Accuracy of carotid plaque detection and intima-media thickness measurement with ultrasonography in routine clinical practice

[TIMMA: Ultrasonographic scale of carotid atherosclerosis by vascular neurologists]

BACKGROUND

Carotid atherosclerosis is a powerful predictive factor of vascular risk at the individual patient level. Ultrasonography is a reference technique for the evaluation of this condition. However, its use in common practice remains difficult due to a lack of standardization and inter-operator variability. We present a new and simple technique for the assessment of carotid atherosclerosis; and evaluate the ability of vascular neurologists to obtain results consistent with those of an expert in vascular ultrasound.

MATERIAL AND METHODS

The TIMMA scale is an acronym for the five classes of carotid atherosclerosis in French, VIMMA in English: very important, important, moderate, minimal and absent. Combined, the first two classes make up the group "significant atheroma" and the last three classes make up the group "no significant atheroma". This scale was evaluated in 38 patients (76 carotid arteries) suffering from ischemic stroke or transient ischemic attack by five operators who are competent in carotid echocardiography: one TIMMA-trained (40 hours of training) vascular neurologist physician (VNP), three VNPs informed on the measurement method (1 hour of information) and one specialized vascular physician (SVP) who was considered to be the reference examiner. We evaluated the concordance between the VNPs and the SVP in classifying patients, firstly into the significant or not atheroma group and, secondly, into the five TIMMA classes.

RESULTS

The evaluation of the two-group clustering scale found a concordance between the informed VNPs and the SVP on 76 carotid arteries of 86% (kappa=0.7) and between the trained VNP and the SVP on 58 carotid arteries of 90% (kappa=0.8). The positive and negative predictive values for significant atheroma diagnosis were 100% and 81%, respectively, for the informed VNPs, and 100% and 80% for the trained VNP. The evaluation of the Five-Class Scale showed a concordance between the informed VNPs and the SVP of 46% (kappa=0.3), and between the trained VNP and the SVP of 74% (kappa=0.7).

CONCLUSION

TIMMA allows VNPs who are competent in carotid ultrasonography to reproducibly identify subjects with significant carotid atheroma. The contribution of this scale to the determination of cardiovascular risk should be evaluated.

Is B-mode ultrasound alone a sufficient screening tool for carotid stenosis? A pilot study

BACKGROUND

Carotid ultrasound is performed solely in hospital ultrasound departments or outpatient labs, using both B- and Doppler modes. We hypothesize that B-mode without Doppler can be used to classify patients as having carotid stenosis (CS) above or below 50%. Our objective is to determine the frequency with which a CS >50% is found using Doppler when no such stenosis was visible using B-mode.

METHODS

This was a retrospective study of 100 patients referred to the stroke clinic and 100 patients referred for carotid endarterectomy (CEA). All patients had an elective carotid ultrasound done at Health Sciences North. The ultrasound reports were mixed together and blinded. Investigators determined if there was a CS of greater or less than 50% based on the carotid diagram. These results were compared to the degree of CS found on Doppler.

RESULTS

In the CEA group, there were 198 ultrasounds, with 153 showing a CS of >50%. Only one case of CS >50% was missed by B-mode. In the clinic group, 32 of 192 ultrasounds showed a CS of >50%. None were missed by B-mode. B-mode had a sensitivity and negative predictive value of 100% and a specificity of 65%.

CONCLUSION

This study supports the theory that it may be possible to use B-mode ultrasound without Doppler to reliably determine if there is CS above or below 50%. Further research is required before carotid ultrasound using B-mode alone can be recommended.

Effect of carotid plaque screening using contrast-enhanced ultrasound on cardiovascular risk stratification

Cardiovascular risk stratification of asymptomatic patients is based on the assessment of risk factors. Noninvasive imaging of subclinical atherosclerosis may improve cardiovascular risk stratification, especially in patients with co-morbidities. The aim of this study was to investigate the effect of contrast-enhanced ultrasound (CEUS) of the carotid arteries on cardiovascular risk assessment. The study population consisted of 100 consecutive asymptomatic patients with ≥1 clinical risk factor for atherosclerosis. Cardiovascular risk was estimated by calculating the Prospective Cardiovascular Münster Heart Study (PROCAM) risk score. This score was divided into 3 subgroups: low (≤5%), intermediate (6% to 19%), and high (≥20%). Subclinical carotid atherosclerosis was assessed using standard ultrasound for intima-media thickness and plaque screening and CEUS for additional plaque screening. CEUS was performed using SonoVue contrast agent. Patients with subclinical atherosclerosis were considered to be at high cardiovascular risk. McNemar's test was used to compare PROCAM score to ultrasound findings. The mean PROCAM risk score was 9 ± 10; the PROCAM risk score was low in 72 patients (72%), intermediate in 17 patients (17%), and high in 11 patients (11%). A total of 21 patients (21%) had abnormal carotid intima-media thickness, 77% had plaques on conventional carotid ultrasound, and 88% had plaques on standard carotid ultrasound combined with CEUS. Detection of atherosclerosis led to the reclassification of 79 patients (79%) to high cardiovascular risk (p <0.001). In conclusion, CEUS changes the risk category as estimated by a traditional risk stratification model in most asymptomatic patients. CEUS may thus be an additional method for cardiovascular risk prediction in patient groups with co-morbidities.

Intima-medial thickness homogeneity in the common carotid artery: measurement method and preliminary clinical study

BACKGROUND

To propose and test in a preliminary clinical study a novel method for calculating intima-medial thickness (IMT) homogeneity (IMTH).

METHODS

IMT was measured off-line on every horizontal pixel line along the far wall of the common carotid artery, with previously validated software. IMTH was assessed by the SD, coefficient of variation, and interval distribution of obtained IMT values. This method was applied to 129 individuals (age, 40-60 years), including 49 healthy control subjects, 44 subjects at high risk of atherosclerosis, and 36 subjects with known atherosclerosis. Differences with a p value <0.05 were considered statistically significant.

RESULTS

SD and coefficient of variation were higher in the high-risk than in the control group, as well as in high-risk and control subgroups with maximal IMT = 0.8 mm or mean IMT = 0.55-0.65 mm. There were 85.7, 62.8, and 36% of IMT values in the 0.4- to 0.6-mm range and 0.89, 13.8, and 21.2% of IMT values in the 0.8- to 1.2-mm range in the control, high-risk, and atherosclerosis groups, respectively.

CONCLUSIONS

IMTH is a promising approach for the assessment of atherosclerosis, in addition to conventional IMT measurement. Further clinical studies are needed to assess its clinical usefulness.

Assessment of subclinical atherosclerosis using contrast-enhanced ultrasound

AIMS

The sensitivity of standard carotid ultrasound and colour Doppler for the detection of subclinical atherosclerotic plaques is suboptimal. The aim of this study is to assess whether contrast-enhanced ultrasound (CEUS) added to standard carotid ultrasound improves the detection of subclinical atherosclerosis.

METHODS AND RESULTS

Carotid intima-media thickness (CIMT) measurement, standard carotid ultrasound including colour Doppler imaging, and CEUS were performed in 100 asymptomatic patients with one or more risk factors for atherosclerosis. CEUS was performed using intravenous administration of SonoVue™ contrast agent (Bracco S.p.A., Milan, Italy). CIMT, standard ultrasound, colour Doppler, and CEUS were reviewed by two independent observers. Standard ultrasound, colour Doppler, and CEUS were scored for the presence of atherosclerotic plaques. Subclinical atherosclerosis was diagnosed if patients had a CIMT above their age-corrected threshold value or if atherosclerotic plaques were present on standard carotid ultrasound clips or CEUS clips. McNemar's test was performed to compare between groups. Twenty-one patients (21%) had a thickened CIMT value and were considered to have subclinical atherosclerosis. Standard carotid ultrasound including colour Doppler demonstrated atherosclerotic plaques in 77 patients (77%). The addition of CEUS to the standard ultrasound protocol demonstrated atherosclerotic plaques in 88 patients (88%). The incorporation of CEUS into the standard carotid ultrasound protocol resulted in a significantly improved detection of patients with subclinical atherosclerosis (P < 0.01).

CONCLUSION

CEUS has an incremental value for the detection of subclinical atherosclerosis in the carotid arteries. Atherosclerotic plaques which were only detected with CEUS and not with standard carotid ultrasound and colour Doppler imaging were predominantly hypoechoic.

The Pathogenesis, Analysis, and Imaging Methods of Atherosclerotic Disease of the Carotid Artery: Review of the Literature

Cerebrovascular (CVA) accidents are the second leading cause of death worldwide and their numbers are increasing. Strokes can arise from several causes, with extracranial carotid artery atherosclerosis (CAS) being one of the leading causes. CAS causes these strokes either by diminishing blood flow distal to the diseased stenotic segment of the artery or, as more recently discovered, by a thromboembolic event of material from the plaque site itself. The specific etiology of CAS is unknown, but causative factors in the formation of atherosclerotic plaque of the carotid arteries have been linked to specific morphological areas within the plaque that may be vulnerable to rupture, leading to thromboemboli into the cerebrovascular circulation. The current means for imaging and reporting CAS is through the measurement of the severity of luminal diameter stenosis caused by atherosclerotic disease. Recent developments in medical imaging techniques have expanded the role of early imaging and detection of CAS. Although current practice uses luminal narrowing as the surrogate marker to assess CAS, it has been recently discovered that plaque morphology and composition may help predict the clinical behavior of CAS and better determine the necessary medical intervention or risk of stroke. Although a single optimized imaging modality for standard CAS imaging has not been established or agreed on, various modalities can provide key elements to a successful exam. This review article will evaluate the most commonly used methods for CAS imaging along with the new and upcoming uses, advantages, and limitations for advanced CAS imaging.