A Review of Noninvasive Ultrasound Image Processing Methods in the Analysis of Carotid Plaque Morphology for the Assessment of Stroke Risk
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paper_title: The relative effect of carotid plaque heterogeneity and echogenicity on ipsilateral cerebral infarction and symptoms of cerebrovascular disease.

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OBJECTIVE ::: To determine the relative effect of carotid plaque heterogeneity and echogenicity as measured by computer on the incidence of ipsilateral cerebral infarction and symptoms of cerebrovascular disease. ::: ::: ::: MATERIALS AND METHODS ::: 138 patients with 209 carotid plaques producing > 50% stenosis were studied. 110 plaques were from symptomatic sides. All patients had computer tomography (CT) brain scans. Images of the carotid plaques obtained by duplex scanner were transferred to a computer. Using an image analysis program plaque echogenicity, measured as the grey scale median (GSM) and heterogeneity, evaluated as the heterogeneity index (HI) was calculated. ::: ::: ::: RESULTS ::: 42% of plaques were associated with cerebral infarction. Symptomatic plaques and those associated with cerebral infarction were more echolucent and less heterogeneous than asymptomatic plaques and those not associated with cerebral infarction. Plaques with GSMs below or equal to 32 were associated with a significantly higher incidence of cerebral infarction. Plaques with GSMs below or equal to 32 were associated with a significantly higher incidence of cerebral infarction and symptoms of cerebrovascular disease than those with GSMs above this level (p < 0.01). Plaques with HIs below or equal to 20 were associated with a significantly higher incidence of symptoms of cerebrovascular disease as compared to those with HIs above this level (p < 0.01). ::: ::: ::: CONCLUSIONS ::: Computer analysis of carotid plaque morphology is an objective tool that can identify high risk plaques. The potential of such analysis in the identification of asymptomatic patients with advanced carotid stenosis at a high risk of stroke should be explored in a natural history study.
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paper_title: Six-Year Effect of Combined Vitamin C and E Supplementation on Atherosclerotic Progression: The Antioxidant Supplementation in Atherosclerosis Prevention (ASAP) Study

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Background— Self-selected supplementation of vitamin E has been associated with reduced coronary events and atherosclerotic progression, but the evidence from clinical trials is controversial. In the first 3 years of the ASAP trial, the supplementation with 136 IU of vitamin E plus 250 mg of slow-release vitamin C twice daily slowed down the progression of carotid atherosclerosis in men but not women. This article examines the 6-year effect of supplementation on common carotid artery (CCA) intima-media thickness (IMT). Methods and Results— The subjects were 520 smoking and nonsmoking men and postmenopausal women aged 45 to 69 years with serum cholesterol ≥5.0 mmol/L (193 mg/dL), 440 (84.6%) of whom completed the study. Atherosclerotic progression was assessed ultrasonographically. In covariance analysis in both sexes, supplementation reduced the main study outcome, the slope of mean CCA-IMT, by 26% (95% CI, 5 to 46, P=0.014), in men by 33% (95% CI, 4 to 62, P=0.024) and in women by 14% (not significant). ...
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paper_title: B-mode ultrasound assessment of pravastatin treatment effect on carotid and femoral artery walls and its correlations with coronary arteriographic findings: a report of the Regression Growth Evaluation Statin Study (REGRESS).

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OBJECTIVES ::: In this B-mode ultrasound study we assessed pravastatin treatment effects on carotid and femoral artery walls and investigated the correlations between the state and evolution of peripheral and coronary atherosclerosis. ::: ::: ::: BACKGROUND ::: The Regression Growth Evaluation Statin Study (REGRESS) was an 11-center, 2-year, double-blind, placebo-controlled, prospective study of 885 men with coronary artery disease (CAD) (total cholesterol 4 to 8 mmol/liter). The study primarily investigated pravastatin treatment effects on the coronary lumen. This report focuses on the 255 patients who participated in the REGRESS ultrasound study. ::: ::: ::: METHODS ::: Carotid and femoral artery walls were imaged at baseline and at 6, 12, 18 and 24 months. Pravastatin treatment effect was defined as the difference in progression of the combined intima-media thicknesses (IMT) between treatment groups. ::: ::: ::: RESULTS ::: Pravastatin treatment effects were highly significant (combined IMT: p = 0.0085; combined far wall IMT: p < 0.0001; common femoral artery far wall IMT: p = 0.004). Correlations between the IMTs of the arterial wall segments ranged from -0.17 to 0.81. Baseline correlations between IMT and percent coronary lumen stenoses ranged from 0.23 to 0.36. Baseline IMT correlated with the mean coronary segment diameter (r = -0.32, p = 0.001) and minimal coronary obstruction diameter (r = -0.27, p = 0.005). There were no individual correlations between IMT and coronary lumen variables (p > 0.30). ::: ::: ::: CONCLUSIONS ::: Pravastatin treatment effects on carotid and femoral artery walls were observed. B-mode ultrasound imaging studies of peripheral arterial walls could not describe the state and evolution of the coronary lumen in the individual patient, but proved to be a highly suitable tool for the assessment of antiatherosclerotic properties of agents.
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paper_title: Association of Coronary Heart Disease Incidence with Carotid Arterial Wall Thickness and Major Risk Factors: The Atherosclerosis Risk in Communities (ARIC) Study, 1987-1993

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Few studies have determined whether greater carotid artery intima-media thickness (IMT) in asymptomatic individuals is associated prospectively with increased risk of coronary heart disease (CHD). In the Atherosclerosis Risk in Communities Study, carotid IMT, an index of generalized atherosclerosis, was defined as the mean of IMT measurements at six sites of the carotid arteries using B-mode ultrasound. The authors assessed its relation to CHD incidence over 4-7 years of follow-up (1987-1993) in four US communities (Forsyth County, North Carolina; Jackson, Mississippi; Minneapolis, Minnesota; and Washington County, Maryland) from samples of 7,289 women and 5,552 men aged 45-64 years who were free of clinical CHD at baseline. There were 96 incident events for women and 194 for men. In sex-specific Cox proportional hazards models adjusted only for age, race, and center, the hazard rate ratio comparing extreme mean IMT (≥1 mm) to not extreme (<1 mm) was 5.07 for women (95% confidence interval 3.08-8.36) and 1.85 for men (95% confidence interval 1.28-2.69). The relation was graded (monotonic), and models with cubic splines indicated significant nonlinearity. The strength of the association was reduced by including major CHD risk factors, but remained elevated at higher IMT. Up to 1 mm mean IMT, women had lower adjusted annual event rates than did men, but above 1 mm their event rate was closer to that of men. Thus, mean carotid IMT is a noninvasive predictor of future CHD incidence.
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paper_title: Ultrasonic classification of carotid plaques causing less than 60% stenosis according to ultrasound morphology and events.

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Abstract Carotid plaque morphology studied by ultrasound has been used to classify 3 types of bifurcation plaques, producing less than 60% stenosis on duplex scanning: Type A, the homogeneous, highly echogenic plaque; Type B, the heterogeneous (mainly echogenic, B-1 or mainly echolucent, B-2) plaque; Type C, the complex plaque with irregular surface, echogenic and/or echolucent with calcifications. One hundred asymptomatic subjects in each plaque group were included in a prospective 4-year follow-up study to evaluate clinical events and brain damage by yearly cerebral CT and MR scans. After four years 96 subjects with type A plaque, 89 with type B-1 and 67 with type C plaques completed the study. While there were no clinical events or positive cerebral scans in subjects with type A plaques there was a significantly increasing number of cerebral and vascular events in subjects with plaque B and C type with a zero mortality in the plaque A group, a 2.24% mortality in type B plaques and a significantly higher (p > 0.05) mortality (13.4%) in type C plaques. CT and MR scans revealed brain damage which had been totally asymptomatic with MR detecting a larger number of lesions. Also the number of cerebral lesions observed by CT/MR were significantly greater than the number of recorded clinical episodes. ECG stress test revealed a larger number of asymptomatic coronary disease in the C type plaques. In conclusion ultrasound plaque morphology is linked to different incidences of cerebral and cardiac events, brain damage and asymptomatic coronary disease. Also CT and MR may reveal lesions which do not cause signs or symptoms.
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paper_title: Carotid Plaque, Intima Media Thickness, Cardiovascular Risk Factors, and Prevalent Cardiovascular Disease in Men and Women : The British Regional Heart Study

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Background and Purpose—B-mode ultrasound is a noninvasive method of examining the walls of peripheral arteries and provides measures of the intima-media thickness (IMT) at various sites (common carotid artery, bifurcation, internal carotid artery) and of plaques that may indicate early presymptomatic disease. The reported associations between cardiovascular risk factors, clinical disease, IMT, and plaques are inconsistent. We sought to clarify these relationships in a large, representative sample of men and women living in 2 British towns. Methods—The study was performed during 1996 in 2 towns (Dewsbury and Maidstone) of the British Regional Heart Study that have an ≈2-fold difference in coronary heart disease risk. The male participants were drawn from the British Regional Heart Study and were recruited in 1978–1980 and form part of a national cohort study of 7735 men. A random sample of women of similar age to the men (55 to 77 years) was also selected from the age-sex register of the general practices ...
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paper_title: Determinants of Carotid Plaque Instability: Echoicity versus Heterogeneity

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Abstract Objective: to identify the echoicity and heterogeneity of carotid plaques associated with ipsilateral symptomatic and asymptomatic neurovascular presentations. Design: cross-sectional study. Materials: a total of 113 patients, with 127 symptomatic and asymptomatic plaques, were studied. Methods: the duplex images of the plaques were analysed echoically in a computer by means of Grey Scale Median (GSM) [hypoechoic (low GSM), hyperechoic (high GSM)]. The presence or absence of at least two plaque regions within the plaque area being echoically uniform (no variation of echoicity), occupying each at least 10% of the plaque area and having GSM difference greater than the plaque GSM was evaluated to distinguish the heterogeneous (presence of this pattern) from the homogeneous (absence of this pattern) plaques. Results: the symptomatic status was associated with plaques of low median GSM (10.5) and 88% prevalence of the homogeneous pattern as contrasted with the asymptomatic status that was associated with high median GSM (28) and 65% prevalence of the homogeneous pattern [( p =0.001 (GSM), p =0.003 (heterogeneity)]. Conclusions: symptomatic plaques were associated with hypoechoic and predominant homogeneous echo-pattern whereas the asymptomatic ones were associated with hyperechoic and less predominant homogeneous pattern.
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paper_title: Ultrasound morphology classification of the arterial wall and cardiovascular events in a 6-year follow-up study.

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A 6-year follow-up based on an arterial morphology classification defined with an ultrasound assessment of carotid and femoral artery bifurcations was conducted on 2322 asymptomatic subjects. Four morphology classes were considered. When 2000 subjects (86% of total subjects; 1124 males, 876 females) completed a 6-year follow-up, the study was terminated. At 6 years, no cardiovascular events were observed in subjects who were in class I (80.05% of the population sample) at inclusion; there were 69 events in classes II, III, and IV (19.95% of the population; incidence, 17.3%); 59 events, including the five deaths, occurred in classes III and IV (10.85% of the population), producing an event incidence of 27.2%. The increased event rate in classes II, III, and IV was significant (log-rank test; P < .05, P < .025, and P < .025, respectively). Thus, the arterial morphology classification identified 19.95% of the population (subjects in classes II, III, and IV) in which all events occurred. There was a higher (P < .05) rate of progression of altered arterial morphology in 6 years in classes III (26.5% of subjects progressed) and IV (41.9% progressed) than in classes I and II. The total number of cigarette-years was higher (P < .05) in classes II, III, and IV than in class I. In conclusion, the ultrasound-based arterial classification was useful in selecting from the population sample 80.05% of subjects (class I) who remained event-free for 6 years. All events occurred in class II, III, and IV subjects (19.95%), and all five deaths (0.25% of the population) occurred in classes III and IV (10.85% of the sample).
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paper_title: Angiographic and Duplex Grading of Internal Carotid Stenosis: Can We Overcome the Confusion?

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The stroke risk reduction benefit of surgical intervention in carotid occlusive disease has been validated in multicenter trials for various angiographically defined lesion severity categories. The two divergent angiographic grading methods used for internal carotid artery stenosis in these trials have caused confusion in the clinical application of their recommendations. Moreover, while today's highly accurate carotid duplex scanning can obviate the need for preoperative angiography in many cases, the duplex criteria must be tailored to achieve sufficiently reliable results on which therapeutic decisions can be made. This review offers a clarification of the discrepancies between the angiographic grading techniques and how their measurements of percent stenosis correlate to the duplex criteria needed to support the treatment decision-making process for carotid obliterative disease.
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paper_title: Carotid plaque histology using real-time ultrasonography: Clinical and therapeutic implications☆☆☆

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Abstract To evaluate the ability of ultrasonographic imaging to detect plaque hemorrhage in carotid atheroma, a study was undertaken that compared pathologic findings to preoperative ultrasonographic findings. Ultrasonography identified two plaque categories based on the heterogeneous and homogeneous echo patterns of the lesions studied. Heterogeneous lesions accounted for 91 percent of intraplaque hemorrhages (30 of 33) and 100 percent of ulcerated lesions (15 of 15). In 41 of 50 specimens (82 percent), ultrasonography correctly identified the presence or absence of plaque hemorrhage. False-negative studies (3 of 50) were due to the minute foci of remote hemorrhages. False-positive studies (6 of 50) resulted from plaques that contained large amounts of lipid or cholesterol. Preoperative ultrasound carotid imaging can be used to detect the histologic characteristics of plaque. Since recent clinicopathologic studies have implicated intraplaque hemorrhage and ulceration in symptomatic carotid disease, this information may be of value in choosing therapy, especially for the asymptomatic patient.
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paper_title: Characterization of symptomatic and asymptomatic carotid plaques using high-resolution real-time ultrasonography

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High-resolution ultrasonography was used to classify carotid plaques into five different types in 72 patients with symptoms and in 49 without, and with stenosis of the origin of the internal carotid artery < 70 per cent. There were 72 plaques in the symptomatic group and 75 in the asymptomatic group. Type 1 plaques were uniformly echolucent, type 2 predominantly echolucent, type 3 predominantly echogenic, type 4 uniformly echogenic and type 5 consisted of plaques that could not be classified owing to heavy calcification and acoustic shadows. Type 1 Plaque was found in 90 per cent of patients with symptoms and in 10 per cent of those without, type 2 plaque was found in 53 and 47 per cent, type 3 in 34 and 66 per cent, and type 4 in 5 and 95 per cent respectively. The preponderance of echolucent plaques in symptomatic patients with stenosis < 70 per cent supports the hypothesis that this type of plaque is unstable and tends to embolize. In contrast, in patients without symptoms there is preponderance of echogenic plaques.
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paper_title: Multiple risk factor intervention reduces cardiovascular risk in hypertensive patients with echolucent plaques in the carotid artery.

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OBJECTIVE ::: In a previously published randomized 6-year study we observed that multiple risk factor intervention reduced cardiovascular risk in high-risk hypertensive men, and that this effect was confined to patients with carotid artery plaques. Hypothetically, the underlying mechanism might have been a stabilization of echolucent, instable, rupture-prone plaques. The aim of the present study was to examine plaque characteristics by B-mode ultrasound in the previous intervention study, and also to investigate the relationship between plaque characteristics at baseline and cardiovascular events during the 6-year follow-up in the two randomization groups. ::: ::: ::: METHODS ::: High resolution B-mode ultrasound was used to characterize plaque echogenicity in four subgroups - dominantly echolucent, substantially echolucent, dominantly echogenic, and uniformly echogenic. ::: ::: ::: RESULTS ::: In the usual care group 17 of 32 (53%) patients with echolucent plaques at baseline suffered from a combined end-point (any death or nonfatal myocardial infarction or nonfatal stroke) during follow-up compared with seven of 28 (25%) patients in the intervention group (P = 0.036). The corresponding numbers in patients with echogenic plaques were n = 4/13 (31%) and n = 4/17 (24%), respectively (NS). In the usual care group 11 of 33 (33%) patients with no plaques suffered from a combined end-point during follow-up compared with 11 of 30 (37%) in the intervention group. ::: ::: ::: CONCLUSION ::: Our data indicate that the beneficial effect of the multiple risk intervention programme was confined to those patients with echolucent plaques. The data have to be confirmed with a large-scale trial.
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paper_title: The objective characterisation of ultrasonic carotid plaque features.

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Objective: To determine the influence of ultrasonic carotid plaque morphology on the incidence of ipsilateral hemispheric symptoms (IHS). Design: Cross-sectional study. Materials: A consecutive series of 80 patients (96 plaques) with more than 50% ICA stenosis was studied. Methods: B mode ultrasonic images were captured and transferred to a computer on magneto-optic disk and standardised using linear scaling so that adventitia would have a grey scale median (GSM) value of 185–195 and blood 0–5. The GSM and the percentage of echolucent pixels (PEP) in plaques were determined to measure echodensity. Homogeneity, entropy, and contrast were also determined to measure spatial distribution (heterogeneity) of grey shades in each plaque. Each measurement was correlated to presence or absence of IHS. Results: Twenty-five plaques were associated with IHS and 71 plaques were asymptomatic. In symptomatic plaques the mean of GSM was 23 and the mean of PEP was 70%, compared to 38 and 55% respectively in asymptomatic plaques ( p =0.02; Wilcoxon test). Sixty per cent of symptomatic plaques were associated with a homogeneity, entropy, and contrast values of >0.2, p =0.001) that are related to presence or absence of IHS. Conclusion: This study indicates that computer aided analysis of ultrasonic B mode features of carotid plaques could identify a potentially high-risk subgroup (patients with IHS). A GSM less than 40 or PEP greater than 50% is a good predictor of IHS related to carotid plaques. The fact that these measurements are operator independent and performed after image standardisation should encourage their use in multicentre clinical trials where different operators and equipment are used.
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paper_title: Pravastatin reduces carotid intima-media thickness progression in an asymptomatic hypercholesterolemic Mediterranean population: The Carotid Atherosclerosis Italian Ultrasound Study

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Purpose The Carotid Atherosclerosis Italian Ultrasound Study (CAIUS) was performed to test the effects of lipid lowering on the progression of carotid intima-media thickness (IMT) in 305 asymptomatic patients from a Mediterranean country. Patients and methods Eligibility included hypercholesterolemia (baseline means: low-density lipoprotein [LDL] = 4.68 mmol/L. high-density lipoprotein [HDL] = 1.37 mmol/L), and at least one 1.3 Results Five serious cardiovascular events (1 fatal myocardial infarction), and 7 drop-outs for cancer were registered. In the pravastatin group, LDL decreased −0.22 after 3 months versus −0.01 in the placebo group, and remained substantially unchanged afterward (−0.23 versus +0.01 at 36 months, respectively). Progression of the MMaxIMT was 0.009 ± 0.0027 versus −0.0043 ± 0.0028 mm/year ( ± SE, P Conclusions Pravastatin stops the progression of carotid IMT in asymptomatic, moderately hypercholesterolemic men and women. This finding extends the beneficial effects of cholesterol lowering to the primary prevention of atherosclerosis in a population with relatively low cardiovascular event rates, and suggests that this benefit is mediated by specific morphological effects on early stages of plaque development.
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paper_title: Carotid Plaque Characterization by Duplex Scanning Observer Error May Undermine Current Clinical Trials

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Background and Purpose—Clinical studies currently in progress are using subjective methods to characterize plaque morphology from ultrasound images. However, there are few studies on the intraobserver and interobserver variability of these classifications. This study was designed to assess these variables. Methods—Grading of plaque morphology from ultrasound images, stored both digitally and to hard copy, was performed by 2 classification schemes. Interobserver agreement was determined by 4 observers. Within-observer agreement was performed at intervals for up to 6 months. Accuracy of the 2 methods was determined by comparison with histology. Results—Within- and between-observer agreement was moderate to good for full-color digital image analyses, with pooled κ values of κp=0.49±0.10 and κp=0.62±0.07 for the 2-category method and κp=0.53±0.06 and κp=0.52±0.05 for the 4-category method, respectively. Hard copy data analyses gave lower κ values. The more experienced observers produced higher within-observer...
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paper_title: Carotid Wall Thickness is Predictive of Incident Clinical Stroke: The Atherosclerosis Risk in Communities (ARIC) Study

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Few studies have determined whether carotid artery intima-media thickness (IMT) is associated prospectively with risk of first ischemic stroke. In the Atherosclerosis Risk in Communities Study, carotid IMT, an index of generalized atherosclerosis, was defined as the mean of IMT measured by B-mode ultrasonography at six sites of the carotid arteries. The authors assessed the relation of mean IMT to stroke incidence over 6-9 years' follow-up (1987-1995) among 7,865 women and 6,349 men aged 45-64 years without prior stroke at baseline in four US communities. There were 90 incident ischemic stroke events for women and 109 for men. In sex-specific Cox proportional hazards models adjusting only for age, race, and community, the hazard rate ratios comparing extreme mean IMT values (> or =1 mm) to values less than 0.6 mm were 8.5 for women (95% confidence interval: 3.5, 20.7) and 3.6 for men (95% confidence interval: 1.5, 9.2). The relation was graded, and models with cubic splines indicated significant nonlinearity, with hazards increasing more rapidly at lower IMTs than at higher IMTs. Thus, models using linear IMT values substantially underestimate the strength of the association at lower IMTs. The strength of the association was reduced by the inclusion of putative stroke risk factors, but it remained elevated at higher IMTs. Hence, mean carotid IMT is a noninvasive predictor of future ischemic stroke incidence.
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paper_title: Carotid artery atheroma: comparison of preoperative B-mode ultrasound appearance with carotid endarterectomy specimen pathology.

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Abstract This paper describes a prospective study comparing the preoperative Duplex ultrasound appearance of carotid bifurcation atheroma with the pathological characteristics found in the endarterectomy specimens of the same vessels. Initial studies of carotid atheroma using Duplex scanning classified plaques into heterogeneous and homogeneous and found a strong correlation between heterogeneous lesions and the presence of intraplaque haemorrhage or ulceration in the endarterectomy specimen. The B-mode classification of plaque appearance described in this paper is an expansion of the above classification. The study group comprised 220 patients who underwent 244 procedures. The indication for carotid endarterectomy was symptomatic disease in the great majority of cases. We found a high incidence of unstable plaque pathology in the operative specimens, and a predominance of the more echolucent ultrasound plaque appearances (types 1 and 2). There is a statistically significant relationship (p less than 0.001) between ultrasound appearance types 1 and 2 and the presence of either intraplaque haemorrhage or ulceration in the endarterectomy specimen.
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paper_title: Validity of B-Mode Ultrasonographic Findings in Patients Undergoing Carotid Endarterectomy in Comparison With Angiographic and Clinicopathologic Features

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Background and Purpose Determining factors for performing carotid endarterectomy (CEA) are the severity of carotid stenosis and the presence of plaque ulcerations. Precise detection of these factors is important. The aim of this study was to assess the applicability of using B-mode ultrasonography for diagnosing carotid lesions in patients undergoing CEA. ::: ::: Methods B-mode examinations were performed on 64 Japanese patients (68 arteries) who subsequently underwent CEA. In each case, the appearance of plaque on B-mode was classified into one of two types: heterogeneous or homogeneous; plaque echogenicity was expressed as hypoechoic, isoechoic, or hyperechoic. Surface characteristics such as ulceration also were examined, and the degree of carotid artery stenosis was calculated. The B-mode findings were compared with angiographic and pathological features. ::: ::: Results B-mode accurately visualized macroscopic ulceration and surface irregularity in 93.8% of the lesions examined, which was superior to angiography. Fifty-four lesions (79.4%) were of the heterogeneous type and 14 lesions (20.6%) were of the homogeneous type on B-mode. Microscopically, 57.4% of the heterogeneous-type lesions were a mixture of atheroma and fibrosis, and all homogeneous-type lesions demonstrated fibrous change. The frequency of calcification was higher in the heterogeneous lesions than in the homogeneous lesions. ::: ::: Conclusions B-mode ultrasonography findings can provide information about macroscopic and microscopic characteristics of carotid lesions.
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paper_title: Ultrasonographic and Histologic Characteristics of Symptom-Free and Symptomatic Carotid Plaque

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The purpose of the study was to determine the reliability of ultrasonography in assessing plaque pathology and to relate it to clinical symptoms. Ten symptom-free patients and 26 with symptomatic carotid plaques with a stenosis >70%. as detected by arteriography, were assessed by duplex. The findings were compared with the clinical presentation and plaque pathology. Pathological specimens of the plaque that had <60% fibrous tissue were associated with an increased incidence of past stroke (P = 0.002). Plaque ulceration, haemorrhage and calcium were all unrelated to the clinical presentation. Using the pathological specimen as the ‘gold standard’, ultrasonography was unable to detect plaque ulceration or haemorrhage. Plaque regularity, irregularity, homogeneity and heterogeneity were not consistent with plaque pathology or the clinical presentation. The fibrous tissue was significantly greater (73%) in plaques with an echogenic character compared with those with an echolucent morphology (63%; P = 0.04). Moreover, echolucent plaques were most common in symptomatic patients and echogenic plaques in symptom-free patients (P = 0.002).
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paper_title: ULTRASONIC TISSUE CHARACTERIZATION OF ATHEROMATOUS PLAQUES USING A HIGH RESOLUTION REAL TIME SCANNER

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Atheromatous plaques obtained at autopsies and surgical carotid endarterectomy specimens were scanned in a water bath with an 8 MHz high resolution real time instrument. The findings were correlated with histology at corresponding sites in each specimen. Fatty streaks were not detectable by ultrasound. Small fibro fatty plaques appeared as localized thickening of the arterial wall with little change in echogenicity or echo texture. In larger fibro fatty lesions, sizable aggregates of amorphous lipid residue appeared less echogenic than adjacent tissues and regions of dense fibrosis more echogenic. Densely calcified foci in plaques were highly echogenic and associated with acoustic shadowing. Surface irregularities of plaque at ultrasound may simulate ulceration. Ulcers, evident at gross inspection, appeared as marked surface irregularities or excavations at ultrasound. The basis of the findings and their relevance to clinical vascular ultrasound imaging are discussed.
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paper_title: Correlation of B-Mode Ultrasound Imaging and Arteriography With Pathologic Findings at Carotid Endarterectomy

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• Presently most noninvasive methods for assessing extracranial carotid disease have relied on hemodynamic change associated with significant stenosis. Recent evidence has suggested that both ulceration and/or plaque hemorrhage may frequently play an important role in the pathophysiology of carotid disease. To assess the ability of B-mode ultrasound to provide this anatomic information, in a prospective blinded manner we compared B-mode ultrasound and selective four-vessel arteriography to pathologic specimens obtained at the time of 89 carotid endarterectomies. The presence of ulceration, plaque characteristics (particularly hemorrhage), and luminal diameter were described for each modality. While arteriography detected only 16 of 27 ulcerations (sensitivity, 59%), B-mode ultrasound had a greater sensitivity (24/27, 89%). Both modalities had comparable specificities (arteriography, 73%; B-mode ultrasound, 87%). Moreover, B-mode ultrasound was highly sensitive for demonstrating plaque hemorrhage (27/29, 93%), as well as being quite specific (84%). Assessment of luminal reduction by B-mode ultrasound improved with technologist/interpreter experience and was significantly improved by adding real-time spectral analysis. Because of B-mode ultrasound's sensitivity for imaging ulceration and plaque hemorrhage, it offers significant advantages for the noninvasive detection of extracranial carotid disease. ( Arch Surg 1985;120:443-449)
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paper_title: Severity of Asymptomatic Carotid Stenosis and Risk of Ipsilateral Hemispheric Ischaemic Events: Results from the ACSRS Study

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OBJECTIVES ::: This study determines the risk of ipsilateral ischaemic neurological events in relation to the degree of asymptomatic carotid stenosis and other risk factors. ::: ::: ::: METHODS ::: Patients (n=1115) with asymptomatic internal carotid artery (ICA) stenosis greater than 50% in relation to the bulb diameter were followed up for a period of 6-84 (mean 37.1) months. Stenosis was graded using duplex, and clinical and biochemical risk factors were recorded. ::: ::: ::: RESULTS ::: The relationship between ICA stenosis and event rate is linear when stenosis is expressed by the ECST method, but S-shaped if expressed by the NASCET method. In addition to the ECST grade of stenosis (RR 1.6; 95% CI 1.21-2.15), history of contralateral TIAs (RR 3.0; 95% CI 1.90-4.73) and creatinine in excess of 85 micromol/L (RR 2.1; 95% CI 1.23-3.65) were independent risk predictors. The combination of these three risk factors can identify a high-risk group (7.3% annual event rate and 4.3% annual stroke rate) and a low risk group (2.3% annual event rate and 0.7% annual stroke rate). ::: ::: ::: CONCLUSIONS ::: Linearity between ECST per cent stenosis and risk makes this method for grading stenosis more amenable to risk prediction without any transformation not only in clinical practice but also when multivariable analysis is to be used. Identification of additional risk factors provides a new approach to risk stratification and should help refine the indications for carotid endarterectomy.
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paper_title: Hypoechoic plaque at US of the carotid artery: an independent risk factor for incident stroke in adults aged 65 years or older. Cardiovascular Health Study.

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PURPOSE ::: To investigate the association between incident (first) stroke and the echogenicity of internal carotid arterial plaque at ultrasonography (US). ::: ::: ::: MATERIALS AND METHODS ::: A cohort of 4, 886 individuals who, at baseline, were 65 years of age or older and without symptoms of cerebrovascular disease was followed up for an average of 3.3 years. Baseline clinical findings were from color Doppler and duplex US studies of the carotid arteries and a record of traditional risk factors: age, sex, presence of diabetes mellitus, pack-years of cigarette smoking, presence of hypertension, elevated systolic and diastolic blood pressure, elevated low-density lipoprotein cholesterol level. ::: ::: ::: RESULTS ::: Incident strokes, excluding hemorrhagic strokes and strokes of cardiac origin, were seen in 104 individuals (2.1%) at risk. Age- and sex-adjusted odds ratios for incident stroke were significant for hypoechoic plaque (odds ratio, 2.53; 95% CI, 1,42,4.53). After controlling for risk factors in a Cox proportional hazards model, the relative risk (RR) of incident stroke was 1.72 (p = .015) for hypoechoic plaque and 2.32 (P = .004) for internal carotid arterial narrowing of at least 50%. In addition, hypoechoic plaque (RR, 2.78; CI, 1.36,5.69) and 50%-100% stenosis (RR, 3.08; CI, 1.28, 7.41) were associated with ipsilateral, nonfatal stroke. ::: ::: ::: CONCLUSION ::: In asymptomatic adults aged 65 years or older, that risk of incident stroke was associated with two US features: hypoechoic internal carotid arterial plaque and an estimated internal carotid arterial stenosis of 50%-100%.
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paper_title: Natural history of asymptomatic carotid plaque.

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• In April 1981, a total of 297 carotid arteries were examined prospectively. All patients were asymptomatic and were referred to the peripheral vascular laboratory at Good Samaritan Medical Center, Phoenix, for real-time B-mode ultrasonography. A measurement of luminal area stenosis was determined to be either greater or less than 75%. In addition, the ultrasound echo pattern was used to classify plaque as either calcified, dense, or soft. If, for any reason, the patient or physician felt that carotid endarterectomy should be performed, the patient was dropped from the study. In addition, the use of antiplatelet medication or anticoagulants constituted disqualification. Three groups of patients were observed for three years or until symptoms became apparent. Patients in all three groups with stenosis greater than 75% at the time of initial study were at greater risk than their peers without significant narrowing; however, even those patients with less than 75% stenosis were at greater risk if the associated plaque was less organized, ie, soft. A definite trend toward higher risk is seen in plaques of lower density. Only 10% of those patients with calcified plaque and a significantly stenotic vessel have developed symptoms. In contrast, only three patients of the original 42 with soft plaque and a tight stenosis are still being observed. This study appears to confirm that soft plaques have a greater tendency toward subintimal hemorrhage, ulceration, or primary embolization than more well-organized plaques. (Arch Surg1985;120:1010-1012)
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paper_title: Consensus Concerning the Morphology and the Risk of Carotid Plaques

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An international consensus meeting to determine criteria for the characterization of extracranial carotid artery stenosis was held in Paris on December 13–14, 1996. Recommendations are the following i
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paper_title: The correlation of ultrasonic carotid plaque morphology and carotid plaque hemorrhage: clinical implications.

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BACKGROUND ::: This study examined the importance of ultrasonic plaque morphology and its correlation to the presence of intraplaque hemorrhage and clinical implications. ::: ::: ::: METHODS ::: One hundred fifty-two carotid plaques associated with > or = 50% internal carotid artery stenoses in 135 patients who had carotid endarterectomies were characterized ultrasonographically into irregular/ulcerative, smooth, heterogeneous, homogeneous, or not defined. All plaques were examined pathologically for the presence of intraplaque hemorrhage. ::: ::: ::: RESULTS ::: The ultrasonic morphology of the plaques included 63 with surface irregularity (41%), 48 smooth (32%), 59 heterogeneous (39%), 52 homogeneous (34%), and 41 not defined (27%). Intraplaque hemorrhage was present in 57 of 63 (90%) irregular plaques and 53 of 59 (90%) heterogeneous plaques, in contrast to 13 of 48 (27%) smooth plaques and 17 of 52 (33%) homogeneous plaques (P < .001). Fifty-three of 63 (84%) irregular plaques and 47 of 59 (80%) heterogeneous plaques had transient ischemic attack (TIA)/stroke symptoms, in contrast to 9 of 48 (19%) for smooth plaques and 15 of 52 (29%) for homogeneous plaques (P < .001). ::: ::: ::: CONCLUSIONS ::: Irregular and/or heterogeneous carotid plaques are more often associated with intraplaque hemorrhage and neurologic events. Therefore, ultrasonic plaque morphology may be helpful in selecting patients for carotid endarterectomy.
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paper_title: The role of plaque morphology and diameter reduction in the development of new symptoms in asymptomatic carotid arteries.

paper_content:

To determine the natural history of changes in plaque morphology and luminal diameter of atherosclerotic carotid arteries, we used duplex scanning to follow-up (1) the contralateral artery in 289 patients who had undergone carotid endarterectomy, with a mean follow-up 22 months and a range of 0 to 48 months and (2) the carotid arteries in 130 patients who had no surgical treatment and had been symptom free, with a mean follow-up period of 15 months and a range of 0 to 48 months. Plaques were graded as to the ratio of echolucency to echogenicity, with type 1 being most echolucent and type 4 being most echogenic. A normal-appearing artery was classified as type 5. Heterogeneous plaques (types 1 and 2) occurred significantly more (p less than 0.001) in symptomatic preoperative arteries than in asympatomatic arteries. Follow-up of the asymptomatic vessels showed that the majority of plaques either remained the same or became more echogenic (fibrous). Approximately one fourth of plaques in each group degenerated (more echolucent). Thirty-one patients (10.7%) developed new symptoms in the contralateral asymptomatic group, with 10 patients (3.5%) having strokes. Fourteen of 130 (10.8%) patients, or 5.4% of vessel territories at risk, in the primary asymptomatic group developed new symptoms, with only two strokes occurring. In the contralateral asymptomatic group those patients who initially had greater than 75% stenoses fared worse than those with primary asymptomatic disease with greater than 75% stenosis. Although the overall development of new symptoms is low in both populations, our data indicate that those patients with heterogeneous plaques or whose plaques have undergone change may be at risk for new symptoms. Longer follow-up studies are needed to define the role of plaque changes in the development of symptoms. For now we advocate a conservative "wait and see" approach to symptom-free patients with greater than 75% stenoses and calcified plaques. We suggest a more aggressive approach, recommending early surgical intervention, to those few patients with heterogeneous plaques.
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paper_title: Carotid plaque histology using real-time ultrasonography: Clinical and therapeutic implications☆☆☆

paper_content:

Abstract To evaluate the ability of ultrasonographic imaging to detect plaque hemorrhage in carotid atheroma, a study was undertaken that compared pathologic findings to preoperative ultrasonographic findings. Ultrasonography identified two plaque categories based on the heterogeneous and homogeneous echo patterns of the lesions studied. Heterogeneous lesions accounted for 91 percent of intraplaque hemorrhages (30 of 33) and 100 percent of ulcerated lesions (15 of 15). In 41 of 50 specimens (82 percent), ultrasonography correctly identified the presence or absence of plaque hemorrhage. False-negative studies (3 of 50) were due to the minute foci of remote hemorrhages. False-positive studies (6 of 50) resulted from plaques that contained large amounts of lipid or cholesterol. Preoperative ultrasound carotid imaging can be used to detect the histologic characteristics of plaque. Since recent clinicopathologic studies have implicated intraplaque hemorrhage and ulceration in symptomatic carotid disease, this information may be of value in choosing therapy, especially for the asymptomatic patient.
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paper_title: Characterization of symptomatic and asymptomatic carotid plaques using high-resolution real-time ultrasonography

paper_content:

High-resolution ultrasonography was used to classify carotid plaques into five different types in 72 patients with symptoms and in 49 without, and with stenosis of the origin of the internal carotid artery < 70 per cent. There were 72 plaques in the symptomatic group and 75 in the asymptomatic group. Type 1 plaques were uniformly echolucent, type 2 predominantly echolucent, type 3 predominantly echogenic, type 4 uniformly echogenic and type 5 consisted of plaques that could not be classified owing to heavy calcification and acoustic shadows. Type 1 Plaque was found in 90 per cent of patients with symptoms and in 10 per cent of those without, type 2 plaque was found in 53 and 47 per cent, type 3 in 34 and 66 per cent, and type 4 in 5 and 95 per cent respectively. The preponderance of echolucent plaques in symptomatic patients with stenosis < 70 per cent supports the hypothesis that this type of plaque is unstable and tends to embolize. In contrast, in patients without symptoms there is preponderance of echogenic plaques.
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paper_title: Morphological characterization of carotid artery stenoses by ultrasound duplex scanning

paper_content:

Abstract Ulcerations and intraplaque hemorrhages are thought to play an important role in the development of neurological deficits in carotid artery stenoses. To assess the ability of duplex scanning to predict plaque morphology we compared different sonographic criteria (plaque border, plaque density, plaque structure) with the morphological findings in 169 consecutive carotid endarterectomies (144 cases with diameter reduction > 50%). Two percent of the sonograms were inadequate, and 20% showed poor image quality. Regular plaque borders revealed a smooth or at most minimally ulcerated surface in 92%. Grossly ulcerated stenoses, however, were only found in 27% of the irregular plaques. Moreover, the plaque border was nonvisible in 35% of all cases. Simple, fibro-atheromatous plaques were found to be echogenic in 72% and echolucency was present in 80% of the stenoses with relevant intraplaque hemorrhage. In conclusion, duplex scanning proved to be capable of detecting smooth, fibro-atheromatous stenoses with high accuracy. Ulcerations, however, cannot be predicted reliably, and intraplaque hemorrhage cannot be differentiated from atheromatous debris.
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paper_title: Duplex scanning and plaque histology in cerebral ischaemia.

paper_content:

Twenty-seven patients undergoing carotid endarterectomy (21 M, 6 F), with a mean age of 62 years, were studied by carotid ultrasound imaging, angiography, and histological examination of endarterectomy specimens, including Perl's stain to detect haemorrhage more than a week old. Haemorrhage into a plaque was seen histologically in 21 patients (78%), compared with 19 (70%) diagnosed preoperatively as echolucent heterogeneous plaques on ultrasound imaging. The remainder were echogenic homogeneous, fibrous plaques. In only one case was the nature of the plaque diagnosed by contrast arteriography. Excised endarterectomy specimens were inspected independently of the ultrasound assessment to determine whether the site of haemorrhage communicated with the base of an atherosclerotic ulcer. Communicating haemorrhages were present in 9 of 11 with episodic symptoms and non-communicating haemorrhages in 7 of 10 patients with a single cerebrovascular event. Perl's stain showed recent haemorrhage in 7 of 11 patients with multiple symptoms, and old haemorrhage in 9 of 10 patients with a single event. These findings suggest that ultrasonically heterogeneous communicating carotid plaques are symptomatically more active than homogeneous non-communicating plaques.
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paper_title: Computer-assisted Carotid Plaque Analysis: Characteristics of Plaques Associated with Cerebrovascular Symptoms and Cerebral Infarction

paper_content:

OBJECTIVE: to correlate the echostructural characteristics of carotid plaques with neurological symptoms and cerebral infarcts. MATERIALS: one hundred and five plaques were studied in 74 patients by colour-flow duplex ultrasound: 39 were symptomatic and 37 were associated with brain infarction on CT scanning. METHODS: the images were digitalised for computer-assisted image standardisation and divided in homogenous (n=67) and heterogenous (n=38) groups. Parameters of the plaque image were analysed. RESULTS: global echogenicity was significantly lower in symptomatic and in CT(+)plaques (p<0.05). For homogenous plaques, an echogenic cap (EC) was visualised in 8.3% of symptomatic vs. 33.9% of asymptomatic (p<0. 05) and in 7.7% for plaques that were CT(+)vs. 37.7% for CT(-)(p<0. 05). Surface disruption was visualised in 50% of symptomatic vs. 8. 5% of asymptomatic (p=0.002) and in 46% of CT(+)vs. 9.4% of CT(-)plaques (p=0.002). For heterogenous plaques, the echolucent region was juxtaluminal in 67% of symptomatic and CT(+)plaques vs. 33% in asymptomatic and CT(-)(p<0.01). CONCLUSION: echolucent plaques are associated with a higher neurological risk. In homogenous plaques the absence of an echogenic cap and disruption of the plaque surface also correlates with symptoms. In heterogenous plaques, juxtaluminal location of the echolucent region is an additional marker of increased risk. (Less)
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paper_title: Carotid artery atheroma: comparison of preoperative B-mode ultrasound appearance with carotid endarterectomy specimen pathology.

paper_content:

Abstract This paper describes a prospective study comparing the preoperative Duplex ultrasound appearance of carotid bifurcation atheroma with the pathological characteristics found in the endarterectomy specimens of the same vessels. Initial studies of carotid atheroma using Duplex scanning classified plaques into heterogeneous and homogeneous and found a strong correlation between heterogeneous lesions and the presence of intraplaque haemorrhage or ulceration in the endarterectomy specimen. The B-mode classification of plaque appearance described in this paper is an expansion of the above classification. The study group comprised 220 patients who underwent 244 procedures. The indication for carotid endarterectomy was symptomatic disease in the great majority of cases. We found a high incidence of unstable plaque pathology in the operative specimens, and a predominance of the more echolucent ultrasound plaque appearances (types 1 and 2). There is a statistically significant relationship (p less than 0.001) between ultrasound appearance types 1 and 2 and the presence of either intraplaque haemorrhage or ulceration in the endarterectomy specimen.
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paper_title: Normalisation of ultrasonic images of atherosclerotic plaques and reproducibility of grey scale median using dedicated software.

paper_content:

AIM ::: Image normalization using ''Adobe Photoshop'' a commercially available software package designed for photography has provided the means of making reproducible measurements of grey scale in ultrasonic images of carotid bifurcation plaques. A dedicated software package ''Plaque Texture Analysis'' has been developed by the authors that is simple to use, provides facilities for measurement of other texture features in addition to grey scale median (GSM) and allows the operator to save the normalised images, plaques and GSM measurements in a database for subsequent analysis. The aim of the study was to determine (a) the intraobserver variability of GSM when the same plaque images were analysed using both Adobe Photoshop and the dedicated software and (b) the interobserver variability when the same plaque images were analysed using the dedicated software by different observers. ::: ::: ::: METHODS ::: A sample of 33 images of carotid bifurcation plaques (16 symptomatic and 17 asymptomatic) producing greater than 50% stenosis of the internal carotid artery were analysed by two observers. ::: ::: ::: RESULTS ::: The intraclass correlation coefficient and correlation coefficient (r) for GSM were 0.992 (95% CI 0.984 to 0.996) and 0.992 respectively for the first observer (MG); they were 0.986 (95% CI 0.972 to 0.993) and 0.987 respectively for the second observer (AN). The interobserver intraclass correlation coefficient and correlation coefficient (r) were 0.932 (95% CI 0.863 to 0.967) and 0.933 respectively. ::: ::: ::: CONCLUSION ::: These findings and the automatic saving of the normalised images and measurements in a database for subsequent statistical analysis make the ''Plaque Texture Analysis'' software a powerful research tool.
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paper_title: Hypoechoic plaque at US of the carotid artery: an independent risk factor for incident stroke in adults aged 65 years or older. Cardiovascular Health Study.

paper_content:

PURPOSE ::: To investigate the association between incident (first) stroke and the echogenicity of internal carotid arterial plaque at ultrasonography (US). ::: ::: ::: MATERIALS AND METHODS ::: A cohort of 4, 886 individuals who, at baseline, were 65 years of age or older and without symptoms of cerebrovascular disease was followed up for an average of 3.3 years. Baseline clinical findings were from color Doppler and duplex US studies of the carotid arteries and a record of traditional risk factors: age, sex, presence of diabetes mellitus, pack-years of cigarette smoking, presence of hypertension, elevated systolic and diastolic blood pressure, elevated low-density lipoprotein cholesterol level. ::: ::: ::: RESULTS ::: Incident strokes, excluding hemorrhagic strokes and strokes of cardiac origin, were seen in 104 individuals (2.1%) at risk. Age- and sex-adjusted odds ratios for incident stroke were significant for hypoechoic plaque (odds ratio, 2.53; 95% CI, 1,42,4.53). After controlling for risk factors in a Cox proportional hazards model, the relative risk (RR) of incident stroke was 1.72 (p = .015) for hypoechoic plaque and 2.32 (P = .004) for internal carotid arterial narrowing of at least 50%. In addition, hypoechoic plaque (RR, 2.78; CI, 1.36,5.69) and 50%-100% stenosis (RR, 3.08; CI, 1.28, 7.41) were associated with ipsilateral, nonfatal stroke. ::: ::: ::: CONCLUSION ::: In asymptomatic adults aged 65 years or older, that risk of incident stroke was associated with two US features: hypoechoic internal carotid arterial plaque and an estimated internal carotid arterial stenosis of 50%-100%.
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paper_title: Reproducibility of Computer-Quantified Carotid Plaque Echogenicity : Can We Overcome the Subjectivity?

paper_content:

BACKGROUND AND PURPOSE ::: We sought to assess the reproducibility, interobserver variability, and application to clinical studies of a new method for the quantitative assessment of carotid plaque echogenicity. ::: ::: ::: METHODS ::: Carotid plaques were scanned with the use of ultrasound, and their images were stored in a computer. They were normalized by assigning certain gray values to blood and adventitia, and the gray scale median (GSM) was used to quantify their echogenicity. The variability between storage media, between degrees of magnification, and between probes was assessed. The method was applied to 232 asymptomatic carotid plaques causing 60% to 99% stenosis in relation to the presence of ipsilateral CT-demonstrated brain infarcts. In all parts of the study the plaque GSM was measured before and after normalization to evaluate its effect. Interobserver agreement for the scanning process was assessed. ::: ::: ::: RESULTS ::: The GSM mean difference before and after normalization for variability studies of storage media, degrees of magnification, and probes was -14.5 and -0.12, 2.24 and 1.68, and -8.3 and -0.7, respectively. The median GSM of plaques associated with ipsilateral nonlacunar silent CT-demonstrated brain infarcts was 14, and that of plaques that were not so associated was 30 (P:=0.003). The interobserver GSM difference was -0.05 (95% CI, -1.7 to 1.6). ::: ::: ::: CONCLUSIONS ::: Our method decreases the variability between storage media and between probes but not the variability between degrees of magnification. It separates echomorphologically the carotid plaques associated with silent nonlacunar CT-demonstrated brain infarcts from plaques that are not so associated.
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paper_title: Repeated visual and computer-assisted carotid plaque characterization in a longitudinal population-based ultrasound study: the Tromsø study.

paper_content:

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.
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paper_title: Carotid Plaque Characterization by Duplex Scanning Observer Error May Undermine Current Clinical Trials

paper_content:

Background and Purpose—Clinical studies currently in progress are using subjective methods to characterize plaque morphology from ultrasound images. However, there are few studies on the intraobserver and interobserver variability of these classifications. This study was designed to assess these variables. Methods—Grading of plaque morphology from ultrasound images, stored both digitally and to hard copy, was performed by 2 classification schemes. Interobserver agreement was determined by 4 observers. Within-observer agreement was performed at intervals for up to 6 months. Accuracy of the 2 methods was determined by comparison with histology. Results—Within- and between-observer agreement was moderate to good for full-color digital image analyses, with pooled κ values of κp=0.49±0.10 and κp=0.62±0.07 for the 2-category method and κp=0.53±0.06 and κp=0.52±0.05 for the 4-category method, respectively. Hard copy data analyses gave lower κ values. The more experienced observers produced higher within-observer...
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paper_title: Comparability of the ultrasonic tissue characteristics of carotid plaques.

paper_content:

Hypoechoic carotid atherosclerotic plaques on ultrasonographic examination were found to be associated with cerebrovascular events. This underlines the need for an accurate evaluation of their echotexture characteristics. The objective of this study was to further validate a proposed method of normalization aiming to facilitate the comparability of these characteristics. The sonographic examination involved imaging of carotid plaques using duplex technique and capturing, digitization, and normalization in a computer in a standard way. In the first part, the interobserver and interscanner variability and the gainlevel variability within the ultrasound unit were examined, before and after normalization, in terms of plaque echotexture. The second part investigated the effect of normalization on the echotexture of 419 symptomatic and asymptomatic plaques. Our results indicated that the normalization reduced the interscanner variability and the gain-level variability. The interobserver variability was excellent. In addition, this process further distinguished the echotexture characteristics of symptomatic and asymptomatic carotid plaques, which encourages the use of this method in natural history studies in persons with asymptomatic carotid atherosclerotic disease, aiming to identify those at higher risk for stroke. These patients might benefit from a carotid endarterectomy. KEY WORDS: Carotid artery, plaque; Plaque, carotid; Stroke.
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paper_title: Reproducibility of Computer-Quantified Carotid Plaque Echogenicity : Can We Overcome the Subjectivity?

paper_content:

BACKGROUND AND PURPOSE ::: We sought to assess the reproducibility, interobserver variability, and application to clinical studies of a new method for the quantitative assessment of carotid plaque echogenicity. ::: ::: ::: METHODS ::: Carotid plaques were scanned with the use of ultrasound, and their images were stored in a computer. They were normalized by assigning certain gray values to blood and adventitia, and the gray scale median (GSM) was used to quantify their echogenicity. The variability between storage media, between degrees of magnification, and between probes was assessed. The method was applied to 232 asymptomatic carotid plaques causing 60% to 99% stenosis in relation to the presence of ipsilateral CT-demonstrated brain infarcts. In all parts of the study the plaque GSM was measured before and after normalization to evaluate its effect. Interobserver agreement for the scanning process was assessed. ::: ::: ::: RESULTS ::: The GSM mean difference before and after normalization for variability studies of storage media, degrees of magnification, and probes was -14.5 and -0.12, 2.24 and 1.68, and -8.3 and -0.7, respectively. The median GSM of plaques associated with ipsilateral nonlacunar silent CT-demonstrated brain infarcts was 14, and that of plaques that were not so associated was 30 (P:=0.003). The interobserver GSM difference was -0.05 (95% CI, -1.7 to 1.6). ::: ::: ::: CONCLUSIONS ::: Our method decreases the variability between storage media and between probes but not the variability between degrees of magnification. It separates echomorphologically the carotid plaques associated with silent nonlacunar CT-demonstrated brain infarcts from plaques that are not so associated.
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paper_title: The relative effect of carotid plaque heterogeneity and echogenicity on ipsilateral cerebral infarction and symptoms of cerebrovascular disease.

paper_content:

OBJECTIVE ::: To determine the relative effect of carotid plaque heterogeneity and echogenicity as measured by computer on the incidence of ipsilateral cerebral infarction and symptoms of cerebrovascular disease. ::: ::: ::: MATERIALS AND METHODS ::: 138 patients with 209 carotid plaques producing > 50% stenosis were studied. 110 plaques were from symptomatic sides. All patients had computer tomography (CT) brain scans. Images of the carotid plaques obtained by duplex scanner were transferred to a computer. Using an image analysis program plaque echogenicity, measured as the grey scale median (GSM) and heterogeneity, evaluated as the heterogeneity index (HI) was calculated. ::: ::: ::: RESULTS ::: 42% of plaques were associated with cerebral infarction. Symptomatic plaques and those associated with cerebral infarction were more echolucent and less heterogeneous than asymptomatic plaques and those not associated with cerebral infarction. Plaques with GSMs below or equal to 32 were associated with a significantly higher incidence of cerebral infarction. Plaques with GSMs below or equal to 32 were associated with a significantly higher incidence of cerebral infarction and symptoms of cerebrovascular disease than those with GSMs above this level (p < 0.01). Plaques with HIs below or equal to 20 were associated with a significantly higher incidence of symptoms of cerebrovascular disease as compared to those with HIs above this level (p < 0.01). ::: ::: ::: CONCLUSIONS ::: Computer analysis of carotid plaque morphology is an objective tool that can identify high risk plaques. The potential of such analysis in the identification of asymptomatic patients with advanced carotid stenosis at a high risk of stroke should be explored in a natural history study.
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paper_title: Comparability of the ultrasonic tissue characteristics of carotid plaques.

paper_content:

Hypoechoic carotid atherosclerotic plaques on ultrasonographic examination were found to be associated with cerebrovascular events. This underlines the need for an accurate evaluation of their echotexture characteristics. The objective of this study was to further validate a proposed method of normalization aiming to facilitate the comparability of these characteristics. The sonographic examination involved imaging of carotid plaques using duplex technique and capturing, digitization, and normalization in a computer in a standard way. In the first part, the interobserver and interscanner variability and the gainlevel variability within the ultrasound unit were examined, before and after normalization, in terms of plaque echotexture. The second part investigated the effect of normalization on the echotexture of 419 symptomatic and asymptomatic plaques. Our results indicated that the normalization reduced the interscanner variability and the gain-level variability. The interobserver variability was excellent. In addition, this process further distinguished the echotexture characteristics of symptomatic and asymptomatic carotid plaques, which encourages the use of this method in natural history studies in persons with asymptomatic carotid atherosclerotic disease, aiming to identify those at higher risk for stroke. These patients might benefit from a carotid endarterectomy. KEY WORDS: Carotid artery, plaque; Plaque, carotid; Stroke.
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paper_title: Normalisation of ultrasonic images of atherosclerotic plaques and reproducibility of grey scale median using dedicated software.

paper_content:

AIM ::: Image normalization using ''Adobe Photoshop'' a commercially available software package designed for photography has provided the means of making reproducible measurements of grey scale in ultrasonic images of carotid bifurcation plaques. A dedicated software package ''Plaque Texture Analysis'' has been developed by the authors that is simple to use, provides facilities for measurement of other texture features in addition to grey scale median (GSM) and allows the operator to save the normalised images, plaques and GSM measurements in a database for subsequent analysis. The aim of the study was to determine (a) the intraobserver variability of GSM when the same plaque images were analysed using both Adobe Photoshop and the dedicated software and (b) the interobserver variability when the same plaque images were analysed using the dedicated software by different observers. ::: ::: ::: METHODS ::: A sample of 33 images of carotid bifurcation plaques (16 symptomatic and 17 asymptomatic) producing greater than 50% stenosis of the internal carotid artery were analysed by two observers. ::: ::: ::: RESULTS ::: The intraclass correlation coefficient and correlation coefficient (r) for GSM were 0.992 (95% CI 0.984 to 0.996) and 0.992 respectively for the first observer (MG); they were 0.986 (95% CI 0.972 to 0.993) and 0.987 respectively for the second observer (AN). The interobserver intraclass correlation coefficient and correlation coefficient (r) were 0.932 (95% CI 0.863 to 0.967) and 0.933 respectively. ::: ::: ::: CONCLUSION ::: These findings and the automatic saving of the normalised images and measurements in a database for subsequent statistical analysis make the ''Plaque Texture Analysis'' software a powerful research tool.
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paper_title: Reproducibility of Computer-Quantified Carotid Plaque Echogenicity : Can We Overcome the Subjectivity?

paper_content:

BACKGROUND AND PURPOSE ::: We sought to assess the reproducibility, interobserver variability, and application to clinical studies of a new method for the quantitative assessment of carotid plaque echogenicity. ::: ::: ::: METHODS ::: Carotid plaques were scanned with the use of ultrasound, and their images were stored in a computer. They were normalized by assigning certain gray values to blood and adventitia, and the gray scale median (GSM) was used to quantify their echogenicity. The variability between storage media, between degrees of magnification, and between probes was assessed. The method was applied to 232 asymptomatic carotid plaques causing 60% to 99% stenosis in relation to the presence of ipsilateral CT-demonstrated brain infarcts. In all parts of the study the plaque GSM was measured before and after normalization to evaluate its effect. Interobserver agreement for the scanning process was assessed. ::: ::: ::: RESULTS ::: The GSM mean difference before and after normalization for variability studies of storage media, degrees of magnification, and probes was -14.5 and -0.12, 2.24 and 1.68, and -8.3 and -0.7, respectively. The median GSM of plaques associated with ipsilateral nonlacunar silent CT-demonstrated brain infarcts was 14, and that of plaques that were not so associated was 30 (P:=0.003). The interobserver GSM difference was -0.05 (95% CI, -1.7 to 1.6). ::: ::: ::: CONCLUSIONS ::: Our method decreases the variability between storage media and between probes but not the variability between degrees of magnification. It separates echomorphologically the carotid plaques associated with silent nonlacunar CT-demonstrated brain infarcts from plaques that are not so associated.
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paper_title: The objective characterisation of ultrasonic carotid plaque features.

paper_content:

Objective: To determine the influence of ultrasonic carotid plaque morphology on the incidence of ipsilateral hemispheric symptoms (IHS). Design: Cross-sectional study. Materials: A consecutive series of 80 patients (96 plaques) with more than 50% ICA stenosis was studied. Methods: B mode ultrasonic images were captured and transferred to a computer on magneto-optic disk and standardised using linear scaling so that adventitia would have a grey scale median (GSM) value of 185–195 and blood 0–5. The GSM and the percentage of echolucent pixels (PEP) in plaques were determined to measure echodensity. Homogeneity, entropy, and contrast were also determined to measure spatial distribution (heterogeneity) of grey shades in each plaque. Each measurement was correlated to presence or absence of IHS. Results: Twenty-five plaques were associated with IHS and 71 plaques were asymptomatic. In symptomatic plaques the mean of GSM was 23 and the mean of PEP was 70%, compared to 38 and 55% respectively in asymptomatic plaques ( p =0.02; Wilcoxon test). Sixty per cent of symptomatic plaques were associated with a homogeneity, entropy, and contrast values of >0.2, p =0.001) that are related to presence or absence of IHS. Conclusion: This study indicates that computer aided analysis of ultrasonic B mode features of carotid plaques could identify a potentially high-risk subgroup (patients with IHS). A GSM less than 40 or PEP greater than 50% is a good predictor of IHS related to carotid plaques. The fact that these measurements are operator independent and performed after image standardisation should encourage their use in multicentre clinical trials where different operators and equipment are used.
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paper_title: Some fundamental properties of speckle

paper_content:

A speckle pattern formed in polarized monochromatic light may be regarded as resulting from a classical random walk in the complex plane. The resulting irradiance fluctuations obey negative exponential statistics, with ratio of standard deviation to mean (i.e., contrast) of unity. Reduction of this contrast, or smoothing of the speckle, requires diversity in polarization, space, frequency, or time. Addition of M uncorrelated speckle patterns on an intensity basis can reduce the contrast by 1/√M. However, addition of speckle patterns on a complex amplitude basis provides no reduction of contrast. The distribution of scale sizes in a speckle pattern (i.e., the Wiener spectrum) is investigated from a physical point of view.
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paper_title: Ultrasound image segmentation: a survey

paper_content:

This paper reviews ultrasound segmentation methods, in a broad sense, focusing on techniques developed for medical B-mode ultrasound images. First, we present a review of articles by clinical application to highlight the approaches that have been investigated and degree of validation that has been done in different clinical domains. Then, we present a classification of methodology in terms of use of prior information. We conclude by selecting ten papers which have presented original ideas that have demonstrated particular clinical usefulness or potential specific to the ultrasound segmentation problem
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paper_title: An Integrated System for the Segmentation of Atherosclerotic Carotid Plaque

paper_content:

The robust border identification of atherosclerotic carotid plaque, the corresponding degree of stenosis of the common carotid artery (CCA), and also the characteristics of the arterial wall, including plaque size, composition, and elasticity, have significant clinical relevance for the assessment of future cardiovascular events. To facilitate the follow-up and analysis of the carotid stenosis in serial clinical investigations, we propose and evaluate an integrated system for the segmentation of atherosclerotic carotid plaque in ultrasound videos of the CCA based on video frame normalization, speckle reduction filtering, M-mode state-based identification, parametric active contours, and snake segmentation. Initially, the cardiac cycle in each video is identified and the video M-mode is generated, thus identifying systolic and diastolic states. The video is then segmented for a time period of at least one full cardiac cycle. The algorithm is initialized in the first video frame of the cardiac cycle, with human assistance if needed, and the moving atherosclerotic plaque borders are tracked and segmented in the subsequent frames. Two different initialization methods are investigated in which initial contours are estimated every 20 video frames. In the first initialization method, the initial snake contour is estimated using morphology operators; in the second initialization method, the Chan-Vese active contour model is used. The performance of the algorithm is evaluated on 43 real CCA digitized videos from B-mode longitudinal ultrasound segments and is compared with the manual segmentations of an expert, available every 20 frames in a time span of 3 to 5 s, covering, in general, 2 cardiac cycles. The segmentation results were very satisfactory, according to the expert objective evaluation, for the two different methods investigated, with true-negative fractions (TNF-specificity) of 83.7 ± 7.6% and 84.3 ± 7.5%; true-positive fractions (TPF-sensitivity) of 85.42 ± 8.1% and 86.1 ± 8.0%; and between the ground truth and the proposed segmentation method, kappa indices (KI) of 84.6% and 85.3% and overlap indices of 74.7% and 75.4%. The segmentation contours were also used to compute the cardiac state identification and radial, longitudinal, and shear strain indices for the CCA wall and plaque between the asymptomatic and symptomatic groups were investigated. The results of this study show that the integrated system investigated in this study can be successfully used for the automated video segmentation of the CCA plaque in ultrasound videos.
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paper_title: Digital Image Enhancement and Noise Filtering by Use of Local Statistics

paper_content:

Computational techniques involving contrast enhancement and noise filtering on two-dimensional image arrays are developed based on their local mean and variance. These algorithms are nonrecursive and do not require the use of any kind of transform. They share the same characteristics in that each pixel is processed independently. Consequently, this approach has an obvious advantage when used in real-time digital image processing applications and where a parallel processor can be used. For both the additive and multiplicative cases, the a priori mean and variance of each pixel is derived from its local mean and variance. Then, the minimum mean-square error estimator in its simplest form is applied to obtain the noise filtering algorithms. For multiplicative noise a statistical optimal linear approximation is made. Experimental results show that such an assumption yields a very effective filtering algorithm. Examples on images containing 256 × 256 pixels are given. Results show that in most cases the techniques developed in this paper are readily adaptable to real-time image processing.
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paper_title: Speckle in ultrasound B-mode scans

paper_content:

Ultrasound images obtained with a simple linear or sector scan show a granular appearance, called "speckle." This speckle is analyzed. The reduction in speckle that can be obtained with a compound scan with maximum amplitude writing is computed. The reduction in speckle is almost as large as can be obtained with averaging. It depends on the number of independent amplitude values that are measured. The condition for the independence of two amplitude values is derived, and thus a limit is given for the possible reduction in speckle.
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paper_title: Visual and quantitative evaluation of selected image combination schemes in ultrasound spatial compound scanning

paper_content:

Multi-angle spatial compound images are normally generated by averaging the recorded single-angle images (SAIs). To exploit possible advantages associated with alternative combination schemes, this paper investigates both the effect of number of angles (N/sub /spl theta//) as well as operator (mean, median, mean-excluding-maximum (mem), root-mean-square (rms), geometric mean and maximum) on image quality (tissue delineation and artifacts), speckle signal-to-noise ratio (SNR/sub s/) and contrast. The evaluation is based on in vitro SAI (/spl plusmn/21/spl deg/ in steps of /spl Delta//spl theta/=7/spl deg/) of formalin fixed porcine tissue containing adipose, connective and muscular tissue. Image quality increased with number of angles up to /spl plusmn/14/spl deg/ after which the improvements became debatable. The mem and median operators, which try to render the images more quantitatively correct by suppressing strong echoes from specular reflectors, provide some improvement in this regard. When combining the SAI with the mean operator, the SNR/sub s/ increases-in general-with N/sub /spl theta//. For N/sub /spl theta//=2, the SNR/sub s/ increases with /spl Delta//spl theta/ as expected. When N/sub /spl theta//=7, the highest SNR/sub s/ is obtained for the mem, rms, and geometric mean operators, while the lowest SNR/sub s/ is obtained for the maximum operator. When comparing SNR/sub s/ for adipose and fibrous tissue, the level is close to 1.91 for adipose tissue but only 1.7 for fibrous tissue which contain relatively few organized scattering structures.
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paper_title: Ultrasonic classification of carotid plaques causing less than 60% stenosis according to ultrasound morphology and events.

paper_content:

Abstract Carotid plaque morphology studied by ultrasound has been used to classify 3 types of bifurcation plaques, producing less than 60% stenosis on duplex scanning: Type A, the homogeneous, highly echogenic plaque; Type B, the heterogeneous (mainly echogenic, B-1 or mainly echolucent, B-2) plaque; Type C, the complex plaque with irregular surface, echogenic and/or echolucent with calcifications. One hundred asymptomatic subjects in each plaque group were included in a prospective 4-year follow-up study to evaluate clinical events and brain damage by yearly cerebral CT and MR scans. After four years 96 subjects with type A plaque, 89 with type B-1 and 67 with type C plaques completed the study. While there were no clinical events or positive cerebral scans in subjects with type A plaques there was a significantly increasing number of cerebral and vascular events in subjects with plaque B and C type with a zero mortality in the plaque A group, a 2.24% mortality in type B plaques and a significantly higher (p > 0.05) mortality (13.4%) in type C plaques. CT and MR scans revealed brain damage which had been totally asymptomatic with MR detecting a larger number of lesions. Also the number of cerebral lesions observed by CT/MR were significantly greater than the number of recorded clinical episodes. ECG stress test revealed a larger number of asymptomatic coronary disease in the C type plaques. In conclusion ultrasound plaque morphology is linked to different incidences of cerebral and cardiac events, brain damage and asymptomatic coronary disease. Also CT and MR may reveal lesions which do not cause signs or symptoms.
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paper_title: Statistics of Speckle in Ultrasound B-Scans

paper_content:

the of the magnitude, i.e., intensity, of the field.) It is shown that Rayleigh statistics govern the fist-order behavior of the magnitude; and the autocorrelation of the resulting image speckle is obtained by the methodof Middleton. The corresponding power spectrum follows immediately by Fourier transformation. Theoretical and experimentally determined autocorrelation functions and power spectra derived from B-scans of a scattering phantom containing many scatterers per resolution cell are presented. These functions lead naturally to the definition of the average speckle spot or cell sue, and this inturn is comparable to the resolution cell. Each independent speckle servesas a degreeof freedom that determines the number of samples of tissue available over a target.As the speckle cell size decreases this number increases in a manner predictable from the physical parameters of the cell size. However, it is found that the speckle cellis broadened, the degrees of freedom diminished, when the object structureis correlated. This yields the possibilityof deducing information about the object structure from the second-order statistics of the speckle texture, in addition to that obtainable from the fiistorder statistics.
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paper_title: Snakes based segmentation of the common carotid artery intima media

paper_content:

Ultrasound measurements of the human carotid artery walls are conventionally obtained by manually tracing interfaces between tissue layers. In this study we present a snakes segmentation technique for detecting the intima-media layer of the far wall of the common carotid artery (CCA) in longitudinal ultrasound images, by applying snakes, after normalization, speckle reduction, and normalization and speckle reduction. The proposed technique utilizes an improved snake initialization method, and an improved validation of the segmentation method. We have tested and clinically validated the segmentation technique on 100 longitudinal ultrasound images of the carotid artery based on manual measurements by two vascular experts, and a set of different evaluation criteria based on statistical measures and univariate statistical analysis. The results showed that there was no significant difference between all the snakes segmentation measurements and the manual measurements. For the normalized despeckled images, better snakes segmentation results with an intra-observer error of 0.08, a coefficient of variation of 12.5%, best Bland-Altman plot with smaller differences between experts (0.01, 0.09 for Expert1 and Expert 2, respectively), and a Hausdorff distance of 5.2, were obtained. Therefore, the pre-processing of ultrasound images of the carotid artery with normalization and speckle reduction, followed by the snakes segmentation algorithm can be used successfully in the measurement of IMT complementing the manual measurements. The present results are an expansion of data published earlier as an extended abstract in IFMBE Proceedings (Loizou et al. IEEE Int X Mediterr Conf Medicon Med Biol Eng POS-03 499:1-4, 2004).
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paper_title: Comparative evaluation of despeckle filtering in ultrasound imaging of the carotid artery

paper_content:

It is well-known that speckle is a multiplicative noise that degrades the visual evaluation in ultrasound imaging. The recent advancements in ultrasound instrumentation and portable ultrasound devices necessitate the need of more robust despeckling techniques for enhanced ultrasound medical imaging for both routine clinical practice and teleconsultation. The objective of this work was to carry out a comparative evaluation of despeckle filtering based on texture analysis, image quality evaluation metrics, and visual evaluation by medical experts in the assessment of 440 (220 asymptomatic and 220 symptomatic) ultrasound images of the carotid artery bifurcation. In this paper a total of 10 despeckle filters were evaluated based on local statistics, median filtering, pixel homogeneity, geometric filtering, homomorphic filtering, anisotropic diffusion, nonlinear coherence diffusion, and wavelet filtering. The results of this study suggest that the first order statistics filter lsmv, gave the best performance, followed by the geometric filter gf4d, and the homogeneous mask area filter lsminsc. These filters improved the class separation between the asymptomatic and the symptomatic classes based on the statistics of the extracted texture features, gave only a marginal improvement in the classification success rate, and improved the visual assessment carried out by the two experts. More specifically, filters lsmv or gf4d can be used for despeckling asymptomatic images in which the expert is interested mainly in the plaque composition and texture analysis; and filters lsmv, gf4d, or lsminsc can be used for the despeckling of symptomatic images in which the expert is interested in identifying the degree of stenosis and the plaque borders. The proper selection of a despeckle filter is very important in the enhancement of ultrasonic imaging of the carotid artery. Further work is needed to evaluate at a larger scale and in clinical practice the performance of the proposed despeckle filters in the automated segmentation, texture analysis, and classification of carotid ultrasound imaging.
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paper_title: Adaptive filtering for reduction of speckle in ultrasonic pulse-echo images

paper_content:

Abstract Current medical ultrasonic scanning instrumentation permits the display of fine image detail (speckle) which does not transfer useful information but degrades the apparent low contrast resolution in the image. An adaptive two-dimensional filter has been developed which uses local features of image texture to recognize and maximally low-pass filter those parts of the image which correspond to fully developed speckle, while substantially preserving information associated with resolved-object structure. A first implementation of the filter is described which uses the ratio of the local variance and the local mean as the speckle recognition feature. Preliminary results of applying this form of display processing to medical ultrasound images are very encouraging; it appears that the visual perception of features such as small discrete structures, subtle fluctuations in mean echo level and changes in image texture may be enhanced relative to that for unprocessed images.
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paper_title: Despeckle Filtering Algorithms and Software for Ultrasound Imaging

paper_content:

Abstract It is well-known that speckle is a multiplicative noise that degrades image quality and the visual evaluation in ultrasound imaging. This necessitates the need for robust despeckling techniques for both routine clinical practice and teleconsultation. The goal for this book is to introduce the theoretical background (equations), the algorithmic steps, and the MATLAB™ code for the following group of despeckle filters: linear filtering, nonlinear filtering, anisotropic diffusion filtering and wavelet filtering. The book proposes a comparative evaluation framework of these despeckle filters based on texture analysis, image quality evaluation metrics, and visual evaluation by medical experts, in the assessment of cardiovascular ultrasound images recorded from the carotid artery. The results of our work presented in this book, suggest that the linear local statistics filter DsFlsmv, gave the best performance, followed by the nonlinear geometric filter DsFgf4d, and the linear homogeneous mask area filte...
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paper_title: A versatile technique for visual enhancement of medical ultrasound images

paper_content:

The paper presents a versatile wavelet domain despeckling technique to visually enhance the medical ultrasound (US) images for improving the clinical diagnosis. The method uses the two-sided generalized Nakagami distribution (GND) for modeling the speckle wavelet coefficients and the signal wavelet coefficients are approximated using the generalized Gaussian distribution (GGD). Combining these statistical priors with the Bayesian maximum a posteriori (MAP) criterion, the thresholding/shrinkage estimators are derived for processing the wavelet coefficients of detail subbands. Consequently, two blind speckle suppressors named as GNDThresh and GNDShrink have been implemented and evaluated on both the artificial speckle simulated images and real US images. The experimental results demonstrate the superiority of the suggested technique both quantitatively and qualitatively as compared to other competitive schemes reported in the image denoising literature, e.g., the proposed method yields a gain of more than 0.36 dB over the best state-of-the-art despeckling method (GenLik), 0.93 dB over SRAD filter, 2.35 dB over Lee filter, and 1.34 dB over Kuan filter in terms of signal-to-noise ratio, when tested on the realistic US images. The visual comparison of despeckled US images and the higher values of quality metrics (coefficient of correlation, edge preservation index, quality index, and structural similarity index) indicate that the new method suppresses the speckle noise well while preserving the texture and organ surfaces. Further, the proposed method will be evaluated on other class of images as well as by employing multiple observer evaluation.
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paper_title: Quality evaluation of ultrasound imaging in the carotid artery based on normalization and speckle reduction filtering

paper_content:

Image quality is important when evaluating ultrasound images of the carotid for the assessment of the degree of atherosclerotic disease, or when transferring images through a telemedicine channel, and/or in other image processing tasks. The objective of this study was to investigate the usefulness of image quality evaluation based on image quality metrics and visual perception, in ultrasound imaging of the carotid artery after normalization and speckle reduction filtering. Image quality was evaluated based on statistical and texture features, image quality evaluation metrics, and visual perception evaluation made by two experts. These were computed on 80 longitudinal ultrasound images of the carotid bifurcation recorded from two different ultrasound scanners, the HDI ATL-3000 and the HDI ATL-5000 scanner, before (NF) and after (DS) speckle reduction filtering, after normalization (N), and after normalization and speckle reduction filtering (NDS). The results of this study showed that: (1) the normalized speckle reduction, NDS, images were rated visually better on both scanners; (2) the NDS images showed better statistical and texture analysis results on both scanners; (3) better image quality evaluation results were obtained between the original (NF) and normalized (N) images, i.e. NF-N, for both scanners, followed by the NF-DS images for the ATL HDI-5000 scanner and the NF-DS on the HDI ATL-3000 scanner; (4) the ATL HDI-5000 scanner images have considerable higher entropy than the ATL HDI-3000 scanner and thus more information content. However, based on the visual evaluation by the two experts, both scanners were rated similarly. The above findings are also in agreement with the visual perception evaluation, carried out by the two vascular experts. The results of this study showed that ultrasound image normalization and speckle reduction filtering are important preprocessing steps favoring image quality, and should be further investigated.
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paper_title: The relative effect of carotid plaque heterogeneity and echogenicity on ipsilateral cerebral infarction and symptoms of cerebrovascular disease.

paper_content:

OBJECTIVE ::: To determine the relative effect of carotid plaque heterogeneity and echogenicity as measured by computer on the incidence of ipsilateral cerebral infarction and symptoms of cerebrovascular disease. ::: ::: ::: MATERIALS AND METHODS ::: 138 patients with 209 carotid plaques producing > 50% stenosis were studied. 110 plaques were from symptomatic sides. All patients had computer tomography (CT) brain scans. Images of the carotid plaques obtained by duplex scanner were transferred to a computer. Using an image analysis program plaque echogenicity, measured as the grey scale median (GSM) and heterogeneity, evaluated as the heterogeneity index (HI) was calculated. ::: ::: ::: RESULTS ::: 42% of plaques were associated with cerebral infarction. Symptomatic plaques and those associated with cerebral infarction were more echolucent and less heterogeneous than asymptomatic plaques and those not associated with cerebral infarction. Plaques with GSMs below or equal to 32 were associated with a significantly higher incidence of cerebral infarction. Plaques with GSMs below or equal to 32 were associated with a significantly higher incidence of cerebral infarction and symptoms of cerebrovascular disease than those with GSMs above this level (p < 0.01). Plaques with HIs below or equal to 20 were associated with a significantly higher incidence of symptoms of cerebrovascular disease as compared to those with HIs above this level (p < 0.01). ::: ::: ::: CONCLUSIONS ::: Computer analysis of carotid plaque morphology is an objective tool that can identify high risk plaques. The potential of such analysis in the identification of asymptomatic patients with advanced carotid stenosis at a high risk of stroke should be explored in a natural history study.
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paper_title: Ultrasound image segmentation: a survey

paper_content:

This paper reviews ultrasound segmentation methods, in a broad sense, focusing on techniques developed for medical B-mode ultrasound images. First, we present a review of articles by clinical application to highlight the approaches that have been investigated and degree of validation that has been done in different clinical domains. Then, we present a classification of methodology in terms of use of prior information. We conclude by selecting ten papers which have presented original ideas that have demonstrated particular clinical usefulness or potential specific to the ultrasound segmentation problem
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paper_title: An Integrated System for the Segmentation of Atherosclerotic Carotid Plaque

paper_content:

The robust border identification of atherosclerotic carotid plaque, the corresponding degree of stenosis of the common carotid artery (CCA), and also the characteristics of the arterial wall, including plaque size, composition, and elasticity, have significant clinical relevance for the assessment of future cardiovascular events. To facilitate the follow-up and analysis of the carotid stenosis in serial clinical investigations, we propose and evaluate an integrated system for the segmentation of atherosclerotic carotid plaque in ultrasound videos of the CCA based on video frame normalization, speckle reduction filtering, M-mode state-based identification, parametric active contours, and snake segmentation. Initially, the cardiac cycle in each video is identified and the video M-mode is generated, thus identifying systolic and diastolic states. The video is then segmented for a time period of at least one full cardiac cycle. The algorithm is initialized in the first video frame of the cardiac cycle, with human assistance if needed, and the moving atherosclerotic plaque borders are tracked and segmented in the subsequent frames. Two different initialization methods are investigated in which initial contours are estimated every 20 video frames. In the first initialization method, the initial snake contour is estimated using morphology operators; in the second initialization method, the Chan-Vese active contour model is used. The performance of the algorithm is evaluated on 43 real CCA digitized videos from B-mode longitudinal ultrasound segments and is compared with the manual segmentations of an expert, available every 20 frames in a time span of 3 to 5 s, covering, in general, 2 cardiac cycles. The segmentation results were very satisfactory, according to the expert objective evaluation, for the two different methods investigated, with true-negative fractions (TNF-specificity) of 83.7 ± 7.6% and 84.3 ± 7.5%; true-positive fractions (TPF-sensitivity) of 85.42 ± 8.1% and 86.1 ± 8.0%; and between the ground truth and the proposed segmentation method, kappa indices (KI) of 84.6% and 85.3% and overlap indices of 74.7% and 75.4%. The segmentation contours were also used to compute the cardiac state identification and radial, longitudinal, and shear strain indices for the CCA wall and plaque between the asymptomatic and symptomatic groups were investigated. The results of this study show that the integrated system investigated in this study can be successfully used for the automated video segmentation of the CCA plaque in ultrasound videos.
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paper_title: Real-time Measurement System for Evaluation of the Carotid Intima-Media Thickness With a Robust Edge Operator

paper_content:

OBJECTIVE ::: The purpose of this report is to describe an automatic real-time system for evaluation of the carotid intima-media thickness (CIMT) characterized by 3 main features: minimal interobserver and intraobserver variability, real-time capabilities, and great robustness against noise. ::: ::: ::: METHODS ::: One hundred fifty carotid B-mode ultrasound images were used to validate the system. Two skilled operators were involved in the analysis. Agreement with the gold standard, defined as the mean of 2 manual measurements of a skilled operator, and the interobserver and intraobserver variability were quantitatively evaluated by regression analysis and Bland-Altman statistics. ::: ::: ::: RESULTS ::: The automatic measure of the CIMT showed a mean bias +/- SD of 0.001 +/- 0.035 mm toward the manual measurement. The intraobserver variability, evaluated with Bland-Altman plots, showed a bias that was not significantly different from 0, whereas the SD of the differences was greater in the manual analysis (0.038 mm) than in the automatic analysis (0.006 mm). For interobserver variability, the automatic measurement had a bias that was not significantly different from 0, with a satisfactory SD of the differences (0.01 mm), whereas in the manual measurement, a little bias was present (0.012 mm), and the SD of the differences was noticeably greater (0.044 mm). ::: ::: ::: CONCLUSIONS ::: The CIMT has been accepted as a noninvasive marker of early vascular alteration. At present, the manual approach is largely used to estimate CIMT values. However, that method is highly operator dependent and time-consuming. For these reasons, we developed a new system for the CIMT measurement that conjugates precision with real-time analysis, thus providing considerable advantages in clinical practice.
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paper_title: Using Snakes to Detect the Intimal and Adventitial Layers of the Common Carotid Artery Wall in Sonographic Images

paper_content:

This study presents an innovative automatic system for detecting the intima-media complex of the far wall of the common carotid artery by applying the snake techniques. Cohen's snake was modified and some criteria were added for our applications. In addition, the oscillating problem of using snakes was solved by properly choosing the time step from analysis of the frequency response of the filters. A time-diminishing gravity window, external forces, and a cost function assist the snake in selecting the optimal shape of intimal and adventitia layers. We compared the proposed snake and ziplock snake with respect to the manual extraction contour. The results show that the system can automatically detect the intimal and adventitial layers without any manual correction.
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paper_title: Snakes based segmentation of the common carotid artery intima media

paper_content:

Ultrasound measurements of the human carotid artery walls are conventionally obtained by manually tracing interfaces between tissue layers. In this study we present a snakes segmentation technique for detecting the intima-media layer of the far wall of the common carotid artery (CCA) in longitudinal ultrasound images, by applying snakes, after normalization, speckle reduction, and normalization and speckle reduction. The proposed technique utilizes an improved snake initialization method, and an improved validation of the segmentation method. We have tested and clinically validated the segmentation technique on 100 longitudinal ultrasound images of the carotid artery based on manual measurements by two vascular experts, and a set of different evaluation criteria based on statistical measures and univariate statistical analysis. The results showed that there was no significant difference between all the snakes segmentation measurements and the manual measurements. For the normalized despeckled images, better snakes segmentation results with an intra-observer error of 0.08, a coefficient of variation of 12.5%, best Bland-Altman plot with smaller differences between experts (0.01, 0.09 for Expert1 and Expert 2, respectively), and a Hausdorff distance of 5.2, were obtained. Therefore, the pre-processing of ultrasound images of the carotid artery with normalization and speckle reduction, followed by the snakes segmentation algorithm can be used successfully in the measurement of IMT complementing the manual measurements. The present results are an expansion of data published earlier as an extended abstract in IFMBE Proceedings (Loizou et al. IEEE Int X Mediterr Conf Medicon Med Biol Eng POS-03 499:1-4, 2004).
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paper_title: Real-Time Vessel Segmentation and Tracking for Ultrasound Imaging Applications

paper_content:

A method for vessel segmentation and tracking in ultrasound images using Kalman filters is presented. A modified Star-Kalman algorithm is used to determine vessel contours and ellipse parameters using an extended Kalman filter with an elliptical model. The parameters can be used to easily calculate the transverse vessel area which is of clinical use. A temporal Kalman filter is used for tracking the vessel center over several frames, using location measurements from a handheld sensorized ultrasound probe. The segmentation and tracking have been implemented in real-time and validated using simulated ultrasound data with known features and real data, for which expert segmentation was performed. Results indicate that mean errors between segmented contours and expert tracings are on the order of 1%-2% of the maximum feature dimension, and that the transverse cross-sectional vessel area as computed from estimated ellipse parameters a, b as determined by our algorithm is within 10% of that determined by experts. The location of the vessel center was tracked accurately for a range of speeds from 1.4 to 11.2 mm/s.
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paper_title: Comparative evaluation of despeckle filtering in ultrasound imaging of the carotid artery

paper_content:

It is well-known that speckle is a multiplicative noise that degrades the visual evaluation in ultrasound imaging. The recent advancements in ultrasound instrumentation and portable ultrasound devices necessitate the need of more robust despeckling techniques for enhanced ultrasound medical imaging for both routine clinical practice and teleconsultation. The objective of this work was to carry out a comparative evaluation of despeckle filtering based on texture analysis, image quality evaluation metrics, and visual evaluation by medical experts in the assessment of 440 (220 asymptomatic and 220 symptomatic) ultrasound images of the carotid artery bifurcation. In this paper a total of 10 despeckle filters were evaluated based on local statistics, median filtering, pixel homogeneity, geometric filtering, homomorphic filtering, anisotropic diffusion, nonlinear coherence diffusion, and wavelet filtering. The results of this study suggest that the first order statistics filter lsmv, gave the best performance, followed by the geometric filter gf4d, and the homogeneous mask area filter lsminsc. These filters improved the class separation between the asymptomatic and the symptomatic classes based on the statistics of the extracted texture features, gave only a marginal improvement in the classification success rate, and improved the visual assessment carried out by the two experts. More specifically, filters lsmv or gf4d can be used for despeckling asymptomatic images in which the expert is interested mainly in the plaque composition and texture analysis; and filters lsmv, gf4d, or lsminsc can be used for the despeckling of symptomatic images in which the expert is interested in identifying the degree of stenosis and the plaque borders. The proper selection of a despeckle filter is very important in the enhancement of ultrasonic imaging of the carotid artery. Further work is needed to evaluate at a larger scale and in clinical practice the performance of the proposed despeckle filters in the automated segmentation, texture analysis, and classification of carotid ultrasound imaging.
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paper_title: Extraction of intima- media layer of arteria- carotis and evaluation of its thickness using active contour approach

paper_content:

A non invasive B-mode ultrasonic imaging of arteria- carotis is used for extracting the Intima -media layer and evaluation of its thickness using contour approach has been proposed in this paper. Analysis of carotid artery wall plays a major role in clinical practices. An accurate segmentation of the different layers of the common carotid artery (CCA) is needed since the intima-media thickness is a risk index for some of the most severe acute cerebrovascular and cardiovascular pathologies. A wide variety of algorithms for the carotid artery wall segmentation have been proposed, but they require a certain degree of manual adjustments in fixing the markers in the artery walls. This paper proposes a novel approach to segment the carotid artery wall without manual interruption. It has been designed for the extraction of intima and media layers of the carotid wall for normal and abnormal subjects. A contour approach can be successfully used in evaluating the intima-media thickness (IMT). The magnitudes of the IMT values have been used to explore the rate of prediction of blockage existing in the cerebrovascular and cardiovascular pathologies and also hypertension and atherosclerosis. The performance of the algorithm is evaluated on a set of images.
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paper_title: User-independent plaque characterization and accurate IMT measurement of carotid artery wall using ultrasound.

paper_content:

Non-invasive plaque characterization of the carotid wall is crucial for the early assessment of pathology, as well as for the monitoring of the progression of a degenerative phenomenon. Specifically, in clinical practice the carotid wall status is assessed by means of B-Mode ultrasound scans. We recently implemented an algorithm for the segmentation of the common tract of the carotid wall using ultrasound relative to healthy subjects. This paper presents a superior strategy for plaque characterization, which accurately determines both echolucent-type II and echogenic plaques in pathologic subjects. We preserve both user-independence and pixel fuzziness in our approach, thereby designing an accurate intima-media thickness (IMT). Our database consists of 20 subjects comprising of normal, stable (echogenic) and unstable (echolucent) plaques. In this database of 45 images, we demonstrate our performance with respect to the gold standard tracings to an accuracy determined as normalized error to be about 8%. The results are very promising and this algorithm is being integrated into clinical setup for automatic pathologic carotid wall analysis.
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paper_title: Duplex ultrasonography and selection of patients for carotid endarterectomy: Plaque morphology or luminal narrowing? *

paper_content:

Abstract Percentage of carotid stenosis and plaque morphology as determined by duplex scanning were correlated with symptoms and CT evidence of infarction in 108 patients. Severity of carotid stenosis less than 49% or greater than 50% narrowing was not associated with an increased risk of ipsilateral symptoms or CT infarction. However, a heterogeneous plaque appearance, suggesting intraplaque hemorrhage, did correlate with ipsilateral cerebral symptoms. Heterogeneous plaque appearance may be a more reliable indication for carotid endarterectomy than a hemodynamically significant stenosis. (J VASC SURG 1988;8:558-62.)
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paper_title: The objective characterisation of ultrasonic carotid plaque features.

paper_content:

Objective: To determine the influence of ultrasonic carotid plaque morphology on the incidence of ipsilateral hemispheric symptoms (IHS). Design: Cross-sectional study. Materials: A consecutive series of 80 patients (96 plaques) with more than 50% ICA stenosis was studied. Methods: B mode ultrasonic images were captured and transferred to a computer on magneto-optic disk and standardised using linear scaling so that adventitia would have a grey scale median (GSM) value of 185–195 and blood 0–5. The GSM and the percentage of echolucent pixels (PEP) in plaques were determined to measure echodensity. Homogeneity, entropy, and contrast were also determined to measure spatial distribution (heterogeneity) of grey shades in each plaque. Each measurement was correlated to presence or absence of IHS. Results: Twenty-five plaques were associated with IHS and 71 plaques were asymptomatic. In symptomatic plaques the mean of GSM was 23 and the mean of PEP was 70%, compared to 38 and 55% respectively in asymptomatic plaques ( p =0.02; Wilcoxon test). Sixty per cent of symptomatic plaques were associated with a homogeneity, entropy, and contrast values of >0.2, p =0.001) that are related to presence or absence of IHS. Conclusion: This study indicates that computer aided analysis of ultrasonic B mode features of carotid plaques could identify a potentially high-risk subgroup (patients with IHS). A GSM less than 40 or PEP greater than 50% is a good predictor of IHS related to carotid plaques. The fact that these measurements are operator independent and performed after image standardisation should encourage their use in multicentre clinical trials where different operators and equipment are used.
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paper_title: A semiautomated ultrasound border detection program that facilitates clinical measurement of ultrasound carotid intima-media thickness.

paper_content:

We have developed a novel, semiautomated carotid intima-media thickness (CIMT) border detection program (AUTO) and evaluated its measurement reproducibility and accuracy. Images from 6 carotid segments were acquired in 50 subjects, for a total of 300 segments. Mean and maximum CIMT values were measured blindly at a reference (REF) lab and in duplicate by experienced (EXP) and novice (NOV) readers using manual (MAN) and AUTO methods. Coefficients of variation for AUTO measurements of mean (3.2%) and maximum (4.1%) CIMT were low, and the AUTO method improved the NOV reader's reproducibility. Compared with the REF lab, mean (0.012 +/- 0.006 mm) and maximum (0.144 +/- 0.006 mm) CIMT biases were small and equivalent to those of the REF lab ( P < .001). The AUTO method shortened reading times by 35% to 46% ( P < .001). We conclude that our novel AUTO CIMT measurement program improved reproducibility and was accurate. Compared with MAN tracing, the AUTO method agreed better with the REF lab and decreased reading time.
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paper_title: Texture Analysis of Ultrasonic Images of Symptomatic Carotid Plaques can Identify Those Plaques Associated with Ipsilateral Embolic Brain Infarction

paper_content:

OBJECTIVES ::: The aim of our study was to determine the association between objective, computerised texture analysis of carotid plaque ultrasonic images and embolic CT-brain infarction in patients presenting with hemispheric neurological symptoms. ::: ::: ::: DESIGN ::: Cross-sectional study in patients with 50%-99% (ECST) carotid stenosis. ::: ::: ::: PATIENTS AND METHODS ::: Carotid plaque ultrasonic images (n=54, 26 with TIAs and 28 with stroke) obtained during carotid ultrasound were normalised and standardised for resolution and subsequently assessed visually for the presence of discrete echogenic or juxtaluminal echolucent components and overall echogenicity (plaque type). Using computer software, 51 histogram/textural features of the plaque outlines were calculated. Factor analysis was subsequently applied to eliminate redundant variables. Small cortical, large cortical and discrete subcortical infarcts on CT-brain scan were considered as being embolic. ::: ::: ::: RESULTS ::: Twenty-five cases (46%) had embolic infarcts. On logistic regression, grey-scale median (GSM), a measure of echolucency, spatial grey level dependence matrices (SGLDM) correlation and SGLDM information measure of correlation-1, measures of homogeneity were significant (p<0.05), but not grey level runlength statistics (RUNL) Run Percentage (RP), stenosis severity, type of symptoms or echolucent juxtaluminal components. Using ROC curves methodology, SGLDM information measure of correlation-1 improved the value of GSM in distinguishing embolic from non-embolic CT-brain infarction. ::: ::: ::: CONCLUSION ::: Computerised texture analysis of ultrasonic images of symptomatic carotid plaques can identify those that are associated with brain infarction, improving the results achieved by GSM alone. This methodology could be applied to prospective natural history studies of symptomatic patients not operated on or randomised trials of patients undergoing carotid angioplasty and stenting in order to identify high-risk subgroups for cerebral infarction.
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paper_title: Textural features corresponding to textural properties

paper_content:

Five properties of texture, namely, coarseness, contrast, business, complexity, and texture strength, are given conceptual definitions in terms of spatial changes in intensity. These conceptual definitions are then approximated in computational forms. In comparison with human perceptual measurements, the computational measures have shown good correspondences in the rank ordering of ten natural textures. The extent to which the measures approximate visual perception was investigated in the form of texture similarity measurements. These results were also encouraging, although not as good as in the rank ordering of the textures. The differences may be due to the complex mechanism of human usage of multiple cues. Improved classification results were obtained using the above features as compared with two existing texture analysis techniques. The application of the features in agricultural land-use classification is considered. >
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paper_title: Computer-assisted carotid plaque characterisation

paper_content:

OBJECTIVE ::: To determine the relationship between plaque echogenicity as measured by computer and the incidence of cerebral brain infarction. ::: ::: ::: PATIENTS AND METHODS ::: Eighty-seven patients with 148 plaques producing more than 50% internal carotid artery stenosis were studied. Sixty-nine plaques were in asymptomatic patients, 35 were associated with amaurosis fugax, 19 with transient ischaemic attacks and 25 with stroke. All patients had a CT brain scan and the presence of ipsilateral cerebral infarction was noted. Images of the plaques obtained with an ATL Ultramark-4 Duplex scanner (7.5 MHz high resolution probe) were transferred to a computer. Using an image analysis program a histogram for each plaque was obtained with the number of pixels plotted against the grey scale (0-225). The median of the grey scale was used as a measure of echogenicity. ::: ::: ::: RESULTS ::: Fifty-three (36%) of the 148 plaques were associated with ipsilateral CT brain infarction. Plaques with a grey scale median more than 32 (echogenic) were associated with an incidence of 11% (7/64) CT infarction. In contrast, plaques with grey scale median below or equal to 32 (echolucent) were associated with 55% (46/84) incidence of CT infarction (chi 2 = 30.35, p < 0.001, relative risk = 22, 95% confidence interval from 4.7 to 108). ::: ::: ::: CONCLUSION ::: This study indicates that computer analysis of carotid plaque can identify high-risk carotid plaques. The potential of such analysis in the identification of asymptomatic high-risk patients should be explored in further studies.
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paper_title: Texture-based classification of atherosclerotic carotid plaques

paper_content:

There are indications that the morphology of atherosclerotic carotid plaques, obtained by high-resolution ultrasound imaging, has prognostic implications. The objective of this study was to develop a computer-aided system that will facilitate the characterization of carotid plaques for the identification of individuals with asymptomatic carotid stenosis at risk of stroke. A total of 230 plaque images were collected which were classified into two types: symptomatic because of ipsilateral hemispheric symptoms, or asymptomatic because they were not connected with ipsilateral hemispheric events. Ten different texture feature sets were extracted from the manually segmented plaque images using the following algorithms: first-order statistics, spatial gray level dependence matrices, gray level difference statistics, neighborhood gray tone difference matrix, statistical feature matrix, Laws texture energy measures, fractal dimension texture analysis, Fourier power spectrum and shape parameters. For the classification task a modular neural network composed of self-organizing map (SOM) classifiers, and combining techniques based on a confidence measure were used. Combining the classification results of the ten SOM classifiers inputted with the ten feature sets improved the classification rate of the individual classifiers, reaching an average diagnostic yield (DY) of 73.1%. The same modular system was implemented using the statistical k-nearest neighbor (KNN) classifier. The combined DY for the KNN system was 68.8%. The results of this paper show that it is possible to identify a group of patients at risk of stroke based on texture features extracted from ultrasound images of carotid plaques. This group of patients may benefit from a carotid endarterectomy whereas other patients may be spared from an unnecessary operation.
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paper_title: Ultrasonographic correlates of carotid atherosclerosis in transient ischemic attack and stroke.

paper_content:

BACKGROUND AND PURPOSE ::: Atherosclerotic plaques in extracranial carotid arteries, particularly in the bifurcation of the common carotid and internal carotid arteries, may cause transient cerebral ischemia and stroke by lumen stenosis or plaque-related thromboembolism. B-mode ultrasound imaging has the capability of providing information on plaque thickness, characteristics, and location in carotid arteries. ::: ::: ::: METHODS ::: A retrospective analysis of 242 stroke and 336 transient ischemic attack (TIA) patients, recruited for the B-Scan Ultrasound Imaging Assessment Program, was performed to determine the ultrasonographic correlates of carotid atherosclerosis and acute cerebral ischemia. A matched case-control study design was used to compare brain hemispheres with ischemic lesions ("cases") to unaffected contralateral hemispheres ("controls") with regard to the presence and characteristics of carotid artery plaques. ::: ::: ::: RESULTS ::: The first set of analyses examined the association between the presence of carotid plaques ipsilateral to the brain lesion and the occurrence of stroke or TIA and showed an association with recent episodes of TIA and stroke (odds ratio [OR], 1.6; P = .03) but not with past episodes. In a subset (n = 232) of patients with plaques in both carotid arteries and recent cerebral ischemic events, stroke was associated with ipsilateral carotid artery occlusion (P = .02). Lumen measurements at the site of the minimum residual lumen (MRL) diameter showed a significant association between a narrower lumen diameter in the carotid artery ipsilateral to case hemisphere and stroke (difference, 1.0 mm; P = .0003). TIA patients showed an association between both hypoechoic carotid plaques (OR, 3.0; P = .005) and the presence of longitudinal lesion motion (OR, 3.0; P = .02) with ipsilateral brain involvement. Plaque thickness at the MRL was positively correlated with both ipsilateral TIA (ipsilateral side, 4.4 +/- 0.15 mm; contralateral side, 3.9 +/- 0.16 mm; P = .007) and stroke (ipsilateral side, 4.2 +/- 0.23 mm; contralateral side, 3.3 +/- 0.21 mm; P = .0006). ::: ::: ::: CONCLUSIONS ::: These data demonstrate significant relationships between carotid artery ultrasound plaque characteristics and ischemic cerebrovascular events. These findings encourage further prospective studies in asymptomatic subjects focused on echographic carotid plaque characteristics as predictors of subsequent TIA or stroke.
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paper_title: Computer-aided diagnosis of carotid atherosclerosis based on ultrasound image statistics, laws' texture and neural networks.

paper_content:

Quantitative characterisation of carotid atherosclerosis and classification into symptomatic or asymptomatic is crucial in planning optimal treatment of atheromatous plaque. The computer-aided diagnosis (CAD) system described in this paper can analyse ultrasound (US) images of carotid artery and classify them into symptomatic or asymptomatic based on their echogenicity characteristics. The CAD system consists of three modules: a) the feature extraction module, where first-order statistical (FOS) features and Laws' texture energy can be estimated, b) the dimensionality reduction module, where the number of features can be reduced using analysis of variance (ANOVA), and c) the classifier module consisting of a neural network (NN) trained by a novel hybrid method based on genetic algorithms (GAs) along with the back propagation algorithm. The hybrid method is able to select the most robust features, to adjust automatically the NN architecture and to optimise the classification performance. The performance is measured by the accuracy, sensitivity, specificity and the area under the receiver-operating characteristic (ROC) curve. The CAD design and development is based on images from 54 symptomatic and 54 asymptomatic plaques. This study demonstrates the ability of a CAD system based on US image analysis and a hybrid trained NN to identify atheromatous plaques at high risk of stroke.
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paper_title: Classification of atherosclerotic carotid plaques using morphological analysis on ultrasound images

paper_content:

The aim of this study was to investigate the usefulness of multilevel binary and gray scale morphological analysis in the assessment of atherosclerotic carotid plaques. Ultrasound images were recorded from 137 asymptomatic and 137 symptomatic plaques (Stroke, Transient Ischaemic Attack (TIA), Amaurosis Fugax (AF)). We carefully develop the clinical motivation behind our approach. We do this by relating the proposed L-images, M-images and H-images in terms of the clinically established hypoechoic, isoechoic and hyperechoic classification. ::: ::: Normalized pattern spectra were computed for both a structural, multilevel binary morphological model, and a direct gray scale morphology model. From the plots of the average pattern spectra, it is clear that we have significant differences between the symptomatic and asymptomatic spectra. Here, we note that the morphological measurements appear to be in agreement with the clinical assertion that symptomatic plaques tend to have large lipid cores while the asymptomatic plaques tend to have small lipid cores. ::: ::: The derived pattern spectra were used as classification features with two different classifiers, the Probabilistic Neural Network (PNN) and the Support Vector Machine (SVM). Both classifiers were used for classifying the pattern spectra into either a symptomatic or an asymptomatic class. The highest percentage of correct classifications score was 73.7% for multilevel binary morphological image analysis and 66.8% for gray scale morphological analysis. Both were achieved using the SVM classifier. Among all features, the L-image pattern spectra, that also measure the distributions of the lipid core components (and some non-lipid components) gave the best classification results.
---
paper_title: An Introduction to Nonlinear Image Processing

paper_content:

From a strict semantic point of view, nonlinear image processing encompasses all image processing that is not based on linear operators; however, from a practical, evolutionary point of view, the name itself is usually associated with the study of nonlinear filters, mainly the deterministic and nondeterministic analysis and design of logic-based operators. This Tutorial Text volume explores logic-based operators with emphasis on representation, design, and statistical optimization of nonlinear filters.
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paper_title: Relationship between ultrasound texture classification images and histology of atherosclerotic plaque.

paper_content:

Structure and content of atherosclerotic plaque varies between patients and may be indicative of their risk for embolisation. This study aimed to construct parametric images of B-scan texture and assess their potential for predicting plaque morphology. Sequential transverse in vitro scans of 10 carotid plaques, excised during endarterectomy, were compared with macrohistology maps of plaque content. Multidiscriminant analysis combined the output of 157 statistical and textural algorithms into five separate texture classes, displayed as ultrasound (US) texture classification images (UTCI). Visual comparison between corresponding UTCI and histology maps found the five texture classes matched with the location of fibrin, elastin, calcium, haemorrhage or lipid. However, histology preparation removes calcium and lipid and, so, can affect the structural integrity of atherosclerotic plaques. Soft tissue regions smaller than the UTCI kernel, (0.87 mm x 0.85 mm x 3.9 mm), such as blood clots, are also difficult to detect by UTCI. These factors demonstrate limitations in the use of histology as a "gold standard" for US tissue characterisation.
---
paper_title: The objective characterisation of ultrasonic carotid plaque features.

paper_content:

Objective: To determine the influence of ultrasonic carotid plaque morphology on the incidence of ipsilateral hemispheric symptoms (IHS). Design: Cross-sectional study. Materials: A consecutive series of 80 patients (96 plaques) with more than 50% ICA stenosis was studied. Methods: B mode ultrasonic images were captured and transferred to a computer on magneto-optic disk and standardised using linear scaling so that adventitia would have a grey scale median (GSM) value of 185–195 and blood 0–5. The GSM and the percentage of echolucent pixels (PEP) in plaques were determined to measure echodensity. Homogeneity, entropy, and contrast were also determined to measure spatial distribution (heterogeneity) of grey shades in each plaque. Each measurement was correlated to presence or absence of IHS. Results: Twenty-five plaques were associated with IHS and 71 plaques were asymptomatic. In symptomatic plaques the mean of GSM was 23 and the mean of PEP was 70%, compared to 38 and 55% respectively in asymptomatic plaques ( p =0.02; Wilcoxon test). Sixty per cent of symptomatic plaques were associated with a homogeneity, entropy, and contrast values of >0.2, p =0.001) that are related to presence or absence of IHS. Conclusion: This study indicates that computer aided analysis of ultrasonic B mode features of carotid plaques could identify a potentially high-risk subgroup (patients with IHS). A GSM less than 40 or PEP greater than 50% is a good predictor of IHS related to carotid plaques. The fact that these measurements are operator independent and performed after image standardisation should encourage their use in multicentre clinical trials where different operators and equipment are used.
---
paper_title: Computer-assisted Carotid Plaque Analysis: Characteristics of Plaques Associated with Cerebrovascular Symptoms and Cerebral Infarction

paper_content:

OBJECTIVE: to correlate the echostructural characteristics of carotid plaques with neurological symptoms and cerebral infarcts. MATERIALS: one hundred and five plaques were studied in 74 patients by colour-flow duplex ultrasound: 39 were symptomatic and 37 were associated with brain infarction on CT scanning. METHODS: the images were digitalised for computer-assisted image standardisation and divided in homogenous (n=67) and heterogenous (n=38) groups. Parameters of the plaque image were analysed. RESULTS: global echogenicity was significantly lower in symptomatic and in CT(+)plaques (p<0.05). For homogenous plaques, an echogenic cap (EC) was visualised in 8.3% of symptomatic vs. 33.9% of asymptomatic (p<0. 05) and in 7.7% for plaques that were CT(+)vs. 37.7% for CT(-)(p<0. 05). Surface disruption was visualised in 50% of symptomatic vs. 8. 5% of asymptomatic (p=0.002) and in 46% of CT(+)vs. 9.4% of CT(-)plaques (p=0.002). For heterogenous plaques, the echolucent region was juxtaluminal in 67% of symptomatic and CT(+)plaques vs. 33% in asymptomatic and CT(-)(p<0.01). CONCLUSION: echolucent plaques are associated with a higher neurological risk. In homogenous plaques the absence of an echogenic cap and disruption of the plaque surface also correlates with symptoms. In heterogenous plaques, juxtaluminal location of the echolucent region is an additional marker of increased risk. (Less)
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paper_title: Texture Analysis of Ultrasonic Images of Symptomatic Carotid Plaques can Identify Those Plaques Associated with Ipsilateral Embolic Brain Infarction

paper_content:

OBJECTIVES ::: The aim of our study was to determine the association between objective, computerised texture analysis of carotid plaque ultrasonic images and embolic CT-brain infarction in patients presenting with hemispheric neurological symptoms. ::: ::: ::: DESIGN ::: Cross-sectional study in patients with 50%-99% (ECST) carotid stenosis. ::: ::: ::: PATIENTS AND METHODS ::: Carotid plaque ultrasonic images (n=54, 26 with TIAs and 28 with stroke) obtained during carotid ultrasound were normalised and standardised for resolution and subsequently assessed visually for the presence of discrete echogenic or juxtaluminal echolucent components and overall echogenicity (plaque type). Using computer software, 51 histogram/textural features of the plaque outlines were calculated. Factor analysis was subsequently applied to eliminate redundant variables. Small cortical, large cortical and discrete subcortical infarcts on CT-brain scan were considered as being embolic. ::: ::: ::: RESULTS ::: Twenty-five cases (46%) had embolic infarcts. On logistic regression, grey-scale median (GSM), a measure of echolucency, spatial grey level dependence matrices (SGLDM) correlation and SGLDM information measure of correlation-1, measures of homogeneity were significant (p<0.05), but not grey level runlength statistics (RUNL) Run Percentage (RP), stenosis severity, type of symptoms or echolucent juxtaluminal components. Using ROC curves methodology, SGLDM information measure of correlation-1 improved the value of GSM in distinguishing embolic from non-embolic CT-brain infarction. ::: ::: ::: CONCLUSION ::: Computerised texture analysis of ultrasonic images of symptomatic carotid plaques can identify those that are associated with brain infarction, improving the results achieved by GSM alone. This methodology could be applied to prospective natural history studies of symptomatic patients not operated on or randomised trials of patients undergoing carotid angioplasty and stenting in order to identify high-risk subgroups for cerebral infarction.
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paper_title: Computer-assisted carotid plaque characterisation

paper_content:

OBJECTIVE ::: To determine the relationship between plaque echogenicity as measured by computer and the incidence of cerebral brain infarction. ::: ::: ::: PATIENTS AND METHODS ::: Eighty-seven patients with 148 plaques producing more than 50% internal carotid artery stenosis were studied. Sixty-nine plaques were in asymptomatic patients, 35 were associated with amaurosis fugax, 19 with transient ischaemic attacks and 25 with stroke. All patients had a CT brain scan and the presence of ipsilateral cerebral infarction was noted. Images of the plaques obtained with an ATL Ultramark-4 Duplex scanner (7.5 MHz high resolution probe) were transferred to a computer. Using an image analysis program a histogram for each plaque was obtained with the number of pixels plotted against the grey scale (0-225). The median of the grey scale was used as a measure of echogenicity. ::: ::: ::: RESULTS ::: Fifty-three (36%) of the 148 plaques were associated with ipsilateral CT brain infarction. Plaques with a grey scale median more than 32 (echogenic) were associated with an incidence of 11% (7/64) CT infarction. In contrast, plaques with grey scale median below or equal to 32 (echolucent) were associated with 55% (46/84) incidence of CT infarction (chi 2 = 30.35, p < 0.001, relative risk = 22, 95% confidence interval from 4.7 to 108). ::: ::: ::: CONCLUSION ::: This study indicates that computer analysis of carotid plaque can identify high-risk carotid plaques. The potential of such analysis in the identification of asymptomatic high-risk patients should be explored in further studies.
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paper_title: Texture-based classification of atherosclerotic carotid plaques

paper_content:

There are indications that the morphology of atherosclerotic carotid plaques, obtained by high-resolution ultrasound imaging, has prognostic implications. The objective of this study was to develop a computer-aided system that will facilitate the characterization of carotid plaques for the identification of individuals with asymptomatic carotid stenosis at risk of stroke. A total of 230 plaque images were collected which were classified into two types: symptomatic because of ipsilateral hemispheric symptoms, or asymptomatic because they were not connected with ipsilateral hemispheric events. Ten different texture feature sets were extracted from the manually segmented plaque images using the following algorithms: first-order statistics, spatial gray level dependence matrices, gray level difference statistics, neighborhood gray tone difference matrix, statistical feature matrix, Laws texture energy measures, fractal dimension texture analysis, Fourier power spectrum and shape parameters. For the classification task a modular neural network composed of self-organizing map (SOM) classifiers, and combining techniques based on a confidence measure were used. Combining the classification results of the ten SOM classifiers inputted with the ten feature sets improved the classification rate of the individual classifiers, reaching an average diagnostic yield (DY) of 73.1%. The same modular system was implemented using the statistical k-nearest neighbor (KNN) classifier. The combined DY for the KNN system was 68.8%. The results of this paper show that it is possible to identify a group of patients at risk of stroke based on texture features extracted from ultrasound images of carotid plaques. This group of patients may benefit from a carotid endarterectomy whereas other patients may be spared from an unnecessary operation.
---
paper_title: Ultrasonographic correlates of carotid atherosclerosis in transient ischemic attack and stroke.

paper_content:

BACKGROUND AND PURPOSE ::: Atherosclerotic plaques in extracranial carotid arteries, particularly in the bifurcation of the common carotid and internal carotid arteries, may cause transient cerebral ischemia and stroke by lumen stenosis or plaque-related thromboembolism. B-mode ultrasound imaging has the capability of providing information on plaque thickness, characteristics, and location in carotid arteries. ::: ::: ::: METHODS ::: A retrospective analysis of 242 stroke and 336 transient ischemic attack (TIA) patients, recruited for the B-Scan Ultrasound Imaging Assessment Program, was performed to determine the ultrasonographic correlates of carotid atherosclerosis and acute cerebral ischemia. A matched case-control study design was used to compare brain hemispheres with ischemic lesions ("cases") to unaffected contralateral hemispheres ("controls") with regard to the presence and characteristics of carotid artery plaques. ::: ::: ::: RESULTS ::: The first set of analyses examined the association between the presence of carotid plaques ipsilateral to the brain lesion and the occurrence of stroke or TIA and showed an association with recent episodes of TIA and stroke (odds ratio [OR], 1.6; P = .03) but not with past episodes. In a subset (n = 232) of patients with plaques in both carotid arteries and recent cerebral ischemic events, stroke was associated with ipsilateral carotid artery occlusion (P = .02). Lumen measurements at the site of the minimum residual lumen (MRL) diameter showed a significant association between a narrower lumen diameter in the carotid artery ipsilateral to case hemisphere and stroke (difference, 1.0 mm; P = .0003). TIA patients showed an association between both hypoechoic carotid plaques (OR, 3.0; P = .005) and the presence of longitudinal lesion motion (OR, 3.0; P = .02) with ipsilateral brain involvement. Plaque thickness at the MRL was positively correlated with both ipsilateral TIA (ipsilateral side, 4.4 +/- 0.15 mm; contralateral side, 3.9 +/- 0.16 mm; P = .007) and stroke (ipsilateral side, 4.2 +/- 0.23 mm; contralateral side, 3.3 +/- 0.21 mm; P = .0006). ::: ::: ::: CONCLUSIONS ::: These data demonstrate significant relationships between carotid artery ultrasound plaque characteristics and ischemic cerebrovascular events. These findings encourage further prospective studies in asymptomatic subjects focused on echographic carotid plaque characteristics as predictors of subsequent TIA or stroke.
---
paper_title: Computer-aided diagnosis of carotid atherosclerosis based on ultrasound image statistics, laws' texture and neural networks.

paper_content:

Quantitative characterisation of carotid atherosclerosis and classification into symptomatic or asymptomatic is crucial in planning optimal treatment of atheromatous plaque. The computer-aided diagnosis (CAD) system described in this paper can analyse ultrasound (US) images of carotid artery and classify them into symptomatic or asymptomatic based on their echogenicity characteristics. The CAD system consists of three modules: a) the feature extraction module, where first-order statistical (FOS) features and Laws' texture energy can be estimated, b) the dimensionality reduction module, where the number of features can be reduced using analysis of variance (ANOVA), and c) the classifier module consisting of a neural network (NN) trained by a novel hybrid method based on genetic algorithms (GAs) along with the back propagation algorithm. The hybrid method is able to select the most robust features, to adjust automatically the NN architecture and to optimise the classification performance. The performance is measured by the accuracy, sensitivity, specificity and the area under the receiver-operating characteristic (ROC) curve. The CAD design and development is based on images from 54 symptomatic and 54 asymptomatic plaques. This study demonstrates the ability of a CAD system based on US image analysis and a hybrid trained NN to identify atheromatous plaques at high risk of stroke.
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paper_title: Ultrasound Image Analysis for Automated Classification of Atherosclerotic Plaque in the Human Carotid Artery

paper_content:

Cardiovascular diseases, caused by atherosclerosis, is one of the most common causes of death in the industrialized world. Two risk factors, that both can be assessed with ultrasound, are the Intima-Media Thickness (IMT) in the arterial wall and the composition of the atherosclerotic plaque. Plaques can be classied according to the subjective Gray-Weale scale. Its four classes are based on the echogenicity of the plaque, where class 1 is the most echolucent class and class 4 the most echogenic. In this thesis class 1 and 2 are merged into an echolucent class, and class 3 and 4 into an echogenic class. The motivation for this grouping is the fact that echolucent plaques are more unstable, and therefore more dangerous, than echogenic plaques. An automatic classication based on thresholding the plaque with an adaptive threshold has been developed. The threshold is a weighted sum of the echogenecity and the noise in the image, and it divides the plaque into black (echolucent) and white ::: (echogenic) regions. The classication rate on the training set was 95% (92 of 97) when using leave-one-out crossvalidation, while the performance on the validation set was 91% (81 of 89). This thesis also contains a description of a computer program for automatic measurements of the IMT. An automatic system decreases both the analysis time and the interobserver variability compared to a manual system.
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paper_title: Classification of atherosclerotic carotid plaques using morphological analysis on ultrasound images

paper_content:

The aim of this study was to investigate the usefulness of multilevel binary and gray scale morphological analysis in the assessment of atherosclerotic carotid plaques. Ultrasound images were recorded from 137 asymptomatic and 137 symptomatic plaques (Stroke, Transient Ischaemic Attack (TIA), Amaurosis Fugax (AF)). We carefully develop the clinical motivation behind our approach. We do this by relating the proposed L-images, M-images and H-images in terms of the clinically established hypoechoic, isoechoic and hyperechoic classification. ::: ::: Normalized pattern spectra were computed for both a structural, multilevel binary morphological model, and a direct gray scale morphology model. From the plots of the average pattern spectra, it is clear that we have significant differences between the symptomatic and asymptomatic spectra. Here, we note that the morphological measurements appear to be in agreement with the clinical assertion that symptomatic plaques tend to have large lipid cores while the asymptomatic plaques tend to have small lipid cores. ::: ::: The derived pattern spectra were used as classification features with two different classifiers, the Probabilistic Neural Network (PNN) and the Support Vector Machine (SVM). Both classifiers were used for classifying the pattern spectra into either a symptomatic or an asymptomatic class. The highest percentage of correct classifications score was 73.7% for multilevel binary morphological image analysis and 66.8% for gray scale morphological analysis. Both were achieved using the SVM classifier. Among all features, the L-image pattern spectra, that also measure the distributions of the lipid core components (and some non-lipid components) gave the best classification results.
---
paper_title: An Introduction to Nonlinear Image Processing

paper_content:

From a strict semantic point of view, nonlinear image processing encompasses all image processing that is not based on linear operators; however, from a practical, evolutionary point of view, the name itself is usually associated with the study of nonlinear filters, mainly the deterministic and nondeterministic analysis and design of logic-based operators. This Tutorial Text volume explores logic-based operators with emphasis on representation, design, and statistical optimization of nonlinear filters.
---
paper_title: Relationship between ultrasound texture classification images and histology of atherosclerotic plaque.

paper_content:

Structure and content of atherosclerotic plaque varies between patients and may be indicative of their risk for embolisation. This study aimed to construct parametric images of B-scan texture and assess their potential for predicting plaque morphology. Sequential transverse in vitro scans of 10 carotid plaques, excised during endarterectomy, were compared with macrohistology maps of plaque content. Multidiscriminant analysis combined the output of 157 statistical and textural algorithms into five separate texture classes, displayed as ultrasound (US) texture classification images (UTCI). Visual comparison between corresponding UTCI and histology maps found the five texture classes matched with the location of fibrin, elastin, calcium, haemorrhage or lipid. However, histology preparation removes calcium and lipid and, so, can affect the structural integrity of atherosclerotic plaques. Soft tissue regions smaller than the UTCI kernel, (0.87 mm x 0.85 mm x 3.9 mm), such as blood clots, are also difficult to detect by UTCI. These factors demonstrate limitations in the use of histology as a "gold standard" for US tissue characterisation.
---
paper_title: Quantitative analysis of ultrasound B-mode images of carotid atherosclerotic plaque: correlation with visual classification and histological examination

paper_content:

This paper presents a quantitative comparison of three types of information available for 52 patients scheduled for carotid endarterectomy: subjective classification of the ultrasound images obtained during scanning before operation, first-and second-order statistical features extracted from regions of the plaque in still ultrasound images from three orthogonal scan planes and finally a histological analysis of the surgically removed plaque. The quantitative comparison was made with the linear model and with separation of the available data into training and test sets. The comparison of subjective classification with features from still ultrasound images revealed an overall agreement of 60% for classification of echogenicity and 70% for classification of structure. Comparison of the histologically determined relative volume of soft materials with features from the still images revealed a correlation coefficient of r = -0.42(p = 0.002). for mean echogenicity of the plaque region. The best performing feature was of second order and denoted Contrast (r = -0.5). Though significant, the latter correlation is probably not strong enough to be useful for clinical prediction of relative volume of soft materials for individual patients. Reasons for this is discussed in the paper, together with suggestions for improvements.
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paper_title: The objective characterisation of ultrasonic carotid plaque features.

paper_content:

Objective: To determine the influence of ultrasonic carotid plaque morphology on the incidence of ipsilateral hemispheric symptoms (IHS). Design: Cross-sectional study. Materials: A consecutive series of 80 patients (96 plaques) with more than 50% ICA stenosis was studied. Methods: B mode ultrasonic images were captured and transferred to a computer on magneto-optic disk and standardised using linear scaling so that adventitia would have a grey scale median (GSM) value of 185–195 and blood 0–5. The GSM and the percentage of echolucent pixels (PEP) in plaques were determined to measure echodensity. Homogeneity, entropy, and contrast were also determined to measure spatial distribution (heterogeneity) of grey shades in each plaque. Each measurement was correlated to presence or absence of IHS. Results: Twenty-five plaques were associated with IHS and 71 plaques were asymptomatic. In symptomatic plaques the mean of GSM was 23 and the mean of PEP was 70%, compared to 38 and 55% respectively in asymptomatic plaques ( p =0.02; Wilcoxon test). Sixty per cent of symptomatic plaques were associated with a homogeneity, entropy, and contrast values of >0.2, p =0.001) that are related to presence or absence of IHS. Conclusion: This study indicates that computer aided analysis of ultrasonic B mode features of carotid plaques could identify a potentially high-risk subgroup (patients with IHS). A GSM less than 40 or PEP greater than 50% is a good predictor of IHS related to carotid plaques. The fact that these measurements are operator independent and performed after image standardisation should encourage their use in multicentre clinical trials where different operators and equipment are used.
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paper_title: Development of 3D ultrasound techniques for carotid artery disease assessment and monitoring

paper_content:

Background ::: Quantitative measurements of carotid plaque burden are used to monitor patients and evaluate established interventions as well as new treatment options.
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paper_title: Measurement of Carotid Plaque Volume by 3-Dimensional Ultrasound

paper_content:

BACKGROUND AND PURPOSE ::: Measurement of carotid plaque volume and its progression are important tools for research and patient management. In this study, we investigate the observer variability in the measurement of plaque volume as determined by 3-dimensional (3D) ultrasound (US). We also investigate the effect of interslice distances (ISD) and repeated 3D US scans on measurement variability. Materials and Methods Forty 3D US patient images of plaques (range, 37.43 to 604.1 mm3) were measured by manual planimetry. We applied ANOVA to determine plaque volume measurement variability and reliability. Plaque volumes were measured with 9 ISDs to determine the effect of ISD on measurement variability. Additional plaque volumes were also measured from multiple 3D US scans to investigate repeated scan acquisition variability. Results Intraobserver and interobserver measurement reliabilities were 94% and 93.2%, respectively. Plaque volume measurement variability decreased with increasing plaque volume (range, 27.1% to 2.2%). Measurement precision was constant for ISDs between 1.0 and 3.0 mm, whereas plaque volume measurement variability increased with ISD. Repeated 3D US scan measurements were not different from single-scan measurements (P=0.867). Conclusions The coefficient of variation in the measurement of plaque volume decreased with plaque size. The volumetric change that must be observed to establish with 95% confidence that a plaque has undergone change is approximately 20% to 35% for plaques <100 mm3 and approximately 10% to 20% for plaques >100 mm3. Measurement precision was unchanged for ISDs <3.0 mm, whereas measurement variability increased with ISD. Repeated 3D US scans did not affect plaque volume measurement variability.
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paper_title: Quantification of carotid vessel wall and plaque thickness change using 3D ultrasound images

paper_content:

Quantitative measurements of carotid plaque burden progression or regression are important in monitoring patients and in evaluation of new treatment options. 3D ultrasound(US) has been used to monitor the progression or regression of carotid artery plaques. This paper reports on the development and application of a method used to analyze changes in carotid plaque morphology from 3D US. The technique used is evaluated using manual segmentations of the arterial wall and lumen from 3D USimages acquired in two imaging sessions. To reduce the effect of segmentation variability, segmentation was performed five times each for the wall and lumen. The mean wall and lumen surfaces, computed from this set of five segmentations, were matched on a point-by-point basis, and the distance between each pair of corresponding points served as an estimate of the combined thickness of the plaque, intima, and media (vessel-wall-plus-plaque thickness or VWT). The VWT maps associated with the first and the second USimages were compared and the differences of VWT were obtained at each vertex. The 3D VWT and VWT-Change maps may provide important information for evaluating the location of plaque progression in relation to the localized disturbances of flow pattern, such as oscillatory shear, and regression in response to medical treatments.
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paper_title: Motion Analysis of the Carotid Artery Wall and Plaque Using B-Mode Ultrasound

paper_content:

Abstract: Motion of the arterial wall and atheromatous plaque, especially in the longitudinal direction, has recently gained attention as a determinant of carotid atherosclerosis. Vessel wall motion, caused by blood pressure, blood flow and tethering to the surrounding tissue, may be responsible for tissue rupture and cerebrovascular symptoms. B-mode ultrasound allows non-invasive recording of arterial wall and plaque motion in two directions, namely radial and longitudinal. Temporal sequences of ultrasound images, recorded at high frame rates, can be used to quantitatively estimate movement of the arterial wall. Motion of the carotid artery wall and plaque from sequences of ultrasound images has been estimated using block matching and optical flow techniques. Block matching is based on tracking blocks of pixels, assuming that the blocks remain constant over time and motion. Optical flow relies on the estimation of the spatiotemporal change of individual pixel intensities throughout a sequence, resulting in a dense vector map where each pixel is represented by a vector corresponding to its velocity between two frames. An important issue in studies of arterial wall motion is the validation of the motion analysis techniques. Tissue-mimicking phantoms as well as computer-generated simulation images have been used to validate motion analysis algorithms. In conclusion, motion of the carotid artery wall and plaque can be quantitatively estimated from B-mode ultrasound and may represent a powerful tool to study further the mechanisms of atherosclerosis.
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paper_title: A modular software system to assist interpretation of medical images application to vascular ultrasound images

paper_content:

Improvements in medical imaging technology have greatly contributed to early disease detection and diagnosis. However, the accuracy of an examination depends on both the quality of the images and the ability of the physician to interpret those images. Use of output from computerized analysis of an image may facilitate the diagnostic tasks and, potentially improve the overall interpretation of images and the subsequent patient care. In this paper, Analysis, a modular software system designed to assist interpretation of medical images, is described in detail. Analysis allows texture and motion estimation of selected regions of interest (ROIs). Texture features can be estimated using first-order statistics, second-order statistics, Laws' texture energy, neighborhood gray-tone difference matrix, gray level difference statistics, and the fractal dimension. Motion can be estimated from temporal image sequences using block matching or optical flow. Image preprocessing, manual and automatic definition of ROIs, and dimensionality reduction and clustering using fuzzy c-means, are also possible within Analysis. An important feature of Analysis is the possibility for online telecollaboration between health care professionals under a secure framework. To demonstrate the applicability and usefulness of the system in clinical practice, Analysis was applied to B-mode ultrasound images of the carotid artery. Diagnostic tasks included automatic segmentation of the arterial wall in transverse sections, selection of wall and plaque ROIs in longitudinal sections, estimation of texture features in different image areas, motion analysis of tissue ROIs, and clustering of the extracted features. It is concluded that Analysis can provide a useful platform for computerized analysis of medical images and support of diagnosis
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paper_title: Four-Dimensional Ultrasonographic Characterization of Plaque Surface Motion in Patients With Symptomatic and Asymptomatic Carotid Artery Stenosis

paper_content:

Background and Purpose—In vitro studies of atherosclerotic plaque fracture mechanics suggest that analysis of local variations in surface deformability may provide information on relative vulnerability to plaque fissuring or rupture. We investigated plaque surface deformations in patients with symptomatic and asymptomatic carotid artery disease using 4-dimensional ultrasonography and techniques for measuring optical flow. Methods—Four-dimensional ultrasound examinations of carotid artery plaques were performed in 23 asymptomatic and 22 symptomatic patients with 50% to 90% stenosis of the internal carotid artery. Plaque surface motion during 1 cardiac cycle was computed with a hierarchical model-based motion estimator. Results were compared with plaque echogenicity and surface structure. Results—Of the 45 patients examined, plaque surface motion estimates were obtained for 18 asymptomatic and 13 symptomatic patients. There were no significant differences in echogenicity or surface structure of asymptomatic...
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paper_title: An AM-FM model for Motion Estimation in Atherosclerotic Plaque Videos

paper_content:

We present new multidimensional amplitude-modulation frequency-modulation (AM-FM) methods for motion estimation. For a single AM-FM component we show that the optical flow constraint leads to separate equations for amplitude modulation (AM) and frequency modulation (FM). We compare our approach with phase-based estimation developed by Fleet and Jepson and also the original optical flow method by Horn and Schunck. An advantage of the proposed method is that it provides for dense estimates that remain accurate over the entire video. We also present preliminary results on atherosclerotic plaques videos where the AM method appears to work best.
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paper_title: A mathematical model of the mechanical deformation of the carotid artery wall and its application to clinical data

paper_content:

The study of arterial wall mechanics, including the study of stresses and strains experienced by the vascular wall, is pivotal in our understanding of arterial physiology. In this paper, a mathematical model is provided describing the deformation of the arterial wall in terms of 6 parameters. Actual deformation waveforms were also obtained from the analysis of B-mode ultrasound image sequences of the carotid artery using block-matching. The mathematical model was fitted to the clinical data using nonlinear least squares to determine the 6 parameters for 6 different locations along the posterior and 6 along the anterior walls, on the interface between the lumen and the intima-media complex (L-IM). On the posterior wall, 6 locations were also investigated at the interface between the intima-media complex and the adventitia (IM-A) as well as at the adventitia-surrounding tissue (A-T) boundary. The root mean square error was low for all locations indicating a good fit of the proposed model to the clinical data. The amplitude of the deformation, expressed through parameter alpha, was significantly lower in the A-T interface compared to the other two interfaces. The time when the systolic peak occurs, expressed through parameter t1, was significantly lower in the L-IM interface compared to the other two interfaces. Preliminary findings from a small group of diseased wall locations suggested that the parameters a, b and t1 were significantly different than healthy cases. This probably reflects alterations of arterial wall mechanics due to disease. This study showed that the proposed mathematical model is a satisfactory representation of the mechanical deformation of the carotid artery wall in the radial direction and can provide valuable information in the understanding of the mechanical behavior of the arterial wall.
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paper_title: Noninvasive Vascular Elastography: Toward A Complementary Characterization Tool of Atherosclerosis in Carotid Arteries

paper_content:

Abstract Only a minority of patients with carotid arterial disease have warning symptoms, because the majority of strokes are caused by previously asymptomatic lesions. Because morbidity and mortality after acute stroke are high, patients should be diagnosed and treated before symptoms develop. The hypothesis of this study is that vascular elasticity maps (or elastograms) of carotids are of predictive value for plaque characterization. The strain tensor from either cross-sectional or longitudinal ultrasound radiofrequency data were assessed by a new implementation of the Lagrangian speckle model estimator (LSME), which considers local echogenicity variations. A 26-year-old healthy male (HS1), a 40-year-old (HS2) normal female subject and two 75-year-old asymptomatic patients with severe carotid stenoses were scanned. Reproducible elastograms were obtained as a function of time over five to seven cardiac cycles. Stress-strain modulus elastograms were computed for normal subjects. Stiffening of healthy carotid walls was estimated to be 148 ± 7 kPa and 163 ± 30 kPa at peak-systole for HS1 and HS2, respectively. For patients with heterogeneous plaques, strain and shear elastograms revealed interesting information about plaque size, tissue composition and mechanical interaction between structures. In conclusion, the LSME provides a promising approach for strain and shear estimates to characterize vulnerable plaque. (E-mail: guy.cloutier@umontreal.ca )
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Title: A Review of Noninvasive Ultrasound Image Processing Methods in the Analysis of Carotid Plaque Morphology for the Assessment of Stroke Risk

Section 1: VISUAL CLASSIFICATION IN THE ASSESSMENT OF ATHEROSCLEROTIC PLAQUES IN ULTRASOUND IMAGING
Description 1: Describe the importance and methods of visual classification for assessing carotid plaques using high-resolution ultrasound imaging.

Section 2: ULTRASOUND-IMAGE PREPROCESSING AND SEGMENTATION
Description 2: Discuss the preprocessing techniques such as image acquisition, normalization, despeckling, and segmentation methods used in ultrasound imaging of carotid plaques.

Section 3: Feature Extraction
Description 3: Explain the various feature extraction methods used post-segmentation to analyze the characteristics of carotid plaques.

Section 4: Classification
Description 4: Describe the different classification techniques and methods used to categorize and assess the risk of carotid plaques.

Section 5: Emerging Approaches
Description 5: Present new and emerging methods in carotid plaque analysis, including 3-D imaging, motion analysis, and stress-strain evaluation.

Section 6: CONCLUDING REMARKS AND FUTURE DIRECTIONS
Description 6: Summarize the conclusions drawn from the review and discuss potential future directions in the field of noninvasive ultrasound imaging for carotid plaque assessment.