Effect of color Doppler system on the twinkling sign associated with urinary tract calculi

PURPOSE: The aim of this study was to assess the effect of the color Doppler system on the artifact known as the "twinkling sign." METHODS: Sixty-five patients with at least 1 urinary tract calculus seen on sonography were examined with color Doppler sonography. Two color Doppler systems of 2 different generations were used. Examinations included gray-scale, color Doppler, power Doppler, and spectral evaluations of the calculus with various settings of Doppler gain, velocity range, color filter, focal depth, and acoustic power. RESULTS: A color artifact was present within and/or distal to 29 (39%) of 75 urinary tract calculi when the old generation system was used. Use of the new generation system produced this color artifact within and/or distal to 72 (96%) of the urinary tract calculi. The intensity of the artifact was affected by the acoustic output of the equipment. CONCLUSIONS: The twinkling sign is an artifact that can not only lead to misdiagnosis of vascular flow within a structure but also help differentiate a very small stone from other small echogenic structures when later generation "all-digital" systems are used. The color sensitivity of the system and acoustic power used are important technical factors that affect the production of this artifact.