EVALUATION OF THE DIAGNOSTIC-VALUE OF INT RAVASCULAR ULTRASOUND BY ROC CURVES - PRACTICAL IMPLICATIONS

Intravascular ultrasound enables detection of the components of athero sclerotic plaques. The diagnostic value was assessed by ROC (receiver operating characteristic) curves on images acquired in vitro and corre lated with the histological: findings in 61 arteries. Five questions w ere asked of each operator : the reply was represented by a continuous variable in order to express all nuances of judgement. The area under the ROC curve, Az, was the criterion of performance (0.5 : chance res ponse; 1.0 : all replies were accurate). Detection of plaque was satis factory (At = 0.89). The three layer appearance of muscular arteries w as well recognised (At = 0.94). The fibrous composition of a plaque wa s only just satisfactory (At = 0.88) with 38.7 % interindividual varia bility. The lipid composition of the plaque was poorly recognised (At = 0.76) with large interindividual variability (52.8 %) : hypoechogeni city was too ambiguous a sign from the acoustic point of view. A hypoe chogenic zone must not be synonymous with a lipid plaque but a cellula r zone. Calcium can almost always be detected (At = 0.98) with a very low interindividual variability (10.7 %), fibrohyaline progression of some plaques can be confusing. The authors present a more objective de scription of endovascular ultrasonographic images. They conclude that the diagnostic performance of 30 MHz intravascular ultrasound is satis factory but several limitations are apparent in the interpretation of images, especially hypoechogenic zone and hyper-reflective zones with high attenuation.