Interrater reliability of plaque morphology classification in patients with severe carotid artery stenosis

Usefulness of Carotid Ultrasonography for Risk Stratification of Cerebral and Cardiovascular Disease

Carotid ultrasonography is useful for the assessments of the risk stratification for stroke or coronary artery disease, because it is a simple, repeatable, and noninvasive procedure. The carotid intima-media thickness (IMT), which is assessed using carotid ultrasonography, is a widely used surrogate marker for the severity of atherosclerosis. Several large clinical studies showed that increased carotid IMT is associated with the future stroke or cardiovascular events. In addition, in many clinical trials, it has been adopted for surrogate markers of clinical endpoints of medical intervention. Moreover, carotid ultrasonography allows the measurement of the presence and characteristics of plaques and the severity of carotid artery stenosis. The unstable morphology of plaque, such as hypoechoic, ulcer, and mobility, is associated with future ischemic stroke events. The screening tool of asymptomatic carotid artery stenosis is also important, although whether routine carotid ultrasonography assessment is recommended in the general population remains controversial. The screening of carotid artery stenosis using ultrasonography is essential for not only daily clinical settings but also management of patients with acute ischemic stroke. The patients with atherothrombotic stroke with severe internal carotid artery stenosis should be considered to surgical intervention, and duplex ultrasound approach is important to estimate for the severity of carotid stenosis. Physicians should keep in mind the usefulness of carotid ultrasonography for risk stratification of cerebral and cardiovascular disease based on various aspects. In addition, visual assessment or dynamic changes using carotid ultrasonography could provide the various and valuable insights in clinical settings.

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.

Imaging of the ulcerated carotid atherosclerotic plaque: a review of the literature

Abstract

Carotid atherosclerotic disease constitutes a major modern health problem whose diagnosis primarily relies on imaging. Grading of stenosis has been long used as the main factor for risk stratification and guiding of management. Nevertheless, increasing evidence has shown that additional plaque characteristics such as plaque composition and surface morphology play an important role in the occurrence of symptoms, justifying the term “vulnerable plaque”. Carotid plaque surface characteristics either in the form of surface irregularities or ulceration represent an important factor of vulnerability and are associated with the occurrence of neurologic symptoms. The delineation of the carotid plaque surface can be performed with virtually all imaging modalities including ultrasound, contrast-enhanced ultrasound, multi-detector computed tomography angiography, magnetic resonance angiography and the traditional reference method of angiography. These techniques have shown varying levels of diagnostic accuracy for the identification of ulcerated carotid plaques or plaque surface irregularities. As a consequence and given its high clinical significance, radiologists should be familiar with the various aspects of this entity, including its definition, classification, imaging findings on different imaging modalities and associations. The purpose of this review is to present the current literature regarding carotid plaque ulcerations and present illustrative images of ulcerated carotid plaques.

Teaching Points

• Plaque surface and ulceration represent risk factors for stroke in carotid disease.

• Characterisation of the plaque surface and ulcerations can be performed with every modality.

• US is the first-line modality for carotid disease and identification of ulcerations.

• The administration of microbubbles increases US accuracy for diagnosis of carotid ulceration.

• MDCTA and MRA are valuable for diagnosing ulceration and evaluating plaque composition.

Relationship between the Carotid Plaque T1 Relaxation Time and the Plaque-to-Muscle Signal Intensity Ratio on Black-Blood Magnetic Resonance Imaging Scans

BACKGROUND

Black-blood magnetic resonance imaging (BB-MRI) is useful for the characterization and assessment of carotid artery plaques. The plaque-to-muscle signal intensity (SI) ratio (plaque/muscle ratio [PMR]) is used widely to evaluate plaques. However, the correlation between the PMR and the T1 relaxation time needs to be determined. We measured the T1 relaxation time of carotid plaques using T1 mapping and compared the results with the PMR on BB-MRI scans.

METHODS

Between April 2014 and July 2015, 20 patients with carotid artery stenosis were treated by carotid artery stenting. All patients underwent preoperative magnetic resonance plaque imaging. The ratio of the plaque SI to the sternocleidomastoid muscle was calculated on T1-weighted BB-MRI scans. T1 mapping was performed in the region where the vessel was narrowest using the inversion recovery technique. The T1 relaxation time was recorded to determine whether there was a correlation with the PMR.

RESULTS

The plaque T1 value was 577.3 ± 143.2 milliseconds; the PMR value obtained on BB-MRI scans was 1.23 ± .27. There was a statistically significant decrease in the T1 value as the PMR increased (P < .0001).

CONCLUSIONS

As the T1 relaxation time was well correlated with the PMR on BB-MRI scans, the evaluation of vulnerable plaques using the PMR was reliable and convenient.

Distribution of calcification in carotid endarterectomy tissues: Comparison of micro-computed tomography imaging with histology

Background:

Calcification in atherosclerotic plaques has been viewed as a marker of plaque stability, but whether calcification accumulates in specific anatomic sites in the carotid artery is unknown. We determined the burden and distribution of calcified plaque in carotid endarterectomy (CEA) tissues.

Methods:

A total of 22 CEA tissues were imaged with high-resolution micro-computed tomography (micro-CT). Total plaque burden and total calcium score using the Agatston method were quantified. The Agatston score (AS) was also normalized for tissue size. Plaque and calcium distribution were analyzed separately for three CEA regions: common segment (CS), bulb segment (BS), and internal/external segments (IES).

Results:

The average CEA tissue length was 40.83 (interquartile range [IQR] 33.31–42.41) mm with total plaque burden of 103.45 (IQR: 78.84–156.81) mm3 and total AS of 38.58 (IQR 11.59–89.97). Total plaque volume was 21.02 (IQR: 14.47–25.42) mm3 in the CS, 37.89 (22.59–48.32) mm3 in the BS, and 54.05 (36.87–74.52) mm3 in the IES. Of the 22 tissues, 15 had no calcium in the CS compared with three in the bulb and two in the IES. Normalized calcified plaque was most prevalent in the BS, the IES and was least prevalent in the CS. The overall correlation of calcification between histology sections and matched micro-CT images was 0.86 ( p<0.001).

Conclusions:

Calcified plaque is heterogeneously distributed in CEA tissues with most in the bulb and IES regions. The amount of calcification in micro-CT slices shows a high correlation with matched histology sections.

Inter-rater reliability of carotid atherosclerotic plaque quantification by 3-dimensional sonography

OBJECTIVES

Embolization from atherosclerotic carotid plaques is the most common cause of ischemic stroke; therefore, identification of high-risk plaques by sonography is important. The aim of this study was to investigate the agreement between 2 investigators in the evaluation of sonographic parameters relating to plaque stability.

METHODS

The following plaque parameters were assessed: echogenicity, homogeneity, surface, maximum content, and total volume. Serial 2-dimensional (2D) image sequences were obtained. Linear motion of the probe was automatically synchronized with the electrocardiogram. The edges of the plaque in each image were manually identified by the investigators. The total plaque volume was calculated after computer transformation of 2D images into a 3-dimensinoal (3D) format. Inter-rater reliability for echogenicity, homogeneity, and the surface was assessed by the weighted κ coefficient. Parametric values were tested by a paired t test.

RESULTS

We enrolled 30 patients (22 male; mean age ± SD, 72 ± 13 years) in the study and evaluated 28 atherosclerotic plaques. Inter-rater agreement values were as follows: homogeneity, 96% (κ = 0.84; P < .001); surface, 90% (κ = 0.77; P < .001); and echogenicity, 86% (κ = 0.60; P < .001). The significance values for plaque content and volume measurement agreement were P = .311 and .312, respectively, and the correlation coefficient was 0.808.

CONCLUSIONS

In our study, the agreement between 2 examiners in the evaluation of 2D and 3D sonographic parameters related to plaque stability was good to excellent. The sonographic measurement of plaque volume growth was the most accurate parameter; therefore, 3D sonography may be used for risk assessment of plaques in the future.

Shear wave elastography assessment of carotid plaque stiffness: in vitro reproducibility study

This study assessed inter- and intra-observer reproducibility of shear wave elastography (SWE) measurements in vessel phantoms simulating soft and hard carotid plaque under steady and pulsatile flow conditions. Supersonic SWE was used to acquire cine-loop data and quantify Young's modulus in cryogel vessel phantoms. Data were acquired by two observers, each performing three repeat measurements. Mean Young's modulus was quantified within 2-mm regions of interest averaged across five frames and, depending on vessel model and observer, ranged from 28 to 240 kPa. The mean inter-frame coefficient of variation (CV) was 0.13 (range: 0.07-0.18) for observer 1 and 0.14 (range: 0.12-0.16) for observer 2, with mean intra-class correlation coefficients (ICCs) of 0.84 and 0.83, respectively. The mean inter-operator CV was 0.13 (range: 0.08-0.20), with a mean ICC of 0.76 (range: 0.69-0.82). Our findings indicate that SWE can quantify Young's modulus of carotid plaque phantoms with good reproducibility, even in the presence of pulsatile flow.

New criteria for the sonographic diagnosis of a plaque ulcer in the extracranial carotid artery

OBJECTIVE

The diagnostic power of carotid sonography in detecting plaque ulcers may be inadequate when using the conventional criteria. We aimed to evaluate the usefulness of new criteria that we devised through a preliminary analysis of 50 endarterectomy cases before the present series.

SUBJECTS AND METHODS

Thirty carotid arteries of 30 consecutive patients who underwent endarterectomy (28 men; age range, 46-83 years) were studied. In the long- and short-axis B-mode images of carotid arteries, the concavity of the plaque surface and the surface echo intensity were carefully investigated. The conventional criteria stipulate a concavity larger than 2 × 2 mm with a well-defined back wall and flow reversal within the recess. Our new criteria specify a concavity in the plaque with the basal border echo weaker than that of the adjacent plaque surface, regardless of size. The final diagnosis was based on surgical and histologic findings.

RESULTS

Among the 30 carotid arteries, 14 arteries had 14 ulcers at surgery. Seventeen concavities were detected by sonography, and 12 of them, including six smaller than 2 × 2 mm, were truly ulcers. Two concavities with an echo intensity of the basal border equal to or greater than that of the adjacent surface were not true ulcers. Only two of 14 ulcers were not detected by sonography. The sensitivity and specificity of the conventional criteria were 35.7% and 75.0%, respectively, and those of our new criteria were 85.7% and 81.3%, respectively.

CONCLUSION

Our new criteria for the sonographic diagnosis of plaque ulcer are more useful than the conventional ones.

Accuracy of a Novel Risk Index Combining Degree of Stenosis of the Carotid Artery and Plaque Surface Echogenicity

Background and Purpose—

The purpose of this study was to determine the accuracy of a risk index in symptomatic or asymptomatic carotid stenoses.

Methods—

Consecutive patients presenting 50% to 99% carotid stenoses were included. A semiautomated gray scale-based color mapping (red, yellow, and green) of the whole plaque and of its surface was achieved. Surface was defined as the region located between the lumen (Level 0) and, respectively, 0.5, 1, 1.5, and 2 mm. Risk index was based on a combination of degree of stenosis and the proportion of the red color (reflecting low echogenicity) on the surface or on the whole plaque.

Results—

There were 67 (36%) symptomatic and 117 (64%) asymptomatic carotid stenoses. Risk index values were higher among symptomatic stenoses (0.46 mean versus 0.29; P <0.0001); on receiver operating characteristic curves, risk index presented a stronger predictive power compared with degree of stenosis or surface echogenicity alone. Also, in a regression model including age, gender, degree of stenosis, surface echogenicity, gray median scale of the whole plaque, and risk index, risk index measured within the surface region located at 0.5 mm from the lumen was the only parameter significantly associated with the presence of symptoms (OR, 4.89; 95% CI, 2.7–8.7; P =0.0000002). The best criterion to differentiate between symptomatic and asymptomatic stenoses was a risk index value >0.36 (sensitivity and specificity of 78% and 65%, respectively).

Conclusions—

Risk index was significantly higher in the presence of symptoms and could therefore be a valuable tool to assess the clinical risk of a carotid plaque.

Prediction of high-risk asymptomatic carotid plaques based on ultrasonic image features

Carotid plaques have been associated with ipsilateral neurological symptoms. High-resolution ultrasound can provide information not only on the degree of carotid artery stenosis but also on the characteristics of the arterial wall including the size and consistency of atherosclerotic plaques. The aim of this study is to determine whether the addition of ultrasonic plaque texture features to clinical features in patients with asymptomatic internal carotid artery stenosis (ACS) improves the ability to identify plaques that will produce stroke. 1121 patients with ACS have been scanned with ultrasound and followed for a mean of 4 years. It is shown that the combination of texture features based on second-order statistics spatial gray level dependence matrices (SGLDM) and clinical factors improves stroke prediction (by correctly predicting 89 out of the 108 cases that were symptomatic). Here, the best classification results of 77 ±1.8% were obtained from the use of the SGLDM texture features with support vector machine classifiers. The combination of morphological features with clinical features gave slightly worse classification results of 76 ±2.6% . These findings need to be further validated in additional prospective studies.

Evaluation of carotid artery atherosclerotic plaque distribution by using long-axis high-resolution black-blood magnetic resonance imaging

Object

The goal of this study was to evaluate the usefulness of long-axis black-blood MR (BB–MR) imaging for assessing plaque morphology and distribution in patients with atherosclerotic carotid artery (CA) stenosis.

Methods

Sixty-eight carotid arteries in 67 patients who were scheduled to undergo CA endarterectomy or CA stent placement due to atherosclerotic stenosis were included in this study. The patients had undergone CA BB–MR imaging and digital subtraction (DS) angiography within 3 weeks of revascularization. The DS angiography studies were performed using the transfemoral artery approach with selective common CA catheterization. The BB–MR images were acquired using a 1.5-T whole-body MR imaging unit, and T1-weighted images parallel to the long axis of the artery at 1-mm intervals were obtained. Plaque distribution was evaluated by measuring the distance between the CA bifurcation and the point that appeared to be the distal extent of the plaque on BB–MR imaging (D–MR imaging) and DS angiography images (D–DS angiography).

Results

Plaque distribution was clearly shown in 88.2% of the cases using long-axis BB–MR images, except for 8 arteries with poor image quality. In 4 arteries, D–DS angiography could not be obtained because the distal plaque end could not be confirmed. In 56 vessels, both the D–DS angiography and D–MR imaging could be measured; the mean D–MR imaging (19.75 ± 6.85 mm [standard deviation]) was significantly longer than the average D–DS angiography (16.32 ± 7.07 mm).

Conclusions

Long-axis BB–MR imaging can provide a noninvasive and accurate way to show CA plaque distribution; it is of great use not only for stroke risk assessment in patients with CA atherosclerosis but also for preoperative evaluation in patients requiring CA endarterectomy or CA stent placement.

Practical noninvasive neurovascular imaging of the neck arteries in patients with stroke, transient ischemic attack, and suspected arterial disease that may lead to ischemia, infarction, or flow abnormalities

Stroke is the third leading cause of death in the United States, killing nearly 157,000 people a year with an estimated society cost of dollar 58 billion in 2006. A large percentage of ischemic strokes is secondary to extracranial carotid and vertebral arterial disease. While digital subtraction angiography has traditionally been used for the initial evaluation of the degree of stenosis, noninvasive imaging has moved to the forefront in the extracranial arterial evaluation. The importance of understanding the imaging techniques, findings, interpretation, artifacts, and pitfalls is essential to appropriate patient management.

Correlation of cerebrovascular symptoms and microembolic signals with the stratified gray-scale median analysis and color mapping of the carotid plaque

BACKGROUND AND PURPOSE

To determine whether a stratified gray-scale median (GSM) analysis of the carotid plaque combined with color mapping correlated better with the presence of neurological symptoms and microembolic signals (MES) than a whole plaque measurement.

METHODS

A total of 131 patients presenting 167 carotid stenoses between 30% and 99% were analyzed by ultrasound. Emboli detection was performed by transcranial Doppler. For each plaque, the GSM values at depth 0 mm (surface) and at one third (30) and one half (50) of the plaque thickness were compared with the values obtained for the whole plaque. The plaque pixels were mapped into 3 colors: red, yellow and green, depending on their GSM value.

RESULTS

Mean GSM values were lower among symptomatic plaques, but a statistically significant difference between values of the whole plaque and those of the surface was obtained only for MES+ stenoses (P<0.01). In a proportional odds logistic regression model based on 4 subgroups with an increasing clinical risk (MES-/symptoms-; MES-/symptoms+; MES+/symptoms-; +; MES+/symptoms+), low mean GSM values and the predominant red color at the surface were independent factors associated with the presence of symptoms or MES (P<0.0005). Furthermore, compared with a whole plaque measurement, analysis of the surface values predicted systematically with a greater sensitivity and specificity (receiver operating characteristic curves) each one of these 4 subgroups.

CONCLUSIONS

Low mean GSM values and predominance of the red color at the surface correlated with most of the symptomatic or MES+ stenoses. This combined approach should be further investigated in a longitudinal study.

Repeated visual and computer-assisted carotid plaque characterization in a longitudinal population-based ultrasound study: the Tromsø study

In a longitudinal population-based ultrasound survey, we evaluated the reproducibility of carotid plaque detection, off-line vs. online visual classification of plaque echogenicity and computer-assisted plaque echogenicity (grey-scale median, GSM) classification and plaque area measurements. The number of paired observations in the reproducibility analyses was 107 in the baseline study and 83 in the follow-up study. In addition, 198 and 222 images were selected from the baseline and the follow-up study for GSM- and plaque-area analyses. The total number of plaque images (11,160) was used to obtain comparative reference values. Despite good agreement in the reproducibility study (kappa values ranging from 0.52 to 0.57), there was a substantial drift in online visual classification of plaque echogenicity during the survey period. Inter- and intraobserver agreement on computer-assisted GSM classification was substantial, with kappa values (95% CI) of 0.77 (0.73 to 0.80) and 0.79 (0.75 to 0.84), respectively. A systematic bias in plaque area measurements was observed. Visual online classification may introduce systematic measurement errors that are not intercepted in a reproducibility study of restricted duration. Computer-assisted off-line classification had better reproducibility. However, the method is influenced by measurement errors, both in the outlining of the plaque and in the standardization procedure.

Low-grade carotid stenosis: looking beyond the lumen with MRI

BACKGROUND AND PURPOSE

The management of carotid atherosclerosis is well-established for symptomatic stenosis above 69%, but the optimal approach for managing lower degrees of narrowing remains uncertain. Because the risk of stroke increases with higher grades of stenosis, we are inclined to consider low-grade disease to be low risk. This approach, however, does not take into account other factors such as plaque size or composition. Plaque may progress to a substantial size before it demonstrates significant stenosis by angiography. We know that low-grade disease can result in cerebrovascular ischemic events, but predicting vulnerable lesions has not been possible by relying on stenosis alone.

SUMMARY OF REVIEW

An understanding of the clinical behavior of plaque causing little to no narrowing is now possible with the advent of high-resolution black blood MRI, a modality that does not rely on luminal narrowing for detection.

CONCLUSIONS

We present the current understanding of the clinical implications of low-grade carotid stenosis with an example of the MRI assessment of high-risk carotid plaque causing minimal narrowing that highlights the importance of looking beyond the lumen.

Noninvasive Evaluation of Carotid Artery Stenosis: Indications, Strategies, and Accuracy

Carotid artery occlusive disease is an important stroke risk factor and accounts for a significant proportion of stroke morbidity and mortality. In this article we survey the major clinical trials related to stroke risk in symptomatic and asymptomatic patients who have internal carotid artery (ICA) stenosis; techniques for noninvasive screening of ICA stenosis including ultrasound, MR angiography, and CT angiography; and evolving algorithms for ICA evaluation. We comment on current interest in plaque morphology as a risk factor for stroke.

Development and validation of an in vivo analysis tool to identify changes in carotid plaque tissue types in serial 3-D ultrasound scans

We have developed a three-dimensional (3-D) B-mode acquisition system suitable for imaging carotid plaques in vivo. A texture classification system using 157 statistical and textural algorithms, previously developed in our laboratory and shown to predict the contents of in vitro carotid plaques, was applied to in vivo 3-D image sets obtained from patients with both symptomatic and asymptomatic carotid artery plaques. Delineation of plaque boundaries is more difficult using in vivo images than in vitro images of excised plaques embedded in agar. This study has examined inter- and intraobserver variability studies to assess the degree of selectivity of the plaque region-of-interest (ROI) and assess the degree of repeatability for potential use in comparing serial scans. An interobserver limit of agreement of +/-12.9% and an intraobserver limit of repeatability of <2% were obtained. These results show that the plaque ROI selection is subjective, but is repeatable within acceptable limits.

Stratified gray-scale median analysis and color mapping of the carotid plaque: correlation with endarterectomy specimen histology of 28 patients

BACKGROUND AND PURPOSE

To determine whether a stratified gray-scale median (GSM) analysis of the carotid plaque combined with color mapping could predict plaque histology better than an overall GSM measurement.

METHODS

Thirty-one carotid plaques derived from 28 patients undergoing carotid endarterectomy were investigated by ultrasound. GSMs of the whole plaque were used as measurement of echogenicity. A profile of the regional GSM as a function of distance from the plaque surface could be generated. Plaque pixels were further mapped into 3 different colors depending on their GSM value.

RESULTS

Plaques with large calcifications presented the highest GSM values, and those with large hemorrhagic areas or with a predominant necrotic core exhibited the lowest. Fibrous plaques had intermediate GSM values. A necrotic core located in a juxtalumenal position was associated with significantly lower GSM values (P=0.009) and with a predominant red color (GSM <50) at the surface (P=0.0019). With respect to the thickness of the fibrous cap and the position of the necrotic core, the sensitivity and specificity of the predominant red color of the whole plaque was respectively 45% and 67% and 53% and 75%; considering the predominant red color of the surface, the sensitivity and specificity increased to 73% and 67% and 84% and 75%, respectively.

CONCLUSIONS

The stratified GSM measurement combined with color mapping showed a good correlation with the different histopathological components and further allowed identification with good accuracy of determinants of plaque instability. This approach should be investigated in a prospective, natural history study.

Relative value of normalized sonographic in vitro analysis of arteriosclerotic plaques of internal carotid artery

BACKGROUND AND PURPOSE

A close correlation between B-mode sonography and the histopathology and surface structure of plaque is rarely seen in vivo with high-grade stenoses of the extracranial carotid artery. The goal of this study was to determine whether normalized gray scale analysis and surface analysis of the plaque are capable of characterizing the attributes correctly.

METHODS

Optimized B-mode images of 107 carotid endarterectomy specimens were captured, and the gray scale median (GSM) was calculated. The specimens were classified histologically into 3 groups: (1) calcium-rich hard plaques, (2) lipid-rich soft plaques, and (3) combined plaques. The surfaces of the plaques were classified as smooth or rough on the basis of standardized reference samples. The endoluminal surface was digitally documented in vitro by videoendoscopy and again classified into the same categories. All stages of the investigation were performed by 2 observers at 2 different times.

RESULTS

Evaluation of the GSM showed close interobserver and intraobserver correlation (P<0.01, R>0.8). However, there was only 46% agreement between the GSM and the histopathological findings. In both in vitro angioscopy (kappa=0.936, P<0.001) and sonographic evaluation (kappa=0.842, P<0.001), there was a high correlation between the observers with regard to the evaluable specimens. In 73%, agreement was observed between the sonographic image and angioscopy.

CONCLUSIONS

Normalized gray scale analysis and evaluation of the plaque surface in an in vitro study make possible observer-independent evaluation. The composition of the plaque cannot be visualized with sufficient accuracy by sonographic GSM analysis. This also applies to the correlation between sonography and actual surface composition of the plaque.

Carotid plaque: comparison between visual and grey-scale median analysis

Plaque morphology plays an important prognostic role in the occurrence of cerebrovascular events. Echolucent and heterogeneous plaques, in particular, carry an increased risk of subsequent stroke. Most of the trials emphasizing the relationship between plaque echo structure and stroke risk are based on high-resolution ultrasound (US) using a visual method of classification. More recently, several studies have suggested that the computerized measurement of the grey-scale median (GSM) may evaluate carotid plaque echogenicity more objectively and accurately. We sought to compare these two types of evaluations. We studied 68 consecutive patients, with 86 carotid bifurcation plaques causing 30% to 99% stenosis on duplex scanning. We assessed the GSM of these plaques and compared it to the visually evaluated echogenicity using the five-type classification system with vessel lumen and adventitia as reference structures. Plaque heterogeneity was also studied in a subgroup of 47 patients with 60 carotid stenoses by comparing visual analysis with the GSM method. The mean GSM value of the plaques increased with the plaque type. The difference of echogenicity between the five types of plaques was statistically significant (p < 0.02). We found a good concordance between visual analysis and the GSM method regarding plaque heterogeneity. Our results suggest that the visual evaluation of plaque echogenicity and heterogeneity based on the five-type classification correlates well with the computerized measurement of the GSM. The visual evaluation of carotid plaque remains, therefore, a valuable method in daily clinical practice.

Ultrasonographic analysis of arteriosclerotic plaques in the internal carotid artery

OBJECTIVES

The aim of this study was to investigate whether ultrasonography can characterise plaque morphology and surfaces independent of the observer.

METHODS

Computer-assisted image analysis of the grey scales of B-mode scans from 15 patients with stenoses of the internal carotid artery was performed and compared with the histopathological reports. In vitro angioscopy, was used to visualise the plaque surfaces of the thromboendarterectomy specimens.

RESULT

Assessment of the internal plaque structure by ultrasound showed close agreement between the two observers (P<0.01) without correlation with the histopathological results. Ultrasonography was able to characterise the plaque surfaces in 93% of cases.

CONCLUSION

This investigation showed that standardised computer-assisted analysis of the internal plaque structure correlates less closely than histological investigation, but agrees closely with the surface structure of the plaque. The exclusive use of digital image processing and standardisation of the investigative technique are expected to provide even better results.

Apolipoproteins and carotid artery atherosclerosis in an elderly multiethnic population: the Northern Manhattan stroke study

The association of apolipoproteins A-I and B (apo A-I and apo B) with cardiovascular disease has been studied in younger populations, but there is sparse information in the elderly. We determined whether apo A-I and apo B were associated with carotid artery atherosclerosis (CAA) in 507 stroke-free elderly community residents (mean age 70.1+/-11.7 years, 60% women, 41% Hispanics, 30% African American, 28% Caucasian). CAA severity was normal (no plaque or carotid stenosis) in 39%, mild (maximum plaque thickness < or =1.8 mm or carotid stenosis <40%) in 25%, and moderate/severe (maximum plaque thickness >1.8 mm or carotid stenosis > or =40%) in 36%. CAA severity increased with age in all race/ethnic groups (P<0.01). CAA was similar among African Americans and Caucasians, but less in Hispanics (age adjusted OR: 0.5, CI: 0.4-0.8). apo A-I <1.2 g/l (OR: 2.0, CI: 1.0-3.3) and apo B > or =1.4 g/l (OR: 2.0, CI: 1.1-3.6) were associated with moderate-severe CAA. An apo B/apo A-I ratio > or =1 was associated with moderate-severe CAA (OR: 2.4, CI: 1.3-4.4), and the association varied by race (Hispanics OR: 4.3, CI: 1.8-10; non-Hispanics, OR: 1.4, CI: 0.6-3.2). Total cholesterol, triglycerides and low density lipoprotein cholesterol were not associated with moderate-severe CAA, while high density lipoprotein cholesterol was protective (OR: 0.4, CI: 0.2-0.8). Thus, in an elderly population, apo A-I and B were determinants of moderate-severe CAA, and the degree of association varied by race/ethnicity

Real-time spatial compound imaging improves reproducibility in the evaluation of atherosclerotic carotid plaques

Compound imaging has the ability of reducing speckle and clutter artifacts demonstrated in in vitro studies compared to conventional, single-angle imaging. We investigated intra- and interobserver agreement of 38 outlines of carotid artery plaque images acquired by these techniques, by measuring the overlapping area after repeated outlines. In general, both techniques showed good agreement. When considering the images with poorest overlap, compound imaging had a significant advantage over conventional imaging regarding both intra- and interobserver agreement. The interobserver variation for the overlapping area after two outlines was 20% for conventional technique and 10% for compound. The interobserver variation of the gray scale median value (GSM) for conventional technique ranged from -32 to +20 and from -6 to +6 for compound. Likewise, the coefficient of repeatability for the GSM value was 13 for conventional imaging and three for compound imaging, and interobserver variation for the GSM value for the overlapping area was 34% and 9% for conventional and compound technique. In conclusion, compound imaging improves intra- and interobserver agreement and reduces interobserver variation in the GSM value in a clinical setting.

An objective method for grading ultrasound images of carotid artery plaques

Plaque composition may improve identification of patients at risk of stroke. A new method of grading ultrasound (US) images to assess plaque composition is described. B-mode US images were obtained from 50 carotid specimens. Image analysis parameters were entered into a discriminant analysis package and compared retrospectively with histology. Discriminant functions were derived and then applied prospectively to image-analysis data obtained from a further 50 plaque specimens. For the prospective analysis, US images were graded according to the relative contribution of calcium, fibrous tissue, haemorrhage and lipid. The accuracy for retrospective classification of calcium was 100%, for fibrous tissue 97%, for lipid 76% and 68% for haemorrhage (kappa = 0.81). Prospective classification showed an overall agreement of 65% (kappa = 0.47). Significant intraplaque haemorrhage was identified with an 81% sensitivity and 83% specificity. The US method described demonstrated improved accuracy compared to previous studies. Further study is required to establish the use of this method for in vivo images and its correlation with patient symptoms.