Quantitative assessment of carotid plaque morphology (geometry and tissue composition) using computed tomography angiography

Imaging of Carotid Stenosis: Where Are We Standing? Comparison of Multiparametric Ultrasound, CT Angiography, and MRI Angiography, with Recent Developments

Atherosclerotic disease of the carotid arteries is a crucial risk factor in predicting the likelihood of future stroke events. In addition, emerging studies suggest that carotid stenosis may also be an indicator of plaque load on coronary arteries and thus have a correlation with the risk of acute cardiovascular events. Furthermore, although in symptomatic patients the degree of stenosis is the main morphological parameter studied, recent evidence suggests, especially in asymptomatic patients, that plaque vulnerability should also be evaluated as an emerging and significant imaging parameter. The reference diagnostic methods for the evaluation of carotid stenosis are currently ultrasonography, magnetic resonance imaging (MRI), and computed tomography angiography (CTA). In addition, other more invasive methods such as 123I-metaiodobenzylguanidine (MIBG) scintigraphy and PET-CT, as well as digital subtraction angiography, can be used. Each method has advantages and disadvantages, and there is often some confusion in their use. For example, the usefulness of MRI is often underestimated. In addition, implementations for each method have been developed over the years and are already enabling a significant increase in diagnostic accuracy. The purpose of our study is to make an in-depth analysis of all the methods in use and in particular their role in the diagnostic procedure of carotid stenosis, also discussing new technologies.

30-Day Risk Score for Mortality and Stroke in Patients with Carotid Artery Stenosis Using Artificial Intelligence Based Carotid Plaque Morphology

OBJECTIVES

The gold standard for determining carotid artery stenosis intervention is based on a combination of percent stenosis and symptomatic status. Few studies have assessed plaque morphology as an additive tool for stroke prediction. Our goal was to create a predictive model and risk score for 30-day stroke and death inclusive of plaque morphology.

METHODS

Patients with a CT angiography head/neck between 2010-2021 at a single institution and a diagnosis of carotid artery stenosis were included in our analysis. Each CT was used to create a 3D image of carotid plaque based off image recognition software. A stepwise backward regression was used to select variables for inclusion in our prediction models. Model discrimination was assessed with receiver operating characteristic curves (AUC). Additionally, calibration was performed and the model with the least Akaike Information Criterion (AIC) was selected. The risk score was modeled from the Framingham Study. Primary outcome was mortality/stroke.

RESULTS

We created three models to predict mortality/stroke from 366 patients: model A using only clinical variables, model B using only plaque morphology and model C using both clinical and plaque morphology variables. Model A used age, sex, PAD, hyperlipidemia, BMI, COPD, and history of TIA/stroke and had an AUC of 0.737 and AIC of 285.4. Model B used perivascular adipose tissue volume, lumen area, calcified volume, and target lesion length and had an AUC of 0.644 and AIC of 304.8. Finally, model C combined both clinical and software variables of age, sex, matrix volume, history of TIA/stroke, BMI, perivascular adipose tissue, lipid rich necrotic core, COPD and hyperlipidemia and had an AUC of 0.759 and an AIC of 277.6. Model C was the most predictive because it had the highest AUC and lowest AIC.

CONCLUSION

Our study demonstrates that combining both clinical factors and plaque morphology creates the best predication of a patient's risk for all-cause mortality or stroke from carotid artery stenosis. Additionally, we found that for patients with even 3 points in our risk score model have a 20% chance of stroke/death. Further prospective studies are needed to validate our findings.

Increased incidence of napkin-ring sign plaques on cervicocerebral computed tomography angiography associated with the risk of acute ischemic stroke occurrence

OBJECTIVES

Carotid atherosclerosis plays an essential role in the occurrence of ischemic stroke. This study aimed to investigate whether a larger burden of napkin-ring sign (NRS) plaques on cervicocerebral computed tomography angiography (CTA) increased the risk of acute ischemic stroke (AIS).

METHODS

This retrospective, single-center, cross-sectional study enrolled patients with NRS plaques identified in the subclavian arteries, brachiocephalic trunk, carotid arterial system, and vertebrobasilar circulation on contrast-enhanced cervicocerebral CTA. Patients were divided into AIS and non-AIS groups based on imaging within 12 h of symptom onset. Univariate and multivariate logistic regression analyses were performed to determine the risk factor of AIS occurrence.

RESULTS

A total of 202 patients (66.72 years ± 8.97, 157 men) were evaluated. Plaques with NRS in each subject of the AIS group (N = 98) were significantly more prevalent than that in the control group (N = 104) (1.96 ± 1.17 vs 1.41 ± 0.62). In the AIS group, there were substantially more NRS plaques on the ipsilateral side than contralateral side (1.55 ± 0.90 vs. 0.41 ± 0.66). NRS located on the ipsilateral side of the AIS showed an area under the receiver curve (AUC) of 0.86 to identify ischemic stroke. NRS plaque amounts were an independent risk factor for AIS occurrence (odds ratio, 1.86) after adjusting for other factors.

CONCLUSIONS

Increased incidence of napkin-ring sign plaques on cervicocerebral CTA was positively associated with AIS occurrence, which could aid in detecting asymptomatic atherosclerotic patients at high risk of AIS in routine screening or emergency settings.

CLINICAL RELEVANCE STATEMENT

Napkin-ring sign plaque provides an important imaging target for estimating acute ischemic stroke risk and identifying high-risk patients in routine screening or emergency settings, so that timely anti-atherosclerotic therapy can be used for prevention.

KEY POINTS

• This cross-sectional study investigated the association between high-risk carotid artery plaques and acute ischemic stroke. • Increased incidence of napkin-ring sign plaques on cervicocerebral computed tomography angiography is positively associated with acute ischemic stroke occurrence. • Napkin-ring signs help identify risky patients prone to acute ischemic stroke to facilitate prevention.

Machine Learning Detects Symptomatic Plaques in Patients With Carotid Atherosclerosis on CT Angiography

BACKGROUND

This study aimed to develop and validate a computed tomography angiography based machine learning model that uses plaque composition data and degree of carotid stenosis to detect symptomatic carotid plaques in patients with carotid atherosclerosis.

METHODS

The machine learning based model was trained using degree of stenosis and the volumes of 13 computed tomography angiography derived intracarotid plaque subcomponents (eg, lipid, intraplaque hemorrhage, calcium) to identify plaques associated with cerebrovascular events. The model was internally validated through repeated 10-fold cross-validation and tested on a dedicated testing cohort according to discrimination and calibration.

RESULTS

This retrospective, single-center study evaluated computed tomography angiography scans of 268 patients with both symptomatic and asymptomatic carotid atherosclerosis (163 for the derivation set and 106 for the testing set) performed between March 2013 and October 2019. The area-under-receiver-operating characteristics curve by machine learning on the testing cohort (0.89) was significantly higher than the areas under the curve of traditional logit analysis based on the degree of stenosis (0.51, P<0.001), presence of intraplaque hemorrhage (0.69, P<0.001), and plaque composition (0.78, P<0.001), respectively. Comparable performance was obtained on internal validation. The identified plaque components and associated cutoff values that were significantly associated with a higher likelihood of symptomatic status after adjustment were the ratio of intraplaque hemorrhage to lipid volume (≥50%, 38.5 [10.1-205.1]; odds ratio, 95% CI) and percentage of intraplaque hemorrhage volume (≥10%, 18.5 [5.7-69.4]; odds ratio, 95% CI).

CONCLUSIONS

This study presented an interpretable machine learning model that accurately identifies symptomatic carotid plaques using computed tomography angiography derived plaque composition features, aiding clinical decision-making.

Identification of vulnerable carotid plaque with CT-based radiomics nomogram

AIM

To develop and validate a radiomics nomogram for identifying high-risk carotid plaques on computed tomography (CT) angiography (CTA).

MATERIALS AND METHODS

A total of 280 patients with symptomatic (n=131) and asymptomatic (n=139) carotid plaques were divided into a training set (n=135), validation set (n=58), and external test set (n=87). Radiomic features were extracted from CTA images. A radiomics model was constructed based on selected features and a radiomics score (rad-score) was calculated. A clinical factor model was constructed by demographics and CT findings. A radiomics nomogram combining independent clinical factors and the rad-score was constructed. The diagnostic performance of three models was evaluated and validated by region of characteristic curves.

RESULTS

Calcification and maximum plaque thickness were the independent clinical factors. Twenty-four features were used to build the radiomics signature. In the validation set, the nomogram (area under the curve [AUC], 0.977; 95% CI, 0.899-0.999) performed better (p=0.017 and p=0.031) than the clinical factor model (AUC, 0.862; 95% CI, 0.746-0.938) and radiomics signature (AUC, 0.944; 95% CI, 0.850-0.987). In external test set, the nomogram (AUC, 0.952; 95% CI, 0.884-0.987) and radiomics signature (AUC, 0.932; 95% CI, 0.857-0.975) showed better discrimination capability (p=0.002 and p=0.037) than clinical factor model (AUC, 0.818; 95% CI, 0.721-0.892).

CONCLUSION

The CT-based nomogram showed satisfactory performance in identification of high-risk plaques in carotid arteries, and it may serve as a potential non-invasive tool to identify carotid plaque vulnerability and risk stratification.

Quantitative imaging biomarkers of coronary plaque morphology: insights from EVAPORATE

Aims

Residual cardiovascular risk persists despite statin therapy. In REDUCE-IT, icosapent ethyl (IPE) reduced total events, but the mechanisms of benefit are not fully understood. EVAPORATE evaluated the effects of IPE on plaque characteristics by coronary computed tomography angiography (CCTA). Given the conclusion that the IPE-treated patients demonstrate that plaque burden decreases has already been published in the primary study analysis, we aimed to demonstrate whether the use of an analytic technique defined and validated in histological terms could extend the primary study in terms of whether such changes could be reliably seen in less time on drug, at the individual (rather than only at the cohort) level, or both, as neither of these were established by the primary study result.

Methods and Results

EVAPORATE randomized the patients to IPE 4 g/day or placebo. Plaque morphology, including lipid-rich necrotic core (LRNC), fibrous cap thickness, and intraplaque hemorrhage (IPH), was assessed using the ElucidVivo® (Elucid Bioimaging Inc.) on CCTA. The changes in plaque morphology between the treatment groups were analyzed. A neural network to predict treatment assignment was used to infer patient representation that encodes significant morphological changes. Fifty-five patients completed the 18-month visit in EVAPORATE with interpretable images at each of the three time points. The decrease of LRNC between the patients on IPE vs. placebo at 9 months (reduction of 2 mm3 vs. an increase of 41 mm3, p = 0.008), widening at 18 months (6 mm3 vs. 58 mm3 increase, p = 0.015) were observed. While not statistically significant on a univariable basis, reductions in wall thickness and increases in cap thickness motivated multivariable modeling on an individual patient basis. The per-patient response assessment was possible using a multivariable model of lipid-rich phenotype at the 9-month follow-up, p < 0.01 (sustained at 18 months), generalizing well to a validation cohort.

Conclusion

Plaques in the IPE-treated patients acquired more characteristics of stability. Reliable assessment using histologically validated analysis of individual response is possible at 9 months, with sustained stabilization at 18 months, providing a quantitative basis to elucidate drug mechanism and assess individual patient response.

Impact of calcified plaque volume on technical and 3-year outcomes after transcarotid artery revascularization

OBJECTIVE

We sought to quantify the percent calcification within carotid artery plaques and assess its impact on percent residual stenosis and rate of restenosis in patients undergoing transcarotid artery revascularization for symptomatic and asymptomatic carotid artery stenosis.

METHODS

A retrospective review of prospectively collected institutional Vascular Quality Initiative data was performed to identify all patients undergoing transcarotid artery revascularization from December 2015 to June 2021 (n = 210). Patient and lesion characteristics were extracted. Using a semiautomated workflow, preoperative computed tomography head and neck angiograms were analyzed to determine the calcified plaque volume in distal common carotid artery and internal carotid artery plaques. Intraoperative digital subtraction angiograms were reviewed to calculate the percent residual stenosis post-intervention according to North American Symptomatic Carotid Endarterectomy Trial criteria. Peak systolic velocity and end-diastolic velocity were extracted from outpatient carotid duplex ultrasound examinations. Univariate logistic regression was performed to analyze the relationship of calcium volume percent and Vascular Quality Initiative lesion calcification to percent residual stenosis in completion angiograms. Kaplan-Meier analysis examined the relationship between calcium volume percent and in-stent stenosis over 36 months.

RESULTS

One hundred ninety-seven carotid arteries were preliminarily examined. Predilation was performed in 87.4% of cases with a mean balloon diameter of 5.1 ± 0.7 mm and a mean stent diameter was 8.8 ± 1.1 mm. The mean calcium volume percent was 11.9 ± 12.4% and the mean percent residual stenosis was 16.1 ± 15.6%. Univariate logistic regression demonstrated a statistically significant difference between calcium volume percent and percent residual stenosis (odds ratio [OR], 1.324; 95% confidence interval [CI], 1.005-1.746; P = .046). Stratified by quartile, only the top 25% of calcified plaques (>18.7% calcification) demonstrated a statistically significant association with higher percent residual stenosis (OR, 2.532; 95% CI, 1.049-6.115; P =.039). There was no statistical significance with lesion calcification (OR, 1.298; 95% C,: 0.980-1.718; P = .069). A Kaplan-Meier analysis demonstrated a statistically significant increase in the rate of in-stent stenosis during a 36-month follow-up for lesions containing >8.2% calcium volume (P = .0069).

CONCLUSIONS

A calcium volume percent of >18.7% was associated with a higher percent residual stenosis, and a calcium volume percent of >8.2% was associated with higher in-stent stenosis at 36 months. There was one clinically diagnosed stroke during the follow-up period, demonstrating the overall safety of the procedure.

Mast cells participate in smooth muscle cell reprogramming and atherosclerotic plaque calcification

BACKGROUND

Calcification, a key feature of advanced human atherosclerosis, is positively associated with vascular disease burden and adverse events. We showed that macrocalcification can be a stabilizing factor for carotid plaque molecular biology, due to inverse association with immune processes. Mast cells (MCs) are important contributors to plaque instability, but their relationship with macrocalcification is unexplored. With a hypothesis that MC activation negatively associates with carotid plaque macrocalcification, we aimed to investigate the link between MCs and carotid plaque vulnerability, and study MC role in plaque calcification via smooth muscle cells (SMCs).

METHODS

Pre-operative computed tomography angiographies of patients (n = 40) undergoing surgery for carotid stenosis were used to characterize plaque morphology. Plaque microarrays (n = 40 and n = 126) were used for bioinformatic deconvolution of immune cell populations. Tissue microarrays (n = 103) were used to histologically validate the contribution of activated and resting MCs in plaques.

RESULTS

Activated MCs and their typical markers were negatively correlated with macrocalcification. The ratio of activated vs. resting MCs was increased in low-calcified plaques from symptomatic patients. There was no modulating effect of medication on MC ratios. In vitro experiments showed that SMC calcification attenuated MC activation, while both active and resting MCs stimulated SMC calcification and induced dedifferentiation towards a pro-inflammatory-, osteochondrocyte-like phenotype, without modulating their migro-proliferative function.

CONCLUSIONS

Integrative analyses from human plaques showed that MC activation is inversely associated with macrocalcification and positively with parameters of plaque vulnerability. Mechanistically, MCs induce SMC osteogenic reprograming, while matrix calcification in turn attenuates MC activation, offering new therapeutic avenues for exploration.

Atherosclerosis risk classification with computed tomography angiography: A radiologic-pathologic validation study

BACKGROUND AND AIMS

The application of machine learning to assess plaque risk phenotypes on cardiovascular CT angiography (CTA) is an area of active investigation. Studies using accepted histologic definitions of plaque risk as ground truth for machine learning models are uncommon. The aim was to evaluate the accuracy of a machine-learning software for determining plaque risk phenotype as compared to expert pathologists (histologic ground truth).

METHODS

Sections of atherosclerotic plaques paired with CTA were prospectively collected from patients undergoing carotid endarterectomy at two centers. Specimens were annotated for lipid-rich necrotic core, calcification, matrix, and intraplaque hemorrhage at 2 mm spacing and classified as minimal disease, stable plaque, or unstable plaque according to a modified American Heart Association histological definition. Phenotype is determined in two steps: plaque morphology is delineated according to histological tissue definitions, followed by a machine learning classifier. The performance in derivation and validation cohorts for plaque risk categorization and stenosis was compared to histologic ground truth at each matched cross-section.

RESULTS

A total of 496 and 408 vessel cross-sections in the derivation and validation cohorts (from 30 and 23 patients, respectively). The software demonstrated excellent agreement in the validation cohort with histological ground truth plaque risk phenotypes with weighted kappa of 0.82 [0.78-0.86] and area under the receiver operating curve for correct identification of plaque type was 0.97 [0.96, 0.98], 0.95 [0.94, 0.97], 0.99 [0.99, 1.0] for unstable plaque, stable plaque, and minimal disease, respectively. Diameter stenosis correlated poorly to histologically defined plaque type; weighted kappa 0.25 in the validation cohort.

CONCLUSIONS

A machine-learning software trained on histological ground-truth tissue inputs demonstrated high accuracy for identifying plaque stability phenotypes as compared to expert pathologists.

A Framework for Evaluating the Technical Performance of Multiparameter Quantitative Imaging Biomarkers (mp-QIBs)

Multiparameter quantitative imaging incorporates anatomical, functional, and/or behavioral biomarkers to characterize tissue, detect disease, identify phenotypes, define longitudinal change, or predict outcome. Multiple imaging parameters are sometimes considered separately but ideally are evaluated collectively. Often, they are transformed as Likert interpretations, ignoring the correlations of quantitative properties that may result in better reproducibility or outcome prediction. In this paper we present three use cases of multiparameter quantitative imaging: i) multidimensional descriptor, ii) phenotype classification, and iii) risk prediction. A fourth application based on data-driven markers from radiomics is also presented. We describe the technical performance characteristics and their metrics common to all use cases, and provide a structure for the development, estimation, and testing of multiparameter quantitative imaging. This paper serves as an overview for a series of individual articles on the four applications, providing the statistical framework for multiparameter imaging applications in medicine.

Evaluating Atherosclerosis of the Abdominal Aorta in Rabbits Using 2-D Strain Imaging

After establishment of an animal model of atherosclerosis, speckle tracking imaging was performed to analyze the correlation between ultrasound characteristics and pathological manifestations. Rabbits were divided into the normal control (NC) and atherosclerosis (AS) groups. Rabbits in the AS group were subjected to ultrasound-guided balloon injury of the abdominal aorta and fed a high-fat diet for 16 wk. Rabbits in the NC group were fed a normal diet for the same period. After 16 wk, all animals underwent serological tests, ultrasound and speckle tracking circumferential strain analysis. In the AS group, 28 hypo-echoic plaques had formed. The circumferential strain of six segments at the short axis of plaques in the AS group was lower than that in the NC group (p < 0.001), and global circumferential strain (GCS) in the AS group was significantly reduced compared with the NC group (p < 0.001). In the AS group, the area ratio of type I to type III collagen fibers was smaller than that in the NC group. The GCS of atherosclerotic plaques was positively correlated with the area ratio of type I to type III collagen fibers in plaques (r = 0.7181, p < 0.001). In conclusion, there is a significant positive correlation between the decreased circumferential strain and the decreased area ratio of type I to type III collagen fibers in hypo-echoic plaques.

Biomechanical Assessment of Macro-Calcification in Human Carotid Atherosclerosis and Its Impact on Smooth Muscle Cell Phenotype

Intimal calcification and vascular stiffening are predominant features of end-stage atherosclerosis. However, their role in atherosclerotic plaque instability and how the extent and spatial distribution of calcification influence plaque biology remain unclear. We recently showed that extensive macro calcification can be a stabilizing feature of late-stage human lesions, associated with a reacquisition of more differentiated properties of plaque smooth muscle cells (SMCs) and extracellular matrix (ECM) remodeling. Here, we hypothesized that biomechanical forces related to macro-calcification within plaques influence SMC phenotype and contribute to plaque stabilization. We generated a finite element modeling (FEM) pipeline to assess plaque tissue stretch based on image analysis of preoperative computed tomography angiography (CTA) of carotid atherosclerotic plaques to visualize calcification and soft tissues (lipids and extracellular matrix) within the lesions. Biomechanical stretch was significantly reduced in tissues in close proximity to macro calcification, while increased levels were observed within distant soft tissues. Applying this data to an in vitro stretch model on primary vascular SMCs revealed upregulation of typical markers for differentiated SMCs and contractility under low stretch conditions but also impeded SMC alignment. In contrast, high stretch conditions in combination with calcifying conditions induced SMC apoptosis. Our findings suggest that the load bearing capacities of macro calcifications influence SMC differentiation and survival and contribute to atherosclerotic plaque stabilization.

Identification Markers of Carotid Vulnerable Plaques: An Update

Vulnerable plaques have been a hot topic in the field of stroke and carotid atherosclerosis. Currently, risk stratification and intervention of carotid plaques are guided by the degree of luminal stenosis. Recently, it has been recognized that the vulnerability of plaques may contribute to the risk of stroke. Some classical interventions, such as carotid endarterectomy, significantly reduce the risk of stroke in symptomatic patients with severe carotid stenosis, while for asymptomatic patients, clinically silent plaques with rupture tendency may expose them to the risk of cerebrovascular events. Early identification of vulnerable plaques contributes to lowering the risk of cerebrovascular events. Previously, the identification of vulnerable plaques was commonly based on imaging technologies at the macroscopic level. Recently, some microscopic molecules pertaining to vulnerable plaques have emerged, and could be potential biomarkers or therapeutic targets. This review aimed to update the previous summarization of vulnerable plaques and identify vulnerable plaques at the microscopic and macroscopic levels.

Patient-specific biomechanical analysis of atherosclerotic plaques enabled by histologically validated tissue characterization from computed tomography angiography: A case study

BACKGROUND

Rupture of unstable atherosclerotic plaques with a large lipid-rich necrotic core and a thin fibrous cap cause myocardial infarction and stroke. Yet it has not been possible to assess this for individual patients. Clinical guidelines still rely on use of luminal narrowing, a poor indicator but one that persists for lack of effective means to do better. We present a case study demonstrating the assessment of biomechanical indices pertaining to plaque rupture risk non-invasively for individual patients enabled by histologically validated tissue characterization.

METHODS

Routinely acquired clinical images of plaques were analyzed to characterize vascular wall tissues using software validated by histology (ElucidVivo, Elucid Bioimaging Inc.). Based on the tissue distribution, wall stress and strain were then calculated at spatial locations with varied fibrous cap thicknesses at diastolic, mean and systolic blood pressures.

RESULTS

The von Mises stress of 152 [131, 172] kPa and the equivalent strain of 0.10 [0.08, 0.12] were calculated where the fibrous cap thickness was smallest (560 μm) (95% CI in brackets). The stress at this location was at a level predictive of plaque failure. Stress and strain at locations with larger cap thicknesses were calculated to be lower, demonstrating a clinically relevant range of risk levels.

CONCLUSION

Patient specific tissue characterization can identify distributions of stress and strain in a clinically relevant range. This capability may be used to identify high-risk lesions and personalize treatment decisions for individual patients with cardiovascular disease and improve prevention of myocardial infarction and stroke.

Relationship between annular calcification of plaques in the carotid sinus and perioperative hemodynamic disorder in carotid angioplasty and stenting

OBJECTIVE

To investigate the correlation between annular plaque calcification in the carotid sinus and perioperative hemodynamic disorder (HD) in carotid angioplasty and stenting (CAS).

METHODS

The clinical data of 49 patients undergoing CAS due to narrowing of the carotid sinus were retrospectively analyzed. All patients had preoperative carotid computed tomography angiography (CTA) and were divided into HD and non-HD groups based on the occurrence of HD in the perioperative period of CAS. HD was defined as persistent bradycardia (heart rate < 60 beats per min) or persistent hypotension (systolic blood pressure < 90 mmHg) in the perioperative period and lasting for at least 1 h. The baseline data, including the degree of carotid artery stenosis, plaque length, plaque thickness, calcified plaque morphologies (i.e., plaque circumferential angle: < 90° defined as dotted calcification; 90°-180° defined as arcuate calcification; > 180° defined as annular calcification), contralateral carotid artery conditions, balloon diameter, and stent types, were compared between the two groups. Binary logistic regression was used to analyze the risk factors for the occurrence of HD.

RESULTS

Among the 49 patients undergoing CAS, 14 (28.57%) developed perioperative HD, and 35 did not. Annular calcification was more common in the patients in the HD group than in the non-HD group. No significant differences in the probabilities of dotted and arcuate calcifications were found between the two groups (p > 0.05). The duration of continuous dopamine consumption in the HD group was 9-71 h. The average hospital stay of the HD group (10.14 ± 4.17 days) was significantly longer than that of the non-HD group (6.57 ± 1.9 days; p < 0.001). Patients in the HD group had significantly more pronounced lumen stenosis (p = 0.033) and longer plaque length (p = 0.034) than those in the non-HD group. After adjusting for age and sex, multivariate regression analysis showed that the presence of annular plaque calcification was an independent predictor of HD (odds ratio: 7.68, 95% confidence interval: 1.46-40.37, p = 0.016).

CONCLUSIONS

The occurrence of annular plaque calcification in the carotid sinus was an independent risk factor for perioperative HD in CAS. Preoperative carotid CTA assists with the early identification of high-risk patients who may develop HD.

The Circulating Biomarker Fractalkine and Platelet-Derived Growth Factor BB are Correlated with Carotid Plaque Vulnerability Assessed by Computed Tomography Angiography

OBJECTIVES

Although studies have demonstrated that inflammatory and lipid/ lipoproteins-related biomarkers, genetic mutations, and epigenetic mechanisms could be candidates for diagnosis and prognosis of ischemic stroke, there is still no consensus on how to identify vulnerable plaques based on circulating biomarkers.

MATERIALS AND METHODS

Histological and immunohistochemical staining were performed in the aorta sections of ApoE^-/^- and WT mice. Eighty-nine patients who underwent CTA were included in this study. The degree of carotid stenosis and the wall features of plaque components were quantitatively analyzed. And the serum concentration of FKN and PDGF-BB were measured.

RESULTS

(1) The type V vulnerable atherosclerotic plaques deposited on the aortas of ApoE^-/^- mice after feeding with western diet for 16 weeks. And the expression of CX3CR1 and PDGFR-β increased in the areas of atherosclerotic plaques, especially inside the fibrous cap of plaque. (2) Patients with symptomatic carotid stenosis showed larger LNRC, smaller calcified plaques and more plaque ulceration detected by CTA than asymptomatic stenosis patients. Plaque ulceration and size of LNRC were high risk factors for stroke while plaque calcification was less frequently associated with cerebrovascular ischemia. (3) The serum concentration of FKN was lower and of PDGF-BB was higher in the patients with carotid artery stenosis. Correlation analysis suggested that FKN and PDGF-BB correlated positively with carotid plaque calcification and LNRC respectively.

CONCLUSIONS

For prediction it is recommended to combine circulating biomarkers (FKN and PDGF-BB) and imaging biomarkersfor comprehensive diagnosis and risk stratification in carotid atherosclerotic stroke.

Imaging Approaches to the Diagnosis of Vascular Diseases

PURPOSE OF REVIEW

Vascular imaging is a complex field including numerous modalities and imaging markers. This review is focused on important and recent findings in atherosclerotic carotid artery plaque imaging with an emphasis on developments in magnetic resonance imaging (MRI) and computed tomography (CT).

RECENT FINDINGS

Recent evidence shows that carotid plaque characteristics and not only established measures of carotid plaque burden and stenosis are associated independently with cardiovascular outcomes. On carotid MRI, the presence of a lipid-rich necrotic core (LRNC) has been associated with incident cardiovascular disease (CVD) events independent of wall thickness, a traditional measure of plaque burden. On carotid MRI, intraplaque hemorrhage (IPH) presence has been identified as an independent predictor of stroke. The presence of a fissured carotid fibrous cap has been associated with contrast enhancement on CT angiography imaging. Carotid artery plaque characteristics have been associated with incident CVD events, and advanced plaque imaging techniques may gain additional prominence in the clinical treatment decision process.

Carotid atherosclerotic disease: A systematic review of pathogenesis and management

Carotid stenosis is an important contributor to ischemic stroke risk with resultant significant impact on neurological disability and death in adults and with worldwide implications. Management of carotid stenosis is impacted by whether there are associated symptoms along with the degree of stenosis. Understanding of the pathogenesis of carotid atherosclerosis or stenosis is important in management of carotid stenosis. Atherosclerotic plaque formation is a chronic insidious process with a number of potential contributors to the formation of such a plaque. The definition of atherosclerosis is not simply limited to abnormal deposition of lipid but also includes a chronic, complex, inflammatory process. Molecularly, in atherosclerosis, there is decreasing nitric oxide (NO) bioavailability, activity and/or expression of endothelial NO synthase, or increasing degradation of NO secondary to enhanced superoxide production. These above changes cause endothelial dysfunction leading to formation of foam cell followed by formation on lipid plaque. After lipid plaque formation, stable or unstable atherosclerotic plaque is formed depending on the calcium deposition over the lipid plaque. It continues to be clearly established that carotid intervention for symptomatic high-grade carotid stenosis is best managed with intervention either by carotid endarterectomy or carotid stenting. However, asymptomatic carotid stenosis is the subject of considerable controversy in terms of optimal management. This review of carotid atherosclerosis is an attempt to incorporate the information provided by more recent studies on pathogenesis and management which may help in the decision-making process for optimal management for protection against stroke.

Carotid Plaque Composition Assessed by CT Predicts Subsequent Cardiovascular Events among Subjects with Carotid Stenosis

BACKGROUND AND PURPOSE

Currently, the characteristics of carotid plaques are considered important factors for identifying subjects at high risk of stroke. This study aimed to test the hypothesis that carotid plaque composition assessed by CTA is associated with an increased risk of future major adverse cardiovascular events among asymptomatic subjects with moderate-to-severe carotid artery stenosis.

MATERIALS AND METHODS

This single-center, retrospective cohort study included 194 carotid plaques from 176 asymptomatic subjects with moderate-to-severe carotid artery stenosis. The association of CTA-determined plaque composition with the risk of subsequent adverse cardiovascular events was analyzed.

RESULTS

During a median follow-up of 41 months, the adverse cardiovascular event incidence among 194 carotid plaques was 19.6%. There were significant differences in plaque Hounsfield units (P < .001) and spotty calcium presence (P < .001) between carotid plaques from subjects with and without subsequent adverse cardiovascular events. Multivariable analysis revealed carotid plaque Hounsfield unit density (P < .001) and spotty calcium (P < .001) as independent predictors of subsequent adverse cardiovascular events. In association with moderate carotid artery stenosis, the plaque Hounsfield unit values were significantly lower among carotid plaques from subjects who experienced subsequent adverse cardiovascular events (P = .002), strokes (P = .01), and cardiovascular deaths (P = .04); the presence of spotty calcium was significantly associated with the occurrence of adverse cardiovascular events (P = .001), acute coronary syndrome (P = .01), and cardiovascular death (P = .04).

CONCLUSIONS

Carotid plaque Hounsfield unit density and spotty calcium were independent predictors of a greater risk of adverse cardiovascular event occurrence.

CT angiographic biomarkers help identify vulnerable carotid artery plaque

OBJECTIVE

Current risk assessment for patients with carotid atherosclerosis relies primarily on measuring the degree of stenosis. More reliable risk-stratification could improve patient selection for targeted treatment. We developed and validated a model to predict major adverse neurological events (MANE; stroke, transient ischemic attack, and amaurosis fugax) incorporating a combination of plaque morphology, patient demographics, and patient clinical information.

METHODS

We enrolled 221 patients with asymptomatic carotid stenosis of any severity who had CT angiography at baseline and at least 6 months later. Images were analyzed for carotid plaque morphology (plaque geometry and tissue composition). Data were partitioned (training and validation cohorts). 190 patients had complete records and were advanced to analysis. The training cohort was used to develop the best model for predicting MANE, incorporating patient and plaque features. First, single-variable correlation and unsupervised clustering were performed. Next, several multi-variable models were implemented for the response variable of MANE. The best model was selected by optimizing area under the receiver operating characteristic curve (AUC, ROC) and Kappa. The model was validated on the sequestered data to demonstrate generalizability.

RESULTS

Sixty-two patients suffered a MANE on follow-up. Unsupervised clustering of patient and plaque features identified single-variable predictors of MANE. Multi-variable predictive modeling showed that a combination of plaque features at baseline (matrix, intra-plaque hemorrhage (IPH), wall thickness, plaque burden) with clinical features (age, BMI, lipid levels) best predicted MANE (AUC 0.79), while percent diameter stenosis performed worst (AUC 0.55). The strongest single variable in discriminating between patients with and without events was IPH, and the most predictive model was produced when IPH was considered together with wall remodeling. The selected model also performed well on the validation dataset (AUC of 0.64) and maintained superiority over percent diameter stenosis (AUC of 0.49).

CONCLUSIONS

A composite of plaque geometry, plaque tissue composition, patient demographics, and clinical information predicts MANE better than the traditionally utilized degree of stenosis alone in carotid atherosclerosis. Implementing this predictive model in the clinical setting can help identify patients at high-risk for major adverse neurological events.

Cardiovascular risk factors and cervical carotid plaque features on CT angiography

BACKGROUND

Little is known about the impact that cardiovascular (CV) risk factors have on the formation of various carotid atherosclerotic plaque features. This study set out to assess the association between CV risk factors and plaque characteristics on computed tomography (CT) angiography (CTA).

MATERIALS AND METHODS

A retrospective review was completed of consecutive patients that underwent a carotid endarterectomy and had CTA imaging of the head and neck vasculature. Atherosclerotic plaques of both carotid arteries were evaluated for calcification(s), low-density plaque (LDP) components, ulceration(s), and degree of stenosis. Various clinical CV risk factors were assessed using medical records. Last recorded laboratory levels were dichotomized into categories: total cholesterol <200 or ≥200 mg/dL, low-density lipoprotein (LDL) <130 or ≥130 mg/dL, high-density lipoprotein <35 or ≥35 mg/dL, and triglyceride <200 or ≥200 mg/dL.

RESULTS

Of 97 included patients, 62 were male (63.9%); the average age was 72.7 (standard deviation = 9.5). Calcifications were in 95/97 (97.9%) of patients (one or both carotid plaques); LDP components were in 73/97 (75.3%), and ulcerations were in 21/97 (21.6%). Elevated total cholesterol and elevated LDL levels were both associated with a higher likelihood of LDP components (p = 0.004 and p = 0.02, respectively). There were no other statistically significant associations between individual plaque features or severity of arterial stenosis and CV risk factors.

CONCLUSION

In carotid atherosclerotic plaques, LDP components are more frequently present in one or both carotid arteries in patients with elevated total cholesterol and/or LDL levels. Such findings raise the possibility that cholesterol levels may be directly related to the formation of specific high-risk plaque features.

Carotid Plaque Phenotyping by Correlating Plaque Morphology from Computed Tomography Angiography with Transcriptional Profiling

OBJECTIVE

Ischaemic strokes can be caused by unstable carotid atherosclerosis, but methods for identification of high risk lesions are lacking. Carotid plaque morphology imaging using software for visualisation of plaque components in computed tomography angiography (CTA) may improve assessment of plaque phenotype and stroke risk, but it is unknown if such analyses also reflect the biological processes related to lesion stability. Here, we investigated how carotid plaque morphology by image analysis of CTA is associated with biological processes assessed by transcriptomic analyses of corresponding carotid endarterectomies (CEAs).

METHODS

Carotid plaque morphology was assessed in patients undergoing CEA for symptomatic or asymptomatic carotid stenosis consecutively enrolled between 2006 and 2015. Computer based analyses of pre-operative CTA was performed to define calcification, lipid rich necrotic core (LRNC), intraplaque haemorrhage (IPH), matrix (MATX), and plaque burden. Plaque morphology was correlated with molecular profiles obtained from microarrays of corresponding CEAs and models were built to assess the ability of plaque morphology to predict symptomatology.

RESULTS

Carotid plaques (n = 93) from symptomatic patients (n = 61) had significantly higher plaque burden and LRNC compared with plaques from asymptomatic patients (n = 32). Lesions selected from the transcriptomic cohort (n = 40) with high LRNC, IPH, MATX, or plaque burden were characterised by molecular signatures coupled with inflammation and extracellular matrix degradation, typically linked with instability. In contrast, highly calcified plaques had a molecular signature signifying stability with enrichment of profibrotic pathways and repressed inflammation. In a cross validated prediction model for symptoms, plaque morphology by CTA alone was superior to the degree of stenosis.

CONCLUSION

The study demonstrates that CTA image analysis for evaluation of carotid plaque morphology, also reflects prevalent biological processes relevant for assessment of plaque phenotype. The results support the use of CTA image analysis of plaque morphology for risk stratification and management of patients with carotid stenosis.

Correlation between computed tomography angiography and histology of carotid artery atherosclerosis: Can semi-automated imaging software predict a plaque's composition?

BACKGROUND

Using computed tomography angiography to differentiate between components of carotid atherosclerotic lesions remains largely elusive. This study sought to validate a semi-automated software for computed tomography angiography plaque analysis using histologic comparisons.

MATERIALS AND METHODS

A retrospective review was performed of consecutive patients that underwent a carotid endarterectomy, with pre-procedural computed tomography angiography imaging of the cervical arterial vasculature available for review. Images were evaluated using a commercially-available software package, which produced segmented analyses of intraplaque components (e.g. intraplaque hemorrhage, lipid-rich necrotic core, and calcifications). On imaging, each component was assessed in terms of its (1) presence or absence, and (2) both volume and proportion of the total plaque volume (if present). On histological evaluation of carotid endarterectomy specimens, each component was evaluated as an estimated proportion of total plaque volume.

RESULTS

Of 80 included patients, 30 (37.5%) were female. The average age was 69.7 years (SD = 9.1). Based on imaging, intraplaque hemorrhage was the smallest contributor to plaque composition (1.2% of volumes on average). Statistically significant linear associations were noted between the proportion of intraplaque hemorrhage, lipid-rich necrotic core, and calcifications on histology and the volume of each component on imaging (p values ranged from 0.0008 to 0.01). Area under curve were poor for intraplaque hemorrhage and lipid-rich necrotic core (0.59 and 0.61, respectively) and acceptable for calcifications (0.73).

CONCLUSION

Semi-automated analyses of computed tomography angiography have limited diagnostic accuracy in the detection of intraplaque hemorrhage and lipid-rich necrotic core in carotid artery plaques. However, volumetric imaging measurements of different components corresponded with histologic analysis.

Proteoglycan 4 Modulates Osteogenic Smooth Muscle Cell Differentiation during Vascular Remodeling and Intimal Calcification

Calcification is a prominent feature of late-stage atherosclerosis, but the mechanisms driving this process are unclear. Using a biobank of carotid endarterectomies, we recently showed that Proteoglycan 4 (PRG4) is a key molecular signature of calcified plaques, expressed in smooth muscle cell (SMC) rich regions. Here, we aimed to unravel the PRG4 role in vascular remodeling and intimal calcification. PRG4 expression in human carotid endarterectomies correlated with calcification assessed by preoperative computed tomographies. PRG4 localized to SMCs in early intimal thickening, while in advanced lesions it was found in the extracellular matrix, surrounding macro-calcifications. In experimental models, Prg4 was upregulated in SMCs from partially ligated ApoE-/- mice and rat carotid intimal hyperplasia, correlating with osteogenic markers and TGFb1. Furthermore, PRG4 was enriched in cells positive for chondrogenic marker SOX9 and around plaque calcifications in ApoE-/- mice on warfarin. In vitro, PRG4 was induced in SMCs by IFNg, TGFb1 and calcifying medium, while SMC markers were repressed under calcifying conditions. Silencing experiments showed that PRG4 expression was driven by transcription factors SMAD3 and SOX9. Functionally, the addition of recombinant human PRG4 increased ectopic SMC calcification, while arresting cell migration and proliferation. Mechanistically, it suppressed endogenous PRG4, SMAD3 and SOX9, and restored SMC markers' expression. PRG4 modulates SMC function and osteogenic phenotype during intimal remodeling and macro-calcification in response to TGFb1 signaling, SMAD3 and SOX9 activation. The effects of PRG4 on SMC phenotype and calcification suggest its role in atherosclerotic plaque stability, warranting further investigations.

Virtual Transcriptomics: Noninvasive Phenotyping of Atherosclerosis by Decoding Plaque Biology From Computed Tomography Angiography Imaging

[Figure: see text].

The Differentiation in Image Post-processing and 3D Reconstruction During Evaluation of Carotid Plaques From MR and CT Data Sources

Background: Carotid plaque morphology and tissue composition help assess risk stratification of stroke events. Many post-processing image techniques based on CT and MR images have been widely used in related research, such as image segmentation, 3D reconstruction, and computer fluid dynamics. However, the criteria for the 3D numerical model of carotid plaque established by CT and MR angiographic image data remain open to questioning.

Method: We accurately duplicated the geometry and simulated it using computer software to make a 3D numerical model. The initial images were obtained by CTA and TOF-MRA. MIMICS (Materialize’s interactive medical image control system) software was used to process the images to generate three-dimensional solid models of blood vessels and plaques. The subsequent output was exported to the ANSYS software to generate finite element simulation results for the further hemodynamic study.

Results: The 3D models of carotid plaque of TOF-MRA and CTA were simulated by using computer software. CTA has a high-density resolution for carotid plaque, the boundary of the CTA image is obvious, and the main component of which is a calcified tissue. However, the density resolution of TOF-MRA for the carotid plaque and carotid artery was not as good as that of CTA. The results show that there is a large deviation between the TOF-MRA and CTA 3D model of plaque in the carotid artery due to the unclear recognition of plaque boundary during 3D reconstruction, and this can further affect the simulation results of hemodynamics.

Conclusion: In this study, two-dimensional images and three-dimensional models of carotid plaques obtained by two angiographic techniques were compared. The potential of these two imaging methods in clinical diagnosis and fluid dynamics of carotid plaque was evaluated, and the selectivity of image post-processing analysis to original medical image acquisition was revealed.

Semiautomated carotid artery plaque composition: are intraplaque CT imaging features associated with cardiovascular risk factors?

BACKGROUND

Little remains known about the connection between cardiovascular (CV) risk factors and carotid plaque morphologies. This study set out to assess for any such associations.

MATERIALS AND METHODS

A retrospective review was completed of consecutive patients that had CTA neck imaging prior to CEA. Body mass index (BMI), tobacco and/or alcohol use, and history of diabetes and/or hypertension were collected from patients' medical records. Lab values were dichotomized based on values: total cholesterol < 200 or ≥ 200; low-density lipoprotein (LDL) < 130 or ≥ 130, high-density lipoprotein < 35 or ≥ 35, and triglycerides < 200 or ≥ 200. A semiautomated analysis of CTA images computed maximum stenosis, intraplaque volumes of intraplaque hemorrhage, lipid-rich necrotic core (LRNC), and matrix, and intraplaque volume and proportional plaque makeup of calcifications of each carotid plaque.

RESULTS

Of 87 included patients, 54 (62.1%) were male. Mean age was 70.1 years old. Both diabetes and hypertension were associated with greater intraplaque calcification volume (p = 0.0009 and p = 0.01, respectively), and greater proportion of calcification within a plaque (p = 0.004 and p = 0.01, respectively). Higher BMI was associated with greater intraplaque volume of LRNC (p=0.02) and matrix (0.0007). Elevated total cholesterol was associated with both larger intraplaque calcification volume (p = 0.04) and greater proportion of calcification within a plaque (p = 0.01); elevated LDL was associated with greater intraplaque calcification volume (p = 0.005).

CONCLUSION

Multiple CV risk factors are associated with morphological differences in carotid artery plaques. Dysregulation of both total cholesterol and LDL and higher BMI are associated with higher volumes of intraplaque LRNC, a marker of plaque vulnerability.

CT imaging features of carotid artery plaque vulnerability

Despite steady advances in medical care, cardiovascular disease remains one of the main causes of death and long-term morbidity worldwide. Up to 30% of strokes are associated with the presence of carotid atherosclerotic plaques. While the degree of stenosis has long been recognized as the main guiding factor in risk stratification and therapeutical decisions, recent evidence suggests that features of unstable, or ‘vulnerable’, plaques offer better prognostication capabilities. This paradigmatic shift has motivated researchers to explore the potentialities of non-invasive diagnostic tools to image not only the lumen, but also the vascular wall and the structural characteristics of the plaque. The present review will offer a panoramic on the imaging modalities currently available to characterize carotid atherosclerotic plaques and, in particular, it will focus on the increasingly important role covered by multidetector computed tomographic angiography.

Plaque imaging volume analysis: technique and application

The prevention and management of atherosclerosis poses a tough challenge to public health organizations worldwide. Together with myocardial infarction, stroke represents its main manifestation, with up to 25% of all ischemic strokes being caused by thromboembolism arising from the carotid arteries. Therefore, a vast number of publications have focused on the characterization of the culprit lesion, the atherosclerotic plaque. A paradigm shift appears to be taking place at the current state of research, as the attention is gradually moving from the classically defined degree of stenosis to the identification of features of plaque vulnerability, which appear to be more reliable predictors of recurrent cerebrovascular events. The present review will offer a perspective on the present state of research in the field of carotid atherosclerotic disease, focusing on the imaging modalities currently used in the study of the carotid plaque and the impact that such diagnostic means are having in the clinical setting.

Assessment of image quality and dose in contrast-enhanced head and neck CT angiography of New Zealand rabbit

BACKGROUND

Although computed tomography (CT) is a powerful diagnostic imaging modality for diagnosing vascular diseases, it is some what risky to human health due to the high radiation dosage. Thus, CT vendors have developed low dose computed tomography (LDCT) aiming to solve this problem. Nowadays, LDCT has gradually become a main stream of CT examination.

OBJECTIVE

This study aimed to assess the feasibility of LDCTAin an animal model and compare the imaging features and doses in two clinical scanners.

METHODS

Twenty-two New Zealand rabbit head and neck CTA images pre- and post-contrast agent injection were performed using256-sliceand 64-slice CT scanners. The tube voltages used in the 256-slice and the 64-slice CTA were 70 kVp and 80 kVp, respectively. Quantitative images indices and radiation doses obtained from CTA in these two scanners were compared.

RESULTS

More neck arterial vessels could be visualized in multi-planar reconstruction (MPR) CTA on the 256-slice CT scanner than on the 64-slice CT scanner. After contrast agent injection, all observed neck arterial vessels had higher CT numbers in 256-slice CTA than in 64-slice CTA. There was no significant difference in contrast-to-noise (CNR) of CTA images between these two scanners. CT dose index (CTDI) and dose length product (DLP) for the 256-slice CTA were lower than those for the 64-slice CTA.

CONCLUSIONS

Low dose CTA of rabbits with 70 or 80 kVp is feasible in a 256-slice or a 64-slice CT scanner. The radiation dose from the 256-slice CTA was much lower than that from the 64-slice CTA with comparable SNR and CNR. The technique can be further applied in longitudinal monitoring of an animal stroke model in the future.

Carotid Intraplaque-Hemorrhage Volume and Its Association with Cerebrovascular Events

BACKGROUND AND PURPOSE

Our aim was to assess the relationship between volume and percentage of intraplaque hemorrhage measured using CT and the occurrence of cerebrovascular events at the time of CT.

MATERIALS AND METHODS

One-hundred-twenty-three consecutive subjects (246 carotid arteries) with a mean age of 69 years who underwent CTA were included in this retrospective study. Plaque volume of components and subcomponents (including intraplaque hemorrhage volume) was quantified with dedicated software.

RESULTS

Forty-six arteries were excluded because no plaque was identified. In the remaining 200 carotid arteries, a statistically significant difference was found between presentation with cerebrovascular events and lipid volume (P = .002), intraplaque hemorrhage volume (P = .002), percentage of lipid (P = .002), percentage of calcium (P = .001), percentage of intraplaque hemorrhage (P = .001), percentage of lipid-intraplaque hemorrhage (P = .001), and intraplaque hemorrhage/lipid ratio (P = .001). The highest receiver operating characteristic area under the curve was obtained with the intraplaque hemorrhage volume with a value of 0.793 (P = .001), percentage of intraplaque hemorrhage with an area under the curve of 0.812 (P = .001), and the intraplaque hemorrhage/lipid ratio with an area under the curve value of 0.811 (P = .001).

CONCLUSIONS

Results of our study suggest that Hounsfield unit values <25 have a statistically significant association with the presence of cerebrovascular events and that the ratio intraplaque hemorrhage/lipid volume represents a strong parameter for the association of cerebrovascular events.