(Stroke. 1999;30:61-65.)
© 1999 American Heart Association, Inc.
Original Contributions |
Carotid Plaque Characterization by Duplex Scanning
Observer Error May Undermine Current Clinical Trials
From the Ultrasonic Angiology Laboratory, Department of Radiological Sciences, and Department of Surgery (P.R.T.), Guy's Campus, King's College, London, UK.
Correspondence to Dr T.S. Padayachee, Ultrasonic Angiology Laboratory, 2nd Floor, New Guy's House, Guy's Hospital, London SE1 9RT, UK. E-mail s.padayachee{at}umds.ac.uk
Background and Purpose—Clinical studies currently in progress are using subjective methods to characterize plaque morphology from ultrasound images. However, there are few studies on the intraobserver and interobserver variability of these classifications. This study was designed to assess these variables.
Methods—Grading of plaque morphology from ultrasound images, stored both digitally and to hard copy, was performed by 2 classification schemes. Interobserver agreement was determined by 4 observers. Within-observer agreement was performed at intervals for up to 6 months. Accuracy of the 2 methods was determined by comparison with histology.
Results—Within- and between-observer agreement was moderate to
good for full-color digital image analyses, with pooled 
values of p=0.49±0.10 and p=0.62±0.07
for the 2-category method and p=0.53±0.06 and
p=0.52±0.05 for the 4-category method, respectively.
Hard copy data analyses gave lower values. The more
experienced observers produced higher within-observer agreements and
higher correlation with histology.
Conclusions—Reproducible grading of ultrasound images is not consistently achievable among experienced observers, and within-observer agreement may vary with time. The current subjective ultrasound characterization of carotid plaque morphology used in clinical trials may be associated with unacceptable levels of reproducibility in some centers. Variability between observers may be reduced by using the simpler 2-category grading of plaque morphology to interrogate full-color digitally stored images. Observer agreement should be audited regularly.
Key Words: atherosclerosis • carotid stenosis • ultrasonography, Doppler, duplex
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