Comparison of colour Doppler imaging with conventional duplex scanning in the evaluation of extracranial carotid stenosis.

OBJECTIVE: To assess the concordance between conventional duplex scanning and colour Doppler imaging in the grading of extracranial carotid artery stenosis. PATIENTS AND METHOD: A total of 67 carotid bifurcations in 48 patients were studied independently by two observers. First, each observer obtained a conventional duplex scan and recorded peak systolic and diastolic velocities. Then, each observer performed a colour Doppler study in which only the point of maximal colour shift was sampled. The stenosis in each case was subsequently classified, first as one of four classes (mild, moderate, severe or critical) on the basis of percent stenosis and peak systolic and diastolic velocities, and then as one of two groups (less than 70% or 70% or greater, with a peak systolic velocity of 2.3 m/second as the cut-off point). RESULTS: For the first observer, the two methods disagreed in 10 (15%) of the 67 cases. In five of these cases, colour Doppler imaging indicated a higher class of stenosis, and in the other five cases conventional duplex scanning indicated a higher class of stenosis. For this observer, the mean of the difference between conventional duplex and colour Doppler scanning for peak systolic and diastolic values was not statistically different from 0 (three-way analysis of variance). With colour Doppler imaging observer 1 detected all of the 14 cases of stenosis of 70% or greater that were detected by conventional duplex scanning. For observer 2, the results of the two methods differed in 12 (18%) of the 67 cases. For all 12 cases, conventional duplex scanning indicated a higher class of stenosis. The mean of the difference between the two methods was -23.8 cm/second (standard deviation 46.0) for peak systolic velocity and -10.7 cm/second (standard deviation 24.7) for peak diastolic velocity (both significantly different from 0). With colour Doppler imaging observer 2 did not identify 3 of the 16 cases of stenosis of 70% or greater that were detected by conventional duplex scanning. CONCLUSION: Discrepancies may exist between conventional duplex scanning and colour Doppler imaging in assessing extracranial carotid artery stenosis.