THE EFFECT OF B-MODE ULTRASONIC IMAGE STANDARDIZATION ON THE ECHODENSITY OF SYMPTOMATIC AND ASYMPTOMATIC CAROTID BIFURCATION PLAQUES

Background. To develop a method that allows B-mode ultrasonic images o f carotid plaques to be standardised so that measurements of plaque ec hodensity become comparable and clinically useful. Methods. Design. Cr oss sectional study. Setting. Teaching hospital, England. Patients: a random consecutive series of 23 patients in part 1, 19 in part II and 77 in part III. Measures. Part I: twenty-three images of carotid bifur cation plaques from 2 duplex scanners were digitised. Images were stan dardised by 4 observers so that the grey scale median (GSM) would be 0 -5 for blood and 185-195 for adventitia. Part II: the effect of three different recording media: video, magneto-optical disk (MOD) and therm al paper on the echodensity of 19 plaques' images was determined. Part III: the echodensity of 91 carotid bifurcation plaques with greater t han 50% stenosis was correlated to the presence or absence of ipsilate ral hemispherical symptoms. Results. Part I: the coefficient of variat ion (CV) among 4 observers was 0.7%, 0% and 4.7% after image standardi sation for the adventitia, blood and plaques respectively. Part II: a near perfect agreement was obtained between the GSM of plaques from im ages on video and MOD (r=0.97) after standardisation. Part III: after standardisation, the GSM of symptomatic plaques was lower (21+/-14.8) than in asymptomatic plaques (38+/-26) p=0.002. Plaque echolucency was more Likely to be associated with symptoms (relative risk 4.1 90% CI 1.8-9.4). Conclusions. Images from different scanners by different ult rasonographers and through different peripherals can be standardised s o that measurements of plaque echodensity may become comparable. The m ethod is recommended for use in future natural history studies on caro tid plaques where stroke is the end-point.