Three-dimensional volumetric analysis of atherosclerotic plaques: a magnetic resonance imaging-based study of patients with moderate stenosis carotid artery disease

Atherosclerotic plaque burden has a strong correlation with plaque vulnerability. Three-dimensional (3D) volumetric assessment of atherosclerotic plaques has been suggested as an accurate method of quantifying plaque burden but has not been performed. In this study we use high-resolution magnetic resonance (MR) imaging to compare 3D volume differences of asymptomatic and acutely symptomatic carotid plaques (i.e. had cerebrovascular ischaemic symptoms within the previous 72 h of MR imaging). One hundred patients (46 acutely symptomatic and 54 asymptomatic) with atherosclerotic carotid artery disease underwent carotid MR imaging. Manual segmentation of plaque components was done to delineate lipid, fibrous tissue and plaque haemorrhage (PH). 3D-volume reconstruction of plaque components was done and used for comparison. Acutely symptomatic plaques had a lower normalized wall index and normalized volume index than the asymptomatic group (P = 0.04 and 0.01 respectively). Median percentage lipid volume was higher for asymptomatic plaques (28 vs. 5%, P = 0.004). However, the median percentage volume and prevalence of PH was higher in the acutely symptomatic group (P = 0.01 and 0.02 respectively). Acutely symptomatic plaques have less lipid content immediately after the acute event than asymptomatic plaques. This is most likely because of the escape of lipid-rich atheromatous debris into the blood stream at the time of plaque rupture. Due to this paradox, “high” lipid content of a plaque may not be a reliable feature of estimating its vulnerability immediately following the acute event. PH, which is prevalent and consistent in such plaques, may be a better indicator of plaque vulnerability during that period.     

Carotid plaque spaces relate to symptoms and ultrasound scattering

We have previously found that spectral analysis of ultrasound (US) can discriminate in vitro plaques from asymptomatic and symptomatic (transient ischemic attack within previous 4 weeks) patients. That study found no differences in percentages of lipid or thrombus between the two groups by optical microscopy/planimetry. The present study was to find out if another feature from the microscopy could show a difference. The number and size of spaces resulting from cell death or new blood vessels were measured to see if they related to symptoms or could help explain US differentiation. Twelve plaques from each group were examined by optical microscopy. The sizes and concentrations of two kinds of spaces, endothelial lined (vessel spaces) and unlined (tissue spaces), were correlated both with symptoms and also with the US tissue characterization scores from the previous study. Symptomatic vs. asymptomatic plaques showed a higher concentration and a larger size: 0.87 vs. 0.21 per mm(2) (p < 0.005) and 154 vs. 110 microm (p < 0.02). A discriminant function of spaces with symptoms as dependent variables correctly identified 91.7% of the plaques (p < 0.001). The concentration in plaques previously designated by US as true positive plaques or true negative was 1.21 vs. 0.22 per mm(2) (p < 0.005). spaces were increased in plaques of symptomatic patients and were related to UTC scores. Both the lined and unlined spaces were useful as predictors.     

Shear-Wave Elastography Enables Identification of Unstable Carotid Plaque

Shear-wave elastography (SWE) is a novel ultrasound technique for quantifying tissue elasticity. The aim of this study was to identify differences in atherosclerotic plaque elasticity measured using SWE among individuals with symptomatic, asymptomatic progressive and asymptomatic stable carotid plaques. Consecutive patients from the Atherosclerotic Plaque Characteristics Associated with a Progression Rate of the Plaque and a Risk of Stroke in Patients with the Carotid Bifurcation Plaque Study were screened for this research. Neurosonography examination of carotid arteries was performed to identify plaque stenosis of ≥50% using B-mode ultrasound and SWE imaging to measure the mean, maximal and minimal elasticity. The set consisted of 97 participants—74 with asymptomatic stable stenosis, 12 with asymptomatic progressive stenosis and 11 with symptomatic stenosis. The mean elasticity in the asymptomatic stable plaque group was significantly higher than in the asymptomatic progressive (52.2 vs. 30.4 kPa; p < 0.001) and symptomatic (52.2 vs. 36.4 kPa; p = 0.033) plaque groups. No significant differences were found between asymptomatic progressive and symptomatic (p > 0.1) plaque groups. Asymptomatic stable, asymptomatic progressive and symptomatic plaques did not differ in echogenicity, calcifications, homogeneity, occurrence of ulcerated surface, or intra-plaque hemorrhage (p > 0.05 in all cases). SWE was a helpful modality for differentiating between stable and unstable atherosclerotic plaques in carotid arteries.     

轻中度颈动脉狭窄患者斑块CT血管造影特征

目的 观察轻中度颈动脉狭窄患者高危斑块CT血管造影（CTA）特征及其诊断价值。方法 纳入63例轻中度颈动脉狭窄患者、共81支狭窄动脉,根据临床表现分为有症状组和无症状组。比较组间基本资料;以组内相关系数（ICC）评价观察者间测量结果的一致性,于血管层面比较狭窄动脉斑块特征及CT参数。采用二元Logistic回归模型筛选有症状组与颈动脉狭窄相关的独立危险因素;绘制受试者工作特征（ROC）曲线,并计算曲线下面积（AUC）,评价根据斑块特征及CT参数诊断高危斑块的效能。结果 2组患者性别、年龄及病史差异均无统计学意义（P均>0.05）。观察者测量结果的一致性均较好（ICC均>0.75,P均<0.05）。有症状组血管周围脂肪（PVAT）CT值及斑块强化值均高于无症状组（P均<0.05）,且二者均为有症状颈动脉狭窄的独立危险因素。根据PVAT 的CT值及斑块强化值诊断高危斑块的AUC分别为0.739和0.662,敏感度分别为70.00%和67.50%,特异度分别为80.50%和63.40%。结论 PVAT 的CT值和斑块强化程度可用于识别轻中度颈动脉狭窄患者的高危斑块。     

Atherosclerotic risk stratification strategy for carotid arteries using texture-based features

Plaques in the carotid artery result in stenosis, which is one of the main causes for stroke. Patients have to be carefully selected for stenosis treatments as they carry some risk. Since patients with symptomatic plaques have greater risk for strokes, an objective classification technique that classifies the plaques into symptomatic and asymptomatic classes is needed. We present a computer aided diagnostic (CAD) based ultrasound characterization methodology (a class of Atheromatic systems) that classifies the patient into symptomatic and asymptomatic classes using two kinds of datasets: (1) plaque regions in ultrasound carotids segmented semi-automatically and (2) far wall gray-scale intima-media thickness (IMT) regions along the common carotid artery segmented automatically. For both kinds of datasets, the protocol consists of estimating texture-based features in frameworks of local binary patterns (LBP) and Law's texture energy (LTE) and applying these features for obtaining the training parameters, which are then used for classification. Our database consists of 150 asymptomatic and 196 symptomatic plaque regions and 342 IMT wall regions. When using the Atheromatic-based system on semiautomatically determined plaque regions, support vector machine (SVM) classifier was adapted with highest accuracy of 83%. The accuracy registered was 89.5% on the far wall gray-scale IMT regions when using SVM, K-nearest neighbor (KNN) or radial basis probabilistic neural network (RBPNN) classifiers. LBP/LTE-based techniques on both kinds of carotid datasets are noninvasive, fast, objective and cost-effective for plaque characterization and, hence, will add more value to the existing carotid plaque diagnostics protocol. We have also proposed an index for each type of datasets: AtheromaticPi, for carotid plaque region, and AtheromaticWi, for IMT carotid wall region, based on the combination of the respective significant features. These indices show a separation between symptomatic and asymptomatic by 4.53 units and 4.42 units, respectively, thereby supporting the texture hypothesis classification.     

Computed tomography angiography vs 3?T black-blood cardiovascular magnetic resonance for identification of symptomatic carotid plaques

Background

The purpose of this prospective study was to perform a head-to-head comparison of the two methods most frequently used for evaluation of carotid plaque characteristics: Multi-detector Computed Tomography Angiography (MDCTA) and black-blood 3 T-cardiovascular magnetic resonance (bb-CMR) with respect to their ability to identify symptomatic carotid plaques.

Methods

22 stroke unit patients with unilateral symptomatic carotid disease and >50% stenosis by duplex ultrasound underwent MDCTA and bb-CMR (TOF, pre- and post-contrast fsT1w-, and fsT2w- sequences) within 15 days of symptom onset. Both symptomatic and contralateral asymptomatic sides were evaluated. By bb-CMR, plaque morphology, composition and prevalence of complicated AHA type VI lesions (AHA-LT6) were evaluated. By MDCTA, plaque type (non-calcified, mixed, calcified), plaque density in HU and presence of ulceration and/or thrombus were evaluated. Sensitivity (SE), specificity (SP), positive and negative predictive value (PPV, NPV) were calculated using a 2-by-2-table.

Results

To distinguish between symptomatic and asymptomatic plaques AHA-LT6 was the best CMR variable and presence / absence of plaque ulceration was the best CT variable, resulting in a SE, SP, PPV and NPV of 80%, 80%, 80% and 80% for AHA-LT6 as assessed by bb-CMR and 40%, 95%, 89% and 61% for plaque ulceration as assessed by MDCTA. The combined SE, SP, PPV and NPV of bb-CMR and MDCTA was 85%, 75%, 77% and 83%, respectively.

Conclusions

Bb-CMR is superior to MDCTA at identifying symptomatic carotid plaques, while MDCTA offers high specificity at the cost of low sensitivity. Results were only slightly improved over bb-CMR alone when combining both techniques.     

MRI评估颈动脉粥样硬化斑块成分、类型及其与临床症状的相关性

目的：应用3.0 T MRI评估颈动脉粥样硬化斑块内成分,并据此对斑块进行分型;探讨斑块成分、类型与临床发生缺血性脑血管事件的相关性,评价应用高场强MR对斑块进行早期诊断的预警作用。方法对108例经超声检查发现颈动脉粥样硬化斑块的患者施行颈动脉斑块的MRI检查。颈动脉MR检查使用Philips或GE 3.0 T MR扫描仪,线圈选用颈动脉专用8通道表面线圈,扫描序列包括3D TOF、T1WI、T2WI、PDWI、MP-RAGE及CE-T1WI。FOV 14 cm,TOF及MP-RAGE序列扫描层厚2 mm,间隔-1 mm,余各序列扫描层厚2 mm,间隔0。对颈动脉分叉前后管腔的狭窄程度、斑块的成分（有无出血、钙化、疏松间质）、纤维帽的状况（厚、薄、破溃）等情况做出判断,依据颈动脉粥样硬化斑块MRI分型标准对每支血管的斑块进行分型。将入组血管按照颈动脉供血区相应脑缺血性症状的有无分为有症状组及无症状组两组,用独立t检验比较两组血管在狭窄程度上的差异;用卡方检验评估两组血管斑块内出现出血、钙化、疏松间质及纤维帽破溃的情况差异,判断斑块类型与临床症状的相关性;用Logistic回归分析狭窄程度、纤维帽破溃、斑块内出血、钙化及疏松间质对临床症状的影响度强弱。结果108例患者中,共发现有斑块血管198支：有症状组血管共计64支;无症状组血管共有134支,其中3支血管因MRI检查前已施行支架置入术不予入组,故无症状组血管共计131支。两组血管在管腔狭窄程度、纤维帽的完整性和斑块是否有出血方面均有统计学差异（P＜0.01或P＜0.05）,而在斑块钙化、疏松间质的出现率上则无统计学差异（P＞0.05）。在有症状组血管中,斑块类型比较密集,Ⅵ型斑块所占比例最大（71.8%）,而在无症状组,Ⅵ型与Ⅳ～Ⅴ型均较多（分别为44.7%和30.4%）;将两组中斑块类型粗略分为Ⅵ型与非Ⅵ型斑块,显示Ⅵ型斑块所占比例在有症状组更显著（P＜0.01）。在血管狭窄度、纤维帽破溃、斑块有出血、钙化及疏松间质这5个因素中,纤维帽是否有破溃与临床症状的关联程度最大,其次为管腔狭窄度的高低,而斑块内出血及疏松间质的有无对临床症状影响较弱,斑块内钙化则与临床症状的发生无关。结论有症状组与无症状组颈动脉斑块的MRI形态学特征具有明显差异;斑块内成分的差异与临床症状的出现有明显相关性,其与临床脑缺血性事件发生的相对危险度依次为：斑块破溃、管腔狭窄程度提升、斑块内存在疏松间质、斑块内有出血、斑块钙化;在斑块分型上,Ⅵ型代表了临床所谓的易损斑块,间接反映出斑块表面纤维帽破溃和斑块出血与临床症状关系密切。提示通过MRI检查分析斑块内成分来预测临床缺血性脑血管事件的发生是可行的,将能为临床采取相应治疗措施预防卒中发生提供可靠信息。     

Transcranial Doppler and Microemboli Detection: Relationships to Symptomatic Status and Histopathology Findings

The purpose of this study was to determine the relationship between symptomatic status, transcranial Doppler (TCD) microemboli presence and plaque histopathology findings. TCD was performed on 60 patients (37 symptomatic, 23 asymptomatic) before undergoing clinically indicated carotid endarterectomy. The frequency of microemboli signals was not significantly different between symptomatic and asymptomatic subject groups (p = 0.88) and there were no differences observed in the macroscopic or histopathology scoring of these plaques (p-values all > 0.05). The presence of microemboli was associated with an ulceration score (regardless of symptomatic or asymptomatic status, p = 0.034), with a one-level increase in ulceration rating associated with an odds ratio of 5.86 (95% [CI] 1.55, 43.4). These findings suggest that both symptomatic and asymptomatic patients may have plaque with similar features of instability and ability to create emboli. Thus, identifying new ways to measure plaque instability may provide important information for optimizing treatment to prevent future stroke.     

Expansive arterial remodeling of carotid arteries in symptomatic ischemic patients

Purpose: The present study aimed to assess the associations of expansive remodeling of carotid arteries with ischemic symptoms and the degree of stenosis.Materials and Methods: A total of 41 symptomatic patients with vulnerable plaques and 25 asymptomatic individuals with stable plaques were included. All patients underwent 3.0T high-resolution MRI of the carotid artery (CA) for measuring the expansive remodeling (ER) ratio and assessing plaque stability. The ER ratio was calculated by dividing the maximum distance between the lumen and the outer border of the plaque in the internal CA by the lumen diameter within 1 centimeter of the plaque at the distal ipsilateral internal CA. ER ratios were compared between the symptomatic and asymptomatic groups. The 41 symptomatic patients were further divided into 4 groups according to stenosis rate (CA stenosis <50%, 50%–74%, 75–89%, and > 90%), and the correlation between the ER ratio and the rate of stenosis was evaluated.Results: There was a significant difference in ER ratio between the symptomatic and asymptomatic groups (p<0.001). When symptomatic patients were divided into 4 subgroups based on degree of stenosis, ER ratios among groups showed statistically significant differences (p=0.014).Conclusion: There were significant associations of the ER ratio with ischemic symptoms. Furthermore, the ER ratio in symptomatic patients continued to increase with stenosis severity. These findings suggested that the ER ratio might be a practical marker of plaque vulnerability in the CA and further prospective studies for asymptomatic patients are warranted.