The effect of B-mode ultrasonic image standardisation on the echodensity of symptomatic and asymptomatic carotid bifurcation plaques.

BACKGROUND

To develop a method that allows B-mode ultrasonic images of carotid plaques to be standardised so that measurements of plaque echodensity become comparable and clinically useful.

METHODS

Design. Cross sectional study. Setting. Teaching hospital, England.

PATIENTS

a random consecutive series of 23 patients in part I, 19 in part II and 77 in part III. Measures. Part I: twenty-three images of carotid bifurcation plaques from 2 duplex scanners were digitised. Images were standardised 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 thermal paper on the echodensity of 19 plaques' images was determined. Part III: the echodensity of 91 carotid bifurcation plaques with greater than 50% stenosis was correlated to the presence or absence of ipsilateral hemispherical symptoms.

RESULTS

Part I: the coefficient of variation (CV) among 4 observers was 0.7%, 0% and 4.7% after image standardisation for the adventitia, blood and plaques respectively. Part II: a near perfect agreement was obtained between the GSM of plaques from images 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 ultrasonographers and through different peripherals can be standardised so that measurements of plaque echodensity may become comparable. The method is recommended for use in future natural history studies on carotid plaques where stroke is the end-point.