Ratio of blood flow velocity between the left and right common carotid arteries: Its value in eliminating inter-equipment, intra-observer and inter-observer variations

We evaluated the repeatability and reproducibility of blood flow velocity measurement of common carotid artery (CCA) using standardized scanning guideline and the ratio between the right and left CCA. Doppler sonography of CCA was undertaken in 29 healthy subjects to study inter-equipment variation. Twenty of them were re-scanned after two weeks to investigate intra-observer variation. Five healthy subjects were also recruited for the study of inter-observer variation, and they were scanned by five operators. Inter-equipment variation in the measurement of blood flow velocity existed but it may be eliminated by the ratio between right and left CCA, and the use of standardized scanning guideline. Intra-observer variation was not significant in measurement of blood flow velocity when standardized scanning guideline was used. Inter-observer variation may be eliminated by the ratio between right and left CCA in routine examination. In conclusion, standardization of scanning procedure and the use of ratio between right and left CCA may be helpful in eliminating inter-equipment, intra-observer and inter-observer variation in measurement of blood flow velocity of CCA. Introduction of a new scanning guideline is not recommended for those who had experience in carotid Doppler sonography.