Intra- and interreader reproducibility of magnetic resonance imaging for quantifying the lipid-rich necrotic core is improved with gadolinium contrast enhancement

Thin Calcification Predicts Lipid Component in Carotid Plaque-Relationship Between Lipid Distribution and Thin Calcification

BACKGROUND

Accurately evaluating plaque characteristics is essential because lesions with lipid-rich plaque put patients at risk of thromboembolic complications from carotid artery stenting. Near-infrared spectroscopy (NIRS) is a diagnostic imaging modality that identifies lipid components from the near-infrared absorption pattern but does not reveal the distribution of calcification. The purpose of this study was to investigate the calcification characteristics of unstable carotid plaques, focusing on relationships between the calcification characteristics revealed by computed tomography angiography and the lipid core distribution derived from NIRS.

METHODS

Participants in this retrospective analysis comprised 35 patients (29 men, 6 women; mean age, 76.0 years; range, 52-89 years) who underwent carotid artery stenting in our institute between January 2021 and December 2022. We evaluated the thickness and length of carotid calcifications at the minimal lumen level from preoperative computed tomography angiography and analyzed the relationship with maximum lipid core burden index (max-LCBI) from NIRS.

RESULTS

Strong negative linear correlations were observed between the thickness of calcification and max-LCBI at Area (any segment in a target lesion) (r = -0.795, P < 0.001), max-LCBI at minimal lumen area (r = -0.795, P < 0.001) and lipid core burden index (LCBI) at lesion (rate of LCBI in entire plaque lesion) (r = -0.788, P < 0.001), respectively. Significant negative linear correlations were observed between distribution of calcification length and max-LCBI at area (r = -0.429, P = 0.01), max-LCBI at minimal lumen area (r = -0.373, P = 0.027), and LCBI at lesion (r = -0.443, P = 0.008).

CONCLUSIONS

Thin and ubiquitous carotid calcification was associated with LCBI values derived from NIRS indicative of carotid lipid plaque distribution, implying the possibility of predicting lesion instability.

Quantifying Carotid Stenosis: History, Current Applications, Limitations, and Potential: How Imaging Is Changing the Scenario

Carotid artery stenosis is a major cause of morbidity and mortality. The journey to understanding carotid disease has developed over time and radiology has a pivotal role in diagnosis, risk stratification and therapeutic management. This paper reviews the history of diagnostic imaging in carotid disease, its evolution towards its current applications in the clinical and research fields, and the potential of new technologies to aid clinicians in identifying the disease and tailoring medical and surgical treatment.

MR Angiography of Extracranial Carotid Disease

Magnetic resonance angiography sequences, such as time-of-flight and contrast-enhanced angiography, provide clear depiction of vessel lumen, traditionally used to evaluate carotid pathologic conditions such as stenosis, dissection, and occlusion; however, atherosclerotic plaques with a similar degree of stenosis may vary tremendously from a histopathological standpoint. MR vessel wall imaging is a promising noninvasive method to evaluate the content of the vessel wall at high spatial resolution. This is particularly interesting in the case of atherosclerosis as vessel wall imaging can identify higher risk, vulnerable plaques as well as has potential applications in the evaluation of other carotid pathologic conditions.

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.

Clinical features and long-term outcomes of symptomatic low-grade carotid stenosis

OBJECTIVE

In symptomatic low-grade stenosis, most of the reports did not clarify the long-term outcome. This study aims to clarify the clinical features and long-term outcomes of symptomatic low-grade stenosis cases.

MATERIALS AND METHODS

We included 123 symptomatic patients with low-grade (<50%) carotid stenosis. The relative plaque signal intensity (rSI) and expansive remodeling rate (ERR) were measured using carotid magnetic resonance imaging (MRI). Antiplatelet therapy and treatment for atherosclerosis risk factors were administered in all cases. Carotid endarterectomy (CEA) was performed when ischemic symptoms appeared, or the percent stenosis progressed despite medical treatment.

RESULTS

The mean percent stenosis, rSI, and ERR on admission were 22.3, 1.70, and 2.01, respectively. The mean volume of the hyperintense plaque on carotid MRI was 641.4± 540 mm3. Sixty percent of cases involved intraplaque hemorrhage and expansive remodeling. During a mean follow-up of 52 months, recurrence of ischemic events was confirmed in 45 cases (36.6%). Of the 67 cases performed follow-up MRI, 34 cases (50%) had an increased volume of T1-hyperintense plaque. CEA or carotid artery stenting was performed in 49 cases. During a mean follow-up of 57.8 months after CEA, two cases of death (fatal intracerebral hemorrhage and asphyxia) and one case of brain stem lacunar infarction were observed, but ipsilateral ischemic events were not.

CONCLUSION

Most of the symptomatic patients with low-grade stenosis had both intraplaque hemorrhage and expansive remodeling and presented a high risk of recurrence and stenosis progression. CEA may have preventive effects against ischemic events in low-grade stenosis.

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.

Assessment of Therapeutic Response to Statin Therapy in Patients With Intracranial or Extracranial Carotid Atherosclerosis by Vessel Wall MRI: A Systematic Review and Updated Meta-Analysis

Background and Aims: Statin therapy is an essential component of cardiovascular preventive care. In recent years, various vessel wall MRI (VW-MRI) techniques have been used to monitor atherosclerosis progression or regression in patients with extracranial or intracranial large-artery atherosclerosis. We aimed to perform a systematic review and meta-analysis on the effects of statin therapy on plaque evolution as assessed by VW-MRI.

Materials and Methods: Prospective studies investigating carotid and intracranial atherosclerotic plaques in patients on statin therapy monitored by serial VW-MRI were systematically identified in the literature. The plaque burden and lipid-rich necrotic core (LRNC) volume of carotid plaque and the imaging features of intracranial plaques were extracted and summarized. For studies investigating carotid artery wall volume and LRNC volume, combined estimates were derived by meta-analysis.

Results: The study identified 21 studies of carotid plaque and two studies of intracranial plaque. While 16 studies investigating carotid plaques that included 780 patients by High-resolution VW-MRI were included in the meta-analysis. There was no significant change in carotid wall volume from baseline to 12 months. A significant change in LRNC volume was observed at > 12 months compared with baseline (Effect = −10.69, 95% CI = −19.11, −2.28, P < 0.01), while no significant change in LRNC volume at 3–6 months or 7–12 months after statin therapy initiation in 6 studies. Increases in fibrous tissue and calcium and reduction in neovascularization density of the plaque were seen in 2/3 studies (including 48/59 patients), 1/3 studies (including 17/54 patients), and 2/2 studies (including 71 patients) after statin therapy, respectively. Two studies with 257 patients in intracranial atherosclerosis showed that statins could effectively decrease wall volume and plaque enhancement volume.

Conclusions: Collective data indicated that statins could potentially stabilize carotid plaques by significantly reducing LRNC with 1 year of therapy as shown on serial carotid VW-MRI. There was no significant decrease in wall volume, which nonetheless indicated that plaque composition changes might be more sensitive to response monitoring than wall volume. It is likely that more sensitive, clinically relevant, and preferably quantitative indicators of therapeutic effects on intracranial vessel plaque morphology will be developed in the future.

Evolving determinants of carotid atherosclerosis vulnerability in asymptomatic patients from the MAGNETIC observational study

MRI can assess plaque composition and has demonstrated an association between some atherosclerotic risk factors (RF) and markers of plaque vulnerability in naive patients. We aimed at investigating this association in medically treated asymptomatic patients. This is a cross-sectional interim analysis (August 2013-September 2016) of a single center prospective study on carotid plaque vulnerability (MAGNETIC study). We recruited patients with asymptomatic carotid atherosclerosis (US stenosis > 30%, ECST criteria), receiving medical treatments at a tertiary cardiac rehabilitation. Atherosclerotic burden and plaque composition were quantified with 3.0 T MRI. The association between baseline characteristics and extent of lipid-rich necrotic core (LRNC), fibrous cap (CAP) and intraplaque hemorrhage (IPH) was studied with multiple regression analysis. We enrolled 260 patients (198 male, 76%) with median age of 71-y (interquartile range: 65-76). Patients were on antiplatelet therapy, ACE-inhibitors/angiotensin receptor blockers and statins (196-229, 75-88%). Median LDL-cholesterol was 78 mg/dl (59-106), blood pressure 130/70 mmHg (111-140/65-80), glycosylated hemoglobin 46 mmol/mol (39-51) and BMI 25 kg/m² (23-28); moreover, 125 out of 187 (67%) patients were ex-smokers. Multivariate analysis of a data-set of 487 (94%) carotid arteries showed that a history of hypercholesterolemia, diabetes, hypertension or smoking did not correlate with LRNC, CAP or IPH. Conversely, maximum stenosis was the strongest independent predictor of LRNC, CAP and IPH (p < 0.001). MRI assessment of plaque composition in patients on treatment for asymptomatic carotid atherosclerosis shows no correlation between plaque vulnerability and the most well-controlled modifiable RF. Conversely, maximum stenosis exhibits a strong correlation with vulnerable features despite treatment.

Plaque Composition as a Predictor of Plaque Ulceration in Carotid Artery Atherosclerosis: The Plaque At RISK Study

BACKGROUND AND PURPOSE

Plaque ulceration is a marker of previous plaque rupture. We studied the association between atherosclerotic plaque composition at baseline and plaque ulceration at baseline and follow-up.

MATERIALS AND METHODS

We included symptomatic patients with a carotid stenosis of <70% who underwent MDCTA and MR imaging at baseline (n = 180). MDCTA was repeated at 2 years (n = 73). We assessed the presence of ulceration using MDCTA. Baseline MR imaging was used to assess the vessel wall volume and the presence and volume of plaque components (intraplaque hemorrhage, lipid-rich necrotic core, and calcifications) and the fibrous cap status. Associations at baseline were evaluated with binary logistic regression and reported with an OR and its 95% CI. Simple statistical testing was performed in the follow-up analysis.

RESULTS

At baseline, the prevalence of plaque ulceration was 27% (49/180). Increased wall volume (OR  = 12.1; 95% CI, 3.5-42.0), higher relative lipid-rich necrotic core (OR = 1.7; 95% CI, 1.3-2.2), higher relative intraplaque hemorrhage volume (OR = 1.7; 95% CI, 1.3-2.2), and a thin-or-ruptured fibrous cap (OR = 3.4; 95% CI, 1.7-6.7) were associated with the presence of ulcerations at baseline. In 8% (6/73) of the patients, a new ulcer developed. Plaques with a new ulceration at follow-up had at baseline a larger wall volume (1.04 cm³ [IQR, 0.97-1.16 cm³] versus 0.86 cm³ [IQR, 0.73-1.00 cm³]; P = .029), a larger relative lipid-rich necrotic core volume (23% [IQR, 13-31%] versus 2% [IQR, 0-14%]; P = .002), and a larger relative intraplaque hemorrhage volume (14% [IQR, 8-24%] versus 0% [IQR, 0-5%]; P < .001).

CONCLUSIONS

Large atherosclerotic plaques and plaques with intraplaque hemorrhage and lipid-rich necrotic cores were associated with plaque ulcerations at baseline and follow-up.

Magnetic resonance imaging of carotid plaques: current status and clinical perspectives

Rupture of a vulnerable carotid plaque is one of the leading causes of stroke. Carotid magnetic resonance imaging (MRI) is able to visualize all the main hallmarks of plaque vulnerability. Various MRI sequences have been developed in the last two decades to quantify carotid plaque burden and composition. Often, a combination of multiple sequences is used. These MRI techniques have been extensively validated with histological analysis of carotid endarterectomy specimens. High agreement between the MRI and histological measures of plaque burden, intraplaque hemorrhage (IPH), lipid-rich necrotic core (LRNC), fibrous cap (FC) status, inflammation and neovascularization has been demonstrated. Novel MRI sequences allow to generate three-dimensional isotropic images with a large longitudinal coverage. Other new sequences can acquire multiple contrasts using a single sequence leading to a tremendous reduction in scan time. IPH can be easily identified as a hyperintense signal in the bulk of the plaque on strongly T₁-weighted images, such as magnetization-prepared rapid acquisition gradient echo images, acquired within a few minutes with a standard neurovascular coil. Carotid MRI can also be used to evaluate treatment effects. Several meta-analyses have demonstrated a strong predictive value of IPH, LRNC, thinning or rupture of the FC for ischemic cerebrovascular events. Recently, in a large meta-analysis based on individual patient data of asymptomatic and symptomatic individuals with carotid artery stenosis, it was shown that IPH on MRI is an independent risk predictor for stroke, stronger than any known clinical risk parameter. Expert recommendations on carotid plaque MRI protocols have recently been described in a white paper. The present review provides an overview of the current status and applications of carotid plaque MR imaging and its future potential in daily clinical practice.

Lipid Core Plaque Distribution Using Near-infrared Spectroscopy Is Consistent with Pathological Evaluation in Carotid Artery Plaques

Carotid artery stenting (CAS) is performed as a treatment for carotid artery stenosis. However, lipid-rich plaques cause embolic complications and sequelae. Near-infrared spectroscopy (NIRS) can identify lipid components by applying a near-infrared absorption pattern, and the distribution of lipid components can be evaluated as the maximum lipid core burden index (maxLCBI). Intravascular ultrasound (IVUS) equipped with NIRS has been clinically applied recently, and its diagnostic usefulness and validation have been reported for coronary arteries; however, its consistency with actual pathological diagnosis in carotid artery lesions has not been validated. In this study, we investigated the consistency between the maxLCBI values and histopathological diagnoses. Patients with cervical carotid artery stenosis who underwent carotid endarterectomy (CEA) were examined in this prospective study. Pathological diagnosis was determined after NIRS evaluation, which was performed on the extracted plaques ex vivo. The histological slices of decalcified and paraffin-embedded sections were stained by hematoxylin–eosin (HE) and Elastica van Gieson (EVG), and for low-density lipoprotein (LDL), C-reactive protein (CRP), CD68, and glycophorin A. The correlation between maxLCBI values and histological findings. Seventy lesions assessed by NIRS were pathologically analyzed. There was a positive linear correlation between maxLCBI values and pathological findings as determined by HE (angle), HE (area%), EVG, CRP, and CD68 staining (respectively, r = 0.624, p <0.001; r = 0.578, p <0.001; r = 0.534, p <0.001; r = 0.723, p <0.001; r = 0.653, p <0.001). In conclusion, the maxLCBI values assessed by NIRS showed a significant positive linear correlation with pathological evaluations in carotid lesions. The maxLCBI values in carotid arteries are consistent with pathological evaluations.

Molecular and Nonmolecular Magnetic Resonance Coronary and Carotid Imaging

Atherosclerosis is the leading cause of cardiovascular morbidity and mortality. Over the past 2 decades, increasing research attention is converging on the early detection and monitoring of atherosclerotic plaque. Among several invasive and noninvasive imaging modalities, magnetic resonance imaging (MRI) is emerging as a promising option. Advantages include its versatility, excellent soft tissue contrast for plaque characterization and lack of ionizing radiation. In this review, we will explore the recent advances in multicontrast and multiparametric imaging sequences that are bringing the aspiration of simultaneous arterial lumen, vessel wall, and plaque characterization closer to clinical feasibility. We also discuss the latest advances in molecular magnetic resonance and multimodal atherosclerosis imaging.

Lipid-Rich Necrotic Core of Basilar Artery Atherosclerotic Plaque: Contrast-Enhanced Black Blood Imaging on Vessel Wall Imaging

Purpose: We wished to evaluate the lipid-rich necrotic core (LRNC) using contrast-enhanced T1-weighted (CE-T1W) black-blood (BB) imaging for vessel walls. Methods: Ninety-five patients with basilar artery (BA) stenosis who underwent magnetic resonance angiography between January 2016 and August 2018 were enrolled into this present study. CE-T1W BB imaging was considered as a reference method for identifying an LRNC. Results: Ten (10.5%) patients were identified as having an LRNC on CE-T1W BB imaging. Of these patients, 9 had acute symptoms. The extent of stenosis in patients with an LRNC on CE-T1W BB imaging was significantly greater than that of patients without an LRNC (p < 0.001). The maximum wall thickness in patients with an LRNC on CE-T1W imaging was significantly thicker than that of patients without an LRNC (p = 0.008). Conclusions: Identification of an LRNC on CE-T1W BB imaging was associated with high-grade stenosis and massive plaque burden from BA atherosclerosis.

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.

Identification of carotid lipid-rich necrotic core and calcification by 3D magnetization-prepared rapid acquisition gradient-echo imaging

BACKGROUND AND PURPOSE

This study sought to investigate the feasibility of three-dimensional MPRAGE in identifying the lipid-rich necrotic core (LRNC) and calcification (CA) of carotid atherosclerotic plaques.

MATERIALS AND METHODS

Twelve patients (mean age 68.4 ± 11.8 years; 7 males) with carotid atherosclerotic plaques on ultrasound were included and underwent multicontrast magnetic resonance (MR) vessel wall imaging. The contrast enhanced T1W (CE-T1W) images were considered as reference for identifying LRNC. The signal intensity of LRNC, CA, sterno-cleidomastoid muscle and fibrous tissue (FT) was measured on CE-T1W, T1W, T2W, and MPRAGE images, respectively. The relative signal intensity (rSI) of LRNC and CA against muscle or FT was compared among four sequences. Area under the curve (AUC) of rSIs of LRNC, CA and FT against muscle on MPRAGE, T1W and T2W images in discriminating the LRNC or CA from FT and the other plaque component was calculated.

RESULTS

Of 352 slices, 88 (25.0%) had LRNC, 31 (8.8%) had CA, 14 (4.0%) had both LRNC and CA, and 247 (70.2%) had no components. Among four imaging sequences, MPRAGE images showed the lowest rSI of LRNC (0.34 ± 0.18) and CA (0.20 ± 0.16) against muscle, followed by T1W (0.48 ± 0.18 and 0.33 ± 0.21), CE-T1W (0.58 ± 0.23 and 0.40 ± 0.21) and T2W (0.71 ± 0.47 and 0.43 ± 0.40) images. In addition, the MPRAGE images showed the lowest rSI of LRNC (0.57 ± 0.26) and CA (0.33 ± 0.23) against FT. MPRAGE showed greater AUC than T2W and T1W in discriminating the LRNC (0.827 vs. 0.703 vs. 0.635) and CA (0.917 vs. 0.838 vs. 0.825).

CONCLUSION

MPRAGE sequence might be a potential non-contrast enhanced imaging tool for identification of carotid LRNC and CA.

Carotid stenting with proximal cerebral protection in symptomatic low-grade vulnerable recurrent carotid stenosis

Background

Although the management of carotid disease is well established for symptomatic lesions ⩾70%, carotid revascularization for symptomatic low-grade (⩽50%) stenosis is not actually supported by data from randomized clinical trials. Such patients may occasionally have recurrent neurological symptoms despite optimal medical treatment owing to vulnerable plaques. In such cases, carotid artery stenting (CAS) may represent an option for treatment but this has not been tested in clinical trials. This study analyzed early and long-term outcomes of CAS performed in patients with low-grade symptomatic recurrent carotid stenosis.

Methods

From a prospective registry of 322 carotid revascularization in symptomatic patients, 21 consecutive patients with low-grade symptomatic recurrent carotid stenosis who underwent CAS with proximal cerebral protection device Mo.Ma, after ruling out any other source of cerebral embolization, were involved in the study.All patients had suggestive evidence of unstable plaque or plaque ulceration.

Results

Procedural technical success rate was 100%. No 30-day stroke or death occurred, and no patients had recurrent neurological events related to the revascularized hemisphere during follow up. No 30-day local complications were reported. No late carotid occlusions were detected. There was one late death, and no stroke-related deaths. Survival rates were 100% at 1 year and 96% at 3 years.

Conclusions

This study shows that CAS is a well-tolerated, effective and durable treatment for patients with recurrent symptomatic low-grade carotid stenosis associated with a vulnerable plaque. Patients had excellent protection against further ischemic events and survived long enough.

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.

Magnetic resonance imaging of intracranial atherosclerosis: Comparison of ex vivo 3T MRI and histologic findings

PURPOSE

Imaging the lipid-rich necrotic core (LRNC) is very important when evaluating the response of lipid-lowering therapy. The purpose of this study was to assess ex vivo LRNC of intracranial atherosclerosis using 3T MRI.

MATERIALS AND METHODS

Thirty-one atherosclerotic lesions from 17 specimens were analyzed (basilar artery=15, middle cerebral artery=16) using 3T MRI. Specimens were not chemically processed for imaging studies. Reconstructed MRI was matched with histologic sections at corresponding locations.

RESULTS

The median plaque thickness of intracranial atherosclerosis was 0.6mm (0.4-2.0mm). All specimens had a LRNC on histologic findings. Three specimens had plaque calcification on histologic findings. LRNC of 30 specimens (96.8%) appeared as homogeneous isointensity/hypointensity on T1-weighted imaging and hypointensity on T2-weighted imaging compared with T1-weighted imaging.

CONCLUSIONS

All specimens with ex vivo intracranial atherosclerosis had LRNC. Intracranial atherosclerosis could be an indication for lipid-lowering therapy, similar to previous carotid MR studies.

Investigation of 3D reduced field of view carotid atherosclerotic plaque imaging

To investigate the feasibility of using CUBE based reduced field of view imaging in atherosclerotic plaque imaging. Twenty-four patients were enrolled in this prospective study (13 males, 11 females, age 63±10). All patients underwent MRI exams consisting of 3D TOF, MPRAGE, iMSDE, DANTE, full FOV and reduced FOV CUBE imaging; 18 patients under went contrast enhanced imaging. The resulting images from different imaging sequences were assessed in terms of blood suppression, SNR, motion artifacts and vascular clarity. Reduced field of view CUBE outperformed MPRAGE, iMSDE and full FOV CUBE in blood suppression (P<0.05); outperformed MPRAGE, iMSDE and DANTE in SNR(P<005); outperformed MPRAGE and iMSDE in motion artifacts (P<005); outperformed MPRAGE and iMSDE in vascular clarity (P<0.05). The identifications of hemorrhage and calcification components were consistent between full FOV CUBE and reduced FOV CUBE (P<0.05). Overall, CUBE combined with reduced field of view imaging would be a promising method in atherosclerotic plaque imaging.

Large coverage black-bright blood interleaved imaging sequence (LaBBI) for 3D dynamic contrast-enhanced MRI of vessel wall

PURPOSE

To propose a large coverage black-bright blood interleaved imaging sequence (LaBBI) for 3D dynamic contrast-enhanced MRI (DCE-MRI) of the vessel wall.

METHODS

LaBBI consists of a 3D black-blood stack-of-stars golden angle radial acquisition with high spatial resolution for vessel wall imaging and a 2D bright-blood Cartesian acquisition with high temporal resolution for arterial input function estimation. The two acquisitions were performed in an interleaved fashion within a single scan. Simulations, phantom experiments, and in vivo tests in three patients were performed to investigate the feasibility and performance of the proposed LaBBI.

RESULTS

In simulation tests, the estimated K^trans and v_p by LaBBI were more accurate than conventional bright-blood DCE-MRI with lower root mean square error in all the tested conditions. In phantom test, no signal interference was found on the 2D scan in LaBBI. Pharmacokinetic analysis of the patients' data acquired by LaBBI showed that K^trans was higher in fibrous tissue (0.0717 ± 0.0279 min^-1 ), while lower in necrotic core (0.0206 ± 0.0040 min^-1 ) and intraplaque hemorrhage (0.0078 ± 0.0007 min^-1 ), compared with normal vessel wall (0.0273 ± 0.0052 min^-1 ).

CONCLUSION

The proposed LaBBI sequence, with high spatial and temporal resolution, and large coverage blood suppression, was promising to probe the perfusion properties of vessel wall lesions. Magn Reson Med 79:1334-1344, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Imaging of the high-risk carotid plaque: magnetic resonance imaging

The emergence of the concept of high-risk atherosclerotic plaque has led to considerable interest in noninvasive imaging techniques to identify high-risk features before clinical sequelae. For plaques in the carotid arteries, magnetic resonance imaging has undergone considerable histologic validation to link imaging features to indicators of plaque instability, including plaque burden, intraplaque hemorrhage, fibrous cap disruption, lipid rich necrotic core, and calcification. Recently introduced imaging technologies, especially those focused on three-dimensional imaging sequences, are now poised for integration into the clinical workup of patients with suspected carotid atherosclerosis. The purpose of this article is to review the carotid plaque magnetic resonance imaging techniques that are most ready for integration into the clinic.

Ipsilateral plaques display higher T1 signals than contralateral plaques in recently symptomatic patients with bilateral carotid intraplaque hemorrhage

BACKGROUND AND AIMS

Prospective studies have shown a strong association between carotid intraplaque hemorrhage (IPH), detected by magnetic resonance imaging (MRI), and cerebrovascular ischemic events. However, IPH is also observed in a substantial number of asymptomatic patients. We hypothesized that there are differences in the characteristics of IPH+ plaques associated with recent symptoms, compared to IPH+ plaques not associated with recent symptoms.

METHODS

Patients with recent (≤2 weeks) anterior circulation ischemic events were scanned using a standardized multisequence protocol. Those showing IPH bilaterally were included and analyzed for differences in T1/T2 signals, plaque morphology, and coexisting plaque characteristics between the ipsilateral symptomatic and contralateral asymptomatic sides.

RESULTS

Thirty-one subjects (67 ± 9 years, 97% males) with bilateral IPH were studied. Despite comparable luminal stenosis (53 ± 42% vs. 53 ± 39%, p = 0.99), T1 signal of IPH measured as signal-intensity-ratio compared to muscle was stronger (SIRIPH-to-muscle: 5.8 ± 2.4 vs. 4.7 ± 1.8, p = 0.004) and tended to be more extensively distributed (IPH volume: 150 ± 199 vs. 88 ± 106 mm3, p = 0.071) on the symptomatic side. IPH+ plaques on the symptomatic side were longer (24 ± 6 vs. 21 ± 7 mm, p = 0.026) and associated with larger necrotic core volume (406 ± 354 vs. 291 ± 293 mm3, p = 0.039) than those on the asymptomatic side.

CONCLUSIONS

In recently symptomatic patients with bilateral carotid IPH, the symptomatic side showed stronger T1 signals, larger necrotic cores, and longer plaque length than the asymptomatic side. Serial studies on the temporal relationship between these imaging features and clinical events will eventually establish their diagnostic and prognostic value beyond the mere presence of IPH.

HDL efflux capacity, HDL particle size, and high-risk carotid atherosclerosis in a cohort of asymptomatic older adults: the Chicago Healthy Aging Study

HDL efflux capacity and HDL particle size are associated with atherosclerotic CVD (ASCVD) events in middle-aged individuals; however, it is unclear whether these associations are present in older adults. We sampled 402 Chicago Healthy Aging Study participants who underwent a dedicated carotid MRI assessment for lipid-rich necrotic core (LRNC) plaque. We measured HDL particle size, HDL particle number, and LDL particle number with NMR spectroscopy, as well as HDL efflux capacity. We quantified the associations between HDL particle size and HDL efflux using adjusted linear regression models. We quantified associations between the presence of LRNC and HDL and LDL particle number, HDL particle size, and HDL efflux capacity using adjusted logistic regression models. HDL efflux capacity was directly associated with large (β = 0.037, P < 0.001) and medium (β = 0.0065, P = 0.002) HDL particle concentration and inversely associated with small (β = -0.0049, P = 0.018) HDL particle concentration in multivariable adjusted models. HDL efflux capacity and HDL particle number were inversely associated with prevalent LRNC plaque in unadjusted models (odds ratio: 0.5; 95% confidence interval: 0.26, 0.96), but not after multivariable adjustment. HDL particle size was not associated with prevalent LRNC. HDL particle size was significantly associated with HDL efflux capacity, suggesting that differences in HDL efflux capacity may be due to structural differences in HDL particles. Future research is needed to determine whether HDL efflux is a marker of ASCVD risk in older populations.

Manual versus Automated Carotid Artery Plaque Component Segmentation in High and Lower Quality 3.0 Tesla MRI Scans

PURPOSE

To study the interscan reproducibility of manual versus automated segmentation of carotid artery plaque components, and the agreement between both methods, in high and lower quality MRI scans.

METHODS

24 patients with 30-70% carotid artery stenosis were planned for 3T carotid MRI, followed by a rescan within 1 month. A multicontrast protocol (T1w,T2w, PDw and TOF sequences) was used. After co-registration and delineation of the lumen and outer wall, segmentation of plaque components (lipid-rich necrotic cores (LRNC) and calcifications) was performed both manually and automated. Scan quality was assessed using a visual quality scale.

RESULTS

Agreement for the detection of LRNC (Cohen's kappa (k) is 0.04) and calcification (k = 0.41) between both manual and automated segmentation methods was poor. In the high-quality scans (visual quality score ≥ 3), the agreement between manual and automated segmentation increased to k = 0.55 and k = 0.58 for, respectively, the detection of LRNC and calcification larger than 1 mm2. Both manual and automated analysis showed good interscan reproducibility for the quantification of LRNC (intraclass correlation coefficient (ICC) of 0.94 and 0.80 respectively) and calcified plaque area (ICC of 0.95 and 0.77, respectively).

CONCLUSION

Agreement between manual and automated segmentation of LRNC and calcifications was poor, despite a good interscan reproducibility of both methods. The agreement between both methods increased to moderate in high quality scans. These findings indicate that image quality is a critical determinant of the performance of both manual and automated segmentation of carotid artery plaque components.

Plaque Imaging to Decide on Optimal Treatment: Medical Versus Carotid Endarterectomy Versus Carotid Artery Stenting

Many of the current guidelines for the management of carotid atherosclerosis are based on clinical trial findings published more than 2 decades ago. The lack of plaque information in clinical decision making represents a major shortcoming and highlights the need for contemporary trials based on characteristics of the atherosclerotic lesion itself, rather than luminal stenosis alone. This article summarizes the major dilemmas clinicians face in current practice, and discusses the rationale and evidence that plaque imaging may help to address these challenges and optimize the clinical management of carotid artery disease in the future.

In vivo semi-automatic segmentation of multicontrast cardiovascular magnetic resonance for prospective cohort studies on plaque tissue composition: initial experience

Automatic in vivo segmentation of multicontrast (multisequence) carotid magnetic resonance for plaque composition has been proposed as a substitute for manual review to save time and reduce inter-reader variability in large-scale or multicenter studies. Using serial images from a prospective longitudinal study, we sought to compare a semi-automatic approach versus expert human reading in analyzing carotid atherosclerosis progression. Baseline and 6-month follow-up multicontrast carotid images from 59 asymptomatic subjects with 16-79 % carotid stenosis were reviewed by both trained radiologists with 2-4 years of specialized experience in carotid plaque characterization with MRI and a previously reported automatic atherosclerotic plaque segmentation algorithm, referred to as morphology-enhanced probabilistic plaque segmentation (MEPPS). Agreement on measurements from individual time points, as well as on compositional changes, was assessed using the intraclass correlation coefficient (ICC). There was good agreement between manual and MEPPS reviews on individual time points for calcification (CA) (area: ICC; 0.85-0.91; volume: ICC; 0.92-0.95) and lipid-rich necrotic core (LRNC) (area: ICC; 0.78-0.82; volume: ICC; 0.84-0.86). For compositional changes, agreement was good for CA volume change (ICC; 0.78) and moderate for LRNC volume change (ICC; 0.49). Factors associated with LRNC progression as detected by MEPPS review included intraplaque hemorrhage (positive association) and reduction in low-density lipoprotein cholesterol (negative association), which were consistent with previous findings from manual review. Automatic classifier for plaque composition produced results similar to expert manual review in a prospective serial MRI study of carotid atherosclerosis progression. Such automatic classification tools may be beneficial in large-scale multicenter studies by reducing image analysis time and avoiding bias between human reviewers.

Advances in MRI for the evaluation of carotid atherosclerosis

Carotid artery atherosclerosis is an important source of mortality and morbidity in the Western world with significant socioeconomic implications. The quest for the early identification of the vulnerable carotid plaque is already in its third decade and traditional measures, such as the sonographic degree of stenosis, are not selective enough to distinguish those who would really benefit from a carotid endarterectomy. MRI of the carotid plaque enables the visualization of plaque composition and specific plaque components that have been linked to a higher risk of subsequent embolic events. Blood suppressed T1 and T2 weighted and proton density-weighted fast spin echo, gradient echo and time-of-flight sequences are typically used to quantify plaque components such as lipid-rich necrotic core, intraplaque haemorrhage, calcification and surface defects including erosion, disruption and ulceration. The purpose of this article is to review the most important recent advances in MRI technology to enable better diagnostic carotid imaging.

Intraluminal thrombus, intraplaque hemorrhage, plaque thickness, and current smoking optimally predict carotid stroke

BACKGROUND AND PURPOSE

Intraplaque hemorrhage (IPH) is associated with acute and future stroke. IPH is also associated with lumen markers of stroke risk including stenosis, plaque thickness, and ulceration. Whether IPH adds further predictive value to these other variables is unknown. The purpose of this study was to determine whether IPH improves carotid-source stroke prediction.

METHODS

In this retrospective cross-sectional study, patients undergoing stroke workup were imaged with MRI and IPH detection. Seven hundred twenty-six carotid-brain image pairs were analyzed after excluding vessels with noncarotid plaque stroke sources (420) and occlusions (7) or near-occlusions (3). Carotid imaging characteristics were recorded, including percent diameter and mm stenosis, plaque thickness, ulceration, intraluminal thrombus, and IPH. Clinical confounders were recorded, and a multivariable logistic regression model was fitted. Backward elimination was used to determine essential carotid-source stroke predictors with a threshold 2-sided P<0.10. Receiver operating characteristic analysis was performed to determine discriminatory value.

RESULTS

Significant predictors of carotid-source stroke included intraluminal thrombus (odds ratio=103.6; P<0.001), IPH (odds ratio=25.2; P<0.001), current smoking (odds ratio=2.78; P=0.004), and thickness (odds ratio=1.24; P=0.020). The final model discriminatory value was excellent (area under the curve=0.862). This was significantly higher than the final model without IPH (area under the curve=0.814), or models using only stenosis as a continuous variable (area under the curve=0.770) or cutoffs of 50% and 70% (area under the curve=0.669), P<0.001.

CONCLUSIONS

After excluding patients with noncarotid plaque stroke sources, optimal discrimination of carotid-source stroke was obtained with intraluminal thrombus, IPH, plaque thickness, and smoking history but not ulceration and stenosis.

Clinical factors associated with high-risk carotid plaque features as assessed by magnetic resonance imaging in patients with established vascular disease (from the AIM-HIGH Study)

Association between clinical factors and high-risk plaque features, such as, thin or ruptured cap, intraplaque hemorrhage, presence of lipid-rich necrotic core (LRNC), and increased LRNC volume as assessed by magnetic resonance imaging (MRI), was examined in patients with established vascular disease in the Atherothrombosis Intervention in Metabolic Syndrome With Low HDL/High Triglycerides (AIM-HIGH) trial. A total of 214 subjects underwent carotid MRI and had acceptable image quality for assessment of plaque burden, tissue contents, and MRI-modified American Heart Association lesion type by a core laboratory. We found that 77% of subjects had carotid plaques, 52% had lipid-containing plaques, and 11% had advanced American Heart Association type-VI lesions with possible surface defect, intraplaque hemorrhage, or mural thrombus. Type-VI lesions were associated with older age (odds ratio [OR] = 2.6 per 5 years increase, p <0.001). After adjusting for age, these lesions were associated with history of cerebrovascular disease (OR = 4.1, p = 0.01), higher levels of lipoprotein(a) (OR = 2.0 per 1 SD increase, p = 0.02), and larger percent wall volume (PWV [OR = 4.6 per 1 SD increase, p <0.001]) but, were negatively associated with metabolic syndrome (OR = 0.2, p = 0.02). Presence of LRNC was associated with the male gender (OR = 3.2, p = 0.02) and PWV (OR = 3.8 per 1 SD, p <0.001); however, it was negatively associated with diabetes (OR = 0.4, p = 0.02) and high-density lipoprotein cholesterol levels (OR = 0.7 per 1 SD, p = 0.02). Increased percent LRNC was associated with PWV (regression coefficient = 0.36, p <0.001) and negatively associated with ApoA1 levels (regression coefficient = -0.20, p = 0.03). In conclusion, older age, male gender, history of cerebrovascular disease, larger plaque burden, higher lipoprotein(a), and lower high-density lipoprotein cholesterol or ApoA1 level have statistically significant associations with high-risk plaque features. Metabolic syndrome and diabetes showed negative associations in this population.

Carotid magnetic resonance imaging for monitoring atherosclerotic plaque progression: a multicenter reproducibility study

This study sought to determine the multicenter reproducibility of magnetic resonance imaging (MRI) and the compatibility of different scanner platforms in assessing carotid plaque morphology and composition. A standardized multi-contrast MRI protocol was implemented at 16 imaging sites (GE: 8; Philips: 8). Sixty-eight subjects (61 ± 8 years; 52 males) were dispersedly recruited and scanned twice within 2 weeks on the same magnet. Images were reviewed centrally using a streamlined semiautomatic approach. Quantitative volumetric measurements on plaque morphology (lumen, wall, and outer wall) and plaque tissue composition [lipid-rich necrotic core (LRNC), calcification, and fibrous tissue] were obtained. Inter-scan reproducibility was summarized using the within-subject standard deviation, coefficient of variation (CV) and intraclass correlation coefficient (ICC). Good to excellent reproducibility was observed for both morphological (ICC range 0.98-0.99) and compositional (ICC range 0.88-0.96) measurements. Measurement precision was related to the size of structures (CV range 2.5-4.9 % for morphology, 36-44 % for LRNC and calcification). Comparable measurement variability was found between the two platforms on both plaque morphology and tissue composition. In conclusion, good to excellent inter-scan reproducibility of carotid MRI can be achieved in multicenter settings with comparable measurement precision between platforms, which may facilitate future multicenter endeavors that use serial MRI to monitor atherosclerotic plaque progression.

High-risk plaque in the superficial femoral artery of people with peripheral artery disease: prevalence and associated clinical characteristics

OBJECTIVE

We used magnetic resonance imaging (MRI) to study the prevalence and associated clinical characteristics of high-risk plaque (defined as presence of lipid-rich necrotic core [LRNC] and intraplaque hemorrhage) in the superficial femoral arteries (SFA) among people with peripheral artery disease (PAD).

BACKGROUND

The prevalence and clinical characteristics associated with high-risk plaque in the SFA are unknown.

METHODS

Three-hundred-three participants with PAD underwent MRI of the proximal SFA using a 1.5 T S platform. Twelve contiguous 2.5 mm cross-sectional images were obtained.

RESULTS

LRNC was present in 68 (22.4%) participants. Only one had intra-plaque hemorrhage. After adjusting for age and sex, smoking prevalence was higher among adults with LRNC than among those without LRNC (35.9% vs. 21.4%, p = 0.02). Among participants with vs. without LRNC there were no differences in mean percent lumen area (31% vs. 33%, p = 0.42), normalized mean wall area (0.71 vs. 0.70, p = 0.67) or maximum wall area (0.96 vs. 0.92, p = 0.54) in the SFA. Among participants with LRNC, cross-sectional images containing LRNC had a smaller percent lumen area (33% ± 1% vs. 39% ± 1%, p < 0.001), greater normalized mean wall thickness (0.25 ± 0.01 vs. 0.22 ± 0.01, p < 0.001), and greater normalized maximum wall thickness (0.41 ± 0.01 vs. 0.31 ± 0.01, p < 0.001), compared to cross-sectional images without LRNC.

CONCLUSIONS

Fewer than 25% of adults with PAD had high-risk plaque in the proximal SFA using MRI. Smoking was the only clinical characteristic associated with presence of LRNC. Further study is needed to determine the prognostic significance of LRNC in the SFA.

CLINICAL TRIAL REGISTRATION-URL

http://www.clinicaltrials.gov. Unique identifier: NCT00520312.

Multi-contrast atherosclerosis characterization (MATCH) of carotid plaque with a single 5-min scan: technical development and clinical feasibility

BACKGROUND

Multi-contrast weighted imaging is a commonly used cardiovascular magnetic resonance (CMR) protocol for characterization of carotid plaque composition. However, this approach is limited in several aspects including low slice resolution, long scan time, image mis-registration, and complex image interpretation. In this work, a 3D CMR technique, named Multi-contrast Atherosclerosis Characterization (MATCH), was developed to mitigate the above limitations.

METHODS

MATCH employs a 3D spoiled segmented fast low angle shot readout to acquire data with three different contrast weightings in an interleaved fashion. The inherently co-registered image sets, hyper T1-weighting, gray blood, and T2-weighting, are used to detect intra-plaque hemorrhage (IPH), calcification (CA), lipid-rich necrotic core (LRNC), and loose-matrix (LM). The MATCH sequence was optimized by computer simulations and testing on four healthy volunteers and then evaluated in a pilot study of six patients with carotid plaque, using the conventional multi-contrast protocol as a reference.

RESULTS

On MATCH images, the major plaque components were easy to identify. Spatial co-registration between the three image sets with MATCH was particularly helpful for the reviewer to discern co-existent components in an image and appreciate their spatial relation. Based on Cohen's kappa tests, moderate to excellent agreement in the image-based or artery-based component detection between the two protocols was obtained for LRNC, IPH, CA, and LM, respectively. Compared with the conventional multi-contrast protocol, the MATCH protocol yield significantly higher signal contrast ratio for IPH (3.1±1.3 vs. 0.4±0.3, p<0.001) and CA (1.6±1.5 vs. 0.7±0.6, p=0.012) with respect to the vessel wall.

CONCLUSIONS

To the best of our knowledge, the proposed MATCH sequence is the first 3D CMR technique that acquires spatially co-registered multi-contrast image sets in a single scan for characterization of carotid plaque composition. Our pilot clinical study suggests that the MATCH-based protocol may outperform the conventional multi-contrast protocol in several respects. With further technical improvements and large-scale clinical validation, MATCH has the potential to become a CMR method for assessing the risk of plaque disruption in a clinical workup.

Early decrease in carotid plaque lipid content as assessed by magnetic resonance imaging during treatment of rosuvastatin

Background

Statin therapy has shown to deplete atherosclerotic plaque lipid content and induce plaque regression. However, how early the plaque lipid depletion can occur with low-density lipoprotein cholesterol (LDL-C) lowering in humans in vivo has not been fully described.

Methods

We enrolled 43 lipid treatment naïve subjects with asymptomatic carotid atherosclerosis and LDL-C ≥ 100 and ≤ 250 mg/dl. Rosuvastatin 5–20 mg/day was used to lower LDL-C levels to < 80 mg/dl. Lipid profile and carotid MRI scans were obtained at baseline, 3, 12, and 24 months. Carotid plaque lipid-rich necrotic core (LRNC) and plaque burden were measured and compared between baseline and during treatment.

Results

Among the 32 subjects who completed the study, at 3 months, an average dose of rosuvastatin of 11 mg/day lowered LDL-C levels by 47% (125.2 ± 24.4 mg/dl vs. 66.7 ± 17.3 mg/dl, p < 0.001). There were no statistically significant changes in total wall volume, percent wall volume or lumen volume. However, LRNC volume was significantly decreased by 7.9 mm³, a reduction of 7.3% (111.5 ± 104.2 mm³ vs. 103.6 ± 95.8 mm³, p = 0.044). Similarly, % LRNC was also significantly decreased from 18.9 ± 11.9% to 17.9 ± 11.5% (p = 0.02) at 3 months. Both LRNC volume and % LRNC continued to decrease moderately at 12 and 24 months, although this trend was not significant.

Conclusions

Among a small number of lipid treatment naïve subjects, rosuvastatin therapy may induce a rapid and lasting decrease in carotid plaque lipid content as assessed by MRI.

Trial registration

ClinicalTrials.Gov numbers NCT00885872

Atherosclerotic plaque component segmentation in combined carotid MRI and CTA data incorporating class label uncertainty

Atherosclerotic plaque composition can indicate plaque vulnerability. We segment atherosclerotic plaque components from the carotid artery on a combination of in vivo MRI and CT-angiography (CTA) data using supervised voxelwise classification. In contrast to previous studies the ground truth for training is directly obtained from 3D registration with histology for fibrous and lipid-rich necrotic tissue, and with μCT for calcification. This registration does, however, not provide accurate voxelwise correspondence. We therefore evaluate three approaches that incorporate uncertainty in the ground truth used for training: I) soft labels are created by Gaussian blurring of the original binary histology segmentations to reduce weights at the boundaries between components, and are weighted by the estimated registration accuracy of the histology and in vivo imaging data (measured by overlap), II) samples are weighted by the local contour distance of the lumen and outer wall between histology and in vivo data, and III) 10% of each class is rejected by Gaussian outlier rejection. Classification was evaluated on the relative volumes (% of tissue type in the vessel wall) for calcified, fibrous and lipid-rich necrotic tissue, using linear discriminant (LDC) and support vector machine (SVM) classification. In addition, the combination of MRI and CTA data was compared to using only one imaging modality. Best results were obtained by LDC and outlier rejection: the volume error per vessel was 0.9±1.0% for calcification, 12.7±7.6% for fibrous and 12.1±8.1% for necrotic tissue, with Spearman rank correlation coefficients of 0.91 (calcification), 0.80 (fibrous) and 0.81 (necrotic). While segmentation using only MRI features yielded low accuracy for calcification, and segmentation using only CTA features yielded low accuracy for necrotic tissue, the combination of features from MRI and CTA gave good results for all studied components.

Prediction of high-risk plaque development and plaque progression with the carotid atherosclerosis score

OBJECTIVES

The goal of this prospective study was to evaluate the carotid atherosclerosis score (CAS) for predicting the development of high-risk plaque features and plaque burden progression.

BACKGROUND

Previous studies have shown that carotid intraplaque hemorrhage (IPH) and a disrupted luminal surface (DLS), as identified by using magnetic resonance imaging, are associated with greater risk for cerebrovascular events. On the basis of data from a large cross-sectional study, a scoring system was developed to determine which plaque features are associated with the presence of IPH and DLS. However, the predictive value of CAS has not been previously tested in a prospective, longitudinal study.

METHODS

A total of 120 asymptomatic subjects with 50% to 79% carotid stenosis underwent carotid magnetic resonance imaging scans at baseline and 3 years thereafter. Presence of IPH and DLS, wall volume, maximum wall thickness, and maximum percent lipid-rich necrotic core area were measured at both time-points. Baseline CAS values were calculated on the basis of previously published criteria.

RESULTS

Of the 73 subjects without IPH or DLS at baseline, 9 (12%) developed 1 or both of these features during follow-up. There was a significant increasing trend between CAS and the development of new DLS (p < 0.001) and with plaque burden progression (p = 0.03) but not with the development of new IPH (p = 0.3). Percent carotid stenosis was not significantly associated with new DLS (p = 0.2), new IPH (p = 0.1), or plaque progression (p = 0.6).

CONCLUSIONS

CAS was found to have a significant increasing relationship with incident DLS and plaque progression in this prospective study. CAS can potentially provide improved risk stratification beyond luminal stenosis.

3D high-resolution contrast enhanced MRI of carotid atheroma--a technical update

OBJECTIVE

Development of a fast 3D high-resolution magnetic resonance imaging (MRI) protocol for improved carotid artery plaque imaging.

METHODS

Two patients with carotid atherosclerosis disease underwent 3D high-resolution MRI which included time-of-flight and T1-weighted variable flip angle, fast-spin-echo (FSE) imaging, pre- and post-intravenous gadolinium-based contrast agent administration.

RESULTS

Good quality images with intrinsic blood suppression were obtained pre- and post-contrast administration using a 3D FSE sequence. The plaque burden, lipid core volume, hemorrhage volume and fibrous cap thickness were well determined.

CONCLUSIONS

3D high-resolution MR imaging of carotid plaque using TOF and 3D FSE can achieve high isotropic resolution, large coverage, and excellent image quality within a short acquisition time.

MRI of carotid atherosclerosis

OBJECTIVE

Although MRI is widely used to observe atherosclerosis impacts on the vessel lumen, MRI also depicts the size of the plaque itself, its composition, and plaque inflammation, providing information beyond simple stenosis. This article summarizes the state of evidence for a clinical role for MRI of carotid atherosclerosis.

CONCLUSION

MRI of carotid atherosclerosis has a proven role in pharmaceutical trials and may improve patient management once large-scale clinical trials have been completed.

Novel anti-inflammatory strategies in atherosclerosis

PURPOSE OF REVIEW

Inflammation has been widely acknowledged to contribute throughout all stages of atherogenesis. However, these recent advances in our understanding have not been translated into clinical practice in which the mainstay of treatment is still lipid-targeted therapy. This review provides an overview of promising anti-inflammatory therapies in atherosclerosis, and discusses potential drawbacks and clinical benefits.

RECENT FINDINGS

Immunosuppressive drugs are likely to beneficially affect atherogenesis. Several novel anti-inflammatory targets have been scrutinized, of which some have reached clinical development stage, such as cytokine targets interleukin-1 and interleukin-6, CCR2 antagonist, selective phospholipase, and leukotriene inhibitors. Novel imaging modalities such as MRI and PET-computed tomography provide valuable surrogate inflammatory endpoints for risk stratification and testing anti-inflammatory agents in cardiovascular randomized trials.

SUMMARY

Anti-inflammatory therapies hold great promise in cardiovascular prevention regimens; however, atherosclerosis is a chronic disease, and systemic long-term use of anti-inflammatory agents carries the risk of complications arising from immunosuppression. In order to successfully add immunosuppressive drugs to our routine armament, we need to identify high-risk patients who benefit from anti-inflammatory treatment, increase our insight into the inflammatory pathogenesis of atherogenesis, and find safe and effective compounds capable of directly suppressing plaque inflammation.

Utilizing imaging tools in lipidology: examining the potential of MRI for monitoring cholesterol therapy

Lipid abnormalities play important roles in the development of atherosclerosis. Lipid therapies result in alterations in atherosclerotic plaques including halting of progression of the plaque, lipid transport out of the plaque and reducing inflammatory activity, which lead to plaque morphologies that are less prone to disruption, the main cause of clinical events. In order to investigate and monitor plaque morphological changes during lipid therapy in vivo we need an imaging method that can provide accurate assessment of plaque tissue components and activity. MRI of atherosclerosis has been validated as a reliable assessment of the size of the vessel lumen, but also the size of the plaque, its tissue composition and plaque activity, including inflammation. The purpose of this review is to summarize the state of evidence for the direct assessment of atherosclerotic plaque and its change by MRI, and to establish the proven role of MRI of atherosclerosis in pharmaceutical trials with lipid therapy.

Carotid artery disease and stroke: assessing risk with vessel wall MRI

Although MRI is widely used to diagnose stenotic carotid arteries, it also detects characteristics of the atherosclerotic plaque itself, including its size, composition, and activity. These features are emerging as additional risk factors for stroke that can be feasibly acquired clinically. This paper summarizes the state of evidence for a clinical role for MRI of carotid atherosclerosis.

Non-invasive anatomic and functional imaging of vascular inflammation and unstable plaque

Over the last several decades, basic cardiovascular research has significantly enhanced our understanding of pathobiological processes leading to formation, progression, and complications of atherosclerotic plaques. By harnessing these advances in cardiovascular biology, imaging has advanced beyond its traditional anatomical domains to a tool that permits probing of particular molecular structures to image cellular behaviour and metabolic pathways involved in atherosclerosis. From the nascent atherosclerotic plaque to the death of inflammatory cells, several potential molecular and micro-anatomical targets for imaging with particular selective imaging probes and with a variety of imaging modalities have emerged from preclinical and animal investigations. Yet, substantive barriers stand between experimental use and wide clinical application of these novel imaging strategies. Each of the imaging modalities described herein faces hurdles-for example, sensitivity, resolution, radiation exposure, reproducibility, availability, standardization, or costs. This review summarizes the published literature reporting on functional imaging of vascular inflammation in atherosclerotic plaques emphasizing those techniques that have the greatest and/or most immediate potential for broad application in clinical practice. The prospective evaluation of these techniques and standardization of protocols by multinational networks could serve to determine their added value in clinical practice and guide their development and deployment.

MR imaging of carotid plaque composition during lipid-lowering therapy a prospective assessment of effect and time course

OBJECTIVES

The purpose of this study was to test the lipid depletion hypothesis and to establish the time course of change in carotid plaque morphology and composition during lipid therapy using high-resolution magnetic resonance imaging (MRI).

BACKGROUND

Lipid therapy is thought to improve plaque stability and reduce cardiovascular events by targeting the plaque rupture risk features such as large lipid core, thin fibrous cap, and high level of inflammatory infiltrates. However, the plaque stabilizing process during lipid therapy has not been clearly demonstrated in humans and in vivo.

METHODS

Subjects with coronary or carotid artery disease, apolipoprotein B ≥120 mg/dl, and lipid treatment history <1 year, were randomly assigned to atorvastatin monotherapy or to atorvastatin-based combination therapies with appropriate placebos for 3 years. All subjects underwent high-resolution, multicontrast bilateral carotid MRI scans at baseline and annually for 3 years. All images were analyzed for quantification of wall area and plaque composition blinded to therapy, laboratory results, and clinical course.

RESULTS

After 3 years of lipid therapy, the 33 subjects with measurable lipid-rich necrotic core (LRNC) at baseline had a significant reduction in plaque lipid content: LRNC volume decreased from 60.4 ± 59.5 mm(3) to 37.4 ± 69.5 mm(3) (p < 0.001) and %LRNC (LRNC area/wall area in the lipid-rich regions) from 14.2 ± 7.0% to 7.4 ± 8.2% (p < 0.001). The time course showed that %LRNC decreased by 3.2 (p < 0.001) in the first year, by 3.0 (p = 0.005) in the second year, and by 0.91 (p = 0.2) in the third year. Changes in LRNC volume followed the same pattern. Percent wall volume (100 × wall/outer wall, a ratio of volumes) in the lipid-rich regions significantly decreased from 52.3 ± 8.5% to 48.6 ± 9.7% (p = 0.002). Slices containing LRNC had significantly more percent wall volume reduction than those without (-4.7% vs. -1.4%, p = 0.02).

CONCLUSIONS

Intensive lipid therapy significantly depletes carotid plaque lipid. Statistically significant plaque lipid depletion is observed after 1 year of treatment and continues in the second year, and precedes plaque regression. (Using Magnetic Resonance Imaging to Evaluate Carotid Artery Plaque Composition in People Receiving Cholesterol-Lowering Medications [The CPC Study]; NCT00715273).

Symptomatic Low-Grade Carotid Stenosis With Intraplaque Hemorrhage and Expansive Arterial Remodeling Is Associated With a High Relapse Rate Refractory to Medical Treatment

BACKGROUND:

Carotid plaque characteristics influence future risk of stroke considerably. However, the severity of stenosis does not accurately reflect plaque burden in patients with expansive arterial remodeling.

OBJECTIVE:

To determine the therapeutic outcome of symptomatic carotid low-grade stenosis with vulnerable plaque based on magnetic resonance imaging (MRI) characterization.

METHODS:

We studied 25 (male, n = 23; age, 74.2 ± 5.6 years) of 29 consecutive patients with symptomatic carotid low-grade stenosis (&lt;50%) and both high-signal plaque and expansive remodeling on T1-weighted MRIs. The remaining 4 were excluded because of impending stroke. A single antithrombotic and statin were administered, and recurrent ischemic stroke was treated with dual antithrombotics. We considered carotid endarterectomy when recurrence was refractory to aggressive medical treatment.

RESULTS:

During a 31.3 ± 16.4-month follow-up, 11 of the 25 patients developed a total of 30 recurrent ischemic events (46.0% per patient-year). The patients' characteristics did not differ significantly between the groups with and without recurrence (n = 11 and n = 14, respectively). Seven of 11 patients in the recurrence group treated with carotid endarterectomy remained free of ischemic events during a postoperative follow-up of 19.1 ± 14.6 months.

CONCLUSION:

Symptomatic low-grade carotid stenosis with vulnerable plaque confirmed by MRI was associated with a high rate of stroke recurrence that was refractory to aggressive medical treatment. However, carotid endarterectomy was safe and effective for such patients. Plaque characterization by MRI has the potential for more accurate stroke risk stratification in the management of carotid low-grade stenosis.

High-resolution MRI of carotid plaque with a neurovascular coil and contrast-enhanced MR angiography: one-stop shopping for the comprehensive assessment of carotid atherosclerosis

OBJECTIVE

The objective of our study was to assess a protocol of study of carotid atherosclerosis coupling vascular wall imaging and luminal imaging in the same examination and to evaluate the accuracy of high-resolution MRI with a neurovascular coil in carotid plaque characterization.

SUBJECTS AND METHODS

Thirty-two consecutive patients with 34 carotid artery stenoses were prospectively enrolled. MRI was performed on a 1.5-T unit. Plaque assessment was performed starting with a diffusion-weighted sequence and followed by a fat-suppressed T1-weighted sequence; after contrast-enhanced MR angiography (CE-MRA), all patients were evaluated with a T1-weighted 3D high-resolution sequence. Carotid plaques were classified as type A, having a large lipid-necrotic core; type B, being a complex fibrotic-calcified plaque with soft content (mixed plaque); or type C, being a fibrotic-calcified plaque (hard). Additional features indicative of vulnerable plaque such as intraplaque hemorrhage (IPH), ulceration, and severe stenosis were registered. MR findings were compared with surgical specimens.

RESULTS

MRI correctly identified 11 of 13 type A, eight of 11 type B, and eight of 10 type C plaques (sensitivity, 84.6%, 72.7%, and 80%, respectively). In the identification of lipid-necrotic core plaque, MRI showed a sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of 84.6%, 100%, 100%, and 91.3%, respectively (κ = 0.87). For reordering all plaques in two groups (i.e., soft vs nonsoft) in the identification of soft plaques, MRI had a sensitivity, specificity, PPV, and NPV of 83.3%, 80%, 90.9%, and 66.7%, respectively (κ = 0.59). IPH, ulcers, and severe stenosis were detected in eight of eight, 11 of 13, and 25 of 25 cases, respectively.

CONCLUSION

In patients with carotid atherosclerosis, ongoing CE-MRA with a neurovascular coil for the simultaneous detection of unstable plaques is feasible. Our MR protocol accurately identifies the major features of vulnerable plaque.