rterial atherosclerosis is closely related to the occurrence of cerebral and myocardial infarction 1 and that occurrence may be predictable if the plaque is adequately characterized. 2,3 It is well known that the degree of coronary stenosis is not related to the likelihood of myocardial infarction, and that pre-infarction coronary stenosis is found in less than 75% of the patients with myocardial infarction. 4 Acute coronary syndromes and acute cerebral infarction are caused in most cases by plaque rupture, and therefore, it is particularly important to assess the stability of the plaque. Recent histological studies clarified that lipid-rich plaque with a thin fibrous cap is dangerous because it may rupture with thrombi followed by sudden occlusion of the lumen. 5 Two-dimensional echography (2DE) can noninvasively visualize the plaque lesion and when used in combination with Doppler the degree of arterial stenosis can also be assessed. Unfortunately, these modalities cannot assess Circulation Journal Vol.67, December 2003 plaque composition or stability. Recently, ultrasonic characterization of the plaque composition has been investigated by analyzing integrated ultrasonic backscatter (IBS), and the studies have shown that IBS values can be used to differentiate fibrofatty, fatty and calcified lesions of the arterial wall. 6,7 However, there has not yet been a study that focused solely on assessing the stability of the plaque. Therefore, we measured the IBS in the carotid artery of patients who underwent carotid endarterectomy.
Methods
SubjectsThe study population consisted of 35 patients who had carotid stenosis of 75% or greater on the cerebral angiogram and who underwent carotid endarterectomy. All patients had a history of stroke or transient ischemic attack within the past 3 months. Their ages ranged from 58 to 71 years (mean: 65 years), and there were 28 males and 7 females. The control group comprised 30 healthy volunteers (15 males, 15 females; age range, 32-59 years, mean: 49). None of the volunteers had hypertension, hyperlipidemia or diabetes mellitus.
Echographic StudyThe ultrasound equipment used in this study was a commercially available echocardiograph (SONOS 5500, Philips Technology) with a 7.5 MHz linear-array transducer. Patients lay down on the bed, and the carotid artery was Histological abnormalities of the atherosclerotic lesion are closely related to the stability of the plaque. Specifically, the plaque is likely to be unstable if the fibrous cap is thin. However, ultrasonic characterization of the atherosclerotic lesion has not been done from this viewpoint. Thus, in the present study ultrasonic tissue characterization of the carotid atherosclerotic lesion was attempted to assess the stability of the plaque. Integrated ultrasonic backscatter (IBS) in the atherosclerotic lesion was compared with histological findings of the respective tissue in 35 patients with carotid artery stenosis who underwent carotid endarterectomy. Carotid IBS was determined by locating the region-of-interest (RO...