Duplex ultrasonography and selection of patients for carotid endarterectomy: plaque morphology or luminal narrowing?

A review of noninvasive ultrasound image processing methods in the analysis of carotid plaque morphology for the assessment of stroke risk

Noninvasive ultrasound imaging of carotid plaques allows for the development of plaque-image analysis methods associated with the risk of stroke. This paper presents several plaque-image analysis methods that have been developed over the past years. The paper begins with a review of clinical methods for visual classification that have led to standardized methods for image acquisition, describes methods for image segmentation and denoising, and provides an overview of the several texture-feature extraction and classification methods that have been applied. We provide a summary of emerging trends in 3-D imaging methods and plaque-motion analysis. Finally, we provide a discussion of the emerging trends and future directions in our concluding remarks.

Neuroimaging of stroke: a review

Advances in neuroimaging technology during the past 30 years have resulted in a virtual explosion in the amount of pathologic information that can be obtained in the clinical stroke setting. This neuroimaging revolution has led to a much better understanding of cerebrovascular and tissue pathology, creating a wide array of opportunities for acute treatment and secondary prevention. Advances include early and accurate detection of ischemic and infarcted tissue and the ability to reveal hypoperfused tissue at risk. Clinicians are increasingly able to noninvasively detect embolic and atherothrombotic intravascular lesions. Vascular lesions associated with stroke can be characterized through endovascular neuroimaging techniques and repaired by various means. In this article, we provide an overview and update on the various techniques used in the neuroimaging of stroke and intracranial hemorrhage, including computed tomography, magnetic resonance imaging, ultrasound, and catheter angiography. We outline the specific role of each modality in clinical practice.

An automated segmentation method for three-dimensional carotid ultrasound images

We have developed an automated segmentation method for three-dimensional vascular ultrasound images. The method consists of two steps: an automated initial contour identification, followed by application of a geometrically deformable model (GDM). The formation of the initial contours requires the input of a single seed point by the user, and was shown to be insensitive to the placement of the seed within a structure. The GDM minimizes contour energy, providing a smoothed final result. It requires only three simple parameters, all with easily selectable values. The algorithm is fast, performing segmentation on a 336 x 352 x 200 volume in 25 s when running on a 100 MHz 9500 Power Macintosh prototype. The segmentation algorithm was tested on stenosed vessel phantoms with known geometry, and the segmentation of the cross-sectional areas was found to be within 3% of the true area. The algorithm was also applied to two sets of patient carotid images, one acquired with a mechanical scanner and the other with a freehand scanning system, with good results on both.

Prognostic value of carotid ultrasound lesion morphology in retinal ischaemia: result of a long term follow up

The importance of carotid plaque morphology in the prognosis of retinal ischaemia was investigated in a group of 165 patients followed for 2-7 years (mean 3.3 years). All patients had an initial carotid duplex ultrasound examination, with the results expressed in terms of the degree of stenosis caused by the lesion, and the lesion morphology. Lesions were divided into two groups, (a) combined homogeneous and simple heterogeneous structures, and (b) complex heterogeneous plaques. Complex heterogeneous plaques had a low echo pool within the lesion and/or an irregular surface pattern. A total of 144 (87%) patients were successfully followed, and of these 37 (26%) had cerebrovascular, cardiovascular, or retinal ischaemic events in the follow up period; 14 (10%) cerebrovascular accidents (eight fatal), 17 (12%) myocardial infarctions (10 fatal), two episodes of amaurosis fugax, and one of tunnel vision caused by a retinal embolus were recorded. There was no report of subsequent blindness. The percentage stenosis caused by the carotid lesions, although more severe in the vascular event group, was not significantly different between the groups. However, a significant difference (p < 0.1) was found in the morphological characteristics of the carotid lesions between the groups. Patients who suffered a vascular event in the follow up period had significantly more complex heterogeneous lesions compared with simple heterogeneous/homogeneous lesions, than those patients who remained alive and well. Carotid endarterectomy and antiplatelet therapy were equally distributed between the event and non-event groups. This suggests that the criteria for selection for treatment should be based on the lesion morphology as well as the degree of stenosis.

Ultrasound morphology of carotid lesions in retinal ischaemia

The extracranial carotid arteries of 165 patients with retinal ischaemic symptoms were examined with duplex ultrasound. Both the degree of stenosis and the morphological appearance of the lesions were examined. Ipsilateral carotid artery disease was found in 88% of patients. Degrees of stenosis of between 50-99% were found in 33% of patients, the majority of these lesions being complex heterogeneous in nature. Stenosis of < 50% was found in 40% of arteries. The majority of lesions causing < 20% stenosis were homogeneous in nature. However, in stenosis of 20-49%, 63% of lesions were found to be complex heterogeneous. A similar distribution of lesions was found in the contralateral carotid arteries. It is important to examine both ipsilateral and contralateral arteries, and to evaluate the morphological characteristics of all lesions causing > 20% stenosis.

Comparison of duplex ultrasound with angiography in assessment of carotid bifurcation disease

This is a study comparing duplex ultrasound against the "gold standard" of angiography in assessing atherosclerotic disease of the carotid bifurcation, prior to prospective endarterectomy surgery. Thirty-nine patients were studied with both sonography and angiography studies being performed within one month of each other. Plaques were described by sonography as being "smooth" or "irregular" in surface and "homogeneous" or "heterogeneous" in composition. Ultrasound showed an overall 92% sensitivity, against the standard of angiography, in its ability to assess the degree of internal carotid stenosis. There was only a 63% sensitivity with the common carotid arteries and only a 65% sensitivity with the external carotid arteries. Ultrasound did not show a high accuracy in detecting plaque ulceration when compared against angio-graphy.