stroke After Intrathecal Cytarabine

We report on 2 patients who developed widespread cerebral vasospasm and arterial ischemic strokes (AIS) after application of intrathecal (IT) cytarabine. In a 3-year-old child with acute lymphoblastic leukemia (ALL), left leg weakness, hyperreflexia, and clonus were noted 4 days after her first dose of IT cytarabine during the induction phase of her chemotherapy. Cerebral MRI revealed multiple acute cerebral ischemic infarcts and widespread cerebral vasospasm. A 5-year-old girl complained of right arm and leg pain and began limping 11 days after IT cytarabine. Symptoms progressed to right dense hemiplegia, left gaze deviation, headache, and speech arrest. MRI revealed 2 large cortical areas of diffusion restriction in the right frontal and left parietal lobes. Cerebral magnetic resonance angiography (MRA) showed irregular narrowing affecting much of the intracranial arterial circulation. Although the first child fully recovered from her neurologic symptoms, the second patient had persistent hemiplegia on follow-up. Including this report, there are now 4 pediatric ALL cases of severe cerebral vasospasm and AIS in the context of IT cytarabine administration, strongly suggesting a true association. Differential diagnosis and management issues are discussed. Along with the more widespread use of MRI and MRA, the true frequency of this severe adverse effect will become clearer in future. For any child with neurologic symptoms within hours or days of receiving IT cytarabine, a low threshold for cerebral imaging with MRI and MRA is recommended.

Patterns and Implications of Intracranial Arterial Remodeling in Stroke Patients

BACKGROUND AND PURPOSE

Preliminary studies suggest that intracranial arteries are capable of accommodating plaque formation by remodeling. We sought to study the ability and extent of intracranial arteries to remodel using 3-dimensional high-resolution black blood magnetic resonance imaging and investigate its relation to ischemic events.

METHODS

Forty-two patients with cerebrovascular ischemic events underwent 3-dimensional time-of-flight magnetic resonance angiography and contrast-enhanced black blood magnetic resonance imaging examinations at 3 T for intracranial atherosclerotic disease. Each plaque was classified by location (eg, posterior versus anterior circulation) and its likelihood to have caused a stroke identified on magnetic resonance imaging (culprit, indeterminate, or nonculprit). Lumen area, outer wall area, and wall area were measured at the lesion and reference sites. Plaque burden was calculated as wall area divided by outer wall area. The arterial remodeling ratio (RR) was calculated as outer wall area at the lesion site divided by outer wall area at the reference site after adjusting for vessel tapering. Arterial remodeling was categorized as positive if RR>1.05, intermediate if 0.95≤RR≤1.05, and negative if RR<0.95.

RESULTS

One hundred and thirty-seven plaques were identified in 42 patients (37% [50] posterior and 63% [87] anterior). Compared with anterior circulation plaques, posterior circulation plaques had a larger plaque burden (77.7±15.7 versus 69.0±14.0; P=0.008), higher RR (1.14±0.38 versus 0.95±0.32; P=0.002), and more often exhibited positive remodeling (54.0% versus29.9%; P=0.011). Positive remodeling was marginally associated with downstream stroke presence when adjusted for plaque burden (odds ratio 1.34, 95% confidence interval: 0.99-1.81).

CONCLUSIONS

Intracranial arteries remodel in response to plaque formation, and posterior circulation arteries have a greater capacity for positive remodeling and, consequently, may more likely elude angiographic detection. Arterial remodeling may provide insight into stroke risk.

Abstract T P108: MRI Measurements of Intracranial Atherosclerosis in the ARIC Neurocognitive Study: Methods, Reliability and Descriptive Statistics

Introduction: A 3D high resolution MRI (HRMRI) vascular protocol was designed to measure intracranial atherosclerosis in a biracial population from the multicenter ARIC Neurocognitive (ARIC-NCS) study.

Hypothesis: HRMRI provides reliable intracranial vessel wall measurements in a population-based study.

Methods: 1980 ARIC-NCS participants (mean age, 77.2±5.3 years; 40% male; 71% white, 28% black) underwent a brain HRMRI protocol designed to identify atherosclerosis in major intracranial arteries, that included 3D time-of-flight MRA and 3D black blood MRI (both acquired at 0.5-mm 3 resolution). Among 1980 participants, 102 were recruited for repeat MRI exams to estimate scan and reader variability. Participants were selected based on identification of at least one intracranial plaque on the baseline MRI scan with adequate or excellent image quality. Exam pairs were read by the same reader to exclude inter-reader variation. Presence of plaque by vessel segment was recorded. Quantitative MRI measurements included lumen size and stenosis, wall/plaque thickness, area, and volume, normalized wall index over each vessel segment, and the largest plaque identified for each vascular territory (Table 1). Reliability was assessed by percent of agreement, kappa statistics and intraclass correlations (ICC).

Results: There were 272 pairs of repeated interpretations. Percent agreement, of plaque identification per participant was 87.0% (inter-reader), 89.2% (intra-reader), and 89.9% (between scans). The reliability for plaque identification was not impacted by the vessel segment. Repeat scan and repeat reader reliability (ICC) for quantitative measurements ranged from 0.69 to 0.98 (Table 1).

Conclusion: HRMRI provides reliable MRI measurements of intracranial vessels, and reliability was not impacted by plaque location.

Carotid artery plaque morphology and composition in relation to incident cardiovascular events: the Multi-Ethnic Study of Atherosclerosis (MESA)

PURPOSE

To determine if carotid plaque morphology and composition with magnetic resonance (MR) imaging can be used to identify asymptomatic subjects at risk for cardiovascular events.

MATERIALS AND METHODS

Institutional review boards at each site approved the study, and all sites were Health Insurance Portability and Accountability Act (HIPAA) compliant. A total of 946 participants in the Multi-Ethnic Study of Atherosclerosis (MESA) were evaluated with MR imaging and ultrasonography (US). MR imaging was used to define carotid plaque composition and remodeling index (wall area divided by the sum of wall area and lumen area), while US was used to assess carotid wall thickness. Incident cardiovascular events, including myocardial infarction, resuscitated cardiac arrest, angina, stroke, and death, were ascertained for an average of 5.5 years. Multivariable Cox proportional hazards models, C statistics, and net reclassification improvement (NRI) for event prediction were determined.

RESULTS

Cardiovascular events occurred in 59 (6%) of participants. Carotid IMT as well as MR imaging remodeling index, lipid core, and calcium in the internal carotid artery were significant predictors of events in univariate analysis (P < .001 for all). For traditional risk factors, the C statistic for event prediction was 0.696. For MR imaging remodeling index and lipid core, the C statistic was 0.734 and the NRI was 7.4% and 15.8% for participants with and those without cardiovascular events, respectively (P = .02). The NRI for US IMT in addition to traditional risk factors was not significant.

CONCLUSION

The identification of vulnerable plaque characteristics with MR imaging aids in cardiovascular disease prediction and improves the reclassification of baseline cardiovascular risk.

Is carotid intima-media thickness as predictive as other noninvasive techniques for the detection of coronary artery disease?

Carotid intima-media thickness (CIMT) measured by B-mode ultrasound is the most widely used noninvasive imaging method to assess atherosclerosis and cardiovascular risk. CIMT has been consistently associated with coronary artery disease and stroke; however, recent meta-analyses and systematic reviews suggest that its clinical usefulness may be limited because the addition of CIMT to traditional risk factors has not improved the risk prediction of cardiovascular events in the general population. Characterizing the carotid wall by MRI may have greater clinical utility compared with CIMT measurements by ultrasound. Unlike CIMT, MRI measurements of wall thickness include the adventitia and may be sensitive to adventitial thickening that results from vasa vasorum proliferation as a sign of early plaque development. MRI also has the ability to image the entire circumference of the carotid wall, including the outer wall of the carotid bulb where plaque forms in its earliest stage, and identify plaque components such as the lipid core, fibrous cap, and intraplaque hemorrhage that are closely related to plaque vulnerability and cardiovascular risk. Additional research is needed to assess the added prognostic value of MRI measurements of wall and plaque features in risk prediction beyond traditional risk factors.

Intracranial plaque enhancement in patients with cerebrovascular events on high-spatial-resolution MR images

PURPOSE

To characterize intracranial plaque inflammation in vivo by using three-dimensional (3D) high-spatial-resolution contrast material-enhanced black-blood (BB) magnetic resonance (MR) imaging and to investigate the relationship between intracranial plaque inflammation and cerebrovascular ischemic events.

MATERIALS AND METHODS

The study was approved by the institutional review board and was HIPAA compliant. Twenty-seven patients (19 men; mean age, 56.8 years ± 12.4 [standard deviation]) with cerebrovascular ischemic events (acute stroke, n = 20; subacute stroke, n = 2; chronic stroke, n = 3; transient ischemic attack, n = 2) underwent 3D time-of-flight MR angiography and contrast-enhanced BB 3-T MR imaging for intracranial atherosclerotic disease. Each identified plaque was classified as either culprit (the only or most stenotic lesion upstream from a stroke), probably culprit (not the most stenotic lesion upstream from a stroke), or nonculprit (not within the vascular territory of a stroke). Plaque contrast enhancement was categorized on BB MR images (grade 0, enhancement less than or equal to that of normal arterial walls seen elsewhere; grade 1, enhancement greater than grade 0 but less than that of the pituitary infundibulum; grade 2, enhancement greater than or equal to that of the pituitary infundibulum), and degree of contrast enhancement was calculated. Associations of the likelihood of being a culprit lesion with both plaque contrast enhancement and plaque thickness were estimated with ordinal logistic regression.

RESULTS

Seventy-eight plaques were identified in 20 patients with acute stroke (21 [27%] culprit, 12 [15%] probably culprit, and 45 [58%] nonculprit plaques). In these patients, grade 2 contrast enhancement was associated with culprit plaques (odds ratio 34.6; 95% confidence interval: 4.5, 266.5 compared with grade 0) when adjusted for plaque thickness. Grade 0 was observed in only nonculprit plaques. Culprit plaques had a higher degree of contrast enhancement than did nonculprit plaques (25.9% ± 13.4 vs 13.6% ± 12.3, P = .003).

CONCLUSION

Contrast enhancement of intracranial atherosclerotic plaque is associated with its likelihood to have caused a recent ischemic event and may serve as a marker of its stability, thereby providing important insight into stroke risk.

Carotid bifurcation geometry is an independent predictor of early wall thickening at the carotid bulb

BACKGROUND AND PURPOSE

Lumen geometry has long been suspected as a risk factor for atherosclerosis by virtue of its influence on blood flow disturbances. Confirmation of this geometric risk hypothesis has, however, proved challenging owing to possible effects of wall thickening on geometry and unproven links between candidate geometric variables and disturbed flow. The purpose of this study was to overcome these challenges.

METHODS

The study relied on imaging and risk factor data from progressively refined subsets of the Atherosclerosis Risk in Communities (ARIC) Carotid MRI study. Group 1 (n=467) included only nonstenotic cases having sufficient quality angiography for 3-dimensional analysis. Group 2 (n=346) excluded cases from group 1 having common and internal carotid artery wall thickness above previously identified thresholds for inward remodeling. Group 3 (n=294) excluded cases from group 2 having lumen irregularities and thus was least likely to include lumen geometries influenced by wall thickening.

RESULTS

Multiple linear regressions showed that for group 3, bifurcation flare and proximal curvature were independent predictors of internal carotid artery wall thickness, consistent with their previously demonstrated roles in predicting disturbed flow. For the broadest group 1, flare was an independent predictor of internal carotid artery wall thickness but with a sign change in regression coefficient reflecting effects of wall thickening on lumen geometry.

CONCLUSIONS

Carotid bifurcation geometry is an independent, albeit weak, predictor of its early wall thickening, but only when assumptions about geometric factors, and the influence of disease on them, are confronted. This highlights pitfalls of previous attempts to confirm geometric risk of atherosclerosis.

Association of SERPINA9 gene variants with carotid artery atherosclerosis: the Atherosclerosis Risk in Communities (ARIC) Carotid MRI Study

The SNP rs11628722 in the SERPINA9 gene was previously associated with incident ischemic stroke in the Atherosclerosis Risk in Communities (ARIC) study. Centerin, the protein encoded by SERPINA9, is involved in maturation and maintenance of naïve B cells, which play a role in atherogenesis. We investigated whether 21 tag SNPs in the SERPINA9 gene are associated with features of carotid artery atherosclerotic plaque measured by magnetic resonance imaging (MRI). Carotid MRI data were obtained from 1,282 European Americans and 341 African Americans of the ARIC Carotid MRI study, which recruited participants from ARIC by a stratified sampling plan that over-sampled participants with carotid intima-media thickening. Five MRI measures, focused on carotid wall volume, wall thickness, and lipid core, were analyzed. Genetic associations between the MRI measurements and each of the 21 SNPs were analyzed in linear regression models with adjustment for sample weights and traditional risk factors. Rs11628722 was tested a priori. In African Americans, rs11628722 was significantly associated with carotid wall volume (p < 0.05). Among the other 20 SNPs, adjusted for multiple testing, rs4905204, which encodes an Ala to Val amino acid change, was significantly associated with maximum wall thickness (p < 0.000625) and suggestively associated with total wall volume (p < 0.0026) in European Americans. In conclusion, SNPs in the SERPINA9 gene showed race-specific associations with characteristics of carotid atherosclerotic plaques. Replications in other populations are needed to validate findings of this study and to establish the SERPINA9 gene as a candidate in the etiology of carotid atherosclerosis.

MRI-measured regression of carotid atherosclerosis induced by statins with and without niacin in a randomised controlled trial: the NIA plaque study

OBJECTIVE

To evaluate the benefit of niacin in addition to statin therapy on plaque regression among older individuals with established atherosclerosis.

DESIGN

Randomised, controlled, double-blind clinical trial.

SETTING

University outpatient center.

PATIENTS

145 patients older than 65 years, half of them older than 75 years of age, with established atherosclerosis were enrolled.

INTERVENTIONS

Participants received either extended release niacin (1500 mg daily) or placebo in addition to statin therapy to reach their National Cholesterol Education Program-defined low density lipoprotein (LDL) cholesterol target.

MAIN OUTCOME MEASURES

The primary endpoint was reduction in the wall volume of the internal carotid artery (ICA) measured by MRI.

RESULTS

After 18 months, high density lipoprotein cholesterol was higher with statins plus niacin compared with statins alone (1.6 ± 0.4 vs 1.4 ± 0.4 mmol/L p<0.001). Both groups had significant decreases in the main outcome measure of ICA wall volume, which regressed at 0.5%/month (SEM 0.2, p=0.004) in the statins plus placebo group and at 0.7%/month in the statins plus niacin group (SEM 0.2, p<0.001). There was no difference in the rate of regression between groups (p=0.49).

CONCLUSIONS

Treatment with statin therapy to presently recommended LDL levels, with or without niacin, resulted in significant atherosclerosis reduction.

Errors in the estimation of wall shear stress by maximum Doppler velocity

OBJECTIVE

Wall shear stress (WSS) is an important parameter with links to vascular (dys)function. Difficult to measure directly, WSS is often inferred from maximum spectral Doppler velocity (Vmax) by assuming fully-developed flow, which is valid only if the vessel is long and straight. Motivated by evidence that even slight/local curvatures in the nominally straight common carotid artery (CCA) prevent flow from fully developing, we investigated the effects of velocity profile skewing on Vmax-derived WSS.

METHODS

Velocity profiles, representing different degrees of skewing, were extracted from the CCA of image-based computational fluid dynamics (CFD) simulations carried out as part of the VALIDATE study. Maximum velocities were calculated from idealised sample volumes and used to estimate WSS via fully-developed (Poiseuille or Womersley) velocity profiles, for comparison with the actual (i.e. CFD-derived) WSS.

RESULTS

For cycle-averaged WSS, mild velocity profile skewing caused ±25% errors by assuming Poiseuille or Womersley profiles, while severe skewing caused a median error of 30% (maximum 55%). Peak systolic WSS was underestimated by ~50% irrespective of skewing with Poiseuille; using a Womersley profile removed this bias, but ±30% errors remained. Errors were greatest in late systole, when skewing was most pronounced. Skewing also introduced large circumferential WSS variations: ±60%, and up to ±100%, of the circumferentially averaged value.

CONCLUSION

Vmax-derived WSS may be prone to substantial variable errors related to velocity profile skewing, and cannot detect possibly large circumferential WSS variations. Caution should be exercised when making assumptions about velocity profile shape to calculate WSS, even in vessels usually considered long and straight.

Impact of T2 decay on carotid artery wall thickness measurements

PURPOSE

To investigate the impact of T2 relaxation of the carotid wall on measurements of its thickness.

MATERIALS AND METHODS

The common carotid artery wall was imaged using a spin echo sequence acquired at four echo times (17 ms to 68 ms) in 65 participants as part of VALIDATE study. Images were acquired transverse to the artery 1.5 cm proximal to the flow divider. Mean wall thickness, mean wall signal intensity, lumen area, and outer wall area were measured for each echo. Contours were also traced on the image from the fourth echo and then propagated to the images from the preceding echoes. This was repeated using the image from the first echo. Mean wall signal intensity measurements at the four echo times were fit to a mono-exponential decay curve to derive the mean T2 relaxation time for each set of contours.

RESULTS

Mean wall thickness decreased with increasing echo time, with an average thickness reduction of 8.6% between images acquired at the first and last echo times (TE) (0.93 mm at TE 17 ms versus 0.85 mm at TE 68 ms, P < 0.001). Average T2 relaxation time of the carotid wall decreased by 3% when the smaller contours from the last echo were used, which excluded the outer-most layer (54.3 ± 7.6 ms versus 52.7 ± 6.6 ms, P = 0.03).

CONCLUSION

Carotid wall thickness measurements decrease with echo time as expected by the fast T2 relaxation time of the outer-most layer, namely the adventitia. A short echo time is needed for thickness measurements to include adventitia, which plays an important role in plaque development.

Differential expression of oxidation-specific epitopes and apolipoprotein(a) in progressing and ruptured human coronary and carotid atherosclerotic lesions

The relationships between oxidation-specific epitopes (OSE) and lipoprotein (a) [Lp(a)] and progressive atherosclerosis and plaque rupture have not been determined. Coronary artery sections from sudden death victims and carotid endarterectomy specimens were immunostained for apoB-100, oxidized phospholipids (OxPL), apo(a), malondialdehyde-lysine (MDA), and MDA-related epitopes detected by antibody IK17 and macrophage markers. The presence of OxPL captured in carotid and saphenous vein graft distal protection devices was determined with LC-MS/MS. In coronary arteries, OSE and apo(a) were absent in normal coronary arteries and minimally present in early lesions. As lesions progressed, apoB and MDA epitopes did not increase, whereas macrophage, apo(a), OxPL, and IK17 epitopes increased proportionally, but they differed according to plaque type and plaque components. Apo(a) epitopes were present throughout early and late lesions, especially in macrophages and the necrotic core. IK17 and OxPL epitopes were strongest in late lesions in macrophage-rich areas, lipid pools, and the necrotic core, and they were most specifically associated with unstable and ruptured plaques. Specific OxPL were present in distal protection devices. Human atherosclerotic lesions manifest a differential expression of OSEs and apo(a) as they progress, rupture, and become clinically symptomatic. These findings provide a rationale for targeting OSE for biotheranostic applications in humans.

Comparison of carotid plaque ulcer detection using contrast-enhanced and time-of-flight MRA techniques

BACKGROUND AND PURPOSE

Ulceration in carotid plaque is a risk indicator for ischemic stroke. Our aim was to compare plaque ulcer detection by standard TOF and CE-MRA techniques and to identify factors that influence its detection.

MATERIALS AND METHODS

Carotid MR imaging scans were acquired on 2066 participants in the ARIC study. We studied the 600 thickest plaques. TOF-MRA, CE-MRA, and black-blood MR images were analyzed together to define ulcer presence (plaque surface niche ≥2 mm in depth). Sixty ulcerated arteries were detected. These arteries were randomly assigned, along with 40 nonulcerated plaques from the remaining 540, for evaluation of ulcer presence by 2 neuroradiologists. Associations between ulcer detection and ulcer characteristics, including orientation, location, and size, were determined and explored by CFD modeling.

RESULTS

One CE-MRA and 3 TOF-MRAs were noninterpretable and excluded. Of 71 ulcers in 56 arteries, readers detected an average of 39 (55%) on both TOF-MRA and CE-MRA, 26.5 (37.5%) only on CE-MRA, and 1 (1.5%) only on TOF-MRA, missing 4.5 (6%) ulcers by both methods. Ulcer detection by TOF-MRA was associated with its orientation (distally pointing versus perpendicular: OR = 5.57 [95% CI, 1.08-28.65]; proximally pointing versus perpendicular: OR = 0.21 [95% CI, 0.14-0.29]); location relative to point of maximum stenosis (distal versus isolevel: OR = 5.17 [95% CI, 2.10-12.70]); and neck-to-depth ratio (OR = 1.96 [95% CI, 1.11-3.45]) after controlling for stenosis and ulcer volume.

CONCLUSIONS

CE-MRA detects more ulcers than TOF-MRA in carotid plaques. Missed ulcers on TOF-MRA are influenced by ulcer orientation, location relative to point of maximum stenosis, and neck-to-depth ratio.

Improved prediction of disturbed flow via hemodynamically-inspired geometric variables

Arterial geometry has long been considered as a pragmatic alternative for inferring arterial flow disturbances, and their impact on the natural history and treatment of vascular diseases. Traditionally, definition of geometric variables is based on convenient shape descriptors, with only superficial consideration of their influence on flow and wall shear stress patterns. In the present study we demonstrate that a more studied consideration of the actual (cf. nominal) local hemodynamics can lead to substantial improvements in the prediction of disturbed flow by geometry. Starting from a well-characterized computational fluid dynamics (CFD) dataset of 50 normal carotid bifurcations, we observed that disturbed flow tended to be confined proximal to the flow divider, whereas geometric variables previously shown to be significant predictors of disturbed flow included features distal to the flow divider in their definitions. Flaring of the bifurcation leading to flow separation was redefined as the maximum relative expansion of the common carotid artery (CCA), proximal to the flow divider. The beneficial effect of primary curvature on flow inertia, via suppression of flow separation, was characterized by the in-plane tortuosity of CCA as it enters the flare region. Multiple linear regressions of these redefined geometric variables against various metrics of disturbed flow revealed R(2) values approaching 0.6, better than the roughly 0.3 achieved using the conventional shape-based variables, while maintaining their demonstrated real-world reproducibility. Such a hemodynamically-inspired approach to the definition of geometric variables may reap benefits for other applications where geometry is used as a surrogate marker of local hemodynamics.

Sex-specific association of age with carotid artery distensibility: multi-ethnic study of atherosclerosis

BACKGROUND

Older women have a higher prevalence of systolic hypertension than do men; however, whether or not this relates to arterial properties, such as distensibility coefficient (DC), is not known. We examined whether the association of carotid artery DC with age differed by sex in the Multi-Ethnic Study of Atherosclerosis (MESA).

METHODS

B-mode ultrasound-measured carotid diameters and brachial pressures were obtained from 6359 participants (53% female, 38% white, 12% Chinese, 27% black, 22% Hispanic, aged 45-85 years) of the MESA baseline examination. The within-individual slopes of 2log(diameter) vs. blood pressure fit using mixed models (MM) are interpreted as the DC, and interaction terms are interpreted as differences in DC. The MM calculation allows for correction of the confounding caused by the association of age, sex, and race with blood pressure, the denominator in the calculation of DC.

RESULTS

DC was associated with age, sex, and race (all p<0.001). Women had a greater age-related lowering of DC compared to men (2.52×10(-5) vs. 2.16×10(-5)/mm Hg lower DC per year of age, p=0.006). Mean diameter of carotid arteries was greater with age (p<0.001); this association also was significantly stronger in women compared to men (0.24% vs. 0.14% larger mean carotid diameter per year of age, p<0.001).

CONCLUSIONS

Greater stiffening and enlargement of arteries are seen in older women compared to older men. This implies that the afterload on the heart of older women is likely to be greater than that among older men.

Cholesterol is associated with the presence of a lipid core in carotid plaque of asymptomatic, young-to-middle-aged African Americans with and without HIV infection and cocaine use residing in inner-city Baltimore, Md., USA

BACKGROUND

Stroke remains a leading cause of death in the United States. While stroke-related mortality in the USA has declined over the past decades, stroke death rates are still higher for blacks than for whites, even at younger ages. The purpose of this study was to estimate the frequency of a lipid core and explore risk factors for its presence in asymptomatic, young-to-middle-aged urban African American adults recruited from inner-city Baltimore, Md., USA.

METHODS

Between August 28, 2003, and May 26, 2005, 198 African American participants aged 30-44 years from inner-city Baltimore, Md., were enrolled in an observational study of subclinical atherosclerosis related to HIV and cocaine use. In addition to clinical examinations and laboratory tests, B-mode ultrasound for intima-media thickness of the internal carotid arteries was performed. Among these 198, 52 were selected from the top 30th percentile of maximum carotid intima-media thickness by ultrasound, and high-resolution black blood MRI images were acquired through their carotid plaque before and after the intravenous administration of gadodiamide. Of these 52, 37 with maximum segmental thickness by MRI >1.0 mm were included in this study. Lumen and outer wall contours were defined using semiautomated analysis software. The frequency of a lipid core in carotid plaque was estimated and risk factors for lipid core presence were explored using logistic regression analysis.

RESULTS

Of the 37 participants in this study, 12 (32.4%) were women. The mean age was 38.7 ± 4.9 years. A lipid core was present in 9 (17%) of the plaques. Seventy percent of the study participants had a history of cigarette smoking. The mean total cholesterol level was 176.1 ± 37.3 mg/dl, the mean systolic blood pressure was 113.1 ± 13.3 mm Hg, and the mean diastolic blood pressure was 78.9 ± 9.5 mm Hg. There were 5 participants with hypertension (13.5%). Twelve (32%) participants had a history of chronic cocaine use, and 23 (62%) were HIV positive. Among the factors investigated, including age, sex, blood pressure, cigarette smoking, C-reactive protein, fasting glucose, triglycerides, serum total cholesterol, coronary calcium, cocaine use, and HIV infection, only total cholesterol was significantly associated with the presence of a lipid core.

CONCLUSIONS

This study revealed an unexpectedly high rate of the presence of lipid core in carotid plaque and highlights the importance of cholesterol lowering to prevent cerebrovascular disease in this population. Further population-based studies are warranted to confirm these results.

Carotid plaque neovascularization and hemorrhage detected by MR imaging are associated with recent cerebrovascular ischemic events

BACKGROUND AND PURPOSE

Pathologic studies suggest that neovascularization and hemorrhage are important features of plaque vulnerability for disruption. Our aim was to determine the associations of these features in carotid plaques with previous cerebrovascular ischemic events by using high-resolution CE-MRI.

MATERIALS AND METHODS

Forty-seven patients (36 men; mean age 72.5 ± 10 years) underwent CE-MRI and MRA examinations for carotid plaque at 3T. IPH presence was recorded. Neovascularity was categorized by the degree of adventitial enhancement (0, absent; 1, <50%; 2, ≥50%). Reader variability was assessed by using weighted κ. Associations with events were determined by using multivariable logistic regression.

RESULTS

Intra- and inter-reader agreement for grading adventitial enhancement were good to excellent. IPH was present in 49% of patients and was associated with events (P = .03). Patients grouped by categories 0, 1, and 2 adventitial enhancement had increasing frequencies of events (14% category 0, 48% category 1, 65% category 2; P = .02). Events were associated with IPH (OR, 10.18; 95% CI, 1.42-72.21) and adventitial enhancement (compared with category 0: OR, 14.90, 95% CI, 0.98-225.93 for category 1; OR, 51.17, 95% CI, 3.4-469.8 for category 2) after controlling for age, sex, cardiovascular risk factors, wall thickness, and stenosis. Stenosis was not associated with events.

CONCLUSIONS

Adventitial enhancement and IPH are independently associated with previous events and may provide important insight into stroke risk not achievable by stenosis.

On the shape of the common carotid artery with implications for blood velocity profiles

Clinical and engineering studies typically assume that the common carotid artery (CCA) is straight enough to assume fully developed flow, yet recent studies have demonstrated the presence of skewed velocity profiles. Toward elucidating the influence of mild vascular curvatures on blood flow patterns and atherosclerosis, this study aimed to characterize the three-dimensional shape of the human CCA. The left and right carotid arteries of 28 participants (63 ± 12 years) in the VALIDATE (Vascular Aging--The Link that Bridges Age to Atherosclerosis) study were digitally segmented from 3D contrast-enhanced magnetic resonance angiograms, from the aortic arch to the carotid bifurcation. Each CCA was divided into nominal cervical and thoracic segments, for which curvatures were estimated by least-squares fitting of the respective centerlines to planar arcs. The cervical CCA had a mean radius of curvature of 127 mm, corresponding to a mean lumen:curvature radius ratio of 1:50. The thoracic CCA was significantly more curved at 1:16, with the plane of curvature tilted by a mean angle of 25° and rotated close to 90° with respect to that of the cervical CCA. The left CCA was significantly longer and slightly more curved than the right CCA, and there was a weak but significant increase in CCA curvature with age. Computational fluid dynamic simulations carried out for idealized CCA geometries derived from these and other measured geometric parameters demonstrated that mild cervical curvature is sufficient to prevent flow from fully-developing to axisymmetry, independent of the degree of thoracic curvature. These findings reinforce the idea that fully developed flow may be the exception rather than the rule for the CCA, and perhaps other nominally long and straight vessels.

Relation of cholesterol and lipoprotein parameters with carotid artery plaque characteristics: the Atherosclerosis Risk in Communities (ARIC) carotid MRI study

OBJECTIVE

There is a paucity of data regarding relations of apolipoproteins (apolipoprotein B [ApoB] and apolipoprotein A-1 [Apo A-1]), lipoprotein particle measures (low-density lipoprotein particle concentration [LDLp] and high-density lipoprotein particle concentration [HDLp]), and lipoprotein cholesterol measures (low-density lipoprotein cholesterol [LDL-C], non-high-density lipoprotein cholesterol [non-HDL-C], and high-density lipoprotein cholesterol [HDL-C]) with atherosclerotic plaque burden, plaque eccentricity, and lipid-rich core presence as a marker of high-risk plaques.

METHODS

Carotid artery magnetic resonance imaging was performed in 1670 Atherosclerosis Risk in Communities study participants. Vessel wall and lipid cores were measured; normalized wall index (NWI), standard deviation (SD) of wall thickness (measure of plaque eccentricity) were calculated; and lipid cores were detected in vessels with ≥ 1.5mm thickness. Fasting concentrations of cholesterol, ApoB and Apo A-1, and LDLp and HDLp were measured.

RESULTS

Measures of plaque burden (carotid wall volume, wall thickness, and NWI) were positively associated with atherogenic cholesterol and lipoproteins (p < 0.05 for total cholesterol, LDL-C, non-HDL-C, ApoB, and LDLp), but not with HDL-C, Apo A-1, or HDLp. SD of wall thickness was associated with total cholesterol (p 0.01) and non-HDL-C (p 0.02). Although measures of atherogenic or anti-atherogenic cholesterol or lipoprotein were not individually associated with detection of a lipid-rich core, their ratios (total cholesterol/HDL-C, non-HDL-C/HDL-C, and LDLp/HDLp) were associated with lipid-rich core presence (p ≤ 0.05).

CONCLUSION

Extent of carotid atherosclerosis is associated with atherogenic cholesterol and lipoproteins. Atherogenic/anti-atherogenic cholesterol or particle ratios were associated with presence of a detectable lipid-rich core.

Scan-Rescan reproducibility of carotid bifurcation geometry from routine contrast-enhanced MR angiography

PURPOSE

To demonstrate the feasibility of rapid and reliable geometric characterization of normal carotid bifurcation geometry from routine 3D contrast-enhanced magnetic resonance (MR) angiograms.

MATERIALS AND METHODS

Repeat scans of 61 participants, acquired as part of the Atherosclerosis Risk in Communities (ARIC) Carotid MRI substudy, were digitally segmented using automated 3D level set methods, relying on an operator only to select the branch endpoints and thresholds for the 3D lumen surface initialization. Geometric factors characterizing the 3D lumen geometry were then extracted automatically.

RESULTS

Of 122 scans, 117 could be segmented within 5 minutes each, with 40% being of sufficiently high quality to require less than 2 minutes each. Irrespective of scan quality, geometric factors were found to be highly reproducible, with intraclass correlation coefficients (ICCs) typically above 0.9. The reconstructed lumen surfaces were reproducible to <0.3 mm on average, comparable to previous MRI-based reproducibility studies. Owing to the automated nature of the analysis, operator reliability was near-perfect (ICC >0.99), with lumen surface differences <0.1 mm.

CONCLUSION

The 3D geometry of the carotid bifurcation can be characterized rapidly and with a high degree of consistency, even for suboptimal image qualities. This bodes well for large-scale retrospective or prospective studies aimed at teasing out the influence of local vs. systemic risk factors for early atherosclerosis.

Effect of common carotid artery inlet length on normal carotid bifurcation hemodynamics

Controversy exists regarding the suitability of fully developed versus measured inlet velocity profiles for image-based computational fluid dynamics (CFD) studies of carotid bifurcation hemodynamics. Here, we attempt to resolve this by investigating the impact of the reconstructed common carotid artery (CCA) inlet length on computed metrics of "disturbed" flow. Twelve normal carotid bifurcation geometries were reconstructed from contrast-enhanced angiograms acquired as part of the Vascular Aging--The Link That Bridges Age to Atherosclerosis study (VALIDATE). The right carotid artery lumen geometry was reconstructed from its brachiocephalic origin to well above the bifurcation, and the CCA was truncated objectively at locations one, three, five, and seven diameters proximal to where it flares into the bifurcation. Relative to the simulations carried out using the full CCA, models truncated at one CCA diameter strongly overestimated the amount of disturbed flow. Substantial improvement was offered by using three CCA diameters, with only minor further improvement using five CCA diameters. With seven CCA diameters, the amounts of disturbed flow agreed unambiguously with those predicted by the corresponding full-length models. Based on these findings, we recommend that image-based CFD models of the carotid bifurcation should incorporate at least three diameters of CCA length if fully developed velocity profiles are to be imposed at the inlet. The need for imposing measured inlet velocity profiles would seem to be relevant only for those cases where the CCA is severely truncated.

Identification of intraplaque hemorrhage on MR angiography images: a comparison of contrast-enhanced mask and time-of-flight techniques

BACKGROUND AND PURPOSE

MRA is widely used to measure carotid narrowing. Standard CE- and TOF-MRA techniques use highly T1-weighted gradient-echo sequences that can detect T1 short blood products, so they have the potential to identify IPH, an indicator of plaque rupture. We sought to determine the accuracy and reliability of these MRA sequences to detect IPH.

MATERIALS AND METHODS

3D TOF and CE carotid MRA scans were obtained at 3T on 15 patients (age range, 58-86 years; 13 men) scheduled for CEA. The source images from the precontrast (mask) CE-MRA and the TOF sequences were reviewed by 2 independent readers for IPH presence (identified as hyperintense signal intensity compared with adjacent muscle). CEA specimens were stained with antibody against glycophorin A and Mallory stain to detect IPH and were correlated with MR images.

RESULTS

Nine of 15 CEA specimens (61 of 144 MR images) contained IPH confirmed by histology. Compared with TOF, CE-MRA mask demonstrated greater sensitivity, specificity, PPV, and NPV for IPH detection. The accuracy for correctly identifying IPH by using CE-MRA mask images and TOF images was 94% and 84%, respectively. Inter- and intraobserver agreement for IPH detection was excellent by mask images (κ = 0.91 and κ = 0.94, respectively) and TOF images (κ = 0.77 and κ = 0.84, respectively).

CONCLUSIONS

CE-MRA mask images are highly accurate and reliable for identifying IPH, more so than the TOF sequence, and can potentially provide valuable information about risk for rupture.

Advanced contrast-enhanced MRI for looking beyond the lumen to predict stroke: building a risk profile for carotid plaque

Carotid plaque MRI can identify components indicative of stroke risk, including the thin/ruptured fibrous cap and lipid core. Gadolinium contrast, typically administered for routine MR angiography acquisitions, can be used to improve plaque characterization, extending risk assessment beyond the plaque's hemodynamic impact on the lumen. Gadolinium preferentially enhances the cap, improves reliability of vessel wall measurements, and highlights neovessels, improving stroke risk stratification. Additionally, the precontrast series from the contrast-enhanced MR angiography can help identify intraplaque hemorrhage, another important risk marker. Prospective validation of these features is needed to develop a carotid plaque risk profile for clinical implementation.

Relationship between circulating levels of RANTES (regulated on activation, normal T-cell expressed, and secreted) and carotid plaque characteristics: the Atherosclerosis Risk in Communities (ARIC) Carotid MRI Study

AIMS

To assess the relationship between regulated on activation, normal T-cell expressed and secreted (RANTES) and carotid atherosclerotic plaque burden and plaque characteristics.

METHODS AND RESULTS

Gadolinium-enhanced magnetic resonance imaging (MRI) of the carotid artery was performed in 1901 participants from the Atherosclerosis Risk in Communities (ARIC) Study. Wall thickness and volume, lipid-core volume, and fibrous cap thickness (by MRI) and plasma RANTES levels (by ELISA) were measured. Regression analysis was performed to study the associations between MRI variables and RANTES. Among 1769 inclusive participants, multivariable regression analysis revealed that total wall volume [beta-coefficient (β) = 0.09, P = 0.008], maximum wall thickness (β = 0.08, P = 0.01), vessel wall area (β = 0.07, P = 0.02), mean minimum fibrous cap thickness (β = 0.11, P = 0.03), and high-sensitivity C-reactive protein (β = 0.09, P = 0.01) were positively associated with RANTES. Total lipid-core volume showed positive association in unadjusted models (β = 0.18, P = 0.02), but not in fully adjusted models (β = 0.13, P = 0.09). RANTES levels were highest in Caucasian females followed by Caucasian males, African-American females, and African-American males (P < 0.0001). Statin use attenuated the relationship between RANTES and measures of plaque burden.

CONCLUSION

Positive associations between RANTES and carotid wall thickness and lipid-core volume (in univariate analysis) suggest that higher RANTES levels may be associated with extent of carotid atherosclerosis and high-risk plaques. Associations between fibrous cap thickness and RANTES likely reflect the lower reliability estimate for fibrous cap measurements compared with wall volume or lipid-core volume measurements. Statin use may modify the association between RANTES and carotid atherosclerosis. Furthermore, RANTES levels vary by race.

Association of combinations of lipid parameters with carotid intima-media thickness and coronary artery calcium in the MESA (Multi-Ethnic Study of Atherosclerosis)

OBJECTIVES

The purpose of this study was to determine the association of combinations of lipid parameters with subclinical atherosclerosis.

BACKGROUND

Carotid intima-media thickness (CIMT) and coronary artery calcium (CAC) are significantly associated with incident cardiovascular disease (CVD). The association between common dyslipidemias (combined hyperlipidemia, [simple] hypercholesterolemia, dyslipidemia of metabolic syndrome, isolated low high-density lipoprotein cholesterol, and isolated hypertriglyceridemia) compared with normolipemia, and CIMT and CAC has not been previously examined.

METHODS

The MESA (Multi-Ethnic Study of Atherosclerosis) participants were White, Chinese, African-American, or Hispanic adults without clinical CVD. Subjects with diabetes mellitus or who were receiving lipid-lowering therapy were excluded. Every participant was classified into only 1 of 6 groups defined by specific low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, or triglyceride cut points. Multivariate linear and relative risk regressions evaluated the cross-sectional associations with CIMT and CAC after adjusting for CVD risk factors. Interactions with race, sex, and high-sensitivity C-reactive protein were evaluated for CIMT and CAC outcomes.

RESULTS

Among 4,792 participants, only those with combined hyperlipidemia and hypercholesterolemia demonstrated both increased common CIMT (combined hyperlipidemia 0.048 mm thicker, 95% confidence interval [CI]: 0.016 to 0.080 mm; hypercholesterolemia 0.048 mm thicker, 95% CI: 0.029 to 0.067 mm) and internal CIMT (combined hyperlipidemia 0.120 mm thicker, 95% CI: 0.032 to 0.208 mm; and hypercholesterolemia 0.161 mm thicker, 95% CI: 0.098 to 0.223 mm) as well as increased risk for prevalent CAC (combined hyperlipidemia relative risk: 1.22, 95% CI: 1.08 to 1.38; hypercholesterolemia relative risk: 1.22, 95% CI: 1.11 to 1.34) compared with normolipemia. The interactions between lipid parameters and race, sex, or high-sensitivity C-reactive protein were not significant for any outcomes.

CONCLUSIONS

Combined hyperlipidemia and simple hypercholesterolemia were associated with increased CIMT and prevalent CAC in a relatively healthy multiethnic population.

Carotid bifurcation hemodynamics in older adults: effect of measured versus assumed flow waveform

Recent work has illuminated differences in carotid artery blood flow rate dynamics of older versus young adults. To what degree flow waveform shape, and indeed the use of measured versus assumed flow rates, affects the simulated hemodynamics of older adult carotid bifurcations has not been elucidated. Image-based computational fluid dynamics models of N=9 normal, older adult carotid bifurcations were reconstructed from magnetic resonance angiography. Subject-specific hemodynamics were computed by imposing each individual's inlet and outlet flow rates measured by cine phase-contrast magnetic resonance imaging or by imposing characteristic young and older adult flow waveform shapes adjusted to cycle-averaged flow rates measured or allometrically scaled to the inlet and outlet areas. Despite appreciable differences in the measured versus assumed flow conditions, the locations and extents of low wall shear stress and elevated relative residence time were broadly consistent; however, the extent of elevated oscillatory shear index was substantially underestimated, more by the use of assumed cycle-averaged flow rates than the assumed flow waveform shape. For studies of individual vessels, use of a characteristic flow waveform shape is likely sufficient, with some benefit offered by scaling to measured cycle-averaged flow rates. For larger-scale studies of many vessels, ranking of cases according to presumed hemodynamic or geometric risk is robust to the assumed flow conditions.

Remodeling of carotid arteries detected with MR imaging: atherosclerosis risk in communities carotid MRI study

PURPOSE

To determine the extent of thickening of the carotid arterial walls that may be accommodated by outward remodeling.

MATERIALS AND METHODS

Institutional review board approval was obtained at each participating site, and informed consent was obtained from each participant. All study sites conducted this study in compliance with HIPAA requirements. A total of 2066 participants (age range, 60-85 years) from the Atherosclerosis Risk in Communities (ARIC) study were enrolled in the ARIC Carotid MRI Study. Maximum wall thickness and luminal area were measured with gadolinium-enhanced magnetic resonance (MR) imaging in both common carotid arteries (CCAs) and in one internal carotid artery (ICA) 2 mm above the flow divider. Complete data were available for 1064 ICAs and 3348 CCAs. The association of maximum wall thickness with lumen area was evaluated with linear regression, and adjustments were made for participant age, sex, race, height, and height squared.

RESULTS

In the ICA, lumen area was relatively constant across patients with a wall thickness of 1.38 mm or less. In patients with a wall thickness of more than 1.38 mm, however, lumen area decreased linearly as wall thickness increased. Wall area represented a median of 61.9% of the area circumscribed by the vessel at a maximum wall thickness of 1.50 mm +/- 0.05 (standard deviation) and 75.4% at a maximum wall thickness of 4.0 mm +/- 0.10. In the CCA, lumen area was preserved across wall thicknesses less than 2.06 mm, representing 99% of vessels.

CONCLUSION

Atherosclerotic thickening in the ICA appears to be accommodated for vessels with a maximum wall thickness of less than 1.5 mm. Beyond this threshold, greater thickness is associated with a smaller lumen. The CCA appears to accommodate a wall thickness of less than 2.0 mm. These estimates indicate that the carotid arteries are able to compensate for a greater degree of thickening than are the coronary arteries.

MMP2 genetic variation is associated with measures of fibrous cap thickness: The Atherosclerosis Risk in Communities Carotid MRI Study

OBJECTIVE

Genetic variation in matrix metalloproteinase (MMP) promoter regions alter the transcriptional activity of MMPs and has been consistently associated with CHD, presumably through plaque degradation and remodeling. We examined the association of MMP promoter variation with multiple plaque characteristics measured by gadolinium-enhanced MRI among 1700 participants in the Atherosclerosis Risk in Communities (ARIC) Carotid MRI Study.

METHODS

For the analyses presented here, 1700 participants of the biracial ARIC Carotid MRI Study ( approximately 1000 participants with thick carotid artery walls and approximately 700 randomly sampled participants) were evaluated for associations of MMP genetic variation with multiple plaque characteristics, including carotid artery wall thickness, lipid core and fibrous cap measures. MRI studies were performed on a 1.5T scanner equipped with a bilateral 4-element phased array carotid coil.

RESULTS

Fifty-one percent of the participants were female, 77% white, 23% African American, and the mean age was 70 years. MMP2 C-1306T variant genotypes (CT+TT) were significantly associated with higher cap thickness measures, but not with wall thickness or lipid core measures. Individuals with the CC genotype had approximately 0.1mm thinner cap thickness compared to those carrying a T allele (P=0.02).

CONCLUSION

Genetic variation within the MMP2 promoter region was associated with cap thickness and therefore may influence the role of MMP2 in plaque vulnerability.

MRI measurements of carotid plaque in the atherosclerosis risk in communities (ARIC) study: methods, reliability and descriptive statistics

PURPOSE

To measure carotid plaque components using MRI and estimate reliability in the population-based Atherosclerosis Risk in Communities (ARIC) study.

MATERIALS AND METHODS

Contrast-enhanced high-resolution (0.51 x 0.58 x 2 mm(3)) MRI images were acquired through internal (ICA) and common carotid arteries (CCA) of 2066 ARIC participants at four sites. Sixty-one exams were repeated and 164 pairs had repeated interpretations. Plaque component thicknesses, areas and volumes over eight slices (1.6-cm segment) were measured. Intraplaque hemorrhage was recorded. Reliability was evaluated by intraclass correlations and kappa statistics.

RESULTS

There were 1769 successful MRI exams (mean age 71 years; 57% females; 81% white; 19% African-Americans). Repeat scan reliability was highest for CCA lumen area (0.94) and maximum wall thickness (0.89), ICA lumen area (0.89) and maximum wall thickness (0.77) and total wall volume (0.79), and lowest for small structures-core volume (0.30) and mean cap thickness (0.38). Overall reliability was primarily related to reader variability rather than scan acquisition. K's for presence of core, calcification and hemorrhage were fair to good. White men had the thickest plaques (average maximum ICA wall thickness = 2.3 mm) and the most cores (34%).

CONCLUSION

The most important limiting factor for MRI measurements of plaque components is reader variability. Measurement error depends largely on the analyzed structure's size.

Association of circulating matrix metalloproteinases with carotid artery characteristics: the Atherosclerosis Risk in Communities Carotid MRI Study

OBJECTIVE

To examine the relationship of plasma levels of matrix metalloproteinases (MMPs) and tissue inhibitor of metalloproteinase 1 (TIMP-1) with carotid artery characteristics measured by MRI in a cross-sectional investigation among Atherosclerosis Risk in Communities Carotid MRI Study participants.

METHODS AND RESULTS

A stratified random sample was recruited based on intima-media thickness from a previous ultrasonographic examination. A high-resolution gadolinium-enhanced MRI examination of the carotid artery was performed from 2004 to 2005 on 1901 Atherosclerosis Risk in Communities cohort participants. Multiple carotid wall characteristics, including wall thickness, lumen area, calcium area, lipid core, and fibrous cap measures, were evaluated for associations with plasma MMPs 1, 2, 3, 7, 8, and 9 and TIMP-1. Plasma MMPs 1, 3, and 7 were significantly higher among participants in the high intima-media thickness group compared with those in the low intima-media thickness group. The normalized wall index was independently associated with MMPs 3 and 7 and TIMP-1. MMP-7 was positively associated with carotid calcification. The mean fibrous cap thickness was significantly higher in individuals with elevated TIMP-1 levels. In addition, TIMP-1 was positively associated with measures of lipid core.

CONCLUSION

Circulating levels of specific MMPs and TIMP-1 were associated with carotid wall remodeling and structural changes related to plaque burden in elderly participants.

Characterization of volumetric flow rate waveforms at the carotid bifurcations of older adults

While it is widely appreciated that volumetric blood flow rate (VFR) dynamics change with age, there has been no detailed characterization of the typical shape of carotid bifurcation VFR waveforms of older adults. Toward this end, retrospectively gated phase contrast magnetic resonance imaging was used to measure time-resolved VFR waveforms proximal and distal to the carotid bifurcations of 94 older adults (age 68 +/- 8 years) with little or no carotid artery disease, recruited from the BLSA cohort of the VALIDATE study of factors in vascular aging. Timings and amplitudes of well-defined feature points from these waveforms were extracted automatically and averaged to produce representative common, internal and external carotid artery (CCA, ICA and ECA) waveform shapes. Relative to young adults, waveforms from older adults were found to exhibit a significantly augmented secondary peak during late systole, resulting in significantly higher resistance index (RI) and flow augmentation index (FAI). Cycle-averaged VFR at the CCA, ICA and ECA were 389 +/- 74, 245 +/- 61 and 125 +/- 49 mL min(-1), respectively, reflecting a significant cycle-averaged outflow deficit of 5%, which peaked at around 10% during systole. A small but significant mean delay of 13 ms between arrivals of ICA versus CCA/ECA peak VFR suggested differential compliance of these vessels. Sex and age differences in waveform shape were also noted. The characteristic waveforms presented here may serve as a convenient baseline for studies of VFR waveform dynamics or as suitable boundary conditions for models of blood flow in the carotid arteries of older adults.

Association of scavenger receptor class B type I polymorphisms with subclinical atherosclerosis: the Multi-Ethnic Study of Atherosclerosis

BACKGROUND

Little is known about the association of scavenger receptor class B type I (SCARB1) single-nucleotide polymorphisms (SNPs) and subclinical atherosclerosis, particularly in subjects of different racial/ethnic backgrounds. We examined this relationship in the Multi-Ethnic Study of Atherosclerosis.

METHODS AND RESULTS

Forty-three SCARB1-tagging SNPs were genotyped. Baseline examinations included fasting lipids and subclinical atherosclerosis phenotypes (coronary artery calcification, common carotid intimal-medial artery thickness [CCIMT], and internal carotid intimal-medial artery thickness). Examining SNP associations with different subclinical atherosclerosis phenotypes across multiple racial/ethnic groups with adjustment for multiple covariates, we found that the C allele of SNP rs10846744 was associated with higher CCIMT in African American (P=0.03), Chinese (P=0.02), European American (P=0.05), and Hispanic participants (P=0.03) and was strongly associated in pooled analyses (P=0.0002). The results also showed that the association of this SNP with CCIMT was independent of lipids and other well-established cardiovascular risk factors. Stratifying by sex, there seemed to be a strong association of rs10846744 with CCIMT in women, but no genotype-sex interactions were observed.

CONCLUSIONS

Variation in SCARB1 at rs10846744 was significantly associated with CCIMT across racial/ethnic groups in Multi-Ethnic Study of Atherosclerosis.

Positive remodeling of the coronary arteries detected by magnetic resonance imaging in an asymptomatic population: MESA (Multi-Ethnic Study of Atherosclerosis)

OBJECTIVES

The purpose of this study was to assess coronary arterial remodeling as a marker of subclinical atherosclerosis using coronary wall magnetic resonance imaging (MRI) in an asymptomatic population-based cohort.

BACKGROUND

In early atherosclerosis, compensatory enlargement of both the outer wall of the vessel as well as the lumen, termed compensatory enlargement or positive remodeling, occurs before luminal narrowing.

METHODS

One hundred seventy-nine participants in the MESA (Multi-Ethnic Study of Atherosclerosis) trial were evaluated using black-blood coronary wall MRI. Coronary cross-sectional area (vessel size), lumen area, and mean wall thickness of the proximal coronary arteries were measured.

RESULTS

Men had a greater vessel size, lumen area, and mean wall thickness than women (38.3 +/- 11.3 mm2 vs. 32.6 +/- 9.4 mm2, 6.7 +/- 3.2 mm2 vs. 5.3 +/- 2.4 mm2, and 2.0 +/- 0.3 mm vs. 1.9 +/- 0.3 mm, respectively, p < 0.05). No significant coronary artery narrowing was present by magnetic resonance angiography. Overall, coronary vessel size increased 25.9 mm2 per millimeter increase in coronary wall thickness, whereas lumen area increased only slightly at 3.1 mm2 for every millimeter increase in wall thickness (difference in slopes, p < 0.0001). Adjusting for age and sex, participants with an Agatston score >0 were more likely to have wall thickness >2.0 mm (odds ratio: 2.0, 95% confidence interval: 1.01 to 3.84).

CONCLUSIONS

Coronary wall MRI detected positive arterial remodeling in asymptomatic men and women with subclinical atherosclerosis.

On the overestimation of early wall thickening at the carotid bulb by black blood MRI, with implications for coronary and vulnerable plaque imaging

Black blood MRI is an attractive tool for monitoring normal and pathological wall thickening; however, limited spatial resolutions can conspire with complex vascular geometries to distort the appearance of the wall in ways hitherto unclear. To elucidate this, a thin-walled cylinder model was developed to predict the composite effects of obliqueness, in-plane resolution and voxel anisotropy on the accuracy of MRI-derived wall thickness measurements. These predictions were validated by means of imaging of a thin-walled carotid bifurcation phantom. Typical thick-slice axial acquisitions were found to result in artifactual wall thickening at the carotid bulb, owing to its obliqueness to the nominal imaging plane. Obliqueness was less problematic for near-isotropic resolutions; however, the obligatory reduction of in-plane resolution served to inflate wall thicknesses uniformly by up to 50%. Moreover, the nonlinear relationship between wall thickness and its overestimation served to mask genuine differences in wall thickness, an effect predicted to be worse for thinner coronary artery walls and plaque caps. Therefore, care must be taken when interpreting black blood MRI wall thickness measurements in the presence-or absence-of observed differences within or between individuals.

Cystatin C and carotid intima-media thickness in asymptomatic adults: the Multi-Ethnic Study of Atherosclerosis (MESA)

BACKGROUND

Persons with early kidney disease have an increased risk of cardiovascular events and mortality, but the importance of accelerated atherosclerosis in promoting these outcomes is unclear. We therefore explored whether serum cystatin C level is associated with carotid intima-media thickness (IMT) in ambulatory adults without clinical heart disease.

STUDY DESIGN

Cross-sectional study.

SETTING & PARTICIPANTS

We evaluated 6,557 ethnically diverse persons free of clinical cardiovascular disease aged 45 to 84 years at the baseline visit of the Multi-Ethnic Study of Atherosclerosis.

PREDICTORS

Kidney function was estimated by using 2 methods: serum cystatin C level and estimated glomerular filtration rate, based on creatinine and cystatin C levels.

OUTCOMES & MEASUREMENTS

Study outcomes were internal and common carotid IMT, measured by using high-resolution B-mode ultrasound. Multivariate linear and logistic regressions were used to evaluate the independent association of kidney function with carotid IMT.

RESULTS

In unadjusted linear analysis, each SD (0.23 mg/L) greater cystatin C level was associated with 0.091-mm greater internal carotid IMT (P < 0.001), but this association was diminished by 70% after adjustment for age, sex, and race/ethnicity (0.027 mm; P < 0.001) and was no longer significant after adjustment for cardiovascular risk factors (0.005 mm; P = 0.5). Similarly, the strong unadjusted associations of cystatin C level with common carotid IMT disappeared after adjustment. Chronic kidney disease, defined by using either creatinine level or cystatin C-based estimated glomerular filtration rate less than 60 mL/min/1.73 m(2), had no independent association with internal and common carotid IMT.

LIMITATIONS

There were few participants with severe kidney disease.

CONCLUSIONS

Cystatin C level had no independent association with carotid IMT in a population free of clinical heart disease. This observation suggests that accelerated atherosclerosis is unlikely to be the primary mechanism explaining the independent association of cystatin C level with cardiovascular risk.

Comparison of Gadolinium-Enhanced Cardiovascular Magnetic Resonance Angiography with High-Resolution Black Blood Cardiovascular Magnetic Resonance for Assessing Carotid Artery Stenosis

PURPOSE

Carotid angiography is used to assess stroke risk, but it cannot reliably characterize plaque burden because the vessel remodels during plaque formation. High-resolution black blood cardiovascular magnetic resonance (BBCMR) depicts the outer wall thereby providing a truer estimate of plaque size. We compared carotid stenosis by gadolinium enhancement cardiovascular magnetic resonance angiography (CMRA) versus high-resolution BBCMR.

METHODS

Twenty-four subjects (M:F = 20:4; ages 57-83 years) with carotid atherosclerosis underwent CMRA and transaxial BBCMR through the stenosis. Area and diameter stenosis measurements by NASCET criteria using CMRA images were compared to area stenosis measurements based on outer wall and lumen contours drawn on corresponding BBCMR images.

RESULTS

Area stenosis by CMRA correlated with area stenosis by BBCMR (r = 0.77; 95% CI: 0.58, 0.89). BBCMR values exceeded corresponding CMRA area measurements in 20 of 24 cases, with the remainder being highly stenotic (> 90%).

CONCLUSION

CMRA yields lower estimates of luminal narrowing compared to BBCMR, which delineates the outer wall and accounts for vascular remodeling. BBCMR could serve as a new measure of narrowing to guide management, but prospective studies are needed to better understand the clinical implications of this new scale of disease.