Computer-assisted carotid plaque characterisation

To determine the relationship between plaque echogenicity as measured by computer and the incidence of cerebral brain infarction.

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.

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).

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.