Quantitative measurement of carotid intima-media roughness—effect of age and manifest coronary artery disease
Introduction
B-mode ultrasound of the carotid arteries is increasingly used to assess the atherosclerotic burden of the arterial system. Since the early eighties many examinations have demonstrated a correlation between different atherosclerotic risk factors and the thickness of the intima-media (IM) complex [1], [2], [3], [4], [5]. In addition, increased IMT of the carotid arteries even proved to be a powerful predictor of future cardio- and cerebro-vascular diseases [6], [7], [8]. However, the increase in the mean and maximum IMT represents only one part of the structural atherosclerotic alterations of the arterial wall visible in ultrasound images.
Fatty streaks and more advanced atherosclerotic lesions, which are only slightly prominent in the carotid wall, are distributed irregularly across the vascular surface [9], [10]. Since the histopathological examinations conducted by Solberg and Eggen [11], it is known that atherosclerotic lesions increase in size and severity from the proximal CCA distally until the carotid bifurcation. These results clearly indicated that fatty streaks occur in the carotid arteries of young individuals in the same anatomical sites as more advanced (and usually more prominent) lesions at a later age. Belcaro et al. [12] described these changes as granulations of the IM layer and showed that this structural alteration was a major criterion for future cardiovascular events. They classified the ultrasonic wall changes in categories. A quantification was not possible. On the basis of a recently presented automatic identification (AI) program of the intimal and adventitial boundaries [13], it should be possible to quantify at least the irregularities of the carotid wall thickness. Before doing so, a suitable procedure had to be found. Thus, one purpose of the study was to adapt the program to the measurement variations in IMT (abbreviated as IM roughness). Furthermore, we examined the relationship between IM roughness to age and manifest coronary artery disease (CAD) in order to evaluate the clinical relevance of this parameter. Finally, the IM roughness of a more distal with a more proximal segment of the CCA was compared in order to evaluate the relationship between IM roughness and the histologically known increase in the atherosclerotic lesions in the CCA towards the carotid bifurcation.
Section snippets
Study population
The study group consisted of 83 subjects. Fifteen younger (age 24.9±2.3 years, 11 men and four women) and 22 older healthy volunteers (age 62.9±3.5 years, 18 men and four women), and 46 patients with known CAD (CAD group, age 62.1±9.3 years, 40 men and six women) took part in the examination.
The patients of the CAD group were consecutive out-patients of the department. They were asked to participate in the study at a routine visit. Five patients refused to participate due to different reasons
Analysis of distal common carotid IMT and IM roughness
The mean and maximum IMT of the CCA were significantly higher in the older than in the younger subjects. The CAD group had significantly higher mean and maximum IMT than the older subjects (Table 2).
The IM roughness was significantly higher in the older subjects than in the younger subjects. In the CAD group, it was nearly twice as high as in the group of the older subjects (Table 2).
No significant differences between the mean and maximum IMT and IM roughness were observed among patient
Discussion
The main findings of this study are that (1) the intima-media (IM) roughness of the CCA far wall IM layers may be quantified in ultrasound images on the basis of a new AI program of the lumen-intima and media-adventitia boundaries; (2) the IM roughness is higher in older than in younger subjects; (3) it differs significantly between CAD patients and age-matched older subjects; and (4) the IM roughness of the intima-media layer increases distally in the CCA in accordance with previous
Acknowledgements
This study was supported by a research grant from the Center for Clinical Research at the Freiburg University Hospital (Project C 3, ZKF II). We gratefully appreciate the technical and statistical analysis support of Adriana Komancsek and Gerta Ruecker, respectively.
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