Associations of Intracranial Artery Length and Branch Number on Time-of-Flight MRA With Cognitive Impairment in Hypertensive Older Males

BACKGROUND

Hypertension-induced impairment of the cerebral artery network contributes to cognitive impairment. Characterizing the structure and function of cerebral arteries may facilitate the understanding of hypertension-related pathological mechanisms and lead to the development of new indicators for cognitive impairment.

PURPOSE

To investigate the associations between morphological features of the intracranial arteries distal to the circle of Willis on time-of-flight MRA (TOF-MRA) and cognitive performance in a hypertensive cohort.

STUDY TYPE

Prospective observational study.

POPULATION

189 hypertensive older males (mean age 64.9 ± 7.2 years).

FIELD STRENGTH/SEQUENCE

TOF-MRA sequence with a 3D spoiled gradient echo readout and arterial spin labeling perfusion imaging sequence with a 3D stack-of-spirals fast spin echo readout at 3T.

ASSESSMENT

The intracranial arteries were segmented from TOF-MRA and the total length of distal arteries (TLoDA) and number of arterial branches (NoB) were calculated. The mean gray matter cerebral blood flow (GM-CBF) was extracted from arterial spin labeling perfusion imaging. The cognitive level was assessed with short-term and long-term delay-recall auditory verbal learning test (AVLT) scores, and with montreal cognitive assessment.

STATISTICAL TESTS

Univariable and multivariable linear regression were used to analyze the associations between TLoDA, NoB, GM-CBF and the cognitive assessment scores, with P < 0.05 indicating significance.

RESULTS

TLoDA (r = 0.314) and NoB (r = 0.346) were significantly correlated with GM-CBF. Multivariable linear regression analyses showed that TLoDA and NoB, but not GM-CBF (P = 0.272 and 0.141), were significantly associated with short-term and long-term delay-recall AVLT scores. These associations remained significant after adjusting for GM-CBF.

DATA CONCLUSION

The TLoDA and NoB of distal intracranial arteries on TOF-MRA are significantly associated with cognitive impairment in hypertensive subjects.

LEVEL OF EVIDENCE

2 TECHNICAL EFFICACY: Stage 3.

Carotid Plaque-RADS: A Novel Stroke Risk Classification System

BACKGROUND

Carotid artery atherosclerosis is highly prevalent in the general population and is a well-established risk factor for acute ischemic stroke. Although the morphological characteristics of vulnerable plaques are well recognized, there is a lack of consensus in reporting and interpreting carotid plaque features.

OBJECTIVES

The aim of this paper is to establish a consistent and comprehensive approach for imaging and reporting carotid plaque by introducing the Plaque-RADS (Reporting and Data System) score.

METHODS

A panel of experts recognized the necessity to develop a classification system for carotid plaque and its defining characteristics. Using a multimodality analysis approach, the Plaque-RADS categories were established through consensus, drawing on existing published reports.

RESULTS

The authors present a universal classification that is applicable to both researchers and clinicians. The Plaque-RADS score offers a morphological assessment in addition to the prevailing quantitative parameter of "stenosis." The Plaque-RADS score spans from grade 1 (indicating complete absence of plaque) to grade 4 (representing complicated plaque). Accompanying visual examples are included to facilitate a clear understanding of the Plaque-RADS categories.

CONCLUSIONS

Plaque-RADS is a standardized and reliable system of reporting carotid plaque composition and morphology via different imaging modalities, such as ultrasound, computed tomography, and magnetic resonance imaging. This scoring system has the potential to help in the precise identification of patients who may benefit from exclusive medical intervention and those who require alternative treatments, thereby enhancing patient care. A standardized lexicon and structured reporting promise to enhance communication between radiologists, referring clinicians, and scientists.

Plaque Evolution and Vessel Wall Remodeling of Intracranial Arteries: A Prospective, Longitudinal Vessel Wall MRI Study

BACKGROUND

Progression of intracranial atherosclerotic disease (ICAD) is associated with ischemic stroke events and can be quantified with three-dimensional (3D) intracranial vessel wall (IVW) MRI. However, longitudinal 3D IVW studies are limited and ICAD evolution remains relatively unknown.

PURPOSE

To evaluate ICAD changes longitudinally and to characterize the imaging patterns of atherosclerotic plaque evolution.

STUDY TYPE

Prospective.

POPULATION

37 patients (69 ± 12 years old, 12 females) with angiography confirmed ICAD.

FIELD STRENGTH/SEQUENCE

3.0T/3D time-of-flight gradient echo sequence and T1- and proton density-weighted fast spin echo sequences.

ASSESSMENT

Each patient underwent baseline and 1-year follow-up IVW. Then, IVW data from both time points were jointly preprocessed using a multitime point, multicontrast, and multiplanar viewing workflow (known as MOCHA). Lumen and outer wall of plaques were traced and measured, and plaques were then categorized into progression, stable, and regression groups based on changes in plaque wall thickness. Patient demographic and clinical data were collected. Culprit plaques were identified based on cerebral ischemic infarcts.

STATISTICAL TESTS

Generalized estimating equations-based linear and logistic regressions were used to assess associations between vascular risk factors, medications, luminal stenosis, IVW plaque imaging features, and longitudinal changes. A two-sided P-value<0.05 was considered statistically significant.

RESULTS

Diabetes was significantly associated with ICAD progression, resulting in 6.6% decrease in lumen area and 6.7% increase in wall thickness at 1-year follow-up. After accounting for arterial segments, baseline contrast enhancement predicted plaque progression (odds ratio = 3.61). Culprit plaques experienced an average luminal expansion of 10.9% after 1 year. 74% of the plaques remained stable during follow-up. The regression group (18 plaques) showed significant increase in minimum lumen area (from 7.4 to 8.3 mm2 ), while the progression group (13 plaques) showed significant decrease in minimum lumen area (from 5.4 to 4.3 mm2 ).

DATA CONCLUSION

Longitudinal 3D IVW showed ICAD remodeling on the lumen side. Culprit plaques demonstrated longitudinal luminal expansion compared with their non-culprit counterparts. Baseline plaque contrast enhancement and diabetes mellitus were found to be significantly associated with ICAD changes.

EVIDENCE LEVEL

2 TECHNICAL EFFICACY: Stage 3.

Alterations in cerebral distal vascular features and effect on cognition in a high cardiovascular risk population: A prospective longitudinal study

BACKGROUND

Alterations in cerebral vasculature are instrumental in affecting cognition. Current studies mainly focus on proximal large arteries and small vessels, while disregarding morphology and blood flow of the arteries between them (medium-to-large arteries).

METHODS

In this prospective study, two types of non-contrast enhanced magnetic resonance angiography (NCE-MRA) techniques, simultaneous non-contrast angiography and intraplaque hemorrhage (SNAP) and 3D Time-of-flight (TOF), were used to measure vascular morphologic features in medium-to-large intracranial arteries. Grey matter (GM) tissue level perfusion was assessed with arterial spin labeling (ASL) MRI. Twenty-seven subjects at high cardiovascular risk underwent baseline and 12-month follow-up MRI to compare the relationship between morphological features measured by NCE MRA, GM CBF by ASL MRI, and cognitive function measured by the Montreal Cognitive Assessment (MoCA).

RESULTS

Changes in both global medium-to-large arteries and posterior cerebral (PCA) distal artery length and branch numbers, measured on SNAP MRA, were significantly associated with alterations in MoCA scores (P < 0.01), after adjusting for clinical confounding factors, total brain volume, and total white matter lesion (WML) volume. There were no associations between MoCA scores and vascular features on TOF MRA or ASL GM CBF.

CONCLUSIONS

Alterations in vascular features of distal medium-to-large arteries may be more sensitive for detecting potential changes in cognition than cerebral blood flow alterations at the parenchymal level captured by perfusion ASL. Hemodynamic information from distal medium-to-large arteries provides an additional tool to advance understanding of the vascular contributions to cognitive function.

Atherosclerotic carotid plaque characteristics vary with time from ischemic event: A multicenter, prospective magnetic resonance vessel wall imaging registry study

Recent studies report that the rate of recurrent stroke is highest in the stages immediately following cerebral infarction and decreases over time in patients with atherosclerotic carotid stenosis. The purpose of this study was to identify temporal differences in early stage carotid plaque components from acute cerebrovascular ischemic events using carotid MRI. Carotid plaque images were obtained on 3 T MRI from 128 patients enrolled in MR-CAS. Among the 128 subjects, 53 were symptomatic and 75 asymptomatic. The symptomatic patients were classified into three groups based on interval from onset of symptoms to the date of the carotid MRI (Group <14 days; 15-30 days; and > 30 days). The volume of each plaque component was identified and quantified from MR images. The presence of juxtaluminal loose matrix/inflammation (LM/I) was identified as a possible indicator of inflammation on the luminal side. Plaque components were compared between groups using the Wilcoxon rank-sum or the Chi-square test. Patient characteristics and carotid plaque morphology were similar among all four groups. The median volume of LM/I in Group >30 days was significantly lower than in other groups (0 mm3 vs 12.3 mm3 and 18.1 mm3; p = 0.003). In addition, the prevalence of juxtaluminal LM/I decreased over time (ptrend = 0.002). There were no statistically significant differences in other plaque components between the symptomatic groups. The volume of LM/I was significantly smaller in Group >30 days and prevalence of juxtaluminal LM/I in the atherosclerotic carotid plaque was high in the early stages after events. This suggests that carotid plaques undergo rapid evolution after an acute cerebrovascular ischemic event.

Survey of the American Society of Neuroradiology Membership on the Use and Value of Extracranial Carotid Vessel Wall MRI

BACKGROUND AND PURPOSE

Extracranial vessel wall MRI (EC-VWI) contributes to vasculopathy characterization. This survey study investigated EC-VWI adoption by American Society of Neuroradiology (ASNR) members and indications and barriers to implementation.

MATERIALS AND METHODS

The ASNR Vessel Wall Imaging Study Group survey on EC-VWI use, frequency, applications, MR imaging systems and field strength used, protocol development approaches, vendor engagement, reasons for not using EC-VWI, ordering provider interest, and impact on clinical care was distributed to the ASNR membership between April 2, 2019, to August 30, 2019.

RESULTS

There were 532 responses; 79 were excluded due to minimal, incomplete response and 42 due to redundant institutional responses, leaving 411 responses. Twenty-six percent indicated that their institution performed EC-VWI, with 66.3% performing it ≤1-2 times per month, most frequently on 3T MR imaging, with most using combined 3D and 2D protocols. Protocols most commonly included pre- and postcontrast T1-weighted imaging, TOF-MRA, and contrast-enhanced MRA. Inflammatory vasculopathy (63.3%), plaque vulnerability assessments (61.1%), intraplaque hemorrhage (61.1%), and dissection-detection/characterization (51.1%) were the most frequent applications. For those not performing EC-VWI, the reasons were a lack of ordering provider interest (63.9%), lack of radiologist time/interest (47.5%) or technical support (41.4%) for protocol development, and limited interpretation experience (44.9%) and knowledge of clinical applications (43.7%). Reasons given by 46.9% were that no providers approached radiology with interest in EC-VWI. If barriers were overcome, 51.1% of those not performing EC-VWI indicated they would perform it, and 40.6% were unsure; 48.6% did not think that EC-VWI had impacted patient management at their institution.

CONCLUSIONS

Only 26% of neuroradiology groups performed EC-VWI, most commonly due to limited clinician interest. Improved provider and radiologist education, protocols, processing techniques, technical support, and validation trials could increase adoption.

Magnetic Resonance Imaging of Intraplaque Hemorrhage and Plaque Lipid Content With Continued Lipid-Lowering Therapy: Results of a Magnetic Resonance Imaging Substudy in AIM-HIGH

BACKGROUND

Intraplaque hemorrhage (IPH) is associated with plaque progression and ischemic events, and plaque lipid content (% lipid core) predicts the residual atherosclerotic cardiovascular disease risk. This study examined the impact of IPH on lipid content change in the setting of intensive lipid-lowering therapy.

METHODS

In total, 214 AIM-HIGH (Atherothrombosis Intervention in Metabolic Syndrome with Low High-Density Lipoprotein/High Triglycerides: Impact on Global Health Outcomes) participants with clinically established ASCVD and low high-density lipoprotein cholesterol received cartoid MRI at baseline and 2 years to assess changes in carotid morphology and composition. Patients were randomized to extended-release niacin or placebo, and all received simvastatin with optional ezetimibe as necessary to lower low-density lipoprotein cholesterol to 40 to 80 mg/dL. Changes in lipid content and carotid morphology were tested using the Wilcoxon signed-rank test. Differences between subjects with and without IPH and between subjects assigned extended-release niacin or placebo were tested using the Wilcoxon rank-sum test. Linear regression was used to test the association of IPH and lipid content changes after adjusting for clinical risk factors.

RESULTS

Among 156 patients (61±9 years; 81% men) with complete MRI, prior statin use: <1 year, 26%; 1 to 5 years, 37%; >5 years, 37%. Triglycerides and ApoB decreased significantly, whereas high-density lipoprotein cholesterol and ApoA1 increased significantly over time. Plaque lipid content was significantly reduced (-0.5±2.4 %/year, P = 0.017) without a significant difference between the 2 treatment groups. However, the lipid content increased in plaques with IPH but regressed in plaques without IPH (1.2±2.5 %/year versus -1.0±2.2, P = 0.006). Additionally, IPH was associated with a decrease in lumen area (-0.4±0.9 mm2/year versus 0.3±1.4, P = 0.033). IPH remained significantly associated with increase in lipid content in multivariable analysis (54.4%, 95% CI: 26.8, 88.0, P < 0.001).

CONCLUSIONS

Carotid plaques under continued intensive lipid-lowering therapy moved toward stabilization. However, plaques with IPH showed greater increases in lipid content and greater decreases in lumen area than plaques without IPH.

REGISTRATION

URL: https://www.

CLINICALTRIALS

gov; Unique identifier: NCT01178320.

Characterization of non-stenotic plaques in intracranial arteries with multi-contrast, multi-planar vessel wall image analysis

OBJECTIVES

Non-stenotic plaques have been observed in intracranial arteries but are less understood compared to those in coronary and carotid arteries. We sought to compare plaque distribution and morphology between stenotic and non-stenotic intracranial plaques with MR vessel wall imaging (VWI) and quantitative image analysis.

MATERIALS AND METHODS

Twenty-four patients with intracranial arterial stenosis or luminal irregularity on clinical imaging were scanned with a multi-contrast VWI protocol. Plaques were detected as focal wall thickening on co-registered multiplanar reformats of multi-contrast VWI, with assessment of the location and morphology. TOF-MRA was independently reviewed for any appreciable stenosis using the WAISD criteria.

RESULTS

Across 504 arterial segments, a total of 80 plaques were detected, including 23 (29%) with stenosis on TOF-MRA, 56 (70%) without, and 1 (1%) not covered by TOF-MRA. Plaques involving the ICA were more likely to be non-stenotic than those involving other segments (80% versus 55%, p = 0.030) whereas the basilar artery (40%) and PCA (33%) had the lowest proportions of non-stenotic plaques. Maximum wall thickness, indicative of plaque burden, correlated poorly with degree of stenosis (p = 0.10) and overlapped substantially between stenotic and non-stenotic plaques (1.9 [1.5, 2.4] versus 2.0 [1.5, 2.2] mm, p = 0.074).

CONCLUSIONS

Intracranial plaques without appreciable stenosis on TOF-MRA represent a large proportion of lesions throughout arterial segments but disproportionately affect the ICA. Morphological characterization of plaques with and without stenosis shows that luminal stenosis is a poor indicator of the underlying burden of intracranial atherosclerosis.

Associations of intracranial artery length and branch number on non-contrast enhanced MRA with cognitive impairment in individuals with carotid atherosclerosis

Developing novel risk markers for vascular contributions to cognitive impairment and dementia is important. This study aimed to extract total length, branch number and average tortuosity of intracranial distal arteries (A2, M2, P2 and more distal) from non-contrast enhanced magnetic resonance angiography (NCE-MRA) images, and explore their associations with global cognition. In 29 subjects (aged 40-90 years) with carotid atherosclerotic disease, the 3 intracranial vascular features on two NCE-MRA techniques (i.e. time of flight, TOF and simultaneous non-contrast angiography and intraplaque hemorrhage, SNAP) were extracted using a custom-developed software named iCafe. Arterial spin labeling (ASL) and phase contrast (PC) cerebral blood flow (CBF) were measured as references. Linear regression was performed to study their associations with global cognition, measured with the Montreal Cognitive Assessment (MoCA). Intracranial artery length and number of branches on NCE-MRA, ASL CBF and PC CBF were found to be positively associated with MoCA scores (P < 0.01). The associations remained significant for artery length and number of branches on NCE-MRA after adjusting for clinical covariates and white matter hyperintensity volume. Further adjustment of confounding factors of ASL CBF or PC CBF did not abolish the significant association for artery length and number of branches on TOF. Our findings suggest that intracranial vascular features, including artery length and number of branches, on NCE-MRA may be useful markers of cerebrovascular health and provide added information over conventional brain blood flow measurements in individuals with cognitive impairment.

Multi-Planar, Multi-Contrast and Multi-Time Point Analysis Tool (MOCHA) for Intracranial Vessel Wall Characterization

BACKGROUND

Three-dimensional (3D) intracranial vessel wall (IVW) magnetic resonance imaging can reliably image intracranial atherosclerotic disease (ICAD). However, an integrated, streamlined, and optimized workflow for IVW analysis to provide qualitative and quantitative measurements is lacking.

PURPOSE

To propose and evaluate an image analysis pipeline (MOCHA) that can register multicontrast and multitime point 3D IVW for multiplanar review and quantitative plaque characterization.

STUDY TYPE

Retrospective.

POPULATION

A total of 11 subjects with ICAD (68 ± 10 years old, 6 males).

FIELD STRENGTH/SEQUENCE

A 3.0 T, 3D time-of-flight gradient echo sequence and T1- and proton density-weighted fast spin echo sequences.

ASSESSMENT

Each participant underwent two IVW sessions within 2 weeks. Scan and rescan IVW images were preprocessed using MOCHA. The presence of atherosclerotic lesions was identified in different intracranial arterial segments by two readers (GC and JS, 12 years of vascular MR imaging experience each) following an established review protocol to reach consensus on each of the reviews. For all locations with identified plaques, plaque length, lumen and vessel wall areas, maximum and mean wall thickness values, normalized wall index and contrast enhancement ratio were measured.

STATISTICAL TESTS

Percent agreement and Cohen's κ were used to test scan-rescan reproducibility of detecting plaques using MOCHA. Intraclass correlation coefficient (ICC) and Bland-Altman analysis were used to evaluate scan-rescan reproducibility for plaque morphologic and enhancement measurements.

RESULTS

In 150 paired intracranial vessel segments, the overall agreement in plaque detection was 92.7% (κ = 0.822). The ICCs (all ICCs > 0.90) and Bland-Altman plots (no bias observed) indicated excellent scan-rescan reproducibility for all morphologic and enhancement measurements.

DATA CONCLUSION

Findings from this study demonstrate that MOCHA provides high scan-rescan reproducibility for identification and quantification of atherosclerosis along multiple intracranial arterial segments and highlight its potential use in characterizing plaque composition and monitoring plaque development.

EVIDENCE LEVEL

4 TECHNICAL EFFICACY: Stage 2.

Stroke Prevention with Extracranial Carotid Artery Disease

PURPOSE OF REVIEW

Carotid artery stenosis is a major risk factor for ischemic stroke. Although effective treatment options exist, careful assessment of benefits and risks for individual patients is needed in clinical decision-making. This article reviews contemporary treatments for carotid artery stenosis, the underlying evidence, and areas of uncertainties.

RECENT FINDINGS

Specific recommendations are available to guide the standard of care of carotid artery stenosis. Nonetheless, significant uncertainties are noted in patient selection for surgical treatment of asymptomatic carotid stenosis and in optimal treatment targets for pharmacological therapies. Advanced imaging has been used to predict future risk of ipsilateral stroke and clarify mechanisms of actions of pharmacological therapies, primarily in observational studies. Pharmacological and surgical treatments for extracranial carotid artery stenosis continue to evolve with many relevant clinical trials completed and clinical guidelines updated in recent years. Future clinical trials to tackle the areas of uncertainties are warranted.

Detection of Advanced Lesions of Atherosclerosis in Carotid Arteries Using 3-Dimensional Motion-Sensitized Driven-Equilibrium Prepared Rapid Gradient Echo (3D-MERGE) Magnetic Resonance Imaging as a Screening Tool

BACKGROUND AND PURPOSE

Two-dimensional high-resolution multicontrast magnetic resonance imaging (2D-MC MRI) is currently the most reliable and reproducible noninvasive carotid vessel wall imaging technique. However, the long scan time required for 2D-MC MRI restricts its practical clinical application. Alternatively, 3-dimensional motion-sensitized driven-equilibrium prepared rapid gradient echo (3D-MERGE) vessel wall MRI can provide high isotropic resolution with extensive coverage in two minutes. In this study, we sought to prove that 3D-MERGE alone can serve as a screening tool to identify advanced carotid lesions.

METHODS

Two hundred twenty-seven subjects suspected of recent ischemic stroke or transient ischemic attack were imaged using 2D-MC MRI with an imaging time of 30 minutes, then with 3D-MERGE with an imaging time of 2 minutes, on 3T-MRI scanners. Two experienced reviewers interpreted plaque components using 2D-MC MRI as the reference standard and categorized plaques using a modified American Heart Association lesion classification for MRI. Plaques of American Heart Association type IV and above were classified as advanced. Arteries of American Heart Association types I to II and III were categorized as normal or with early lesions, respectively. One radiologist independently reviewed only 3D-MERGE and labeled the plaques as advanced if they had a wall thickness of >2 mm with high or low signal intensity compared with the adjacent sternocleidomastoid muscle. Sensitivity, specificity, and accuracy for 3D-MERGE were calculated.

RESULTS

Four hundred forty-nine arteries from 227 participants (mean age 61.2 years old, 64% male) were included in the analysis. Sensitivity, specificity, and accuracy for identification of advanced lesions on 3D-MERGE were 95.0% (95% CI, 91.8-97.2), 86.9% (95% CI, 81.4-92.0), 93.8% (95% CI, 91.1-95.8), respectively.

CONCLUSIONS

3D-MERGE can accurately identify advanced carotid atherosclerotic plaques in patients suspected of stroke or transient ischemic attack. It has a more extensive coverage and higher sensitivity and specificity for advanced plaque detection with a much shorter acquisition time than 2D-MC MRI.

REGISTRATION

URL: https://www.clinicaltrials.gov; Unique identifier: NCT02017756.

Urinary sodium and potassium excretion and cerebrovascular health: a multimodal imaging study

PURPOSE

Dietary sodium and potassium intake are associated with stroke, but the potential mechanisms are unclear. We aimed to study the association between sodium and potassium intake and subclinical cerebrovascular health in hypertensive older males using multimodal magnetic resonance imaging.

METHODS

A total of 189 hypertensive male subjects without previous cardiovascular or cerebrovascular disease were included. Daily urinary sodium and potassium excretion were estimated from a fasting spot urine sample using a formula approach. A dedicated cerebrovascular health imaging protocol including vessel wall imaging, angiography, arterial spin labeling imaging and T2-weighted fluid-attenuated inversion recovery imaging was performed to study intracranial atherosclerosis, vascular rarefaction (defined as fewer discernible vessels on angiography), brain perfusion and small vessel disease, respectively.

RESULTS

The mean age was 64.9 (± 7.2) years. The average daily urinary and potassium excretion was 4.7 (± 1.4) g/L and 2.1 (± 0.5) g/L, respectively. Increased urinary sodium excretion was associated with decreased cerebral blood flow and elevated urinary potassium excretion was associated with reduced prevalence of intracranial plaque. The associations remained significant after adjusting for covariates, even including blood pressure control. Quadratic regression analysis indicated a marginally significant U-shaped association between urinary sodium intake and white matter hyperintensity, which lost significance in fully adjusted models. No significant association of urinary sodium and potassium excretion with other cerebrovascular health measures was noted.

CONCLUSION

We concluded that in hypertensive older males without overt cardiovascular disease, increased sodium intake and reduced potassium intake are associated with impaired subclinical cerebrovascular health.

Arterial elasticity, endothelial function and intracranial vascular health: A multimodal MRI study

Vascular dysfunctions, including arterial stiffness and endothelial dysfunction, are prevalent in hypertensive subjects. We aimed to study their relations to subclinical intracranial vascular health in this study. A total of 200 older hypertensive males without overt cardiovascular or cerebrovascular diseases were recruited. Arterial elasticity was measured as carotid-femoral pulse wave velocity (cfPWV) and endothelial function was measured as digital reactive hyperemia index (RHI). Cerebrovascular health was evaluated using MRI in four aspects: intracranial atherosclerosis, brain perfusion as cerebral blood flow (CBF), vascular rarefaction analyzed as visible arterial branches on angiography using a custom-developed analysis technique and small vessel disease measured as white matter hyperintensity (WMH). There was a significant negative association between cfPWV and CBF, suggesting a link between arterial stiffness and CBF decline. Higher cfPWV was also associated with presence of intracranial stenotic plaque and greater WMH volume. RHI was positively related to CBF, indicating that endothelial dysfunction was associated with reduced CBF. All the associations remained significant after adjustment for confounding variables. Arterial stiffness and endothelial dysfunction are associated with reduced brain perfusion in older hypertensive males. Arterial stiffness is also associated with global cerebral vascular injury, affecting both small and medium-to-large arteries.

Regression in carotid plaque lipid content and neovasculature with PCSK9 inhibition: A time course study

BACKGROUND AND AIMS

Proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibitors reduce cardiovascular events, but their effects on atherosclerotic plaque remain elusive. Using serial magnetic resonance imaging (MRI), we studied changes in carotid plaque lipid content and neovasculature under PCSK9 inhibition with alirocumab.

METHODS

Among patients with low-density lipoprotein cholesterol (LDL-C) ≥70 mg/dl but ineligible for high-dose statin therapy, those with lipid core on carotid MRI were identified to receive alirocumab 150 mg every 2 weeks. Follow-up MRI was performed at 3, 6, and 12 months after treatment. Pre- and post-contrast MRI were acquired to measure percent lipid core volume (% lipid core). Dynamic contrast-enhanced MRI was acquired to measure the extravasation rate of gadolinium contrast (K^trans), a marker of plaque neovasculature.

RESULTS

Of 31 patients enrolled, 27 completed the study (mean age: 69 ± 9; male: 67%). From 9.8% at baseline, % lipid core was progressively reduced to 8.4% at 3 months, 7.5% at 6 months, and 7.2% at 12 months (p = 0.014 for trend), which was accompanied by a progressive increase in % fibrous tissue (p = 0.009) but not % calcification (p = 0.35). K^trans was not reduced until 12 months (from 0.069 ± 0.019 min^-1 to 0.058 ± 0.020 min^-1; p = 0.029). Lumen and wall areas did not change significantly during the study period.

CONCLUSIONS

Regression in plaque composition and neovasculature were observed under PCSK9 inhibition on carotid MRI, which provides unique insight into the biological process of plaque stabilization with disease-modifying therapies.

Atherosclerotic Burden and Remodeling Patterns of the Popliteal Artery as Detected in the Magnetic Resonance Imaging Osteoarthritis Initiative Data Set

Background

An artificial intelligence vessel segmentation tool, Fully Automated and Robust Analysis Technique for Popliteal Artery Evaluation (FRAPPE), was used to analyze a large databank of popliteal arteries imaged through the OAI (Osteoarthritis Initiative) to study the impact of atherosclerosis risk factors on vessel dimensions and characterize remodeling patterns.

Methods and Results

Magnetic resonance images from 4668 subjects contributing 9189 popliteal arteries were analyzed using FRAPPE. Age ranged from 45 to 79 years (median, 61), and 58% were women. Mean lumen diameter, mean outer wall diameter, and mean wall thickness (MWT) were measured per artery. Their median values were 5.8 mm (interquartile range, 5.2–6.5 mm), 7.3 mm (interquartile range, 6.7–8.1 mm), and 0.78 mm (interquartile range, 0.73–0.84 mm) respectively. MWT was associated with multiple cardiovascular risk factors, with age (4.2% increase in MWT per 10‐year increase in age; 95% CI, 3.9%–4.5%) and sex (8.6% higher MWT in men than women; 95% CI, 7.7%–9.3%) being predominant. On average, lumen and outer wall diameters increased with increasing MWT until the thickness was 0.92 mm for men and 0.84 mm for women. After this point, lumen diameter decreased steadily, more rapidly in men than women (−7.9% versus −6.1% per 25% increase in MWT; P<0.001), with little change in outer wall diameter.

Conclusions

FRAPPE has enabled the analysis of the large OAI knee magnetic resonance imaging data set, successfully showing that popliteal atherosclerosis is predominantly associated with age and sex. The average vessel remodeling pattern consisted of an early phase of compensatory enlargement, followed by a negative remodeling, which is more pronounced in men.

Domain adaptive and fully automated carotid artery atherosclerotic lesion detection using an artificial intelligence approach (LATTE) on 3D MRI

PURPOSE

To develop and evaluate a domain adaptive and fully automated review workflow (lesion assessment through tracklet evaluation, LATTE) for assessment of atherosclerotic disease in 3D carotid MR vessel wall imaging (MR VWI).

METHODS

VWI of 279 subjects with carotid atherosclerosis were used to develop LATTE, mainly convolutional neural network (CNN)-based domain adaptive lesion classification after image quality assessment and artery of interest localization. Heterogeneity in test sets from various sites usually causes inferior CNN performance. With our novel unsupervised domain adaptation (DA), LATTE was designed to accurately classify arteries into normal arteries and early and advanced lesions without additional annotations on new datasets. VWI of 271 subjects from four datasets (eight sites) with slightly different imaging parameters/signal patterns were collected to assess the effectiveness of DA of LATTE using the area under the receiver operating characteristic curve (AUC) on all lesions and advanced lesions before and after DA.

RESULTS

LATTE had good performance with advanced/all lesion classification, with the AUC of >0.88/0.83, significant improvements from >0.82/0.80 if without DA.

CONCLUSIONS

LATTE can locate target arteries and distinguish carotid atherosclerotic lesions with consistently improved performance with DA on new datasets. It may be useful for carotid atherosclerosis detection and assessment on various clinical sites.

Multinational Survey of Current Practice from Imaging to Treatment of Atherosclerotic Carotid Stenosis

BACKGROUND

In the last 20-30 years, there have been many advances in imaging and therapeutic strategies for symptomatic and asymptomatic individuals with carotid artery stenosis. Our aim was to examine contemporary multinational practice standards.

METHODS

Departmental Review Board approval for this study was obtained, and 3 authors prepared the 44 multiple choice survey questions. Endorsement was obtained by the European Society of Neuroradiology, American Society of Functional Neuroradiology, and African Academy of Neurology. A link to the online questionnaire was sent to their respective members and members of the Faculty Advocating Collaborative and Thoughtful Carotid Artery Treatments (FACTCATS). The questionnaire was open from May 16 to July 16, 2019.

RESULTS

The responses from 223 respondents from 46 countries were included in the analyses including 65.9% from academic university hospitals. Neuroradiologists/radiologists comprised 68.2% of respondents, followed by neurologists (15%) and vascular surgeons (12.9%). In symptomatic patients, half (50.4%) the respondents answered that the first exam they used to evaluate carotid bifurcation was ultrasound, followed by computed tomography angiography (CTA, 41.6%) and then magnetic resonance imaging (MRI 8%). In asymptomatic patients, the first exam used to evaluate carotid bifurcation was ultrasound in 88.8% of respondents, CTA in 7%, and MRA in 4.2%. The percent stenosis upon which carotid endarterectomy or stenting was recommended was reduced in the presence of imaging evidence of "vulnerable plaque features" by 66.7% respondents for symptomatic patients and 34.2% for asymptomatic patients with a smaller subset of respondents even offering procedural intervention to patients with <50% symptomatic or asymptomatic stenosis.

CONCLUSIONS

We found heterogeneity in current practices of carotid stenosis imaging and management in this worldwide survey with many respondents including vulnerable plaque imaging into their decision analysis despite the lack of proven benefit from clinical trials. This study highlights the need for new clinical trials using vulnerable plaque imaging to select high-risk patients despite maximal medical therapy who may benefit from procedural intervention.

Automated Artery Localization and Vessel Wall Segmentation using Tracklet Refinement and Polar Conversion

Quantitative analysis of blood vessel wall structures is important to study atherosclerotic diseases and assess cardiovascular event risks. To achieve this, accurate identification of vessel luminal and outer wall contours is needed. Computer-assisted tools exist, but manual preprocessing steps, such as region of interest identification and/or boundary initialization, are still needed. In addition, prior knowledge of the ring shape of vessel walls has not been fully explored in designing segmentation methods. In this work, a fully automated artery localization and vessel wall segmentation system is proposed. A tracklet refinement algorithm was adapted to robustly identify the artery of interest from a neural network-based artery centerline identification architecture. Image patches were extracted from the centerlines and converted in a polar coordinate system for vessel wall segmentation. The segmentation method used 3D polar information and overcame problems such as contour discontinuity, complex vessel geometry, and interference from neighboring vessels. Verified by a large (>32000 images) carotid artery dataset collected from multiple sites, the proposed system was shown to better automatically segment the vessel wall than traditional vessel wall segmentation methods or standard convolutional neural network approaches. In addition, a segmentation uncertainty score was estimated to effectively identify slices likely to have errors and prompt manual confirmation of the segmentation. This robust vessel wall segmentation system has applications in different vascular beds and will facilitate vessel wall feature extraction and cardiovascular risk assessment.

Intracranial vascular feature changes in time of flight MR angiography in patients undergoing carotid revascularization surgery

PURPOSE

To characterize the intracranial vascular features extracted from time of flight (TOF) images and their changes from baseline to follow-up in patients undergoing carotid revascularization, using arterial spin labeling (ASL) cerebral blood flow (CBF) measurement as a reference.

METHODS

In this retrospective study, brain TOF and ASL images of 99 subjects, acquired before, within 48 h, and/or 6 months after, carotid revascularization surgery were analyzed. TOF images were analyzed using a custom software (iCafe) to quantify intracranial vascular features, including total vessel length, total vessel volume, and number of branches. Mean whole-brain CBF was calculated from ASL images. ASL scans showing low ASL signal in the entire flow territory of an internal carotid artery (ICA), which may be caused by labeling failure, were excluded. Changes and correlations between time points were analyzed separately for TOF intracranial vascular features and ASL CBF.

RESULTS

Similar to ASL CBF, TOF vascular features (i.e. total vessel length, total vessel volume and number of branches) increased dramatically from baseline to post-surgery, then returned to a level slightly higher than the baseline in long-term follow-up (All P < 0.05). Correlation between time points was observed for all three TOF vascular features but not for ASL CBF.

CONCLUSION

Intracranial vascular features, including total vessel length, total vessel volume and number of branches, extracted from TOF images are useful in detecting brain blood flow changes induced by carotid revascularization surgery.

Fully automated and robust analysis technique for popliteal artery vessel wall evaluation (FRAPPE) using neural network models from standardized knee MRI

PURPOSE

To develop a fully automated vessel wall (VW) analysis workflow (fully automated and robust analysis technique for popliteal artery evaluation, FRAPPE) on the popliteal artery in standardized knee MR images.

METHODS

Popliteal artery locations were detected from each MR slice by a deep neural network model and connected into a 3D artery centerline. Vessel wall regions around the centerline were then segmented using another neural network model for segmentation in polar coordinate system. Contours from vessel wall segmentations were used for vascular feature calculation, such as mean wall thickness and wall area. A transfer learning and active learning framework was applied in training the localization and segmentation neural network models to maintain accuracy while reducing manual annotations. This new popliteal artery analysis technique (FRAPPE) was validated against manual segmentation qualitatively and quantitatively in a series of 225 cases from the Osteoarthritis Initiative (OAI) dataset.

RESULTS

FRAPPE demonstrated high accuracy and robustness in locating popliteal arteries, segmenting artery walls, and quantifying arterial features. Qualitative evaluations showed 1.2% of slices had noticeable major errors, including segmenting the wrong target and irregular vessel wall contours. The mean Dice similarity coefficient with manual segmentation was 0.79, which is comparable to inter-rater variations. Repeatability evaluations show most of the vascular features have good to excellent repeatability from repeated scans of same subjects, with intra-class coefficient ranging from 0.80 to 0.98.

CONCLUSION

This technique can be used in large population-based studies, such as OAI, to efficiently assess the burden of atherosclerosis from routine MR knee scans.

Uncontrolled hypertension associates with subclinical cerebrovascular health globally: a multimodal imaging study

OBJECTIVES

The study aimed to analyze the association between hypertension control and subclinical cerebrovascular health using a comprehensive multimodal imaging approach.

METHODS

The study included 200 hypertensive older males without previous cardiovascular diseases. Clinic blood pressure (BP) was measured using a standard approach. Cerebrovascular health was evaluated using magnetic resonance imaging in the following four aspects: Intracranial atherosclerosis as determined by vessel wall imaging; Vascular rarefaction (defined as less discernible vessels on angiography) was evaluated using a custom-developed technique. Cerebral blood flow (CBF) and white matter hyperintensity (WMH) were assessed using arterial spin-labeling imaging and fluid-attenuated inversion recovery imaging, respectively.

RESULTS

A total of 189 subjects had MRI scans. The mean age was 64.9 (± 7.2) years. For intracranial atherosclerosis, there was a significant association between uncontrolled hypertension and presence of intracranial plaque. When systolic and diastolic BP were analyzed separately, the association remained significant for both. For vascular rarefaction, uncontrolled hypertension was associated with less discernible vessel branches or shorter vessel length on angiography. Further analysis revealed that this is due to uncontrolled diastolic BP, but not uncontrolled systolic BP. There was an association between uncontrolled hypertension and reduced CBF, which was also mainly driven by uncontrolled diastolic BP. We also found that uncontrolled diastolic BP, but not uncontrolled systolic BP, was associated with increased WMH volume.

CONCLUSIONS

Uncontrolled hypertension was associated with subclinical cerebrovascular injury globally, with both small and medium-to-large arteries being affected.

KEY POINTS

• In this study, we leveraged the advantage of a series of cutting-edge MR imaging and analysis techniques and found uncontrolled hypertension is associated with subclinical globally compromised cerebrovascular health. • The detrimental consequences of uncontrolled BP affect not only the small vessels but also the medium-to-large arteries, and uncontrolled systolic and diastolic BP are both independently associated with certain types of cerebrovascular injury. • Our data suggest that cerebrovascular health is impaired globally in uncontrolled hypertension before the onset of stroke.

Differences in atheroma between Caucasian and Asian subjects with anterior stroke: A vessel wall MRI study

Background and purpose

While extracranial carotid artery stenosis is more common among Caucasians and intracranial artery stenosis is more common among Asians, the differences in atherosclerotic plaque characteristics have not yet been extensively examined. We sought to investigate plaque location and characteristics within extracranial carotid and intracranial arteries in symptomatic Caucasians and Chinese using vessel wall MRI.

Methods

Subjects with recent anterior circulation ischaemic stroke were recruited and imaged at two sites in the USA and China using similar protocols. Both extracranial carotid and intracranial arteries were reviewed to determine plaque location and characteristics.

Results

The prevalence of extracranial carotid plaque in Caucasians and Chinese was 73.1% and 49.1%, respectively (p=0.055). Prevalence of intracranial plaque was 38.5% and 69.1% in Caucasians and Chinese, respectively (p=0.02). Furthermore, 42% of Caucasians and 16% of Chinese had high-risk plaque (HRP) features (intraplaque haemorrhage, luminal surface disruption) in the extracranial carotid artery (p=0.03). The prevalence of HRP features in intracranial arteries was not significantly different between the two cohorts (4% vs 11%; p=0.42).

Conclusions

Differences in the location and characteristics of cerebrovascular atherosclerosis were identified by vessel wall MRI in US Caucasian and Chinese subjects with recent anterior circulation ischaemic stroke. Extracranial carotid plaques with HRP features were more common in Caucasians. Intracranial plaques were more common in Chinese subjects, but no significant difference between the two cohorts in intracranial HRP prevalence was found. Larger studies using vessel wall imaging to investigate racial differences in cerebrovascular disease may inform underlying mechanisms of HRP development and may ultimately help guide appropriate therapy.

A novel sequence for simultaneous measurement of whole-brain static and dynamic MRA, intracranial vessel wall image, and T1 -weighted structural brain MRI

PURPOSE

To propose a highly time-efficient imaging technique named improved simultaneous noncontrast angiography and intraplaque hemorrhage (iSNAP) for simultaneous assessment of lumen, vessel wall, and blood flow in intracranial arteries.

METHODS

iSNAP consists of pulsed arterial spin labeling preparations and 3D golden angle radial acquisition. Images were reconstructed by k-space weighted image contrast (KWIC) method with optimized data-sharing strategies. Dynamic MRA for blood flow assessment was obtained from iSNAP by reconstruction at multiple inversion times and image subtraction, static MRA by both image subtraction approach and phase-sensitive inversion recovery technique, and vessel wall images by both reconstruction at zero-crossing time-point of blood and phase-sensitive inversion recovery. A T₁ -weighted brain MRI was also reconstructed from iSNAP. Preliminary comparison of iSNAP against the dedicated dynamic MRA sequence 4D-TRANCE, MRA/vessel wall imaging sequence SNAP, and vessel wall imaging sequence T₁ -weighted VISTA was performed in healthy volunteers and patients.

RESULTS

iSNAP has whole-brain coverage and takes ~6.5 min. The dedicated reconstruction strategies are feasible for each iSNAP image contrast and beneficial for image SNR. iSNAP-dynamic MRA yields similar dynamic flow information as 4D-TRANCE and allows more flexible temporal resolution. The 2 types of iSNAP static MRA images complement each other in characterizing both proximal large arteries and distal small arteries. Depiction of vessel wall lesions in iSNAP vessel wall images is better than SNAP and may be similar to T₁ -weighted VISTA, although the images are slightly blurred.

CONCLUSION

iSNAP provides a time-efficient evaluation of intracranial arteries and may have great potential for comprehensive assessment of intracranial vascular conditions using a single sequence.

Characterization of Carotid Atherosclerotic Plaques Using 3-Dimensional MERGE Magnetic Resonance Imaging and Correlation With Stroke Risk Factors

Background and Purpose- High-resolution magnetic resonance imaging is capable of characterizing carotid atherosclerotic plaque morphology and composition. Most reported carotid plaque imaging techniques are 2-dimensional (2D) based with limited longitudinal coverage of ≈30 mm, which may be insufficient for complete visualization of extracranial carotid atheroma. A 3D black-blood imaging technique, motion-sensitized driven equilibrium prepared rapid gradient echo technique (3D-MERGE) can provide larger coverage. We sought to use 3D-MERGE to investigate carotid atherosclerosis plaque distribution and to analyze their correlation with clinical information and stroke risk factors. Methods- From 5 hospitals in China, 97 subjects suspected of recent stroke or transient ischemic attack were imaged with 3D-MERGE within 2 weeks of symptoms using 3T magnetic resonance imaging. Images were analyzed by 2 reviewers. Plaque length was calculated and categorized as plaques within, partially outside, or completely outside of typical 2D magnetic resonance imaging coverage. Associations between plaque features and clinical information, stroke risk factors were assessed. Results- Ninety-seven subjects with 194 carotid arteries (70 men and 27 women, mean age 60 years) were analyzed. Of the 136 plaques identified, 68 (50%) were within, 46 (33.8%) were partially outside, and 22 (16.2%) were completely outside of 2D magnetic resonance imaging coverage. Total plaque length was significantly positively associated with male sex (P<0.001), hypertension (P=0.011), and history of smoking (P<0.001). Hypertensive subjects were more likely to have at least one plaque completely outside the 2D magnetic resonance imaging coverage than nonhypertensive subjects (P=0.007). Conclusions- The 3D-MERGE allows for the identification of substantially more carotid plaques than 2D black-blood techniques. The extent and distribution of plaque, identified by the larger coverage afforded by 3D-MERGE, were found to correlate significantly with male sex and risk factors that are common among patients with stroke, including hypertension and history of cigarette smoking.

Evaluation of 3D multi-contrast carotid vessel wall MRI: a comparative study

Background

Conventional reference multi-contrast black-blood (BB) MRI can be used for measuring luminal stenosis severity and plaque components, and its performance has been validated by intra- and inter-reader reproducibility test and histology. Recently, a set of 3D multi-contrast BB sequences have been developed, but its accuracy and reliability have not been well investigated. In this study, we evaluated the performance of 3D multi-contrast MRI (3D-MERGE, T2-VISTA, and SNAP) by comparing it with reference multi-contrast vessel wall MRI and assessing the inter-reader reproducibility.

Methods

In total, 27 patients were recruited in this study. Twenty-six participants underwent reference and 3D multi-contrast imaging in a 3.0T MR scanner. One participant underwent carotid endarterectomy (CEA) after 3D MR imaging. Two trained reviewers interpreted reference and 3D datasets. Lumen area (LA), wall area (WA), normalized wall index (NWI), maximum wall thickness (MaxWT), and mean wall thickness (MWT) were measured, and the presence of lipid-rich necrotic core (LRNC), intra-plaque hemorrhage (IPH) and calcification (CA) were identified. Inter-reader reproducibility of 3D interpretation was assessed.

Results

3D imaging provided comparable measurements with reference imaging in LA (43.81±25.74 vs. 43.35±24.66 mm²) and MaxWT (1.65±1.33 vs. 1.62±1.10 mm), with a lower NWI (0.40±0.15 vs. 0.43±0.11), WA (29.40±21.92 vs. 30.64±16.17 mm²) and MWT (1.09±0.69 vs. 1.14±0.47), and showed good agreement for identification of LRNC (κ=0.66, 95% CI: 0.30-1.00) and CA (κ=0.69, 95% CI: 0.42-0.97), and excellent agreement for IPH (κ=1.00, 95% CI: 1.00-1.00). Inter-reader agreement of 3D analysis was good (LRNC, κ=0.87, 95% CI: 0.61-1.00; CA, κ=0.66, 95% CI: 0.36-0.96; IPH, κ=1.00, 95% CI: 1.00-1.00).

Conclusions

3D multi-contrast vessel wall imaging provides comparable performance in morphological measurements and identification of carotid plaque components as reference multi-contrast MRI, with good inter-reader reproducibility.

Four Different Carotid Atherosclerotic Behaviors Based on Luminal Stenosis and Plaque Characteristics in Symptomatic Patients: An in Vivo Study

Correct stratification of ischemic stroke risk allows for the proper treatment of carotid atherosclerotic disease. We seek to differentiate plaque types based on stenosis level and plaque morphology. The Chinese Atherosclerosis Risk Evaluation (CARE-II) study is a cross-sectional, observational, multicenter study to assess carotid atherosclerotic plaques in symptomatic subjects using vessel wall magnetic resonance imaging. Plaque morphology and presence of plaque components were reviewed using multi-contrast magnetic resonance imaging. The carotid arteries were divided into four groups based on stenosis level and plaque components. Out of 1072 ischemic stroke subjects, 452 ipsilateral side carotid arteries were included. Significant stenosis (SS) (≥50% stenosis) with high-risk plaque (HRP) features was present in 37 arteries (8.2%), SS(+)/HRP(-) in 29 arteries (6.4%), SS(-)/HRP(+) in 57 arteries (12.6%), and SS(-)/HRP(-) in 329 arteries (72.8%). The prevalence of SS(-)/HRP(+) arteries in this cohort was substantial and had greater wall thickness than the SS(+)/HRP(-) group. These arteries may be misclassified for carotid revascularization by current guidelines based on the degree of luminal stenosis only. These findings have implications for further studies to assess stroke risk using vessel wall imaging.

Combining morphological and biomechanical factors for optimal carotid plaque progression prediction: An MRI-based follow-up study using 3D thin-layer models

Plaque progression prediction is of fundamental significance to cardiovascular research and disease diagnosis, prevention, and treatment. Magnetic resonance image (MRI) data of carotid atherosclerotic plaques were acquired from 20 patients with consent obtained. 3D thin-layer models were constructed to calculate plaque stress and strain. Data for ten morphological and biomechanical risk factors were extracted for analysis. Wall thickness increase (WTI), plaque burden increase (PBI) and plaque area increase (PAI) were chosen as three measures for plaque progression. Generalized linear mixed models (GLMM) with 5-fold cross-validation strategy were used to calculate prediction accuracy and identify optimal predictor. The optimal predictor for PBI was the combination of lumen area (LA), plaque area (PA), lipid percent (LP), wall thickness (WT), maximum plaque wall stress (MPWS) and maximum plaque wall strain (MPWSn) with prediction accuracy = 1.4146 (area under the receiver operating characteristic curve (AUC) value is 0.7158), while PA, plaque burden (PB), WT, LP, minimum cap thickness, MPWS and MPWSn was the best for WTI (accuracy = 1.3140, AUC = 0.6552), and a combination of PA, PB, WT, MPWS, MPWSn and average plaque wall strain (APWSn) was the best for PAI with prediction accuracy = 1.3025 (AUC = 0.6657). The combinational predictors improved prediction accuracy by 9.95%, 4.01% and 1.96% over the best single predictors for PAI, PBI and WTI (AUC values improved by 9.78%, 9.45%, and 2.14%), respectively. This suggests that combining both morphological and biomechanical risk factors could lead to better patient screening strategies.

Imaging biomarkers of vulnerable carotid plaques for stroke risk prediction and their potential clinical implications

Stroke represents a massive public health problem. Carotid atherosclerosis plays a fundamental part in the occurence of ischaemic stroke. European and US guidelines for prevention of stroke in patients with carotid plaques are based on quantification of the percentage reduction in luminal diameter due to the atherosclerotic process to select the best therapeutic approach. However, better strategies for prevention of stroke are needed because some subtypes of carotid plaques (eg, vulnerable plaques) can predict the occurrence of stroke independent of the degree of stenosis. Advances in imaging techniques have enabled routine characterisation and detection of the features of carotid plaque vulnerability. Intraplaque haemorrhage is accepted by neurologists and radiologists as one of the features of vulnerable plaques, but other characteristics-eg, plaque volume, neovascularisation, and inflammation-are promising as biomarkers of carotid plaque vulnerability. These biomarkers could change current management strategies based merely on the degree of stenosis.

Quantitative assessment of the intracranial vasculature in an older adult population using iCafe

Comprehensive quantification of intracranial artery features may help us assess and understand variations of blood supply during brain development and aging. We analyzed vasculature features of 163 participants (age 56-85 years, mean of 71) from a community study to investigate if any of the features varied with age. Three-dimensional time-of-flight magnetic resonance angiography images of these participants were processed in IntraCranial artery feature extraction technique (a recently developed technique to obtain quantitative features of arteries) to divide intracranial vasculatures into anatomical segments and generate 8 morphometry and intensity features for each segment. Overall, increase in age was found negatively associated with number of branches and average order of intracranial arteries while positively associated with tortuosity, which remained after adjusting for cardiovascular risk factors. The associations with number of branches and average order were consistently found between 3 main intracranial artery regions, whereas the association with tortuosity appeared to be present only in middle cerebral artery/distal arteries. The combination of time-of-flight magnetic resonance angiography and IntraCranial artery feature extraction technique may provide an effective way to study vascular conditions and changes in the aging brain.

Semiautomatic carotid intraplaque hemorrhage volume measurement using 3D carotid MRI

BACKGROUND

Presence of intraplaque hemorrhage (IPH) is a known risk factor for stroke and plaque progression. Accurate and reproducible measurement of IPH volume are required for further risk stratification.

PURPOSE

To develop a semiautomatic method to measure carotid IPH volume.

STUDY TYPE

Retrospective.

POPULATION

Patients scheduled for carotid endarterectomy and patients with 16-79% asymptomatic carotid stenosis by ultrasound.

FIELD STRENGTH

3T.

SEQUENCE

Simultaneous noncontrast angiography and intraplaque hemorrhage (SNAP) MRI.

ASSESSMENT

A semiautomated volumetric measurement of IPH using signal intensity thresholding of 3D SNAP volume was implemented. Fourteen carotid endarterectomy patients were enrolled to determine the signal intensity threshold of IPH using histology. Thirty-three patients with 16-79% asymptomatic stenosis were scanned twice within 1 month to evaluate reproducibility. The normalized SNAP intensity with the highest Youden index for predicting IPH on histology was used for thresholding. Scan-rescan reproducibility of IPH measurement was assessed using the intraclass correlation coefficient (ICC) and coefficient of variation (CV).

STATISTICAL TESTS

Receiver operating characteristic curve, area under the curve, Cohen's kappa, intraclass correlation coefficient, coefficient of variance (CV), and paired t-test.

RESULTS

IPH detection by the algorithm had substantial agreement with manual review (kappa: 0.92; 95% confidence interval [CI]: 0.83, 1.00) and moderate agreement with histology (kappa: 0.55; 95% CI: 0.34, 0.68). IPH volume measurements by the algorithm were strongly correlated with histology (Spearman's rho = 0.76, P = 0.002). IPH measurements were also reproducible, with ICCs of 0.86 (95% CI: 0.57, 0.96), 0.77 (95% CI: 0.32, 0.94), and 0.99 (95% CI: 0.93, 1.00) for maximum/mean normalized intensity and IPH volume, respectively. The corresponding CVs were 10.6%, 5.2%, and 11.8%.

DATA CONCLUSION

IPH volume measurements on SNAP MRI are highly reproducible using semiautomatic measurement. Level of Evidence 2 Technical Efficacy Stage 2 J. Magn. Reson. Imaging 2019;50:1055-1062.

Abstract 184: The Relationship Between Carotid Plaque on Magnetic Resonance Plaque Imaging and Time From Stroke Onset

Introduction: Previous studies report that rate of recurrent stroke, as well as the risk of carotid surgery, is highest in the early stages following cerebral infarction and decreases over time, which suggests a process of plaque healing and stabilization. The purpose of this study is to identify differences in carotid plaque components according to the time from stroke onset, using carotid magnetic resonance plaque imaging (MRPI) to evaluate the dynamic phase of plaque development following an acute cerebrovascular ischemic event.Methods and

Results: MRPI on 3T scanners was obtained in 128 patients enrolled in the Carotid Artery Stenting study (MRCAS). MRCAS is a non-randomized multicenter prospective observational study to compare the plaque characteristics evaluated by MRI and ischemic complications after CAS in Japan. Among the 128 subjects, 60 presented with TIA or stroke and 68 were asymptomatic. The 60 TIA/stroke cases were classified into four groups based on the interval from the onset of symptoms to the date of carotid MRPI (Group 1: <14 days [n=25]; Group 2: 15-30 days[n=13]; and Group 3: >31 days [n=22]). The 68 asymptomatic cases were classified as Group 4. The volume of intraplaque hemorrhage (IPH), necrotic core, calcification and loose matrix was quantified on MRPI using Radiant DICOM viewer. Further, the presence of inner Loose Matrix (iLM) was identified as a high intensity area located between the vessel lumen and necrotic core or IPH on both T2WI and proton density weighted images.Patients characteristics were not significantly different among all groups. The mean volume of loose matrix in Group 3 was significantly lower than Group 1 and Group 4 (0 mm3 vs 12.3 mm3 and 15.5 mm3; p= 0.01, 0.03, respectively). The prevalence of iLM in Group 1 was higher than in Group 3 and 4 (68% vs 18.2%, 38.3% ; p<0.01, <0.01, respectively).

Conclusions: The prevalence of inner Loose Matrix, located at the interface between the lumen surface and the necrotic core or IPH, is significantly higher in the early stage after stoke/TIA. This study suggests that carotid plaques undergo rapid evolution, especially adjacent to the luminal surface, after an acute cerebrovascular ischemic event.

Quantification of morphometry and intensity features of intracranial arteries from 3D TOF MRA using the intracranial artery feature extraction (iCafe): A reproducibility study

BACKGROUND

Accurate and reliable vascular features extracted from 3D time-of-flight (TOF) magnetic resonance angiography (MRA) can help evaluate cerebral vascular diseases and conditions. The goal of this study was to evaluate the reproducibility of an intracranial artery feature extraction (iCafe) algorithm for quantitative analysis of intracranial arteries from TOF MRA.

METHODS

Twenty-four patients with known intracranial artery stenosis were recruited and underwent two separate MRA scans within 2 weeks of each other. Each dataset was blinded to associated imaging and clinical data and then processed independently using iCafe. Inter-scan reproducibility analysis was performed on the 24 pairs of scans while intra-/inter-operator reproducibility and stenosis detection were assessed on 8 individual MRA scans. After tracing the vessels visualized on TOF MRA, iCafe was used to automatically extract the locations with stenosis and eight other vascular features. The vascular features included the following six morphometry and two signal intensity features: artery length (total, distal, and proximal), volume, number of branches, average radius of the M1 segment of the middle cerebral artery, and average normalized intensity of all arteries and large vertical arteries. A neuroradiologist independently reviewed the images to identify locations of stenosis for the reference standard. Reproducibility of stenosis detection and vascular features was assessed using Cohen's kappa, the intra-class correlation coefficient (ICC), and within-subject coefficient of variation (CV).

RESULTS

The segment-based sensitivity of iCafe for stenosis detection ranged from 83.3-91.7% while specificity was 97.4%. Kappa values for inter-scan and intra-operator reproducibility were 0.73 and 0.77, respectively. All vascular features demonstrated excellent inter-scan and intra-operator reproducibility (ICC = 0.91-1.00, and CV = 1.21-8.78% for all markers), and good to excellent inter-operator reproducibility (ICC = 0.76-0.99, and CV = 3.27-15.79% for all markers).

CONCLUSION

Intracranial artery features can be reliably quantified from TOF MRA using iCafe to provide both clinical diagnostic assistance and facilitate future investigative quantitative analyses.

Association of variant arch anatomy with type B aortic dissection and hemodynamic mechanisms

OBJECTIVE

Congenital aortic arch variations are more common in patients with thoracic aortic disease for reasons unknown. Additionally, little is understood about their relation to type B aortic dissections (TBAD) specifically. We investigated the prevalence of variant aortic arch anatomy in patients with TBAD compared with controls. To understand the implications of how variant aortic arch anatomy may contribute to degenerative aortic disease, we compared flow hemodynamics of three variations of aortic arches using four-dimensional flow magnetic resonance imaging (4D flow MRI).

METHODS

Arch anatomy on computed tomography imaging was reviewed and compared between patients with TBAD and age/sex-matched controls free of aortic pathology. Arch variants were defined as follows: common origin of innominate and left common carotid artery (bovine arch), aberrant right subclavian artery, and right-sided aortic arch. Demographics, TBAD characteristics, and follow-up data were abstracted. Patients with TBAD with variant and conventional aortic arches were compared. Additionally, three matched healthy controls with conventional, bovine, and aberrant right subclavian artery arches underwent 4D flow MRI evaluation to assess if there were differences in flow patterns by arch type. Indices of regional hemodynamic wall sheer stress were compared.

RESULTS

Computed tomography scans of 185 patients with TBAD (mean age, 58.1 ± 12.4 years; 72.4% males; 71.4% Caucasian) and 367 controls (mean age, 62.5 ± 13.4 years; 67% males; 77.9% Caucasian) were reviewed. Variant arch anatomy was more prevalent in patients with TBAD (40.5% vs 24.5%; P < .001). In patients with TBAD, there were no differences in the mean age of presentation and descending thoracic aorta diameter among those with variant or conventional arch anatomy. Patients with TBAD with variant arch anatomy had a higher percentage of dissection related thoracic aortic repairs (54.7% vs 33.6%; P = .004) with repairs occurring predominantly in the acute phase. 4D flow MRI demonstrated a higher systolic wall shear stress along the inner curve of the bovine arch compared with the conventional aberrant right subclavian artery arches.

CONCLUSIONS

Variant aortic arch anatomy is significantly more prevalent in patients with TBAD. patients with TBAD with variant arch anatomy had a higher percentage of dissection-related aortic repair. Preliminary 4D flow MRI data show differences in hemodynamic flow patterns between variant and conventional arches. Studies of long-term outcomes based on arch anatomy may offer additional insight to TBAD genesis and possibly influence management decisions.

Abstract 345: Combining Morphological and Mechanical Risk Factors May Improve Carotid Plaque Progression Prediction: an Magnetic Resonance Image-Based Follow-Up Study

It has been hypothesized that combining morphological and mechanical risk factors may improve plaque progression prediction. In this paper, plaque burden (PB), cap thickness (CT), lipid percent (LP), plaque wall stress (PWS), plaque wall strain (PWSn) and their combinations were used as predictors to identify the best predictor(s) for plaque progression measured by plaque area increase (PAI) from baseline (T1) and follow-up (T2).

In vivo magnetic resonance image (MRI) carotid plaque data were acquired from 8 patients (5 m, mean age 71) with follow-up (18 months) with informed consent obtained. We built 3D thin-layer models for the 41 matched slices to obtain plaque stress/strain data using patient-specific material properties determined from Cine MRI and patient arm blood pressure. The mean values of the 5 predictors from all lumen points of each slice were obtained for analysis. For each predictor Y, a threshold value Yc was determined so that optimal agreement rate was obtained (agreement cases are either {(Y>Yc) and (PAI >0)} or {(Y≤Yc) and (PAI ≤0)}). For PWS and PWSn, we used (either {(Y<Yc) and (PAI >0)} or {(Y≥Yc) and (PAI ≤0)}). Two combinations of predictors

COM1=a1*PB+a2*CT+a3*LP,

COM2=b1*PB+b2*CT+b3*LP+b4*PWS+b5*PWSn

were considered, where COM1 combines PB with morphological features, and COM2 combines all 5 predictors. The coefficients in these formulas were determined by using iterative linearly fitting method and initial guess of threshold values from single predictor results.

The optimal threshold values for the 5 single predictors and 2 combination predictors are given in Table 1. PWSn was the best single predictor and COM2 was the best combination predictor.

The threshold value-based method is simple and easy for clinical implementation. Our preliminary results indicate that combining PB, CT, LP, PWS, and PWSn could improve the agreement rate by nearly 10%, compared to using PB alone. Large-scale patient studies are needed to confirm our findings.

Carotid Artery Remodeling Is Segment Specific: An In Vivo Study by Vessel Wall Magnetic Resonance Imaging

OBJECTIVE

Early atherosclerosis is often undetected due in part to compensatory enlargement of the outer wall, termed positive remodeling. Variations in hemodynamic conditions and clinical factors influence the patterns of remodeling. The carotid artery provides an opportunity to examine these variations because of the unique geometry of the carotid bulb. This study aimed to determine differences in remodeling of the common, internal, and bifurcation segments of the carotid using magnetic resonance imaging.

APPROACH AND RESULTS

Carotid arteries of 525 subjects without history of cardiovascular disease were imaged by magnetic resonance imaging. The carotid artery was divided into 3 segments: common carotid artery; bifurcation; and internal carotid artery. Remodeling patterns were characterized using linear regression analysis of lumen and total vessel areas (dependent variables) compared with maximum wall thickness (independent variable) for each segment, adjusted for age, sex, and height. The common carotid artery demonstrated a pattern consistent with positive remodeling, whereas the bifurcation demonstrated negative remodeling. The internal carotid artery demonstrated a mixed pattern of outer wall expansion and lumen constriction. Females and subjects with diabetes mellitus showed more positive remodeling, hypertension was associated with attenuated positive remodeling, and those with hypercholesterolemia showed more negative remodeling.

CONCLUSIONS

In this cohort of 55- to 80-year-old individuals without history of cardiovascular disease, the pattern of early carotid artery remodeling was segment specific and appeared to be associated with sex and clinical characteristics. These findings provide the groundwork for longitudinal studies to define local and systemic factors such as hemodynamic and clinical conditions on carotid artery remodeling.

Abstract WP135: Location and Composition of Extracranial Carotid and Intracranial Atheroma in Symptomatic U.S. and Chinese Patients Detected by Vessel Wall Magnetic Resonance Imaging

Introduction: Atherosclerosis of the extracranial carotid and intracranial arteries is an important contributor to stroke. Autopsy studies suggest that the location and components of atheroma may vary between different ethnic groups. Advances in cerebrovascular vessel wall imaging with 3D-magnetic resonance imaging (MRI) have provided a critical tool to assess these differences in vivo .

Hypothesis: We tested the hypothesis that carotid culprit plaques are more common in U.S. patients, and that intracranial culprit plaques are more common in Chinese patients.

Methods: As part of the ongoing Culprit Plaque in Acute Cerebral Infarction study, patients with acute anterior circulation ischemic stroke were recruited at the University of Washington and the Beijing Tiantan Hospital. Plaque presence, location, and composition (intraplaque hemorrhage [IPH], lipid core, calcification, disrupted luminal surface [DLS]) in the carotid and intracranial arteries on the symptomatic side were evaluated using a 3D multi-contrast vessel wall MRI protocol. Carotid and intracranial arteries were reviewed independently by an experienced reader blinded to clinical characteristics and ethnic group.

Results: Twenty patients from the U.S. (median age: 59 years; 65% male) and 26 patients from China (58 years; 69% male) were evaluated. Of those, 18 U.S. patients (90%) and 20 Chinese patients (77%) had at least one plaque in either the carotid or intracranial arteries (p=0.4). Of those with plaque, 17 U.S. (94%) and 12 Chinese (60%) patients had carotid artery plaques (p= 0.02), and 11 U.S. (61%) and 19 Chinese (95%) patients had intracranial artery plaques (p=0.02). Features of possible culprit plaque (IPH and/or DLS) in the carotid artery were found in 8 U.S. patients (47%) but only 1 Chinese patient (8%) (p=0.04). Plaque composition in intracranial arteries was not significantly different between the two groups.

Conclusion: Possible culprit plaques in the carotid artery were more common in symptomatic U.S. patients than Chinese patients, while intracranial plaques were more common in the Chinese patients. Accurate localization of the culprit plaque has important implications for treatment.

Carotid Artery Wall Imaging: Perspective and Guidelines from the ASNR Vessel Wall Imaging Study Group and Expert Consensus Recommendations of the American Society of Neuroradiology

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

Lp(a) (Lipoprotein(a)) Levels Predict Progression of Carotid Atherosclerosis in Subjects With Atherosclerotic Cardiovascular Disease on Intensive Lipid Therapy: An Analysis of the AIM-HIGH (Atherothrombosis Intervention in Metabolic Syndrome With Low HDL/High Triglycerides: Impact on Global Health Outcomes) Carotid Magnetic Resonance Imaging Substudy-Brief Report

OBJECTIVE

To assess whether Lp(a) (lipoprotein(a)) levels and other lipid levels were predictive of progression of atherosclerosis burden as assessed by carotid magnetic resonance imaging in subjects who have been treated with LDL-C (low-density lipoprotein cholesterol)-lowering therapy and participated in the AIM-HIGH trial (Atherothrombosis Intervention in Metabolic Syndrome With Low HDL/High Triglycerides: Impact on Global Health Outcomes).

APPROACH AND RESULTS

AIM-HIGH was a randomized, double-blind study of subjects with established vascular disease, elevated triglycerides, and low HDL-C (high-density lipoprotein cholesterol). One hundred fifty-two AIM-HIGH subjects underwent both baseline and 2-year follow-up carotid artery magnetic resonance imaging. Plaque burden was measured by the percent wall volume (%WV) of the carotid artery. Associations between annualized change in %WV with baseline and on-study (1 year) lipid variables were evaluated using multivariate linear regression and the Bonferroni correction to account for multiple comparisons. Average %WV at baseline was 41.6±6.8% and annualized change in %WV over 2 years ranged from -3.2% to 3.7% per year (mean: 0.2±1.1% per year; P=0.032). Increases in %WV were significantly associated with higher baseline Lp(a) (β=0.34 per 1-SD increase of Lp(a); 95% confidence interval, 0.15-0.52; P<0.001) after adjusting for clinical risk factors and other lipid levels. On-study Lp(a) had a similar positive association with %WV progression (β=0.33; 95% confidence interval, 0.15-0.52; P<0.001).

CONCLUSIONS

Despite intensive lipid therapy, aimed at aggressively lowering LDL-C to <70 mg/dL, carotid atherosclerosis continued to progress as assessed by carotid magnetic resonance imaging and that elevated Lp(a) levels were independent predictors of increases in atherosclerosis burden.

Carotid Plaque Lipid Content and Fibrous Cap Status Predict Systemic CV Outcomes: The MRI Substudy in AIM-HIGH

OBJECTIVES

The aim of this study was to investigate whether and what carotid plaque characteristics predict systemic cardiovascular outcomes in patients with clinically established atherosclerotic disease.

BACKGROUND

Advancements in atherosclerosis imaging have allowed assessment of various plaque characteristics, some of which are more directly linked to the pathogenesis of acute cardiovascular events compared to plaque burden.

METHODS

As part of the event-driven clinical trial AIM-HIGH (Atherothrombosis Intervention in Metabolic Syndrome with Low HDL/High Triglycerides: Impact on Global Health Outcomes), subjects with clinically established atherosclerotic disease underwent multicontrast carotid magnetic resonance imaging (MRI) to detect plaque tissue composition and high-risk features. Prospective associations between MRI measurements and the AIM-HIGH primary endpoint (fatal and nonfatal myocardial infarction, ischemic stroke, hospitalization for acute coronary syndrome, and symptom-driven revascularization) were analyzed using Cox proportional hazards survival models.

RESULTS

Of the 232 subjects recruited, 214 (92.2%) with diagnostic image quality constituted the study population (82% male, mean age 61 ± 9 years, 94% statin use). During median follow-up of 35.1 months, 18 subjects (8.4%) reached the AIM-HIGH endpoint. High lipid content (hazard ratio [HR] per 1 SD increase in percent lipid core volume: 1.57; p = 0.002) and thin/ruptured fibrous cap (HR: 4.31; p = 0.003) in carotid plaques were strongly associated with the AIM-HIGH endpoint. Intraplaque hemorrhage had a low prevalence (8%) and was marginally associated with the AIM-HIGH endpoint (HR: 3.00; p = 0.053). High calcification content (HR per 1 SD increase in percent calcification volume: 0.66; p = 0.20), plaque burden metrics, and clinical risk factors were not significantly associated with the AIM-HIGH endpoint. The associations between carotid plaque characteristics and the AIM-HIGH endpoint changed little after adjusting for clinical risk factors, plaque burden, or AIM-HIGH randomized treatment assignment.

CONCLUSIONS

Among patients with clinically established atherosclerotic disease, carotid plaque lipid content and fibrous cap status were strongly associated with systemic cardiovascular outcomes. Markers of carotid plaque vulnerability may serve as novel surrogate markers for systemic atherothrombotic risk.

Development of a quantitative intracranial vascular features extraction tool on 3D MRA using semiautomated open-curve active contour vessel tracing

PURPOSE

To develop a quantitative intracranial artery measurement technique to extract comprehensive artery features from time-of-flight MR angiography (MRA).

METHODS

By semiautomatically tracing arteries based on an open-curve active contour model in a graphical user interface, 12 basic morphometric features and 16 basic intensity features for each artery were identified. Arteries were then classified as one of 24 types using prediction from a probability model. Based on the anatomical structures, features were integrated within 34 vascular groups for regional features of vascular trees. Eight 3D MRA acquisitions with intracranial atherosclerosis were assessed to validate this technique.

RESULTS

Arterial tracings were validated by an experienced neuroradiologist who checked agreement at bifurcation and stenosis locations. This technique achieved 94% sensitivity and 85% positive predictive values (PPV) for bifurcations, and 85% sensitivity and PPV for stenosis. Up to 1,456 features, such as length, volume, and averaged signal intensity for each artery, as well as vascular group in each of the MRA images, could be extracted to comprehensively reflect characteristics, distribution, and connectivity of arteries. Length for the M1 segment of the middle cerebral artery extracted by this technique was compared with reviewer-measured results, and the intraclass correlation coefficient was 0.97.

CONCLUSION

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

Prevalence and Characteristics of Carotid Artery High-Risk Atherosclerotic Plaques in Chinese Patients With Cerebrovascular Symptoms: A Chinese Atherosclerosis Risk Evaluation II Study

Background

Carotid atherosclerotic plaque rupture is an important source of ischemic stroke. However, the prevalence of high‐risk plaque (HRP) defined as plaques with luminal surface disruption, a lipid‐rich necrotic core occupying >40% of the wall, or intraplaque hemorrhage in Chinese population remains unclear. This study uses carotid magnetic resonance imaging (CMRI) to investigate HRP prevalence in carotid arteries of Chinese patients with cerebrovascular symptoms.

Methods and Results

Patients with cerebral ischemic symptoms in the anterior circulation within 2 weeks and carotid plaque determined by ultrasound were recruited and underwent CMRI. The HRP features were identified and compared between symptomatic and asymptomatic arteries. Receiver‐operating‐characteristic analysis was used to calculate area‐under‐the‐curve (AUC) of stenosis and maximum wall thickness for discriminating presence of HRP. In 1047 recruited subjects, HRP detected by CMRI was nearly 1.5 times more prevalent than severe stenosis (≥50%) in this cohort (28% versus 19%, P<0.0001). Approximately two thirds of HRPs were found in arteries with <50% stenosis. The prevalence of HRP in symptomatic carotid arteries was significantly higher than that of the contralateral asymptomatic carotid arteries (23.0% versus 16.4%, P=0.001). Maximum wall thickness was found to be a stronger discriminator than stenosis for HRP (AUC: 0.93 versus 0.81, P<0.0001).

Conclusions

There are significantly more high‐risk carotid plaques than carotid arteries with ≥50% stenosis in symptomatic Chinese patients. A substantial number of HRPs were found in arteries with lower grade stenosis and maximum wall thickness was a stronger indicator for HRP than luminal stenosis.

Clinical Trial Registration

URL: https://www.clinicaltrials.gov/. Unique identifier: NCT02017756.

Association between Snoring and High-Risk Carotid Plaque Features

Objectives Previous studies have demonstrated an association between snoring and carotid disease independent of sleep apnea. The aim of this study was to quantify the association between self-reported snoring and high-risk carotid plaque features on magnetic resonance imaging (MRI) that predict stroke. Study Design Cross-sectional. Setting Tertiary care university hospital and affiliated county hospital. Methods We surveyed 133 subjects with asymptomatic carotid artery disease that had been previously evaluated with high-resolution MRI. The survey captured data on self-reported snoring (exposure) and covariates (age, sex, body mass index, and sleep apnea via the STOP-Bang questionnaire). A subset of patients underwent home sleep apnea testing. High-risk carotid plaque features were identified on the high-resolution MRI and included thin/ruptured fibrous cap and intraplaque hemorrhage (outcomes). We quantified the association between snoring and high-risk carotid plaque features with the chi-square test (unadjusted analysis) and multivariate logistic regression adjusting for the covariates. Results Of 133 subjects surveyed, 61 (46%) responded; 32 (52%) reported snoring. Significantly higher proportions of snorers than nonsnorers had a thin/ruptured fibrous cap (56% vs 25%, P = .01) and intraplaque hemorrhage (63% vs 29%, P < .01). In multivariate analysis, snoring was associated with thin/ruptured fibrous cap (odds ratio, 4.4; 95% CI, 1.1-16.6; P = .04) and intraplaque hemorrhage (odds ratio, 8.2; 95% CI, 2.1-31.6; P < .01) after adjusting for age, sex, body mass index, and sleep apnea. Conclusion This pilot study suggests a significant independent association between snoring and high-risk carotid plaque features on MRI. Further study is warranted to confirm these results in a larger cohort of subjects.

A vascular image registration method based on network structure and circuit simulation

Background

Image registration is an important research topic in the field of image processing. Applying image registration to vascular image allows multiple images to be strengthened and fused, which has practical value in disease detection, clinical assisted therapy, etc. However, it is hard to register vascular structures with high noise and large difference in an efficient and effective method.

Results

Different from common image registration methods based on area or features, which were sensitive to distortion and uncertainty in vascular structure, we proposed a novel registration method based on network structure and circuit simulation. Vessel images were transformed to graph networks and segmented to branches to reduce the calculation complexity. Weighted graph networks were then converted to circuits, in which node voltages of the circuit reflecting the vessel structures were used for node registration. The experiments in the two-dimensional and three-dimensional simulation and clinical image sets showed the success of our proposed method in registration.

Conclusions

The proposed vascular image registration method based on network structure and circuit simulation is stable, fault tolerant and efficient, which is a useful complement to the current mainstream image registration methods.

Abstract 562: Human Carotid Atherosclerosis Plaque Progression and Vessel Material Stiffness at Follow Up Had Positive Correlation: An in vivo Vessel Stiffness MRI Follow Up Study

It is hypothesized that artery stiffness may be associated with plaque progression. However, in vivo vessel material stiffness follow-up data is lacking in the literature.

In vivo 3D multi-contrast and Cine magnetic resonance imaging (MRI) carotid plaque data were acquired from 8 patients with follow-up (18 months) with written informed consent obtained. Cine MRI and 3D thin-layer models were used to determine parameter values of the Mooney-Rivlin models for the 81slices from 16 plaques (2 scans/patient) using our established iterative procedures. Effective Young’s Modulus (YM) values for stretch ratio [1.0,1.3] were calculated for each slice for analysis.

Stress-stretch ratio curves from Mooney-Rivlin models for the 16 plaques and 81 slices are given in Fig. 1. Average YM value of the 81 slices was 411kPa. Slice YM values varied from 70 kPa (softest) to 1284 kPa (stiffest), a 1734% difference. Average slice YM values by vessel varied from 109 kPa (softest) to 922 kPa (stiffest), a 746% difference. Location-wise, the maximum slice YM variation rate within a vessel was 306% (139 kPa vs. 564 kPa). Average slice YM variation rate within a vessel for the 16 vessels was 134%. Average variation of YM values from baseline (T1) to follow up (T2) for all patients was 61.0%. The range of the variation of YM values was [-28.4%, 215%]. For progression study, YM increase (YMI=YM T2 -TM T1 ) showed negative correlation with plaque progression measured by wall thickness increase (WTI), (r= -0.6802, p=0.0634). YM T2 showed strong negative correlation with WTI (r= -0.7764, p=0.0235). Correlation between YM T1 and WTI was not significant (r= -0.4353, p= 0.2811).

Conclusion In vivo carotid vessel material properties have large variations from patient to patient, along the vessel segment within a patient, and from baseline to follow up. Use of patient-specific, location specific and time-specific material properties could potentially improve the accuracy of model stress/strain calculations.