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Serial ultrasonic B-mode measurements of intimal-medial thickness(IMT)of the carotid artery are commonly used as surrogates for describing atherosclerosis progression.This report describes the longitudinal reliability of IMT measurement during a multicenter clinical trial, quantifies the error attributable to differences among readers,and discusses how studies can be efficiently designed.Serial B-mode measurements of carotid IMT from the 3-year Asymptomatic Carotid Artery Progression Study(ACAPS;formerly Asymptomatic Carotid Artery Plaque Study) were used to estimate the contributions to longitudinal measurement error of systematic reader effects,nonvisualization,and nonsystematic error and to describe the distribution of"true"progression rates that underlie the observed data.The ACAPS measurement protocol provided highly reliable serial IMT data.Moderate-sized multicenter studies using B-mode outcomes are feasible. |
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